Author(s):

Lali Jat, RK Naresh, Mohan Lal Jat, Swati Chaturvedi, Richa Tiwari and Alka Dev

Abstract: Tillage systems can changes in soil organic carbon dynamics and soil microbial biomass by changing aggregate formation and C distribution within the aggregate. However, the effects of tillage method or straw return on soil organic C (SOC) have showed inconsistent results in different soil/climate/ cropping systems. Soil TOC and labile organic C fractions contents were significantly affected by straw returns, and were higher under straw return treatments than non-straw return at three depths. At 0–7 cm depth, soil MBC was significantly higher under plowing tillage than rotary tillage, but EOC was just opposite. Rotary tillage had significantly higher soil TOC than plowing tillage at 7–14 cm depth. However, at 14–21 cm depth, TOC, DOC and MBC were significantly higher under plowing tillage than rotary tillage except for EOC. Compared with conventional intensive tillage (CT) and no tillage (NT) treatments increased MBC by 11.2%, 11.5%, and 20%, and dissolved organic carbon (DOC) concentration by 15.5%, 29.5%, and 14.1% of bulk soil, >0.25 mm aggregate, and <0.25 mm aggregate in the 0−5 cm soil layer, respectively. Compared with preceding crop residue returning (S, 2100−2500 kg C ha⁻¹ treatments, and removal (NS, 0 kg C ha^-1) treatments significantly increased MBC by 29.8%, 30.2%, and 24.1%, and DOC concentration by 23.2%, 25.0%, and 37.5% of bulk soil, >0.25 mm aggregate, and <0.25 mm aggregate in the 0−5 cm soil layer, respectively. Conservation tillage (NT and S) increased microbial metabolic activities and microbial index in >0.25 and <0.25 mm aggregates in the 0−5 cm soil layer. Responses of macro-aggregates to straw return showed positively linear with increasing SOC concentration. Straw-C input rate and clay content significantly affected the response of SOC. Overall, straw return was an effective means to improve SOC accumulation, and soil quality. Straw return-induced improvement of soil nutrient availability may favor crop growth, which can in turn increase ecosystem C input. Tillage reduction and residue retention both increased the proportion of organic C and total N present in soil organic matter as microbial biomass. Microbial immobilization of available-N during the early phase of crops and its pulsed release later during the period of greater N demand of crops enhanced the degree of synchronization between crop demand and N supply. The maximum enhancement effects were recorded in the minimum tillage along with residue retained treatment.

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