Effects of aquaculture wastewater application on growth, yield and water use efficiency of sweet pepper (Capsicum annum) and okra (Abelmoschus esculentus) intercrop

1 Introduction

Water is widely recognized as a global common resource that is essential for sustaining human livelihoods and agricultural production. However, freshwater scarcity has become a major global challenge driven by population growth, climate change, and increasing anthropogenic activities, and it is projected to intensify by 2050 (Ray et al., 2013; Eludire et al., 2025). Nigeria is among the West African countries experiencing increasing water stress, making the identification of alternative water resources a priority for sustainable agriculture. Consequently, the reuse of treated and untreated wastewater for irrigation has emerged as an important strategy for reducing groundwater depletion while improving agricultural water security.

Sustainable management of water, soil, and land resources is critical for improving crop productivity under increasing environmental constraints. Water scarcity, declining soil fertility, and limited arable land continue to threaten food production worldwide (Zhang et al., 2013; Garcia et al., 2015). Improving water use efficiency through appropriate irrigation strategies is therefore essential for sustainable vegetable production. Full irrigation (FI) and deficit irrigation (DI) are widely adopted approaches for optimizing crop water use (Qassim et al., 2013). However, their effectiveness depends on complementary management practices such as nutrient availability, irrigation water quality, and cropping systems because these factors influence soil fertility, plant nutrient uptake, root development, water availability, and the efficiency with which crops convert water into biomass and yield (Akindele et al., 2021; Rao et al., 2016). Consequently, integrating efficient irrigation with nutrient-rich alternative water sources and intercropping may enhance crop productivity while conserving water resources.

Okra is a vegetable with a lot of stored nutrients is okra containing antioxidants which are important for healing digestive disorder, improves learning rates and heal memory loss, and alleviate body pains. Okra (Abelmoschus esculentus) and sweet pepper (Capsicum annuum) are economically important vegetable crops because of their high nutritional value and market demand. Their production, however, is often constrained by inadequate water supply and declining soil fertility, particularly in developing countries. Sustainable nutrient and water management strategies are therefore required to improve their productivity while minimizing dependence on costly inorganic fertilizers.

Previous studies have shown that soil fertility can be improved through inorganic fertilizers and organic soil amendments, leading to increased crop growth and yield (Kumar and Rai, 2005; Nadeem et al., 2011; Chen et al., 2023). However, inorganic fertilizers are often expensive for smallholder farmers and may contribute to nutrient leaching and eutrophication (Faloye et al., 2024a). Aquaculture wastewater has recently attracted considerable attention as an alternative irrigation source because it contains appreciable amounts of nitrogen, phosphorus, potassium, and organic matter that can simultaneously supply irrigation water and plant nutrients (Akindele et al., 2021). Constructed wetlands using Azolla pinnata have also been proposed as an environmentally friendly approach for improving wastewater quality before agricultural reuse. Intercropping is another sustainable agronomic practice that enhances land use efficiency, resource utilization, and crop productivity by cultivating two or more crops simultaneously (Ndaeyo et al., 2005). It improves light interception, suppresses weeds, and often increases overall system productivity. When combined with efficient irrigation and nutrient-rich wastewater, intercropping may further improve crop yield and water use efficiency.

Despite the growing interest in wastewater reuse and intercropping, previous studies have largely investigated these management strategies independently. Most available studies have focused either on the use of aquaculture wastewater for sole-cropped vegetables or on the effects of intercropping under conventional irrigation systems (Akindele et al., 2021; Rao et al., 2016; Oyelade et al., 2003). There is limited information regarding the combined effects of untreated aquaculture wastewater, constructed wetland-treated wastewater, deficit irrigation, and sweet pepper–okra intercropping on crop productivity, soil properties, and water use efficiency under drip irrigation. Therefore, the novelty of this study lies in integrating treated and untreated aquaculture wastewater with two irrigation regimes (100% and 60% full irrigation) and sole/intercropping systems to comprehensively evaluate their combined effects on crop growth, yield, water use efficiency, nutritive quality, and soil physicochemical properties. This integrated assessment provides new information for developing sustainable irrigation strategies that improve vegetable production while promoting wastewater reuse and efficient resource utilization.

Accordingly, the objectives of this study were to: (i) evaluate the growth, yield, and water use efficiency of sole and intercropped okra and sweet pepper irrigated with treated aquaculture wastewater, untreated aquaculture wastewater, and groundwater; (ii) determine the main and interaction effects of cropping system, irrigation water source, and irrigation level on crop productivity and water use efficiency; (iii) assess the influence of irrigation water source and cropping system on the nutritive quality of sweet pepper; and (iv) evaluate the effects of treated and untreated aquaculture wastewater on the hydro-physical and chemical properties of the soil under drip irrigation.

2 Materials and methods

2.1 Description of the experimental study area

The location of the experiment is situated at latitude 7° 14’ N and longitude 5° 08’ E, and the study was conducted on a cleared 50 m x 45 m land area approximately 30 m from the fish pond of the Department of Fisheries and Aquaculture Technology, Teaching and Research Farm, Federal University of Technology, Akure, Nigeria. With an average yearly rainfall of 1300–1600 mm and an average temperature of 27 °C, Akure is located in the rain forest zone. Approximately 2,303 square kilometers, Akure is located 350 meters above mean sea level in the western upland region. There are peaks in June and September in the bimodal distribution pattern of rainfall. While the wet season begins in mid-March and ends in October, the dry season begins in November and lasts until March. Prior to planting, the experimental soil was primarily sandy. The Alfisol is the type of soil found at the trial location, which is sandy clay loam (Faloye et al., 2024a). The soil is well-drained and it is fairly nutrient and organic matter rich for the cultivation of Okra and Sweet pepper. The ability to retain moisture is mediocrely good. Pre-Cambrian basement complexes, which are mostly made of igneous and metamorphic minerals, cover more than half of Nigeria’s humid zone.

2.1.1 Meteorological data of the study area

The monthly total rainfall during the period of the experiment (first experiment) (February – July, 2019) is shown in Figure 1. Rainfall trend for the second experiment was not presented, since there was no rainfall recorded during the growing period. Heavy rainfall was observed late in the experimental period between March and June. The rainfall trend for the experiment period (Figure 1) showed a gradual rise from March and reached its peak in the month of May, only to recede in July. This is similar to the observation of Osunbitan et al. (2005) who worked in the same region. The first experimental season proved to be a very wet year, and only require supplementary irrigation. As such, when to apply water and the amount to apply was decided through the measured soil moisture content. The total seasonal amount of rainfall was 1618 mm.

