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Long-term fertilization and manuring with different organics alter stability of carbon in colloidal organo-mineral fraction in soils of varying clay mineralogy

Das, Ruma, Purakayastha, T.J., Das, Debarup, Ahmed, Nayan, Kumar, Rahul, Biswas, Sunanda, Walia, S.S., Singh, Rohitashav, Shukla, V.K., Yadava, M.S., Ravisankar, N., Datta, S.C.
The Science of the total environment 2019 v.684 pp. 682-693
Alfisols, Inceptisols, Mollisols, NPK fertilizers, Vertisols, aluminum oxide, animal manures, best management practices, carbon, clay, crystallites, desorption, fertilizer application, green manures, illite, iron oxides, nitrogen, nitrogen fertilizers, organic matter, phosphorus, potassium, smectite
Majority of organic matter is bound to clay minerals to form stable colloidal organo-mineral fraction (COMF) in soil. Stability of carbon (C) in COMF is crucial for long-term C sequestration in soil. However, information on the effect of long-term fertilization and manuring with various organic sources on C stability in such fraction in soils with varying clay mineralogy is scarce. The present study was, therefore, carried out to assess the effect of thirty-one years of continuous fertilization and manuring with different organics on C-stability in COMF extracted from an Inceptisol, a Vertisol, a Mollisol, and an Alfisol. The treatments comprised of control (no fertilization), 100% NPK (100% of recommended N, P and K through fertilizer), 50% NPK+ 50% of recommended N supplied through either farm yard manure (FYM) or cereal residue (CR) or green manure (GM). The stability of C (1/k) in COMF was determined from desorption rate constant (k) of humus-C by sequential extraction and correlated with extractable amorphous Fe-Al-Si-oxides, and crystallite size of illite minerals. Long-term fertilization and manuring with the above sources of organic altered the contents of amorphous Fe-Al-Si-oxides, and decreased the crystallite size of illite in all the soil orders. Fifty percent substitution of fertilizer N by various organics significantly increased C-stability in COMF by 27–221% (mean 111%) over full dose of NPK (100% NPK). Smectite dominating Vertisol exhibited highest stability of C followed by the Mollisol, the Inceptisol and the Alfisol. Stability of such C in soil was correlated positively with the amount of amorphous Fe and Al oxides but negatively with crystallite size of illite (r = −0.46, P < 0.01). Application of NPK + GM or NPK + FYM in Inceptisol, Vertisol and Mollisol and NPK + GM or NPK + CR in Alfisol emerged as the best management practices for higher stabilization of C in COMF for long-term C sequestration.