Nitrogen Use Efficiency of Transplanted Rice as Influenced by N, P and K Levels

The effect of three levels each of N (150, 200 and 250 kg ha⁻¹), P (33, 44 and 55 kg ha⁻¹) and K (62, 83 104 kg ha⁻¹) on grain yield and N-use efficiency in irrigated rice was studied at Agricultural Research Station, Gangavathi, Karnataka during kharif 2000 and summer 2001. Application of 250 kg N ha⁻¹ recorded higher N uptake (150 and 151 kg ha⁻¹ during kharif and summer 2001, respectively) than recommended 150 kg N ha⁻¹ (122.8 and 112.8 kg N uptake ha⁻¹, respectively during kharif and summer). Agronomic-N-use efficiency decreased at 250 kg N ha⁻¹ (17.5 kg grain kg⁻¹ N) as compared to150 kg N ha⁻¹ (21.6 kg grain kg⁻¹ N) in the summer, while in kharif it was higher at 200 kg N ha⁻¹ than 150 kg N ha⁻¹ but decreased with further increase in N rate. Application of P up to 55 kg ha⁻¹ in kharif and up to 44 kg ha⁻¹ in summer recorded higher N-recovery (36.2 and 40.9% in kharif and summer, respectively) and agronomic efficiency (11.0 and 20.1kg grain kg⁻¹, N respectively during kharif and summer). Potassium at different levels ranging from 62 to 104 kg ha⁻¹ had no significant effect on N-use efficiency. Application of 200:44:62 and 250:44:62 kg N, P and K ha⁻¹ in kharif and summer resulted in higher grain yields than recommended practice mainly by improving N uptake.