Variations in the daily total rainfall over the experiment period were shown by the daily rainfall (Figure 1). With 111 mm of rain falling on day 115 of planting, it was the wettest day. The experiment’s rainfall trend (Figure 1) revealed a steady rise in daily rainfall that peaked in the fourth week of May and then steadily decreased until the experiment’s conclusion.

Figure 2 displays the average monthly temperature in the research area for the years 2000–2015, 2019–2020, and 15 years of data. The two years of the experiment had the lowest mean temperature of 24.10 °C, while the highest mean temperatures of 27.6 °C and 26.5 °C, respectively, were recorded in 2005 and 2006. Throughout the two growth seasons, January and September had the greatest and lowest mean air temperatures, respectively.

During the trial period, the site had the highest average relative humidity, measuring 95.81 and 93.89% (Figures 3, 4). The relative humidity values obtained throughout the experiment fall within the range that Faloye et al. (2024a) recorded who similarly worked in the same study area.

2.2 Field experimentation

2.2.1 Soil sampling

The field tests were carried out throughout the 2018–2019 (Experiment I) and 2019–2020 (Experiment II) dry seasons, respectively. The experiment’s 110.5 m² plot of land is situated in the Federal University of Technology, Akure’s Teaching and Research Farm (Aquaculture division). A total of 1111.11 stands were used for all water treatments, with nine stands per replication (1 m × 1 m) spaced 0.3 m by 0.3 m between the stands and between rows. Before and after harvest, soil samples were taken at random from eighteen (18) observational locations in each of the created plots, ranging in depth from 0 to 20 cm. After being put in a plastic container, the samples were taken to the soil laboratory. To get homogenous aggregate, the samples were allowed to air dry before being sieved using a 2 mm sieve. The physico-chemical characteristics of the sieved samples were examined. Before and after each trial, the site’s soil was chemically characterized to ascertain the impact of treated and untreated aquaculture effluent on the soil and, in turn, crop yield and growth. As a result, six soil samples were randomly selected for chemical analysis from six plots of the three water treatments.

2.2.2 Soil physico-chemical characterization

Soil organic matter (SOM), organic carbon (SOC), cation exchange capacity (CEC) at pH 7.0, and soil pH are among the chemical characteristics of soil samples that were identified. The Walkley-Black wet oxidation method was used to estimate the organic carbon, and the SOC was multiplied by 1.72 to determine the soil organic matter content (Osunbitan et al., 2005; Craswell and Lefroy, 2001). Bray-1 extraction and molybdenum blue colorimetry were also used to measure the number of exchangeable cations and available phosphorus (P) (Omotade et al., 2019). Ammonium acetate solution was used to extract the exchangeable potassium (K⁺) and sodium (Na⁺), and flame photometry was used to measure their concentrations. Following extraction using ammonium acetate, the exchangeable magnesium (Mg²⁺) and calcium (Ca²⁺) were measured using an atomic absorption spectrophotometer (Omotade et al., 2019). Using a pH meter and a 1:2 water ratio, the pH of the soil was measured in distilled water. Ammonium acetate was used to calculate the cation exchange capacity (CEC) at pH 7.0. The Kjeldahi method’s wet-oxidation process was used to calculate the total nitrogen. Exchangeable acidity was ascertained by titrating the soil samples with sodium hydroxide after they had been saturated with potassium chloride solution (Osunbitan et al., 2005). Undisturbed soil samples were taken from each plot at depths of 0–10, 10–20, and 20–30 cm under three distinct water treatments using a soil sampler (10 cm length by 4.8 cm in diameter) in order to determine the physical properties of the soil. To make it easier to remove the soil core while ensuring minimal disturbance of the soil samples, a hand trowel was used to dig around the cylinder, before the eventual removal of the soil sample. The weight of soil that had been oven-dried at 105 °C over the volume of the soil core (cylinder) was then used to calculate the bulk density. Equation 1 was used to measure the bulk density (ρb) in Mg m^-3 (Blake and Hartge, 1986).

(1) Bulk density of soil=Mass of soilVolume of soil

At harvest, infiltration tests were conducted in each experimental plot for the hydraulic measurement. The water infiltration rates of the soil were computed using the data that was gathered.

2.2.3 Experimental design and treatment description

Three blocks made up the experimental arrangement. The untreated (raw) aquaculture wastewater (UT) made up the first block. The sedimentation tank, built wetlands (TW), and reservoir tank were used to irrigate the second block with treated aquaculture effluent, which was then discharged straight onto the field. The treated aquaculture wastewater was carried out in a constructed wetland using Azolla pinnata, with a retention time of 5 days allowed. The physico-chemical characterization of the raw and treated wastewater are shown in Supplementary Table 1. The untreated aquaculture water, treated aquaculture water and ground water were characterized using standard procedure (Mapandaa et al., 2005). The physicochemical characteristics of the untreated aquaculture wastewater (UAW), treated aquaculture wastewater (TAW), and groundwater (GW) used for irrigation are summarized in Supplementary Table 1. Across the two experimental seasons, the constructed wetland treatment substantially improved the quality of the aquaculture wastewater by reducing electrical conductivity (approximately 50%), chemical oxygen demand (45–75%), total dissolved solids (35–50%), chloride, alkalinity, sulphate, phosphate, and biological oxygen demand compared with untreated aquaculture wastewater. The treated wastewater also exhibited lower concentrations of heavy metals, particularly Pb, with removal efficiencies of approximately 27% during 2018/2019 and 82% during 2019/2020, while Cu and Fe concentrations remained well below the FAO permissible limits for irrigation.

