The agronomic and economic value of treated wastewater reuse for some field crops in desert soil

To evaluate the agronomic and economic value of wastewater reuse in desert soil, demonstration field trials were conducted in desert (virgin) soil to evaluate the effect of irrigation with secondary treated wastewater from El Berka wastewater treatment plant on food and non-food crops. The results showed that considerable amounts of macronutrients (NPK) were applied to the grown crops through the treated wastewater irrigation: N (36–176%), P2O5 (72–360%), and K2O (99–357%) of the recommended fertilizer rates according to the crop. Crop yields showed significant differences when treated wastewater was combined with the recommended fertilizer rates for most crops. Maize, cotton, sunflower, and wheat seemed to be better cropped for irrigation with secondary treated wastewater. The calculation of fertilizer value in EGP based on market prices in Egypt showed that nitrogen addition value ranged between 315 and 1178 EGP, P between194 and 1128 while K ranged between 585 and 2398 EGP according to the crop and the period of wastewater irrigation. The Economic value of fertilizer inputs applied to the field crops indicates that the total NPK value ranged between 1049 and 4303 LE. It could be concluded from this study that treated wastewater has substantial agronomic value for most of the field crops studied. Wastewater irrigation could save partial NPK crop requirements and needs fertilizer compensation. The advantage of field crop irrigation with treated wastewater is evident from the agronomic and economic scene. A crucial conclusion of this work is that it serves in wastewater pricing plans in the new lands in Egypt and similar countries.


Introduction
In Egypt, the annual water demand exceeds the available freshwater by 6 billion m 3 year -1 (Abu Zeid, (1992). Water reuse is arising because of the water crisis with Nile basin countries, ambitious land reclamation programs, growing populations, increasing rural development, and crop demands. However, there are attendant risks involved with reuse to the plant, soil, groundwater, and health (Oron et al., 1992;Shatanawi & Fayyad, 1996, Aissi et al., 1997, Oron et al., 2007. One of the most recognized benefits of wastewater use in agriculture is the associated decrease in pressure on freshwater sources (Jaramillo and Restrepo, 2017). Thus, wastewater serves as an alternative irrigation source (Winpenny et al., 2013), specially for agriculture, the greatest global water user, which consumes 70% of available water (Pimentel et al., 1999). Furthermore, wastewater reuse increases agricultural production in regions experiencing water shortages, thus contributing to food safety (Pimentel et al., 1999). WRC (2001) estimated that wastewater could offer about 30% of the crop requirements of N and 100% or more from crop requirements of K in sandy calcareous soil in Alexandria. Additionally, the nutrients naturally present in wastewater allow savings of fertilizer expenses to be realized (Drechsel et al., 2010;Winpenny et al., 2013;Corcoran 2010 andMoscoso, 2017), thus ensuring a closed and environmentally favorable nutrient cycle that avoids the indirect return of macro-(especially nitrogen and phosphorous) and microelements to water bodies. Depending on the nutrients, wastewater may be a potential source of macro- (N, P, and K Ca, Mg, B, Mg,) and micronutrients (Fe, Mn, or Zn) (Barreto et al., 2013 andJimenez, 1995). Wastewater reuse has been proven to improve crop yield (Moscoso, 2017;Jimenez, 1995) and result in the reduced use of fertilizers in agriculture (Toze, 2006). Therefore, this work aims to evaluate the effect of treated wastewater on irrigation of field crops yields and the agronomic and economic value of the nutrients applied through wastewater irrigation in sandy soil.

