Vol. 9, Issue 2 (2020)

Author(s):
RK Naresh, Vivek, M Sharath Chandra and Yogesh Kumar

Abstract:
Tillage intensive cropping practices have deteriorated soil physical quality and decreased soil organic carbon (SOC) levels in cereal–growing areas of North West India. Consequently, crop productivity has declined over the years demonstrating the need for sustainable alternative Tillage significantly reduced the proportion of macro-aggregate fractions (>2.00 mm) and thus aggregate stability was reduced by 35% compared with (ridge with no tillage) RNT, indicating that tillage practices led to soil structural change for this subtropical soil. The highest SOC was in the 1.00 – 0.25 mm fraction (35.7 and 30.4 mgkg-1for RNT and CT, respectively), while the lowest SOC was in micro-aggregate (<0.025 mm) and silt +clay (<0.053mm) fractions (19.5 and 15.7mgkg^-1 for RNT and CT, respectively). Labile C fractions: particulate organic C (POC), microbial biomass C (MBC) and dissolved organic C (DOC) were all significantly higher in NT and ST than in CT in the upper 15 cm. Higher SOC content of 19.44 gkg^-1 of soil was found in zero tilled residue retained plots followed by 18.53 g kg^-1 in permanently raised bed with residue retained plots. Whereas, the lowest level of SOC content of 15.86 g kg^-1 of soil were found in puddled transplanted rice followed by wheat planted under conventionally tilled plots. Zero–till crop establishment treatments increased very–labile C faction (Cfrac₁) by 21% followed by labile fraction (Cfrac₂) (16%), non–labile fraction (Cfrac₄) (13%) and less–labile fraction (Cfrac₃) (7%). Notably, higher passive C–pool in conservation tillage practices over CTTPR–CT suggests that conservation tillage could stabilize the recalcitrant form of carbon that persists longer in the soil. Meantime, zero–till crop establishment treatments had higher water stable macro–aggregates, macro–aggregates: micro–aggregates ratio and aggregate carbon content over CTTPR–CT. DSR combined with zero tillage in wheat along with residue retention (T₆) had the highest capability to hold the organic carbon in surface (11.57 g kg^-1soil with the highest stratification ratio of SOC (1.5). A considerable proportion of the total SOC was found to be captured by the macro-aggregates (>2–0.25 mm) under both surface (67.1%) and sub-surface layers (66.7%) leaving rest amount in micro-aggregates and silt + clay sized particles. However, macro‐ and water‐stable aggregates increased to a large extent (26 and 11%, respectively) in full CA and to a lesser extent in partial CA, mostly due to increase in coarse macro-aggregate (2–8 mm) contents in the 0–10 and 10–20‐cm depth soil layers. The CA increased OC associated with all size fractions of aggregates in the surface soil layer (0–10 cm), but a higher amount of C was associated with macro-aggregates, indicating relative stabilization of OC in the soil under CA. However, adoption of conservation tillage practices involving zero-tillage, crop establishment, residue management in cereal based system can significantly improve the systems productivity by improving SOC pools and soil aggregate associated carbon. Therefore, conservation tillage in cereal based system can help directly in building–up of soil organic carbon, labile organic carbon fractions and improve the fertility status of soil and production sustainability.