Although untreated aquaculture wastewater contained higher concentrations of nutrients, including nitrate and phosphate, together with greater organic matter content than groundwater, most measured water-quality parameters remained within the recommended irrigation limits of FAO and WHO, indicating that both treated and untreated aquaculture wastewater were generally suitable for agricultural reuse. Groundwater consistently exhibited the lowest electrical conductivity, total dissolved solids, chemical oxygen demand, nutrient concentrations, and heavy metal contents among the three irrigation water sources. Complete physicochemical and heavy metal data for both growing seasons are provided in Supplementary Table 1. Details of the water sampling, characterization and results are presented in our previously published paper (Adabembe et al., 2022). Vertical flow constructed wetlands were developed using a plastic basin, characterized by a total surface area of 0.97m² and at a depth of 0.62 m. Different sizes of gravels and fine sand were placed in the constructed wetland to filtering purpose, as detailed in Adabembe et al. (2022). The raw aquaculture water was treated in this study to reduce the heavy metals present in the raw aquaculture water (Supplementary Table 1), which was achieved through the use of the Azolla Pinnata. Plots irrigated with groundwater treatment (GW) made up the third block in the design, which acted as the control. Three cropping patterns (okra alone, sweet pepper alone, and okra/sweet pepper intercrop), three water treatments, and two irrigation water management strategies—100% and 60% Full Irrigation (FIT)—were all part of the 3 x 3 x 2 experimental design. For the intercropping of the two vegetable crops, the ratio adopted was 2:1 for the sweet pepper to the okra crop, respectively. The higher portion was given to the sweet pepper than the okra crop, since the okra crop canopy occupies more space than sweet pepper. Combining them in this ratio would produce a complementary effect on the utilization of sunlight, which is beneficial to crop. Three replications of each treatment were conducted using a Randomized Complete Block Design. With careful consideration of water management techniques, a drip irrigation system was employed to supply crops with water. A total of 54 plots were created by three replications of the treatments (Figure 5). The description of the experimental treatment is as indicated below (Table 1).

Table 1. Irrigation water sources, irrigation amount and cropping pattern treatments combination of the field experiment.

Where; OK is okra, SP is sweet pepper, GW is ground water and FIT is full irrigation treatment, UAW is Untreated Aquaculture Wastewater and TAW is Treated Aquaculture Wastewater.

For Experiment I and Experiment II, or both growing seasons, an improved variety of okra (V35) and sweet pepper (Bower) seeds were manually seeded in nursery trays. In experiment I, planting was done in February 2019, while planting was done in November 2020 for Experiment II. Five weeks after planting, the sweet pepper was moved (5 WAP), and two weeks later, it was thinned to one plant per stand (2 WAT). Every week, weeding and other agronomic procedures were carried out. During the growth season, standard cultural methods were adhered to in order to effectively control weeds and diseases (cypermetherin). For early crop establishment, all plots were watered to field capacity. Plots were then irrigated in accordance with the irrigation design calculation, which calls for 60% full irrigation (60 FI) and 100% full irrigation (100% FI). After 40% of the soil water at field capacity had been used up, 100% of the irrigation needed to restore the soil water to field capacity was applied. In contrast, 60% of the irrigation water needed to restore the soil water to field capacity was applied in the 60% FI irrigation treatment. A handheld moisture meter (Campbell gadget) was used to continuously measure the soil’s water content. The following formula (Equation 2) was used to determine the amount of irrigation water applied (I_A) by drip irrigation for each irrigation treatment (Faloye et al., 2023).

(2) IA= WA × I

where W_A is the wetted area (m²) by emitters, I is the irrigation (mm), which was applied to bring the soil water to field capacity, and I_A is the irrigation amount, which was expressed as the the volume of irrigation water applied in cubic meter per irrigation event.

2.3 Agronomic and yield measurements of sweet pepper and okra

Plant height, leaves, stem girth, fruit height, and fruit diameter of sweet pepper and okra were among the crop agronomic parameters that were assessed weeks after transplantation. A venier caliper was used to measure the stem girth of the sweet pepper and okra, while a steel meter rule was used to measure the soil surface from the base of the plant to the peak of the plant. A venier caliper was also used to measure the fresh harvestable fruit’s height and diameter. Manual counting was used to ascertain the number of leaves. The production of sweet peppers was initiated at eight weeks after transplanting (8 WAT), while the yield of okra was initiated seven weeks after planting (7 WAP), and harvest was done in batches till the crop stop producing fruits. Using field water usage efficiency, the effects of intercropping, treated aquaculture wastewater, and untreated aquaculture effluent on the yield under drip irrigation were assessed. Equation 3 was used to calculate the field water use efficiency (FWUE) (Faloye et al., 2024b). This approach is necessary for the optimization of the input resources (water). This is because optimization is generally important for the best use of input resources and parameters in agriculture, and different areas of sciences and engineering applications (Faloye et al., 2024b).

(3) FWUE = Fruit yield (Kg/ha)TWS (mm)

where FWUE has been previously defined and TWS is the total amount of water that was used as input, which includes both irrigation and rainfall from planting to final harvest (Kg/ha.mm).

After harvest, proximate analyses were carried out on the sweet pepper/Okra. Moisture content, fat, crude fiber, ash and protein were determined according to Association of Official Analytical Chemists (AOAC, 2000).

2.4 Performance evaluation of the okra/sweet pepper intercropping by estimating the land equivalent ration

Willey introduced the concept of the Land Equivalent Ratio (LER) in 1972. It explained how much land area would be needed for a pure stand of crop species to produce the same amount of output as an intercropping at the same degree of management (Maitra et al., 2021). The LER of the lone crop is assumed to be unity (1). The LER of intercropped plots is evaluated for each component crop independently by adding the estimated total of two varieties. The LER in this investigation was determined using the following formula (Maitra et al., 2021) (Equation 4).

(4) LER = YabYaa + YbaYbb

Where Y_ab is the yield of ‘a’ crop grown in association with ‘b’ crop and Y_ba is the yield of ‘b’grown in association with ‘a’ crop. Yaa and Y_bb represent the yields of ‘‘a’’ and ‘‘b’’ crops grown in a pure stand, respectively.

2.5 Statistical analysis

Normality test for the soil, growth and yield parameters of the crops was conducted by using the Ryan-Joiner (similar to Shapiro-Wilk) method. The normality test was carried out in order to determine its suitability for further analysis, such as Analysis of Variance (ANOVA). The data were assumed normally distributed when P-value is greater than 0.05. In order to determine whether there are significant differences at p < 0.05, measured soil, water, and crop data were gathered, processed, and compared using Analysis of Variance (ANOVA) using data sets from different treatments. Tukey’s test was performed using Minitab software version 18 to determine the significant difference within the treatments (cropping pattern: intercropping, irrigation, and water source) at p < 0.05. Aquaculture wastewater, treated aquaculture wastewater, and ground water were tested for their primary and combined impacts on growth, fruit yield, and field water use efficiency using a three-way ANOVA.