Materials and methods
This paper is a part of a study entitled the "Cairo East Bank Effluent Re-use Study". The client is the Cairo Wastewater Organization (CWO) and the study is partially funded by the Kuwait Fund for Arab Economic Development (KFAED). The study was implemented by a joint venture consortium of Montgomery, Watson, Gibb International, and some other Arab companies. Demonstration field trials were carried out in winter and summer seasons in the El Berka site located about 20 km northeast of Cairo. As it was intended to use secondary treated wastewater and to be secured the experimental site was located inside the El Berka wastewater treatment plant; the soil is gravelly sand and could be classified as the virgin soil. The experimental area was divided into 32 large experimental units 8 allocated for each crop selected according to the crop and the irrigation method. The design of each trial was Complete Randomized Block Design with 4 replicates were 4 plots received wastewater only and the other 4 received wastewater plus supplementary fertilizer to be adjusted for each crop according to the normal recommended rates. Four crops were planned to grow in each season, crop selection included a range of food, fodder, and industrial (fiber and oil) crops according to WHO (1989). For the summer season, cotton (Giza 85 variety) soybean (Giza82 variety), maize (Single Hybrid 129 variety), and sunflower (local variety) were grown. In the winter season, wheat (Sakha 8 variety), faba bean (Giza 3 variety), lupine (Giza 1 variety), and canola (Pactol variety) were grown. Ddrip and sprinkler irrigation systems were used. .Sprinkler irrigation was used for soybean, wheat and canola; drip irrigation for cotton, maize, sunflower, lupin, and fababean. The experimental plot area was 200m 2 (10x20m). Fertilizers were applied according to the normal recommended rates in Egypt for each crop. Nitrogen , phosphorus and potassium were applied as ammonium nitrate(33.5% N), calcium superphosphate (15.5%P2O5) and potassium sulphate (48%K2O), respectively.

Crop growth and yield assessment
During the two crop cycles, the crops were routinely inspected for diseases, pests, and weed control. At crop maturity, the growth characteristics and yield components were assessed according to the type of the crop. The individual plant measurements included plant height and weight, number of branches or tillers per plant as well as the number, weight, and dimensions of fruiting organs (pods, capsules, cobs, bolls, spikes, etc.). The conventional assessment practices were followed to provide mean individual plot performance as well as biological, straw, and grain or seed yield /feddan. This research will focus only on the economic yield parameters.

Treated wastewater analysis
Samples of treated wastewater from El Berka were taken during crop cycles and analyzed for a range of agronomic and environmental parameters. Nutrient and heavy metal loading rates to field trials were calculated according to the irrigation quantities applied to each crop to assess the acceptability of these wastewaters for reuse in the short and long-term. Another objective of these analyses was to determine wastewater compliance with the Egyptian limit values (Decree 44/2000). Treated wastewaters were analyzed according to APHA (1992).

Wastewater fertilizer inputs to field crops
It was calculated from total water quantity irrigated to each crop and nutrient concentration in wastewater according to WRc (2001).

The economic value of nutrient addition
It was calculated from nutrient addition to each crop on fertilizer prices basis in Egyptian market.

Treated wastewater quality
Final wastewater samples collected from El Berka WWTP throughout the trials were monthly routinely analysed for nutrients and heavy metals ( Table 1). The results showed that the pH of the wastewaters was within the acceptable range for reuse, normally 6.5-8.5 according to the Egyptian decree for wastewater reuse (Decree 44, 2000). The nutrient contents of the wastewater were broadly similar in their suitability for reuse. It is worthy to mention that considerable amounts of macronutrients (NPK) were applied to the grown crops through the treated wastewater irrigation: N (36-176%), P2O5 (72-360%), and K2O (99-357%) of the recommended fertilizer rates according to the crop.
The heavy metal concentrations were very small in wastewater, and are well below the limit values for secondary wastewater reuse, usually by at least one order of magnitude where the limit values of the heavy metals according to the Egyptian decree for wastewater reuse (Decree 44/2000) are (0.01 for Cd and Cr; 0.2 for Cu, Ni and Mn, 0.05 for Co, and 5 mg kg -1 for Fe). The numbers of fecal coliforms found in treated wastewater were at 10 6 MPN/L, far more than that permitted by the guidelines of WHO (1989), and Salmonella were present in all samples. Nematode ova were found in all samples of treated wastewater over the limit value for reuse (mean 49 ova/L). Table 1 presents the mean concentrations of treated wastewater chemistry and microbiology. Units: All determinants in mg/L except EC (dS/m); salmonella qualitative range 0 = absent, 1 = low, 3 = high; faecal coliform bacteria 10 5 MPN/100 ml; helianthus ova/L.

