1. Introduction
Egypt’s expected population of 110 million people by 2023 will necessitate increased food production that will outpace the need for improved arable soil and water obtainability and quality [
1]. Egypt is compelled to increase water productivity and utilize all poor-quality unconventional water supplies due to the pressures of a growing population and a food deficit [
2]. The use of saline or brackish water for irrigation and aquaculture in areas with a limited supply of water requires the adoption of cutting-edge technology and environmentally friendly farming practices. Diverse approaches, such as aquaponics, are urgently required to increase water productivity [
3,
4]. Agriculture uses around 85% of the water allocation for the Nile, with irrigated agriculture being the main consumer. The situation is made worse by the fact that surface irrigation, the main irrigation technique used in the Nile Valley and Delta regions, even in desert sandy soils with application effectiveness below 50%, is severely depleting groundwater, a priceless resource [
5].
Due to its fixed share of the Nile’s water (55.5 billion m
3/year) and a lack of water resources, Egypt is currently experiencing serious problems and dealing with severe issues [
2,
6]. The Nile River has been the artery of life for the Egyptian population and any kind of sustainable development chiefly relies on the availability of Nile water. Water shortage occurs when there are not enough available water resources to meet the country’s needs. There are two probable causes of a water deficit: an economic shortage of water, which results from inefficient management of the scarce water resources, or physical water scarcity, which is brought on by insufficient natural water supplies [
5,
7]. Egypt’s water deficit is mostly physical since there are not enough water resources, and it is also economic because those resources are not managed well.
Despite the challenges associated with arid conditions, including an absence of water, poor soil fertility, the spread of sandy soils, deforestation, saline water, and low yields of crops, agricultural output remains one of the key elements influencing the economy and the availability of food. Large-scale agricultural areas in Egypt are subject to dry and semi-arid climate conditions, as well as severe salinization problems brought on by irrigation with subpar quality of water, inadequate drainage systems, and a lack of soil fertility or nutrient availability. Because of this, farmers in arid areas are being forced to find innovative ways to preserve water, increase crop quality, and do so without harming the environment [
8,
9].
In order to effectively manage irrigated agriculture in arid regions, attention must be diverted from maximizing output per unit of water spent to maximizing output per water drop consumed [
5,
6]. This will expand crop output globally and enhance agricultural irrigation techniques. In areas with limited rainfall, it is not just the quantity of water that is becoming scarce: it is also the quality of the water [
6]. Using salty or brackish water continuously to grow crops increases soil salinity [
10,
11]. Agricultural soil productivity and crop value can be dramatically reduced by a soluble salt build-up in the soil and root rhizosphere. The persistent use of high-salinity, low-quality irrigation water is one of the major issues facing agriculture in many nations around the world [
4,
12].
Aquaculture uses water and is logically and coherently integrated with agriculture to become a non-consumptive producing sector that does not compete with agriculture, which increases the advantages of sustainable farming [
13]. Due to the multiple uses of water in aquaculture-integrated agriculture systems, farm and water productivity are increased, fishpond water quality is improved, and the environmental impact of nutrient-rich water discharge, water costs, and the quantity of chemical fertilizer required for crops are all decreased. Even though aquaponics is widely used in Egypt, there is not much information available on aquaponics as an integrated farming system, and only a small amount of aquaculture water is used for crop irrigation since some researchers continue to underestimate its benefits on soil and water productivity [
14,
15]. Aquaculture water is currently used to irrigate many farms in recently fertilized soils, making it feasible to realize the value of irrigation with it. Therefore, it was necessary to conduct a realistic experiment to ascertain which types of aquaponics could be most useful in helping to address the food problem in Egypt as an alternative to conventional farming techniques. Due to the high price of aquaponics system installation and maintenance, this experiment was conducted using the Egyptian farmer aquaponics method to imitate the modern aquaponics system in an attempt to produce food and fish on a large scale under field conditions with little cost and dual-use of water as a scarce resource in Egypt.
Therefore, the current investigation aimed to investigate the impacts of aquaculture water used for irrigation on water productivity, soil quality, and watercress production as well as its applicability to sustainable farming methods under conditions of desert sandy soils. The following objectives of the current work were to accomplish this goal: (1) To evaluate catfish and tilapia aquaculture water quality for the irrigation of watercress. (2) To assess the impact of using aquaculture water for irrigation alone or in combination with various synthetic NPK fertilizers on watercress yield and quality characteristics. (3) To assess the impact of aquaculture water irrigation on some sandy soil quality parameters.
