Author(s):

Vineet Kumar, RK Naresh, Satendra Kumar, Sumit Kumar, Sunil Kumar, Vivak, SP Singh and NC Mahajan

Abstract: Labile soil organic carbon pools are valuable indicators of soil quality, early changes in soil total organic carbon (SOC) stocks, and (hence) changes in soil carbon sequestration pools and dynamics induced by changes in soil management practices. To improve the management of Typic Ustochrept soil in North West India, we have examined effects of tillage, crop residue and N management methods applied in a 02-year experiment on SOC and the various fractions: particulate organic carbon (POC), light fraction organic carbon (LFOC), microbial biomass carbon (MBC) and dissolved Organic Carbon (DOC). The tillage crop establishment methods wereT₁- Zero tillage with residue retention;T₂-,Zero tillage without residue retention;T₃-Reduced tillage with residue retention;T₄-Reduced tillage without residue retentioT₅-Conventional tillage with residue incorporation;T₆- Conventional tillage without residue incorporation. Tillage crop establishment was combined with the following nutrient management treatments: F₀-Control; F₁- 80 kg Nha^-1; F₂-120 kg Nha^-1; F₃-160 kg Nha^-1 and F₅-200 kg Nha^-1. After 2 years, the Conventional tillage without residue treatment resulted in significantly lower SOC by 24% and labile C fractions by 27–48% than T₂ and T₃, respectively. However, treatment T₁ markedly increased all labile C fractions by 32–52% except POC relative to T₃, but treatments T₁ and T₃ resulted in similar SOC contents (21.2 g kg^−1 and 20.3 g kg^−1, respectively). Of the four C fractions, LFOC and DOC were the most sensitive indicators of changes in SOC induced by the tillage crop establishment methods. Under T₁, SOC contents were in 200kg Nha^-1>160kg Nha^-1 > and 120kg Nha^-1plots, and significantly higher than those in control plots (by 37, 33 and 21%, respectively).Labile C fractions were also significantly higher following the treatments including residue retention/incorporation than following applications solely of chemical fertilizers. Application solely of 80kg Nha^-1 chemical fertilizers had no significant effects on LFOC and DOC fractions compared with control. Nevertheless, application of 200kg Nha^-1 or 160kg Nha^-1 significantly increased contents of POC and MBC relative to control (by 50 and 46% or 41 and 44%, respectively). Thus, LFOC and DOC fractions were not sensitive indicators of changes in SOC induced by mineral nutrient practices under current conditions. Overall, given the minor differences between the effects of the 200kg Nha^-1 and160kg Nha^-1 treatments, zero tillage with residue retention appears to be the most suitable practice for improving soil labile organic carbon fractions in the Typic Ustochrept soil.

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