Statistical analysis
The obtained results were subjected to the proper statistical analysis using the MSTAT-C package, program according to MSTAT-C. For means comparison LSD at 5% was used.

Wastewater fertilizer inputs to field crops
Irrigation quantities were accurately recorded for each plot at both sites during the summer and winter seasons. Table (2) summarises the amounts of wastewater irrigated to each crop and fertilizer treatment, as a means of four replicate plots of each treatment. Although a fixed irrigation schedule was envisaged, this had to be adapted according to crop water requirements as observed in the field. The quantities of wastewater applied are broadly in line with normal practice, with exceptions, and these are related to the basic water requirement which varies between crops and the length of the growing season. For instance, cotton requires a long season to mature and consequently, this had the largest amount of wastewater applied. Conversely, lupin has a small water requirement, as indicated by the quantities irrigated. Table (3) lists the normally recommended application rates of inorganic fertilizer to the range of crops tested in these trials. The recommendations for some crops are different according to the fertility level of the soil and recommended for each crop.
Nevertheless, the wastewaters provide a significant proportion of the normal recommended fertilizer rates. Cotton received 176% of its recommended N rate, but this was due to the high irrigation demand of this crop on desert soil and would not normally be grown under these conditions (Fig 1). These observations are important because one of the problems encountered by wastewater reuse in other countries has been the over-supply of nitrogen at normal crop irrigation duties due to the high concentrations in the wastewater. This can lead to luxurious growth at the expense of economic yield and give rise to nitrate leaching and pollution of groundwater. This is not likely to occur in Egypt as wastewaters generally have relatively low nitrogen contents. The addition of phosphorus by the wastewater was closer to the recommended rates for the crops at both sites, with the excess being applied only to cotton and maize. However, surplus P addition is not a significant environmental concern since this element is readily fixed in the soil where it forms insoluble calcium phosphate. The potassium contents of the wastewaters were large relative to crop requirements, compared with those for N and P. Consequently, crop requirements for potassium (as K2O) were generally exceeded by large margins for most crops. However, potassium is held strongly by soils, particularly those with high cation exchange capacities, and even where this is exceeded and leaching occurs, this will be adsorbed further down the soil profile. In the long-term, groundwater quality could be affected but not adversely as there are no environmental problems associated with this, other than its contribution to salinity level. The data of chemical additions through treated wastewater varies according to crop water requirements at the duration of cropping. The data show that El Berka soils received small additions of heavy metals; moreover, some elements as Cd, Mo, and Co were below the detection limit as shown in Table (1). These results reflect minimum pollution in the short and long terms and indicate the suitability of Cairo wastewater for reuse on the agricultural land. Similar results were obtained by Mahmoud et al (1998) in Jordan and(WRc,2001) in Egypt. Barreto et al., 2013 andLiu et al., 2011 indicated that depending on the nutrients, wastewater may be a potential source of (N, P, and K) and micronutrients (Ca, Mg, B, Mg, Fe, Mn or Zn). Also, Abd El Lateef et al (2020 a and b) came to similar results. The general chemistry of the treated wastewater does not impose any constraints on the types of crops that may be grown or the types of soil to which it may be applied. Beneficial additions of NPK to the grown crops were evident and by the results of WRC (2001); they showed that these treated wastewaters would generally provide approximately 50% of N and about 70% of P requirements but about 200% of K requirement, although this varied widely according to the specific crop and whether this was calculated for fertile or infertile soil. The potential long-term consequences to soil quality of irrigating these treated wastewaters were modeled in other studies (WRC, 2001) which showed that it would take several hundred years to reach precautionary soil limit concentrations, but if crop off-take is taken into account, then heavy metal input and output would be more-or-less in balance and there would be the minimal net impact on soil quality. Similar results were obtained by Mahmoud et al. (1998). WRC (2001) in Egypt reported that the concentrations were variable and reflect minimum pollution in the short and long terms and indicate the suitability of Cairo wastewater for reuse on the agricultural land. In another study (Abd El Lateef et al., 2010;Derfasi, 2014; and Abd El Monsef and Abd El Lateef 2020) came to a similar conclusion

