**4. Conclusions**

*Recent Advances in Numerical Simulations*

**(cm) n AE (cm3**

*efficient and CRM= coefficient of residual mass.*

*Statistical criteria for the simulated and measured soil water content.*

**Depth Statistical criteria**

**N balance components Applied – Inflow kg N ha−1**

To evaluate the Hydrus model performance with respect to nitrogen transport and transformations, the simulated nitrogen concentrations (NH4-N and NO3-N) are compared for different treatments at different depths of soil profile, (7.5, 22.5, 37.5, 52.5 and 120 cm from soil surface). **Figure 3 (A**–**C)** gives the daily variations in the simulated Urea-N, NH4-N and NO3-N concentrations respectively. It takes about 4 days to convert 90% of urea into ammonium and it takes about 70 days to convert 90% of ammonium into nitrate. Urea fertilizer is easily dissolved in water and transferred to the soil. After fertilization, urea is hydrolysed in the soil a urea concentration decreased over time between irrigations and ammonium is formed and then, during the nitration process by bacteria in the soil, convert ammonium to nitrite and then to nitrate. Immediately after fertigation, at 3.73 days, the urea was

*Components of nitrogen balance at the end of simulation period in kg N ha−1 for a soil depth of 150 cm.*

**N applied by wastewater Ammonium-N Nitrate-N Nitrate-N**

T1 = 100 5.3 47 **-** 82510 T2 = 75 5.2 47 81830 T2 = 50 4.1 39 7812 T2 = 25 1.7 23 63253 T3 = N-manure =100 4.2 43 21 78956 T4 = N-fertilizer =90 5.8 44 25 77582 T4 = split application 4.9 43 23 78962 T5 = well water = 0 — — — 51254

 365 −0.078 0.115 0.953 0.277 365 −0.094 0.115 0.958 0.303 365 −0.085 0.106 0.964 0.274 365 −0.032 0.058 0.989 0.098 *Note: n = number of measurements, AE = average error, RMSE = relative root mean square error, EF = modeling* 

> **Losses – Outflow kg N ha−1 Corn grain yield Crop uptake Leaching kg ha−1**

 **cm−3) RMSE (%) EF CRM**

For all treatments ammonium accumulated in the topsoil immediately (**Figure 4**). Because of soil adsorption and subsequent fast nitrification and/or root uptake, there was only a slight movement of ammonium in the soil profile. The results obtained in this study indicated that nitrate moved continuously downwards during the 28-day of growing season simulation. Also, nitrate is easily exposed to leaching due to its high mobility and is not adsorbed to the soil,

Nitrogen is applied to the soil solution by fertilizer application, treated wastewa-

**142**

**Table 7.**

**Table 6.**

concentrated near the soil surface.

ter irrigation and animal manure.

therefore denitrification was assumed negligible.

The HYDRUS-1D software was performed to simulated water flow and nitrogen transport in tomato crop soil for wastewater irrigation and fertilization. Based on the study carried out in the field, the ability of the model to predict the moisture in the soil at various depths is accurate. This can be due to an acceptable method in the simulation model.

The results reported from nitrogen balance components show that nitrate leaching losses (0%, 23% and 25%) in treatments T1, T3, T4 respectively and mainly occurred during the winter period. The reduced level of leaching is explained by low amount of drainage water, and excessive nitrogen uptake by the crop. Since the nitrate transport through the soil profile and out into field drains or deep groundwater, is usually controlled by water movement. It was fund that the slightly smaller leaching percentages for the urea–ammonium–nitrate wastewater compared to the nitrate- fertilizer and manure. Fertilizer use efficiency ranged from 54% (treatment T4) to 84.9% (treatment T1). Based on these results we conclude that nitrogen from wastewater has smaller nitrate leaching compared to nitrogen from animal manure and commonly fertilizer. Nevertheless, our simulation results provide guidance on the appropriate fertigation strategy for use of waste water in irrigation.

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