Effects of Long-Term Fertilization on Irrigated Desert Soil Organic Carbon Stock and Soil Aggregate in Hexi Oasis

Soil organic carbon is closely related to soil quality and global climate change. In order to clarify the change regulation of irrigated desert soil organic carbon stock in Hexi oasis, an investigation was carried out to study the influence of fertilization on soil organic carbon stock and soil aggregate through the long-term fertilization experiment that was established on irrigated desert soil at arid region of Northwest China in 1982. The results showed that compared with the initial value of soil organic carbon stock in 1982, no matter chemical fertilizers applied either alone or combined, soil organic carbon stock annually decreased by 160 kg hm-2in tillage layer(0 ~ 20 cm). However,organic manure addition at the amount of 2342 kg hm-2every year could offset the downward trend, and soil organic carbon stock annually increased at the rate of 260 kg hm-2. Compared with the initial value in 1982, soil organic carbon and total nitrogen stocks increased by 7015 kg hm-2and 1298 kg hm-2respectively after 27 years continuous application of organic manure, which were equal to 31% organic carbon and 25% total nitrogen in organic manure carried into soil. Therefore, to maintain or promote irrigated desert soil organic carbon stock in Hexi oasis, the least input amount of the organic carbon was 516 kg hm-2every year. Long-term application of organic manure significantly increased the quantities of soil macro water-stable aggregates( 0.25 mm) and the proportion of soil organic carbon distributed in macro water-stable aggregates, and then promoted the soil organic carbon sequestration ratio.