الفهرس 
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Abstract
The present study was conducted at the experimental Farm of Sids Agricultural Research Station, Beni Suef Governorate, Egypt, during two successive growing seasons of 2002/2003 and 2003/2004.
The aim study at investigating the effect of different sources and rates of the nitrogen fertilization on the soil, groundwater, yield and chemical composition of spinach and maize. The experimental design was factorial in a completely randomized blocks with four replications for both spinach and maize experiments. The field experiments included sixteen treatments representing five nitrogen sources. The sixteen treatments consisted of five sources of nitrogen as follows:
1- Ammonium sulphate (20.6 % N), denoted as AS. 2- Ammonium nitrate (33.5 % N), denoted as AN. 3- Urea (46.5 % N), denoted as U.
4- Farmyard manure, denoted as FYM. 5- Chicken manure, denoted as CM
Each nitrogen source was applied in four levels of 0.0, 40, 80 and 120 kg N/feddan to the spinach plants, while the levels applied to maize plants were 0.0, 60, 120 and 180 kg N/feddan.The experimental design consisted of 64 plots in both growing seasons of spinach and maize. The size of each plot was 10:5 m2 (3.5 m x 3). Sixteen pizometric observation points were setup at ten days before planting the spinach seeds and maize grains in every growing seasons to collect water samples in order to study the chemical composition of the leaching water.
The obtained results could be summarized as follows: 1. Nitrate, nitrite and ammonium contents in the soil:
- The nitrate, nitrite and ammonium contents were increased with increasing the nitrogen level, however it decreased with increasing soil depth.
- The leached nitrate, nitrite and ammonium ions at 32 days after planting gave the highest values followed by the time at 22 days, while the lowest values were obtained at the harvest time. - The chemical fertilizers increament higher values of nitrate, nitrite and ammonium ions than the organic manures through the growing period while the reverse results were obtained after harvest time.
2. Nitrate and nitrite contents in the groundwater for the two plants:
- Increasing nitrogen levels increased the nitrate and nitrite contents in the groundwater.
- The values of nitrate and nitrite content in the groundwater at 22 and 32 days from planting due to applying different nitrogen sources could be arranged in the following descending order: AN> U> AS> CM>FYM.
3. Spinach and maize growth:
- Increasing nitrogen levels significantly increased plant height for both plants, fresh and dry weights for spinach.
- Applying of ammonium sulphate gave the highest values of plant height for the two plants and fresh and dry weights for spinach followed by urea, ammonium nitrate, chicken manure then farmyard manure.
4. Maize grain and stover yields.
Increasing nitrogen level up to 180 kg N/feddan were significantly increased both grain and stover yields.
- The highest values of grain and stover yields obtained by fertilized maize plants with ammonium sulphate followed by U, AN, CM and then FYM.
5.Nitrate concentration III spinach shoots and roots and maize grain, stover and roots:
- Nitrate concentration was significantly increased by increasing nitrogen level.
- Addition of ammonium nitrate gave the highest values of nitrate concentration followed by U, AS, CM and then FYM.
6.Nitrate uptake by spinach and maize plants:
Nitrate uptake was significantly increased by increasing nitrogen level.
- The treatment of ammonium sulphate gave the nitrate uptake higher than that ofU, AN, FYM and then CM.
7.NPK concentration and protein percentage m spinach plants and maize grain and stover:- NPK concentration and protein percentage were significantly increased by increasing nitrogen level.
- Addition of ammonium sulphate gave higher nitrogen concentration and protein percentage than U, AN, CM and then FYM.
- Applying of chicken manure gave highest values of phosphorus concentration followed by FYM, AS, U and then AN.
Addition of chicken manure produced higher potassium concentration than those obtained by FYM, AN, U and then AS
8. NPK uptake and nitrogen use efficiency by spinach and maize plants:
- NPK uptake by spinach and maize plants was significantly increased by increasing nitrogen level, while the nitrogen use efficiency was significantly decreased by increasing nitrogen level.
- Applying ammonium sulphate resulted in higher NPK uptake by maize plants and nitrogen uptake by spinach plants than U, AN, CM and then FYM, while phosphorus and potassium uptake by spinach plants followed by the descending order: AS> CM> U> FYM> AN.
- Applying of AS gave nitrogen use efficiency than that of U, AN, CM and then FYM.