2. Materials and Methods
A watercress pot study was carried out to assess the effects of irrigation by catfish and tilapia aquaculture water on the examined sandy soil quality properties as well as the growth and yield parameters of watercress with various combinations of artificial NPK fertilizers. At the Faculty of Agriculture, Minia University, El-Minia Governorate of Egypt (28°18′16″ N latitude and 30°34′38″ E longitude), watercress pot experiments and aquaculture of catfish and tilapia were implemented. The following experimental techniques, materials, and research procedures were used in the current study:
2.1. Experimental Design, Procedures, and Treatments
The experimental design implemented was a complete randomized design (CRD) with 24 pots and three replicates (
Table 1). The first factor was the irrigation type of water (catfish and tilapia); second factor was the artificial NPK fertilizer rate (0%, 25%, 50%, and 100%) of the levels that Ministry of Agriculture advised. Three replicates of catfish and then tilapia aquaculture samples of water were gathered prior to the start of the experimental procedures and sent for physicochemical analysis. The experimental design was summarized as shown in
Table 1.
A total of 24 pots (30 cm diameters × 30 cm depth) were filled with 15 kg of sandy soil after air drying and sieved to a size of 2 mm. To create stable soil conditions, these pots were placed in the greenhouse at a temperature of 25 ± 10 °C and irrigated over three days with various fish farm waters at a rate of 60% of field capacity without filtering. After three days, watercress seedlings were planted in pots and watered with allotted water until harvest. To achieve high soil water percolation for the purpose of examining water quality parameters and determining whether the infiltrated water could be utilized again for fish farming, fish farm water was allotted while maintaining the soil moisture content above its water retention capacity by regular weight analyses and dropwise water applications.
2.2. Soil Properties Analyses
Physical and chemical characteristics of the experimental soil were analyzed before and after irrigation with aquaculture water to assure soil quality and to protect these sandy soils from salinity build-up and soil degradation. Consequently, soil samples were collected before and after irrigation with aquaculture water, then air dried, crushed, and sieved to pass through a 2.0 mm stainless steel sieve. Sieved soil samples were mixed thoroughly, and a subsample was taken for soil analyses using standard methods as explained by [
16,
17,
18,
19]. Some soil physicochemical properties before irrigation are illustrated in
Table 2.
2.3. Fishponds Design and Experimental Materials
Earthen fishponds were established ten years ago for catfish and tilapia production in the nursery at the Faculty of Agriculture, Minia University. Watercress pot experiments were conducted in the agricultural greenhouse belonging to the soil department, 50 m away from fishponds. Irrigation water was transferred from the fishponds to irrigate the watercress experiment in the greenhouse and back again to the fishponds manually after soil percolation. Water was added to the fishponds to feed the system with additional tap water as needed to maintain overall levels if the infiltrated water from the watercress experiment was not sufficient to compensate.
At the beginning of the experiment, two cubic tanks were placed inside the main tilapia and catfish fishponds in the nursery to separate the experimental fish from the original farm in the nursery. The Nile tilapia fish unit consists of cubic tank (2 m3) stocked with 100 Nile tilapia (Oreochromis niloticus) weighing 100 g ± 15 g representing intensive fish production. The North African catfish (Pseudoplatystoma corruscans) unit consists of cubic tank (2 m3) stocked with 100 catfish weighing 300 g ± 35 g. Catfish and Nile tilapia were purchased alive after fishing directly from a local fisherman from the Nile. The fish were raised daily on poultry manure taken from the poultry farm at the Faculty of Agriculture, Minia University, using the equivalent of 2% of the weight of the fish. Aquariums were heavily aerated with air stones as the oxygen level rises and carbon dioxide is removed. Every three days, after the sludge at the bottom of the tank was disturbed and the solid portion of the wastewater was not purified for use as high-quality fertilizer, water was removed from the fishponds for watercress irrigation. In order to obtain filtered water for use in fish farming again, this water was subsequently used to irrigate watercress in the greenhouse utilizing the intensive flood irrigation method above the water holding capacity of the examined sandy soil.
