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

Abstract

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 N2 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 UN100, PM100, WMR100, PM50 + WMR50, UN50 + PM50, UN50 + WMR50, UN50 + PM25 + WMR25, 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 UN100 treatments, the organic amendments applied alone or combined with UN significantly increased the number and mass of root nodules and N2 fixation by 36 to 68, 26 to 62, and 8 to 31%, respectively. Poultry manure (PM100) displayed the highest nodulation (49 and 129 nodules) and N2 fixation (43 and 73 kg N ha−1), while UN100 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 UN50 + PM50 was comparable to that recorded under the UN100 treatment. There was a positive correlation between nodule number and mass with N2 fixation (r = 0.86 and 0.79), suggesting that root nodulation can be used as an indicator for N2 fixation. Results of this study confirmed the beneficial effects of organic amendments on N2 fixation and in combination with UN represents a successful and sustainable management strategy for soybean production in mountainous ecosystems.