Effect of nitrogen fertilization on productivity and nitrogen balance in soil in gobhi sarson (Brassica napus)-based crop sequences

An experiment was conducted during 1997–98 to 1999–2000 at the Oilseeds Research Station, Kangra, consisting of 4 rainy-season crops, viz. maize (Zea mays L.), dhaincha (Sesbania aculeata Pers.), soybean [Glycine max (L.) Merr.] and blackgram (Phaseolus mungo L.), followed by gobhi sarson (Brassica napus ssp. oleifera var annua) at 5 levels of N (0, 40, 80, 120 and 160 kg N/ha). Dhaincha-gobhi sarson sequence snowed the maximum N balance in soil at all levels of N application. This was followed by soybean-gobhi sarson, blackgram-gobhi sarson and maize-gobhi sarson where positive N balance was observed at 40–160 kg N/ha. The balance sheet of N showed that there was gain of N in soybean-gobhi sarson and blackgram-gobhi sarson sequences, whereas it was negative in dhaincha-gobhi sarson and maize-gobhi sarson sequences. The gain of N in balance sheet was higher at lower levels of N application. The maximum grain yield of gobhi sarson was obtained in dhaincha-gobhi sarson sequence. The yield in dhaincha-gobhi sarson at 40 kg N/ha, blackgram-gobhi/sarson at 80 kg N/ha and maize-gobhi sarson at 120 kg N/ha also remained at par with one another.