Summer Crops
Data presented in Table 4 and Fig 2 show the overall yield criteria of summer crops showed statistically significant increases due to the addition of fertilizer. The coefficients of variation of the means of data derived from individual plant measurements were quite small, but the CVs of the yields derived from area assessments were relatively large due to crop variability. Application of recommended fertilizer rate to maize significantly increased all yield characters. Maize grain yields were large for this soil type, and the addition of fertilizer increased yields by 52%, approaching the national average yield of 2.3 t/fd. The grain to straw ratio was 1:3.5, indicating that a greater proportion of the nutrients were supporting grain production, rather than straw. These ratios were the same whether fertilizer was applied or not, which suggests that maximum potential grain yields for these sites may not have been achieved, as an increased straw production may be expected relative to grain if excessive levels of nutrients are applied. Cotton responded well to irrigation with treated wastewater (Table 4 and Fig 2). Seed cotton yield per plant (total of two picks), as measured on an individual plant basis, was increased significantly by the addition of fertilizer (P<0.0001), with yields of fertilizer treatments being three times that from the treated wastewater only, however, the large CV indicates the high variability of these data. When yields were measured on an area basis, there were no significant effects on seed cotton yield at either pick. The straw yield was significantly increased by fertilizer application to wastewater, the increase was similar to that observed for seed cotton (19% vs 13%). The first pick accounted for 75% of the total yield on both treatments. Highly significant increases in all of the yield parameters of soybean characters were achieved by the addition of fertilizer over those achieved by the treated wastewater on its own (Table 4 and Fig 2). The treated wastewater alone provided insufficient nutrients since fertilizer increased the measured parameters by about 150%. Seed yield increased from 0.35 t/fd to 0.88 t/fd, and the latter compares favorably with the national average yield of 1.1 t/fd, considering the poor quality of this soil. Straw yield also increased substantially with the addition of fertilizer but the seed: the straw ratio was slightly smaller, indicating that optimum yield had not been reached.

Fig 1: Macronutrient additions of treated wastewater to field crops as a percentage of the recommended NPK rate for each crop in desert land
Data presented in table 4 and Fig 2 indicate that tere were highly significant effects of fertilizers on all of the yield parameters of sunflower, with substantial increases in seed and straw yields, compared with those achieved with only treated wastewater . The addition of fertilizer increased seed yield by 67%, but increased straw yield by 141%. This may be attributed in part to the nutrient supply from El Berka effluent which closely met with recommended amounts of fertilizer for this crop. Similar results were reported by Mahmoud (1998) and Abd El Lateef et al (2014) on maize, cotton and mungbean .They added that crops irrigated with secondary treated wastewater perform equally as well as, or significantly better than, with canal water.

