Quantitative and qualitative changes of organic matter in an Ando soil induced by mineral fertilizer and cattle manure applications for 20 years

The effects of continuous application of cattle manure on the quantity and quality of soil organic matter (OM) were investigated in an Ando soil (Mela nudand). Surface soil samples were periodically taken from NPK and NPK + ma nure (80, 160, and 320 Mg ha(-1) y(-1)) plots over a period of 20 y. Partic ulate (> 53 mum) and mineral-associated (< 53 mum) OM fractions were separa ted from the soil samples by sieving after mechanical dispersion. For the N PK treatment, both the organic C and total N concentrations Of the whole so il continued to decrease, the reduction reaching about 10% after 20 y. Manu re application at the rate of 80 Mg ha(-1) y(-1) did not lead to an increas e in the amounts of organic C and total N in the whole soil. In contrast, b oth the organic C and total N concentrations increased by the application o f 160 and 320 Mg ha(-1) y(-1) manure. Manure application at the rate of 320 Rig ha(-1) y(-1) increased the organic C concentration by 30% and total N concentration by 48% after 20 y. The decrease in the organic C and total N concentrations in soil with NPK fertilization was attributed to a decrease in the amount of mineral-associated OM. Manure application increased signif icantly the amount of particulate OM, while it did not affect the amount of mineral-associated OM. It also resulted in a decrease in the C/N ratio of soil (OM, especially of the particulate OM. The analysis of humic acids sho wed that manure application induced a decrease in the degree of humificatio n and an accumulation of high molecular weight components. The quantitative and qualitative changes of OM in the Ando soil upon manure application wer e mainly due to the accumulation of manure-derived articulate OM.