Soybean Response to Single or Mixed Soil Amendments in Kashmir, Pakistan

The application of animal‐ and plant‐derived organic substrates with minimal additions of commercial N fertilizers is an important management strategy for sustainable agriculture production systems in mountain upland soils subjected to continuous erosion. A 3‐yr (2009, 2010, and 2011) field experiment was conducted to evaluate the effects of separate and combined use of poultry manure (PM), wheat ( Triticum aestivum L.) milling residues (WMR), and urea N (UN) on the productivity and N 2 fixation of rainfed soybean [ Glycine max (L.) Merr.] grown in the Himalayan region of Rawalakot Azad Jammu and Kashmir, Pakistan. The experiment was conducted in a randomized complete block design with three replications. Treatments included UN 100 , PM 100 , WMR 100 , PM 50 + WMR 50 , UN 50 + PM 50 , UN 50 + WMR 50 , UN 50 + PM 25 + WMR 25 , and an unfertilized control. Nitrogen from all amendments was applied at an equivalent rate of 100 kg total N ha −1 . Compared with the control and UN 100 treatments, the organic amendments applied alone or combined with UN significantly increased the number and mass of root nodules and N 2 fixation by 36 to 68, 26 to 62, and 8 to 31%, respectively. Poultry manure (PM 100 ) displayed the highest nodulation (49 and 129 nodules) and N 2 fixation (43 and 73 kg N ha −1 ), while UN 100 did not differ from the control. Yield and yield components (residue dry matter yield and seed yield) and N use efficiency in the combined treatment UN 50 + PM 50 was comparable to that recorded under the UN 100 treatment. There was a positive correlation between nodule number and mass with N 2 fixation ( r = 0.86 and 0.79), suggesting that root nodulation can be used as an indicator for N 2 fixation. Results of this study confirmed the beneficial effects of organic amendments on N 2 fixation and in combination with UN represents a successful and sustainable management strategy for soybean production in mountainous ecosystems.