Effect of preceding kharif crops and nitrogen levels on dry matter accumulation and nitrogen use efficiency in wheat

A field experiment was carried out during 2003–04 and 2004–05 on loamy sand soil at Punjab Agricultural University, Ludhiana to study the effect of preceding kharif crops (soybean, groundnut, moong, maize, rice_FYM and rice) and five levels of nitrogen (0, 60, 90, 120 and 150 kg ha⁻¹ to succeeding wheat. Results revealed that dry matter accumulation by wheat varied from 108.3 and 104.3 q ha⁻¹ preceded by rice to 135.2 and 133.3 q ha⁻¹ preceded by soybean during both the years respectively. The response to N levels was recorded upto 120 kg N ha⁻¹. Significant increase in total dry matter (grains + straw) was recorded with increasing N levels upto 90 and 120 kg N ha⁻¹ preceded by legumes and cereal crops, respectively. Maximum 146.6 and 141.3 kg N was removed preceded by soybean compared to 94.8 and 93.6 kg N ha⁻¹ preceded by rice. Wheat grown after legumes recorded higher N uptake as compared to crop preceded by cereals. N uptake increased significantly with application of N upto 90 and 120 kg ha⁻¹ after legumes and cereal crops, respectively. Mean values of agronomic efficiency (kg added kg⁻¹ N), apparent nitrogen recovery (%) partial factor productivity of applied N (kg kg⁻¹ N) and physiological efficiency (kg grain kg⁻¹ N) were lower when wheat crop was preceded by leguminous crops as compared with cereal. Successive increase in N doses from 60 to 150 kg ha⁻¹ resulted in progressive decrease in agronomic efficiency, apparent N recovery, partial factor productivity to applied N and physiological efficiency in both the years. Optimum economic dose of N for wheat was 97, 109, 113, 125, 127 and 133 kg ha⁻¹ after soybean, moong, groundnut, maize, rice_FYM and rice, respectively.