Tillage, irrigation levels and rice straw mulches effects on wheat productivity, soil aggregates and soil organic carbon dynamics after rice in sandy loam soils of subtropical climatic conditions

Soil organic carbon is considered to be of central importance in maintaining soil quality. We assessed the adoption of different combinations of tillage, crop residue and irrigation on soil organic carbon (SOC) dynamics in different sized soil aggregates and also on crop yield after 4 years in wheat monoculture field plot experiment in a sandy loam soil under subtropical climatic conditions. Results showed that tillage crop residue and irrigation significantly increased water stable aggregates and had profound effects in increasing the mean weight diameter as well as the formation of macro-aggregates, which were the highest in both surface (14.5 &12.5%) and subsurface (13.4 & 12.1%) soil layers under FIRB and ZT with application rice straw and I5 treatments after 3 years. Hence, better aggregation was found with FIRB with 6t rice straw + I5 where macro-aggregates were greater than 30% of total soil mass. The same treatment also enhanced the labile C and N fractions such as water soluble C, particulate and light fraction organic matter from 7.1 mg·kg-1 conventional tillage to 17.6 mg·kg-1 in surface layer and from 6.5 to 16.3 mg·kg-1 in subsurface layer after 3 years leading to the 42% and 39% higher water soluble C stocks over CT in 0-15 cm soil layers, respectively. The changes in water soluble C stocks after 4 years were 45% and 40%. WUE increased as mulching increased for the I2, I3, and I4 treatments, but not for the I5 treatment. We conclude that variants of conservation tillage increase SOC stock in the sandy loam soils of subtropical climatic conditions of western U. P., India and are therefore more sustainable practices than those currently being used.