3 Results and discussion

3.1 Soil moisture content (SMC) under soil treated with the different water sources

In this study, the treatment that received the most water had the highest soil moisture content (SMC) (Table 2). Weather conditions have a significant impact on the soil water content measured in this investigation. The evaporative demand was satisfied by the treatment that got the most water. As a result, plants could absorb and utilize more water. Furthermore, when the data were averaged from week 1 to week 20, the soil treated with aquaculture wastewater had the highest average water content. The highest amount of organic matter found in soil treated with aquaculture wastewater may be the cause of improved water retention. Akindele et al. (2021) made a similar observation. Another possible explanation could be changes in the structure of the soil upon the aquaculture wastewater application, which might have resulted in increased binding effect in the soil, thus resulting in increased water content (Osunbitan et al., 2005; Castro et al., 2006). Changes in the structure of some engineering materials have resulted in the improvement utilizations and functionality. For example, in soil, the modification of its structure results in alteration of water flow, and consequently increased water content (Ajayi et al., 2016). For both irrigation treatments, 100% and 60% FI, the average soil water content increases in a consistent order: ground water (GW) < treated aquaculture wastewater (TAW) < untreated aquaculture wastewater (UAW). The capacity of soil organic matter to act as a soil sponge and so increase soil moisture may be the reason for the highest soil water content in soil treated with aquaculture wastewater (Akindele et al., 2021; Adabembe et al., 2021). The highest number of organic materials found in the UAW (Supplementary Table 1) makes this clear. According to Supplementary Table 1, soil organic matter typically forms aggregates by binding soil particles into clods. This ultimately led to enhanced permeability and structure, which in turn affected the infiltration rate (Akindele et al., 2021). It is commonly known that adding organic materials to soils improves their water content, water infiltration, and hydraulic conductivity (Supplementary Table 6) (Akindele et al., 2021; Adabembe et al., 2021). The promotion of organic agriculture is justified by the fact that organic amendments are an excellent way to improve soil hydrology, which may lead to increased yields in organic agriculture using aquaculture wastewater (Akindele et al., 2021).

Table 2. Volumetric soil moisture content in cm³ cm^-3 in soil applied with un/treated aquaculture wastewater.

FIT is full irrigation treatment, IS is irrigation source, UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, and GW is ground water.

3.2 Influence of irrigation waters on soil physico-chemical properties

First, the irrigation appropriateness of the crops’ ground water and untreated aquaculture wastewater was evaluated. The results of comparing the physico-chemical characteristics of irrigation waters to international standards (FAO, 2008) indicated that they were suitable for use in irrigation in 2018/2019 and 2019/2020, with the majority of the values falling within the irrigation range for both treated and untreated irrigation (Supplementary Table 1). Plots in this study that were watered with untreated aquaculture wastewater had higher levels of organic matter than those that were irrigated with treated and groundwater (Supplementary Table 1). Similar findings were made by Omotade et al. (2019) and Akindele et al. (2021), who found that soil treated with untreated aquaculture wastewater had higher levels of organic matter. Additionally, when comparing untreated aquaculture wastewater to treated aquaculture wastewater and ground water, the untreated wastewater significantly (P<0.05) yielded the highest values for several soil chemical characteristics such as nitrogen (N), phosphorus, potassium (K), calcium, magnesium, organic carbon, and sodium (Na) (Supplementary Table 1). The biochemical activities of the fish may be responsible for the highest values of the soil physico-chemical parameters found in the untreated aquaculture effluent (Adabembe et al., 2021). The linked interactions between the water’s physical, chemical, and biological characteristics, fish food, and fish excrement can help to further explain this. When taken as a whole, these variables could change the water’s characteristics in fish ponds. In both growth seasons, the primary impact of the untreated aquaculture wastewater on the soil characteristics was significant at the 5% level of significance (Supplementary Tables 2–5).

3.2.1 Influences of water sources and intercropping on soil physico-chemical properties

Additionally, during both growing seasons, the amount of irrigation had a substantial impact on the soil’s total nitrogen, calcium, magnesium, CEC, and other soil nutrients. In order to improve nutrient availability, including nitrogen for plant uptake, aquaculture effluent may be used to slow down the fast flow of water into the soil. At the 5% level of significance, the cropping pattern also had a substantial and significant impact on the soil nutrients. This demonstrated how cropping pattern affected crop nutrient uptake. This further established that soil nutrients are strongly influenced by untreated aquaculture wastewater, cropping pattern and irrigation amount. According to Maitra et al. (2021), intercropping is crucial because it improves soil nutrients, which encourages the utilization of natural resources (light and land). This is made possible by intercropping, which lessens crop competition for available nutrients. The interaction effects were often significant whether taking into account the two-way and three-way analyses of the treated and ground water, untreated aquaculture wastewater, or both growing seasons.

3.3 Agronomic performance of sweet pepper (Capsicum annuum) and okra (Abelmoschus esculentus)

3.3.1 Plant height

The result of the measured average plant heights in all the treatments are presented in Tables 3–6. It was obvious that soil treated with untreated aquaculture wastewater performed remarkably better than other treatments in both irrigation water treatments. This is an indication that there is obvious relationship between the plant’s heights with respect to the quantity of fish pond water (untreated aquaculture wastewater) applied. Meanwhile, with respect to soil that received ground water, higher percentage of the voids may have been filled with water, thus enhancing the amount of water uptake, hence increasing the performance of the plant (Faloye et al., 2020; Bosma and Verdegem, 2011; Chavez-Crooker and Obreque-Contreras, 2010). The plant height did not show any significant difference at 5% level of significance for the cropping pattern and water sources under the different water applications. The highest plant height obtained using untreated aquaculture wastewater in this study is in agreement with the report of Castro et al. (2006).

Table 3. Effects of irrigation source, irrigation amount and cropping system on Sweet pepper and Okra growth and yield for 2018/2019 growing season.

FIT is full irrigation treatment, UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, OK is sole okra, SOSP is sole sweet pepper. Means with different letter in column are significantly different at 5% level of significance.

Table 4. Main and interaction effects of irrigation source, irrigation amount and cropping system on the growth and fruit yield of okra/sweet pepper for 2018/2019 growing season.

UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, SOK is sole okra, SOSP is sole sweet pepper, IA is Irrigation amount, IS irrigation source, CP is cropping pattern. NS means not significant, *mean significant at 5% level, mean significant at 1% level, *mean significant at 0.1%, ****mean significant at 0.01%.

Table 5. Effects of irrigation source, irrigation amount and cropping system on Sweet pepper and Okra growth and yield for 2019/2020 growing season.

FIT is full irrigation treatment, UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, SOK is sole okra, SOSP is sole sweet pepper. Means with different letter in column are significantly different at 5% level of significance.

