Nutrient removal by weeds and crops as affected by herbicide combinations in soybean-wheat cropping system

Eight weed control treatments in soybean and three in wheat were evaluated in soybean-wheat cropping system during 2009–10 and 2010–11 at Palampur. Commelina benghalensis followed by Echinochloa colona were the most competitive weeds in soybean. In wheat, Phalaris minor and Avena ludoviciana were the most predominant weeds. Pendimethalin fb chlorimuron reduced dry weight of Aeschynomene, Ageratum, Cyperus, Echinochloa and Panicum significantly over the unweeded check. Isoproturon 1000 g/ha + 2, 4-D 500 g/ha reduced dry weight of Phalaris minor over the weedy check. In soybean, application of pendimethalin fb chlorimuron-ethyl allowed weeds to remove 89.2, 89.1 and 88.9% less N, P and K, respectively as compared to the unweeded check. Application of isoproturon 1000 g/ha + 2,4-D 500 g/ha reduced N, P and K depletion by weeds by more than 24% over the unweeded check. Application of pendimethalin fb chlorimuron-ethyl resulted in 187.5% higher N and 166.3% higher K uptake by soybean over weedy check. Unchecked weed growth reduced P uptake by 62.4% as compared to pendimethalin fb chlorimuron ethyl. Isoproturon 1000 g/ha + 2,4-D 500 g/ha and isoproturon 750 g/ha + 2,4-D 500 g/ha resulted in significantly higher N, P and K uptake by wheat over unweeded check. Weedy check reduced soybean equivalent yield by 37.4 and 28.8% during 2009 and 2010, respectively. Imazethapyr fb imazethapyr produced higher soybean equivalent yield (3.34 t/ha) during 2009, whereas, pendimethalin fb chlorimuron (3.16 t/ha) was better during 2010. Isoproturon 1000 g/ha + 2,4-D 500 g/ha ( 1,17,736) and isoproturon 750 g/ha + 2,4-D 500 g/ha ( 1,16,861) resulted in higher net returns and net per invested as compared to weedy check.