Using N-15 Technique for Assessing Organic – N Turnover in Sandy Soil.
Soliman M. Soliman Sr., Atomic Energy Auth., Nuclear Res. Center, Soils and Water Res. Dept, Abou Zaabal, Cairo, Egypt
Sandy soil of Egypt is classified as poor unfertile soils. Nowadays, an interest has been paid for controlling the environmental pollution via using the organic wastes and plant residues in farming that achieve the concept of clean and low input agriculture systems. Turnover of organic – N was traced under greenhouse condition. 15N-labelled wheat and/or soybean residues were used as organic additives applied individually or in combinations. These residues were applied at rates of 100, 75 and 25 µg N g-1 soil. Also, ammonium sulfate with 2% 15N atom excess, was applied either alone or in combination with the plant residues, at the rates of 100, 75 and 25 µg N g-1 soil as single dose after 10 days from planting. Relative positive effect of the nitrogen plant residues on N-uptake and yield components can be arranged as follows: Soybean > wheat + > soybean > wheat residues. Application of labeling technique indicated that mixing of labeled residues with ammonium sulfate at rates of (*50 + 50) and (*25 + 75), was effective on dry matter and N uptake. Effect of organic and inorganic nitrogen sources on portions (Ndfr & Ndff) derived to wheat could be arranged as following: ammonium sulfate >soybean >mixture >wheat. Higher 15N recovery percentage was noticed in grains as affected by addition of soybean residues combined with ordinary ammonium sulfate at rates of (*25 + 75) and *50 + 50), respectively. Key words: Plant residues, Sandy soil, Wheat, 15-N technique.