Table 6. Main and interaction effects of irrigation source, irrigation amount and cropping system on the growth and yield of okra/sweet pepper for 2019/2020 growing season.

UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, SOK is sole okra, SOSP is sole sweet pepper, IA is Irrigation amount, IS irrigation source, CP is cropping pattern. NS means not significant, *mean significant at 5% level, mean significant at 1% level, *mean significant at 0.1%, ****mean significant at 0.01%.

3.3.2 Stem girth

Similarly, during the experiment, it was observed that there was insignificant difference (P > 0.05) among the treatments (cropping pattern and water sources) under the different water applications for both growing seasons (Tables 3–6). There is a close relationship between plant height and girth diameter when compared with the volume of pond water used. However, the soil that received ground water had the least girth diameter. This result is similar to the findings of Campiglia et al. (2011) who revealed that soil nutrient especially nitrogen and phosphorus have potential influence on the growth and development of girth diameter. Thus, affirmed that irrigating with fish pond water positively impact.

3.3.4 Number of leaves

The average number of leaves is directly related to the quantity of fish pond water received. The values of the average number of leaves are positively impacted by the soil nutrient benefited through the application of aquaculture wastewater (untreated) (Akindele et al., 2021). Similar to the plant height, and stem girth, soil that received ground water, had the least number of leaves in both irrigation water treatments and growing seasons. This might be due to insufficient nutrient. Also, insignificant differences (P > 0.05) were recorded for the number of leaves considering the cropping patterns and water sources under different water applications (Tables 3–6). These results below reveal the tremendous impact of fish pond water containing soil enriching nutrient such as nitrogen and phosphorus. Thus, fish pond water might have contributed to the root and shoots zones development of the crop, leading to improved nutrient uptake. Under well – watered conditions, photosynthesis with chlorophyll brings out the lust green and radiant coloration of leaves, which is also a function of nutrient and water availability for uptake from the root zones.

3.3.5 Leaf area

Treatment that received untreated aquaculture wastewater gave the highest value of leaf area in both irrigation water treatments. However, the lowest value of leaf area was recorded in treatment that received the least amount of water using ground water. The influence of water source and cropping pattern on the leaf area was insignificant (P > 0.05) under the different water applications. The main effect of cropping pattern was significant (P < 0.05) on the leaf area (Tables 7–10). The significant effect of the cropping pattern on sweet pepper and okra leaf area showed that cropping pattern may result in plant difficult to capture sufficient sunlight and consequently affect photosynthesis. Hence, this may affect crop yield, growth and development. Agronomic practices that enhance photosynthesis due to higher total leaf area usually result in improved yield (Campiglia et al., 2011). However, this simply explains possible reason why treatment that received ground water gave the lowest yield. This is also coupled with insufficient nutritional ingredient in the ground water used as irrigation source.

Table 7. Field water use efficiency as influenced by irrigation water sources, amount and cropping pattern for the 2018/2019 growing season.

FIT is full irrigation treatment, UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, SOK is sole okra, SOSP is sole sweet pepper, IS irrigation source, CP is cropping pattern. Means with different letter in column are significantly different at 5% level of significance.

Table 8. Main and interaction effects on field water use efficiency as influenced by irrigation water sources, amount and cropping pattern for 2018/2019 growing season.

FWUE is field water use efficiency, UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, SOK is sole okra, SOSP is sole sweet pepper, IA is Irrigation amount, IS irrigation source, CP is cropping pattern. NS mean not significant, *mean significant at 5% level, mean significant at 1% level, *mean significant at 0.1%, ****mean significant at 0.01.

Table 9. Field water use efficiency as influenced by irrigation water sources, irrigation amount and cropping pattern for the 2019/2020 growing season.

FWUE is field water use efficiency, UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, SOK is sole okra, SOSP is sole sweet pepper, IA is Irrigation amount, IS irrigation source, CP is cropping pattern. Means with the same letter in column are insignificantly different at 5% level of significance.

NS means not significant, *mean significant at 5% level, mean significant at 1% level, *mean significant at 0.1%, ****mean significant at 0.01%.

Table 10. Land equivalent ratio (LER) of crops grown alone and mixed with each other with and without compost application.

FIT is full irrigation treatment, UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater GW is ground water.

Overall, the highest increase in the growth parameters (plant height, stem girth, number of leaves and leaf area) as observed under the UAW was followed by the TAW and lastly by the GW. Also, the 100% FIT produced the highest plant height at the UAW, in treatment where intercrop was practiced for both growing seasons. The highest value of the growth parameters as observed at the 100% FIT can be attributed to the high amount of moisture enjoyed by the crops (sweet pepper and Okra) at this treatment level (Oyelade et al., 2003; Castro et al., 2006; Adabembe et al., 2021). Moreso, the high value of growth parameters (plant height, stem girth, number of leaves and leaf area) obtained at the intercropped treatment can be attributed to the beneficial effects of planting two different crops on the same plot of land.

This is because crop intercropping practices or system ensures that larger percentage of the ground area were the crops are planted are covered by the crops’ canopy. Therefore, the increased crops’ canopy as indicated by the leaf area, ensures that higher transpiration takes, thereby creating a cooler microclimate, and eventually facilitates the minimization of the surrounding soil temperature (Maitra et al., 2021). Due to the cooler microclimate, which might have been created when the two crops (sweet pepper and okra) the highest growth parameters were commonly obtained under the intercropping treatment for each crop for both growing seasons (Maitra et al., 2021).

3.4 Fruit growth and yield response to treatments

Across both growing seasons, treatments irrigated with untreated and treated aquaculture wastewater generally produced greater fruit growth and fruit yield of sweet pepper and okra than those irrigated with groundwater, although the magnitude of improvement varied among irrigation levels and cropping systems (Tables 3–6). Highest increase in fruit growth and yield of sweet pepper and okra are recorded in the treatments that received aquaculture wastewater. However, the lowest fruit growth and yield values were obtained in treatment that received groundwater. The higher productivity observed under aquaculture wastewater irrigation is consistent with its greater nutrient content, particularly nitrogen and phosphorus, which may have enhanced vegetative growth and assimilate production. This is because of reduction in leaf area limits photosynthesis and further decreases fruit growth and yield productivity (Omotade et al., 2019; Sullivan, 2003).

