Effects of Long-Term Fertilization and Water Regime Management On Soil-Profile Carbon in Clay Soil.

Soil carbon (SC) sequestration estimates are needed to improve our understanding of management influences on soil fertility and carbon cycle related to greenhouse gas emission. We evaluated the effects of 33 years of long term experiment which include a factorial combination of nutrient management (No fertilization, NPK, NPK+Silicate, NPK+Compost) and soil type (paddy, upland), on soil profile distribution (Ap, Bt1, Bt2, Bt3) of soil carbon. Average total carbon in Ap fractions and Bt1 fraction of paddy soil was higher than upland soil, but content of alkali soluble humic carbon not influenced by soil type. Compared with the corresponding initial value of top soil, stable isotope (C1) contents of paddy soil were significantly increased with depth. In contrast, contents of C13 in upland soil were roughly maintained with depth. Although carbon sequestration in soil was influenced by physico-chemical status and organic matter composition etc, these results are imply that carbon distribution with soil profile was mainly affected by inorganic carbon such as carbonate, bicarbonate.