Winter Crops
Yield parameters of lupine are summarised in Table 5. The addition of fertilizer increased crop performance and the results showed that the performance of individual plants under drip irrigation was superior due to the few plant densities (26,000 plants per feddan) due to the wider row spacing under the drip irrigation system. Data in Table 5 and Fig. 3 show that under either irrigation system, fertilizer increased crop performance. Data presented in Table 5 show that all of wheat yield parameters were increased although straw and biological yields were not significantly increased The harvest index was greater with fertilizer application where relatively more grain was produced relative to straw yield.
These results emphasize that the recommended amounts of fertilizer are necessary to achieve adequate yields of wheat on this type of soil, even when irrigated by treated wastewater. This is maybe due to them that the addition of nutrients by treated wastewater irrigation is cumulative over the growing period of the crop, whilst fertilizer is applied in several doses, planned according to the growth of the crop to ensure appropriate nutrition throughout. This is demonstrated by the improved harvest indexes where fertilizer was applied. All of the yield parameters of canola under surface irrigation were greater than under sprinkler irrigation (Table), even though a larger quantity of treated wastewater was irrigated by sprinkler (mean of 2830 m 3 /fd compared with 2682 m 3 /fd). This indicates greater water efficiency under surface irrigation and may be due to larger evaporative losses from sprinkler irrigation. However, statistically, significant differences were only detected for the number of seeds per pod, straw, and biological yields. The harvest index was greater under surface irrigation, without significant differences. From the same table, significant increases in yield response due to the addition of fertilizer were observed for seed, straw, and biological yields. There were small but significant interactions between irrigation method and fertilizer treatments for straw and biological yields. Yields under sprinkler irrigation with fertilizer added were poor. Data presented in Table (5 and Fig 3)) show that as expected, the lower plant density under drip irrigation produced larger individual plants with more pods, but seed weight was smaller. The increase in plant yield did not compensate for the low plant density under drip irrigation. Consequently, the harvest index was better under surface irrigation (the normal method of irrigation) and had the largest seed and straw yields on an area basis. The addition of fertilizer increased all yield parameters insignificantly except for seed yield (P= 0.0409). These results derived from all crops clearly show that some field crops respond well to irrigation with treated wastewater i.e.; maize, cotton, wheat, and fababean . However, other crops like lupin, canola, and soybean showed less response for irrigation with treated wastewater under the poor desert conditions. Several investigators obtained yield increases due to wastewater application (Vazquez-Montial et al., 1996;WRc, 2000and 2001Abd El Lateef et al., 2014and Abd El Monsef and Abd El Lateef 2020. Such an increase in crop yields due to wastewater irrigation could be attributed to the nutrient content about specific crop requirements. In this respect, Campbell, et al, (1983) stated that weekly application of 25 mm wastewater was enough to supply 40-80% of corn requirements and all of the P requirements while other researchers pointed out that the increase in corn yield was due to the enhancement of nutrient uptake and the improvement of the physical properties of the soil. Indeed, wastewater reuse has been proven to improve crop yield (Moscoso, 2017 andJimenez, 1995) and result in the reduced use of fertilizers in agriculture (Toze 2006).

The economic value of treated wastewater
Considerable amounts of macronutrients (NPK) were applied to the grown crops through the treated wastewater irrigation. Table 6 shows the calculation of fertilizer value in EGP based on market prices in Egypt. Nitrogen addition ranged between 315 and 1178 EGP, P between194, and 1128 while K ranged between 585 and 2398 EGP ( LE ) according to the crop and the period of wastewater irrigation. The most beneficial value of N,P, and K was reported by cotton ( Fig  4). This could be attributed to the longer period of cotton irrigation with treated wastewater than other crops. The Economic input of fertilizer applied to the field crops indicate that the total NPK value ranged between 1049 and 4303 LE according to the crop NPK requirements and the duration of irrigation These results emphasize that the nutrients naturally present in wastewater allow savings on fertilizer expenses to be realized (Drechsel et al., 2010;Winpenny et al., 2013;Corcoran, 2010;Moscoso, 2017;Abd El Lateef et al., 2014 and.

Fig. 2 Productivity of summer field crops irrigated with treated wastewater
The advantage of field crop irrigation with treated wastewater is evident from the agronomic and economic scene. Several investigators assured that the nutrients naturally present in wastewater allow savings on fertilizer expenses to be realized (Drechsel et al., 2010;Winpenny et al., 2013;Corcoran, 2010 andMoscoso, 2017)

Conclusions
It could be concluded from this study that treated wastewater has substantial agronomic value for most of the field crops. Wastewater irrigation could save partial NPK crop requirements and needs fertilizer compensation. The results emphasize that the recommended amounts of fertilizer are necessary to achieve adequate yields of wheat on this type of soil, even when irrigated by treated wastewater. This is maybe due to that the addition of nutrients by treated wastewater irrigation is cumulative over the growing period of the crop, whilst fertilizer is applied in several doses, planned according to the growth of the crop to ensure appropriate nutrition. The importance of this work is that it serves in wastewater pricing plans in the new lands in Egypt and similar countries.