Isotope studies on the comparative efficiency of nitrogenous sources

Abstract

In a growth chamber experiment with 15N-labelled potassium nitrate, ammonium sulphate and urea at 75 and 150 kg nitrogen/ha and ammonium nitrate at 150 kg nitrogen/ha, nitrogen application produced significant responses of dry matter yield and total nitrogen uptake by shoot and root of barley in chernozemic dark brown Elstow silt loam and deep black Hoey clay soil. Total nitrogen removal per pot and isotope-derived criteria, viz. percentage nitrogen derived from fertilizer, 'A' value and percentage fertilizer nitrogen utilization, indicated that potassium nitrate was the most efficient and urea the least. At 75 kg nitrogen/ha, the recovery of fertilizer nitrogen in shoot and root was 47, 42 and 34% in Elstow silt loam and 65, 54 and 50% in Hoey clay with potassium nitrate ammonium sulphate and urea respectively. At 150 ppm nitrogen, these values were 62, 46 and 45 % in Elstow silt loam and 75,51 and 53 % in Hoey clay and that of ammonium nitrogen from ammonium nitrate, 17 and 43 % in the two soils respectively. The percentage excess of 15N in soil total nitrogen after the harvest of barley showed that urea was tied up more in the soil, causing lower efficiency for crop recovery. The contribution of root portion for different parameters in such evaluation studies needed equal consideration. The availability of fertilizer nitrogen for crop utilization was more in Hoey clay than in Elstow silt loam. Immobilization and losses of fertilizer nitrogen were greater in Elstow silt loam.