The fruit growth had similar values (P > 0.05) considering cropping pattern and water source under the different water applications. This indicates that fruit size remained relatively stable across the treatment combinations. However, the fruit yield was significantly impacted by the cropping pattern (P < 0.05) in both growing seasons under the different water applications (Tables 3–6). This finding suggests that cropping pattern influenced overall crop productivity more than individual fruit development, possibly through differences in resource utilization and interspecific competition.

Results from Tables 3–6 revealed that treatments receiving untreated aquaculture wastewater consistently recorded the highest mean fruit yields across most treatment combinations, treatment that received untreated aquaculture wastewater had the highest value of yield over other treatments in both growing seasons under the different water applications. However, these differences were not always statistically significant, indicating that the observed yield advantage are interpreted as a positive trend rather than definitive superiority under all conditions. These results are in agreement with the findings of Hussain and Al-Jaloud (1995), who reported increased yields of wheat and French bean following irrigation with aquaculture wastewater from Tilapia polyculture. Similarly, Naddafi et al. (2005) reported improved growth and quality of garden purslane, sweet basil, radish, and cucumber irrigated with fish pond water, while Wood et al. (2001) observed increased fresh bean pod and kale leaf yields when fish pond water was used as a nutrient source. These previous studies support the positive response observed in the present study and suggest that the nutrient-rich nature of aquaculture wastewater can contribute to improved vegetable productivity. These results showed that irrigating with fish pond water results in greater yield, as also established in our study under different water applications and cropping patterns, cultivating sweet pepper and okra for two seasons. This result is attributable to the nutritional values present in the fish pond water, which is obvious factors responsible for the improved growth and yield increase, consequent upon aquaculture wastewater application.

The insignificant difference (P > 0.05) in the yield of okra and sweet pepper among the untreated aquaculture wastewater, treated aquaculture wastewater, and groundwater for some yield variables showed that aquaculture wastewater can be considered a viable alternative irrigation source where freshwater availability is limited, without reducing crop productivity under the conditions of this experiment. untreated aquaculture wastewater could be used where ground water is limited. This is particularly evident in the second planting season when there was no rainfall.

In the first season, the main effects of the irrigation amount and cropping pattern were significant on fruit yield, whereas the irrigation source was not significant. This suggests that the amount of water applied and crop arrangement had a greater influence on yield than water source during this season. The insignificant (P > 0.05) main effect observed for the irrigation source on fruit yield may be associated with the relatively high rainfall received during the first growing season, which likely supplemented crop water requirements and reduced differences among irrigation water sources might be attributed to large amount of rainfall that accompany the irrigation event in the first season.

The significant main effects of irrigation amount and cropping pattern on okra and sweet pepper fruit yield demonstrate that these management factors are important determinants of crop productivity under drip irrigation. showed that cropping pattern (sole or intercrop) is important in the management of okra and sweet pepper to obtained an improved yield. A similar pattern was observed during the second growing season. However, the main effect of irrigation source became significant on fruit yield. Unlike the first season, rainfall was absent during the second growing season, allowing the influence of irrigation water quality to become more evident. Consequently, treatments irrigated with aquaculture wastewater generally produced higher yields than those irrigated with groundwater. This might be because no rainfall neutralizes the effect of aquaculture wastewater on the fruit yield in the second experiment, with markedly higher yield obtained using the aquaculture wastewater.

The three-way interaction among irrigation amount, irrigation source, and cropping pattern was not significant during the second growing season, interaction between the treatments on the fruit yields were insignificant while significant interactions were observed between irrigation amount and irrigation source, and between irrigation amount and cropping pattern. These results indicate that crop response to irrigation level depended partly on both the irrigation water quality and the cropping system adopted. Therefore, optimizing vegetable production under limited water availability requires integrated consideration of irrigation management and cropping practice rather than either factor alone. This showed that irrigation amount depends on the irrigation source for improved yield. Also, cropping pattern depend on irrigation amount for improved yield.

Overall, the findings demonstrate that aquaculture wastewater, particularly untreated aquaculture wastewater, has the potential to improve sweet pepper and okra productivity under drip irrigation. Nevertheless, the magnitude of these benefits depended on seasonal rainfall and management practices. Therefore, these conclusions should be interpreted within the context of this two-season field experiment rather than being generalized to all production environments.

3.5 Field water use efficiency as influenced by okra/sweet pepper intercropping

Field water use efficiency (FWUE), calculated as the ratio of marketable yield to total water supplied (irrigation plus rainfall), increased as irrigation application decreased from full irrigation (100% FI) to deficit irrigation (60% FI). This indicates that the reduction in irrigation water was proportionally greater than the reduction in yield, resulting in more efficient water utilization under deficit irrigation. The ratio between yield and total water supplied (irrigation + rainfall) increased from full water application through to the deficit irrigation treatment. This event resulted in an increased FWUE to the deficit irrigation treatment. These findings are consistent with Sezen et al. (2006), who reported the highest FWUE under water-stressed conditions, and with Faloye et al. (2019), who similarly observed greater FWUE in treatments receiving lower irrigation amounts.

Among the different irrigation water sources, untreated aquaculture wastewater (UAW) generally produced the highest FWUE, followed by treated aquaculture wastewater (TAW), whereas groundwater (GW) produced the lowest FWUE across both growing seasons (Tables 6–8). Although UAW consistently recorded higher mean FWUE values, the magnitude of these differences varied among treatments. Among the different water sources (UAW, TAW and GW), the plot treated with UAW received the highest amount of FWUE compared to plot treated with TAW and GW, irrespective of the irrigation treatment. This trend may be associated with the greater nutrient and organic matter contents of UAW, which could have supported higher crop productivity without increasing water application. However, because nutrient uptake, root growth, and soil water dynamics were not directly measured, these explanations should be regarded as plausible mechanisms rather than confirmed causes. The increased FWUE observed at the plot.

The present findings are consistent with Maitra et al. (2021), who suggested that aquaculture wastewater can improve water productivity through enhanced nutrient availability. Similarly, Faloye et al. (2019) reported increased FWUE following soil amendment application, attributing the improvement to enhanced crop growth per unit of water supplied. In the present study, the higher organic matter associated with UAW may also have improved soil moisture retention and nutrient availability, thereby contributing to higher crop yields and improved FWUE. Nevertheless, these mechanisms were not directly quantified and therefore require further investigation. Moreover, the treatment applied with raw aquaculture wastewater had higher organic matter. This organic matter was important for the storage of water and enhancing nutrient storage for plant use and uptake. The enhancement of the soil nutrient with the moisture content could result in higher yield, which ultimately lead to increase in water use efficiency. Treatment plots that recorded relatively lower soil nutrient status and lower soil moisture generally exhibited lower FWUE values. This observation suggests that both soil fertility and water availability contributed to efficient crop water use under the experimental conditions, although their individual contributions were not quantified in this study. This observation is clear in this study, since lower FWUE were recorded in the treatment plots where lower soil nutrient and soil moisture content was recorded.