2.4. General Methods and Analytical Procedures
In accordance with Avery et al. [
18], Chapman et al. [
19], Baird et al. [
20], and the 23rd edition of Standard Methods for the Examination of Water and Wastewater [
21], water and soil physical and chemical parameters were analyzed. According to the Standard Methods, the chemical oxygen demand (COD) and biological oxygen demand (BOD) were calculated [
22]. A Shimadzu UV–VIS spectrophotometer was used (model UV-1201) to measure the content of the nutrient’s ammonia (NH
4−N), nitrate (NO
3−N), and total phosphorus (TP). ICP-MS (Perkin Elmer NexION 300D) was used to assess total essential metals (Cu, Zn, Mn, and Fe) and non-essential elements (Ni, Cr, Cd, and Pb) in water and soil in accordance with [
22,
23].
The following list includes formulae used in the course of this experiment:
2.4.1. SAR, Sodium Adsorption Ratio
The following formula, which uses concentrations given in meq/L as reported in [
24], is used to compute the sodium adsorption ratio (SAR).
2.4.2. RSC, Residual Sodium Carbonate
In accordance with Szabolcs and Darab [
25], the following formula in meq/L was used to compute residual sodium carbonate (RSC).
2.4.3. Magnesium Hazard Percentage
Calculating the magnesium hazard levels was completed using the following formula (in which the values are given in meq/L) [
26,
27].
2.4.4. Sodium Percentage
The proportion of sodium (Na%) is another parameter widely used to assess irrigation suitability of water quality [
28]. The units of measurement for levels of ions are meq/L.
2.5. Fishponds Water Properties Analyses
To assess the water’s suitability for irrigating vegetables and forecast its effects on watercress growth and yield as well as some sandy soil quality properties under investigation, water samples from both aquaculture systems available for irrigation were collected and analyzed prior to irrigation. Water samples were collected in a clean, dry plastic bottle, filtered, and then either immediately analyzed or conserved in accordance with the recommendations of the American Public Health Association [
21]. In the lab, pH, electrical conductivity (E.C), and total dissolved salt (TDS) characteristics of aquaculture water were analyzed. The basic metrics utilized to assess the quality of irrigation water were pH, soluble salt content (EC), primary soluble anions and cations, sodium adsorption ratio (SAR), Ca
2+/Mg
2+ ratio, magnesium hazard (MH%), Na
+/Cl
− ratio, sodium percentage (Na%), and residual sodium carbonate (RSC). The parameters and chemical composition of water samples collected from fishponds before watercress was irrigated are shown in
Table 3.
2.6. Watercress Yield and Quality Parameters
At the time of harvest (after 40 days from cultivation date), representative samples of vegetable plants were used to determine the following plant quality parameters of fresh and dry weight, TN concentration, and nitrate (mg kg
−1 fresh weight). Dried and ground plant material was digested with sulfuric acid (H
2SO
4) and hydrogen peroxide (H
2O
2) using the Digestor (Buchi, speed digestor, model: K-425 Digestion unit). The amount of nitrogen in the plant digests was measured using the digested vegetable plant material and the Kjeldahl equipment (Buchi, model: 426 distillation unit), according to Baird [
20] and AOAC [
22] description.
2.7. Statistical Analysis
The obtained results were subjected to analysis of variance using the least significant difference (L.S.D.) test at 5% level of probability using the MSTAT-C v. 1.42 for completely randomized design (CRD) with three replicates. Significance of the differences was compared using least significant difference (LSD) at a 5% level of probability (p < 0.05)
4. Conclusions
Due to Egypt’s current water shortage, improving water productivity through dual water use in an integrated aquaponic farming system is the most important outcome of on-farm water management interventions. This will also enhance crop and fish yields and quality, as well as mitigate negative environmental effects. Aquaponics in its modern style and inputs is still not widespread in rural Egypt, although it was carried out by Egyptian farmers in its own style on a large scale long ago without knowing what they were doing. This is to some extent because today’s modern aquaponic systems require significant capital, operating, and maintenance expenses. It is necessary to find innovative and cheap aquaponic techniques. This study contributes in a positive way to facing the challenge by evaluating the implementation of the integrated crop and fish farming system invented by Egyptian farmers. It will be an effective alternative to modern aquaponic plant and fish farming techniques with double water use with higher crop yields. This research finding suggested that the integrated aquaponic invented by the Egyptian farmer is a farming method that is environmentally feasible because it has had a favorable effect on soil characteristics, crop and water productivity, and the environment. The various integrated aquaponic systems for sustainable agriculture still need to be better understood; hence, more research is needed.