Sustainable soil amendments for improving the soil quality, yield and nutrient content of Brassica juncea (L.) grown in different agroecological zones of eastern Uttar Pradesh, India

Sustainable soil amendments are important for enhancing the yield and nutritional quality of agricultural produce while reducing the soil carbon efflux. In this backdrop, a two-year field experiment was conducted to examine the effect of different soil amendments such as humicil, sheep manure and humicil + sheep manure on soil structure, organic carbon, microbial biomass carbon, soil and microbial respiration as well as the growth and yield of Brassica juncea (L.) grown in different agroecological zones of eastern Uttar Pradesh, India. For this, field experiments were performed at three different experimental sites in three different agroecological sub-zones i.e. Varanasi, Sultanpur and Gorakhpur of Uttar Pradesh, India. Experimental results indicate that the application of humicil + sheep manure significantly improved (p < 0.05) the soil moisture (29%), cation exchange capacity (6.5%) and soil aggregation (1.5-fold) at Varanasi site followed by sheep manure and humicil. Furthermore, these changes were also lead to the enhancement in organic carbon (1.2 fold), available nitrogen (19.6%) and microbial biomass carbon (48.0%) content of the soil. Sheep manure addition resulted in higher bacterial and fungal counts (195.1 × 107 and 118.3 × 107 g-1 soil) than humicil and thereby enhanced the soil β-glucosidase activities (66 to 86%) than the combined amendments at different experimental site whereas the highest soil (43, 44 and 40%) and microbial (70, 73 and 64%) respiration was observed under sheep manure amended field than humicil. The effect of various amendments on soil and microbial respiration was found in the order of sheep manure > humicil + sheep manure > humicil > control whereas maximum agroecological sub-zone wise variation was observed at Sultanpur followed by Varanasi and Gorakhpur. Increase in plant height (37 to 45%), biomass (33 to 45%), yield (140 to 190%) and harvest index of B. juncea was found under combined amendment than the control. Similarly, the N, P, K, protein and oil content of the test plant was higher under the combined treatments. The present study conclude that combined application of humicil and sheep manure is better than the individual amendments and therefore suitable package of practices based on such combined amendments must be validated at larger scale for improving the soil quality, yield and nutritional quality of agricultural crops while reducing the carbon emission.