The statistical analysis further showed that the main effect of irrigation amount on FWUE was not significant (P > 0.05) during the first growing season (Table 8). This result suggests that differences in irrigation level had limited influence on FWUE under the prevailing environmental conditions. A possible explanation is the relatively high rainfall received during the first season, which supplemented irrigation water and reduced differences among irrigation treatments. In contrast, irrigation amount significantly affected FWUE (P < 0.05) during the second growing season, when rainfall was absent. Under these conditions, differences in irrigation application became more pronounced, allowing deficit irrigation to improve water productivity more effectively than during the wetter season.

Similarly, irrigation water source and cropping system significantly influenced FWUE (P < 0.05) in both growing seasons. However, their interaction effects were generally not significant (P > 0.05), indicating that the effects of water source and cropping system on FWUE were largely independent of one another. Therefore, the results indicate that intercropping and the use of aquaculture wastewater can contribute to improved field water use efficiency under drip irrigation. However, the extent of this improvement depended on seasonal conditions and should be interpreted within the scope of this two-season field experiment rather than as evidence of universal applicability. Sweet pepper received a greater total irrigation depth than okra under the same irrigation treatment because additional water was applied during the nursery establishment period before transplanting. This additional volume was included in the calculation of total seasonal water use (Tables 6, 7), explaining the higher irrigation amount reported for sweet pepper. Finally, the results may vary under different climatic conditions, soil types, and aquaculture systems; long-term monitoring is required to evaluate potential accumulation of nutrients, or trace elements under continuous wastewater irrigation; additional multi-location studies are needed before broad recommendations can be made.

3.6 Performance evaluation of okra/sweet pepper under the different water sources and irrigation amount

Because two crops need different resources when grown together, yield gains arise. Regarding the water source used for irrigation and the amount of water used, the land equivalent ratio (LER), which was used to assess the performance of the okra/sweet pepper intercrop, was generally good (Table 10). The LER was less than 1 in a small percentage of cases, but it was larger than 1 in the majority. The study’s 2:1 imbalanced sweet pepper/okra intercropping pattern (rather than 50:50) may be the cause of the observed discrepancy in LER levels. In most instances, the LER was higher than 1 even with this intercropping configuration. High LER has also been recorded in a number of studies involving the combination of several crops under soil modification. For instance, intercropping common beans and maize under compost plots increased LER. A positive correlation between the two harvests is shown by an LER value larger than 1 (Maitra et al., 2021). There have also been reports of maize-soybean (Solanki et al., 2011), maize-cowpea (Dahmardeh et al., 2009), and maize-common beans (Yilmaz et al., 2008) having an LER higher than 1.0.

The component crops’ excellent complementary and effective utilization of growth resources may have contributed to the two-crop intercropping’s superior production (as indicated by LER values greater than 1) compared to monocropping (Yilmaz et al., 2008). In another study, Bhatti et al. (2006) reported beneficial effect of intercropping maize and legumes as a result of ground cover by the crop and nitrogen fixing ability by legumes like beans, thus making it complementary. There would be a complementary benefit since the crop canopies would be able to intercept more radiation due to the increased ground cover. The results of Ananthi et al. (2016), who found that light is the most significant element determining LER of crops intercropping, can be used to explain the increased LER achieved in our investigation, regardless of the treatments. This study shows this regardless of the intercropping configuration. Additionally, the ground cover of okra and sweet pepper differs significantly because of the leaf architecture, which may have helped the soil conserve water through ground shading. In our study, nearly all the intercropped treatment had greater than one LER. Therefore, Okra/Sweet pepper intercropping should be encouraged and practiced under different soil water and nutrient conditions, to increase crop yields and to improve land use efficiency (Liu et al., 2010). This strategy reduces weed population, increase land utilization and economic benefit (Li et al., 2006).

Moreover, because inorganic fertilizers are often unaffordable for smallholder farmers, aquaculture wastewater offers a cost-effective alternative for vegetable production, particularly in areas where land and freshwater resources are limited. The use of the aquaculture wastewater for an enhanced vegetable crop productivity offers an economically viable agriculture production system. This is because the use of other agricultural inputs like inorganic fertilizer can promote leaching due to the soil textural type of the study location which is predominantly sandy. Moreso, the predominant rainfall pattern of the study area, particularly during periods when only supplementary irrigation is required, could make the area to suffer from leaching of nutrients, which are not beneficial to crop growths and productivity, thereby necessitating the need to optimize the crop water use in the face of increasing population (Fernández, 2023). Therefore, advantageously, the use of aquaculture wastewater would solve this nutrient leaching problems, because the pores in the soil are partly clogged by the aquaculture wastewater, thus resulting in higher soil nutrient and water retention, as observed in this study. These attributes contributed to enhanced growth and yield of crops in the untreated aquaculture wastewater treatment. This advantage was observed in the greater than 1 (> 1) value obtained for the LER. Therefore, despite the higher sand content and the rainfall events that accompany the irrigation events the highest plant growth and yields were recorded in the untreated aquaculture wastewater treatment, revealing the advantage of cultivating crops with the aquaculture wastewater source. However, caution must be taken to avoid over clogging of the soil pores in an alfisol soil and other soil types, while using aquaculture wastewater for irrigation purposes, particularly for a long term, as this could lead to the emergence of diseases and pest. This is mostly possible in situation whereby the microbial counts of the raw aquaculture wastewater are not within the permissible range for irrigation. Moreover, despite the high temperature recorded during the growing season, which is part of the characteristics of a tropical region like Nigeria, higher growth was recorded in the intercropping treatment (Maitra et al., 2021). This is because the combination of the crops might have created a soothing microclimate with less evaporation (Maitra et al., 2021). Overall, intercropping system and the re-use of aquaculture wastewater can be considered to require very low agricultural practice with higher output in terms of higher farm output and agricultural sustainability. Another possible explanation for the increased organic carbon/matter observed in the intercropped plot. The intercropping system ensures a greater use of available resources like land area and carbon dioxide. The enhanced sequestration of organic carbon in the soil could offer an opportunity to mitigate climate change and other sustained ecosystem services (Maitra et al., 2021).

