Aggregate-Associated Carbon Fractions Under Forty-Eight Years of Fertilization in North-Western Himalayas

Abstract

ABSTRACT The present investigation was carried out in an on-going long-term fertilizer experiment, initiated during 1972 at experimental farm of Department of Soil Science, CSK HPKV Palampur, to study the long-term effect of fertilizers and amendments on soil aggregate stability and carbon dynamics in an acid Alfisol under maize-wheat cropping system. The experiment comprised of eleven treatments. The soil of the experimental site was silt loam and classified taxonomically as “Typic Hapludalf” (subgroup). Soil samples were collected from surface (0–0.15 m) layer after the harvest of wheat (rabi, 2019–2020) and were analyzed for different aggerate size and their carbon fractions. The addition of FYM enhanced the macroaggregates (>0.25 mm) as compared to microaggregates (<0.25 mm). Incorporation of FYM alone or in combination with chemical fertilizers enhanced the accumulation of different C pools in all aggregate fractions over unfertilized control. Among the macroaggregates, 1–0.5 mm fraction had higher total organic carbon (TOC), organic carbon (OC), labile carbon (LC) and non-labile carbon (NLC) as compared to microaggregates. Aggregate-associated carbon is less susceptible to physical, microbiological, and enzymatic degradation, and is a potential carbon reservoir that is protected from mineralization. Addition of FYM along with 100% NPK recorded highest SOC stocks, SOC sequestration rate and highest carbon buildup. Different aggregate fractions of TOC, OC, LC and NLC were found to be positively and significantly correlated with available N, P and K and negatively and significantly correlated with bulk density whereas, positively and non-significantly correlated with soil pH and electrical conductivity. Different aggregate fractions of TOC, OC, LC and NLC were positively and significantly correlated with grain and straw yield of wheat.