Effect of surface residue management under minimum tillage on crop yield and soil quality indices after 6 years in sorghum (Sorghum bicolor (L.) moench)-Cowpea (Vigna unguiculata) system in rainfed alfisols

This experiment was conducted in rainfed semi-arid tropical Alfisol at Hayathnagar Research Farm of Central Research Institute for Dryland Agriculture, Hyderabad, India, during the period 2005 to 2010 to study the long-term effect of varying levels of surface residue application under minimum tillage on crop yields and soil quality in sorghum-cowpea system. The experiment was conducted in a randomized block design with minimum tillage (MT) as main block. The experimental treatments comprised of application of four levels of dry sorghum residues (@ 0, 2, 4 and 6 t/ha) as surface application. After 6th year of the experimentation, the pooled mean sorghum grain yield varied from 1607 to 1819 kg/ha across the treatments and was significantly influenced by the residue application. The percent increase in pooled grain yields with residue application @ 2, 4 and 6 t/ha was to the extent of 5, 9 and 13.0% respectively over the control (no residue application). Similarly, the pooled mean cowpea yield varied from 335 to 541 kg/ha across the treatments and was significantly influenced by the residue application. The percent increase in cowpea grain yield with @ 2, 4 and 6 t/ha was to the extent of 28, 61 and 45% respectively no residue application. Significantly higher organic carbon (6.80 g/kg) content was recorded with the application of sorghum stover @ 6 t/ha which was 55.89% higher compared to control (4.36 g/kg). The increase in available N with the application of 6t and 4t crop residue was to the extent of 19.5 and 28% respectively while significantly higher contents of soil available P (10.67 kg/ha) and K (288.8 kg/ha) were observed with application of sorghum residue @ 4 t/ha. Among the biological properties, significantly higher microbial biomass carbon (MBC) and dehydrogenase activity (DHA) were recorded with the application of sorghum stover @ 4 t/ha. Besides reducing the bulk density, the application of residues had a significant influence on the mean weight diameter (MWD) of the soil aggregates. The highest overall soil quality index (SQI: 9.58) was observed with the residue application @ 6 t/ha. A significant positive relationship was observed between SQI and pooled cowpea seed yield (R2=0.82) and pooled sorghum grain yield (R2=0.69).