Changes in soil organic carbon, nutrients and aggregation after conversion of native desert soil into irrigated arable land

摘要

This study aimed at investigating the effects of agricultural exploitation on desert soil organic C, N and P, and soil aggregation. Four land uses were assessed: (1) 5-year wheat (Triticum aestivum L.)/barley (Hordeum vulgare L.)+5-year maize (Zea mays L.); (2) 5-year wheat/barley+5-year alfalfa (Medicago sativa L.); (3) 6-year wheat/barley+4-year acacia (Robinia pseudoacacia L.) and (4) uncultivated desert soil. The desert soil contained total organic C (TOC) of 3.1, 3.7 and 4.2gkgp# and particulate organic C (POC) of 0.6, 0.7 and 0.8gkgp# at 0-10, 10-20 and 20-30cm depths, respectively. The soil TOC concentration was increased by 32-68% under wheat-maize rotation and by 27-136% under wheat-acacia at 0-20cm depth, and by 48% under wheat-alfalfa only at 0-10cm depth. This contrasted with an increase in the soil POC concentration by 143-167% at depth 0-20cm under wheat-maize and by 217%, 550% at depth 0-10cm under wheat-alfalfa and wheat-acacia, respectively. The desert soil had 13Mghap# TOC stock and 2Mghap# POC stock at depth 0-30cm, whereas crop rotations increased the soil TOC stock by 30-65% and POC stock by 200-350%. Over the 10-year period, the rates of TOC accumulation were 0.6, 0.3, 0.8Mghap# yearp# and the rates of POC accumulation were 0.4, 0.4 and 0.7Mghap# yearp# under wheat-maize, wheat-alfalfa and wheat-acacia rotations, respectively. At 0-30cm depth, total soil N was increased by 61-64% under wheat-maize and wheat-acacia, but total soil P was reduced by 38% under wheat-alfalfa. A significant improvement in clay stability but not in aggregate water-stability was observed in cultivated soils. The results showed a significant increase in soil organic C pool but unimproved macro-aggregation of the desert soil after 10 years of cultivation.