3.7 Nutritional analyses of sweet pepper and okra fruits

The proximate composition analysis conducted during the 2019–2020 growing season showed that irrigation water source significantly affected (P < 0.05) the moisture, crude fiber, ash, protein, and carbohydrate contents of both sweet pepper and okra (Tables 11, 12). Across most quality attributes, fruits irrigated with untreated aquaculture wastewater (UAW) recorded the highest mean values, followed by treated aquaculture wastewater (TAW), whereas groundwater (GW) generally produced the lowest values. The water sources under the various water applications had a substantial impact on the nutritional characteristics; the treatment that got aquaculture wastewater for both growing seasons had the highest value.

Table 11. Fruit nutritional qualities of sweet pepper and okra as influenced by water sources, irrigation amount and cropping pattern.

FIT is full irrigation treatment, UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, SOK is sole okra, SOSP is sole sweet pepper, IA is Irrigation amount, IS irrigation source, CP is cropping pattern. Means with different letter in column are significantly different at 5% level of significance.

Table 12. Main and interaction effects of irrigation sources, irrigation amount and cropping pattern on sweet pepper and okra fruit nutritional qualities (2019/2020 growing season).

UAW is untreated aquaculture wastewater, TAW is treated aquaculture wastewater, GW is ground water, SOK is sole okra, SOSP is sole sweet pepper, IA is Irrigation amount, IS irrigation source, CP is cropping pattern. NS means not significance, *mean significant at 5% level, mean significant at 1% level, *mean significant at 0.1%, ****mean significant at 0.01%.

These findings indicate that the use of aquaculture wastewater improved fruit nutritional quality under the experimental conditions. The improved nutritional quality observed in the present study may be associated with the greater nutrient availability in aquaculture wastewater, which could have promoted nutrient accumulation in the fruits (Esayas et al., 2011). The crude fat content of sweet pepper and okra ranged from 2.36 to 6.59%, with sweet pepper generally exhibiting higher values than okra. These values are comparable with those reported by Akindele et al. (2021), although differences exist compared with those reported by Adetuyi et al. (2012) and Nwachukwu et al. (2014). Such variations are likely attributable to differences in cultivar, environmental conditions, agronomic practices, and analytical procedures among studies. By absorbing and holding onto flavour. Moisture content varied from 79.2 to 88.5%, which is comparable to the range reported by Akindele et al. (2021). The relatively high moisture content observed is characteristic of fresh vegetables and contributes to their freshness and texture. However, high moisture content may also reduce storage stability and increase susceptibility to post-harvest deterioration.

Protein content ranged from 2.11 to 3.95%, indicating that both crops are moderate sources of dietary protein. Although the differences among irrigation treatments were statistically significant, the magnitude of these differences was relatively small, suggesting that irrigation water source influenced protein accumulation without fundamentally altering the nutritional classification of the crops. This observation is generally consistent with Nwofia et al. (2012), who emphasized the nutritional importance of adequate protein content in vegetables. Crude fiber content ranged from 0.82 to 5.93 g 100 g^-1, with sweet pepper generally recording higher values than okra. The significant effect of irrigation water source on fiber content suggests that wastewater irrigation influenced fruit composition in addition to crop yield. Comparable fiber contents have been reported by Akindele et al. (2021), although differences among studies may reflect varietal characteristics and environmental conditions.

Similarly, ash content was significantly affected by irrigation treatment, with sweet pepper generally recording higher ash concentrations than okra. Because ash content reflects the total mineral composition of plant tissues, these results suggest that irrigation with aquaculture wastewater enhanced mineral accumulation in the harvested fruits. This suggests that sweet pepper would offer more of the vital, beneficial minerals required for bodily growth than okra. The ANOVA results further showed that treatment effects were primarily associated with the main effects of irrigation water source, while several two-way and three-way interactions were also significant (Table 12). These significant interactions indicate that the influence of irrigation water quality on fruit nutritional composition depended partly on irrigation level and cropping system. Overall, the results demonstrate that aquaculture wastewater, particularly untreated aquaculture wastewater, can improve several nutritional quality attributes of sweet pepper and okra under drip irrigation. However, these improvements are interpreted within the environmental conditions and duration of this two-season field experiment, and further long-term studies are required to confirm the consistency of these responses under different production environments.

4 Conclusion

This study investigated the influence of treated and untreated aquaculture wastewater, applied under full and deficit irrigation, on the growth, yield, field water use efficiency (FWUE), and selected soil physicochemical properties of sole and intercropped sweet pepper and okra under drip irrigation. The results showed that irrigation water source, irrigation level, and cropping system significantly influenced several soils, crop growth, yield, and FWUE parameters, although the magnitude of these effects varied among the measured variables. Untreated aquaculture wastewater generally produced higher soil nutrient levels and, in many cases, greater crop growth, yield, and FWUE than treated aquaculture wastewater and groundwater. However, these advantages were not statistically significant for all measured parameters or treatment combinations. The findings therefore suggest that aquaculture wastewater, particularly untreated aquaculture wastewater, has potential as an alternative irrigation water source under the conditions of this study. The measured physicochemical characteristics of both treated and untreated aquaculture wastewater were generally within the recommended limits for irrigation, supporting their potential reuse for vegetable production.

Significant main and, for some variables, interaction effects of irrigation water source, irrigation level, and cropping system were observed, indicating that crop response depended on the combined influence of these management practices. Deficit irrigation generally improved FWUE, while aquaculture wastewater irrigation was associated with higher productivity and improved nutritional quality of the harvested crops in several treatment combinations. The findings of this study are limited to the experimental conditions, including the two growing seasons, the study location, the soil type, and the irrigation management adopted. Consequently, caution should be exercised in extrapolating these results to other environments without further validation.

Future research should evaluate the long-term effects of repeated aquaculture wastewater irrigation on soil physicochemical properties, nutrient dynamics, crop productivity, and environmental sustainability. Multi-location and multi-season experiments are also needed to determine the consistency of these findings under different climatic conditions, soil types, and cropping systems before broad recommendations can be made.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fagro.2026.1842238/full#supplementary-material.

Supplementary material Supplementary material at the source

Footnotes

Edited by: Amrakh I. Mamedov, Tottori University, Japan

Reviewed by: Nijat Pashayev, ADSEA, Azerbaijan

Marcos H. G. Ribeiro, Federal University of Rio Grande do Sul, Brazil