Organic carbon and black carbon with fertilization in paddy and upland soils.

Abstract

Soil organic carbon is a vital soil component that affects the physical, chemical and biological properties of soils. The soil organic carbon pool is mainly composed of two components, that is, the inert or recalcitrant component and the labile or active fraction. Black carbon (BC), the main form of the inert or recalcitrant component of soil organic carbon pool. Maintenance of their contents in the soil has been the important measure for improving productivity and stabilizing ecosystems. In this paper, the impact of fertilization on organic carbon and black carbon was studied in subtropical China by sampling in field. Soils were collected from sites where a long-term fertility experiment had been carried out for over 30 years in Jinxian County, Jiangxi Province. A fully randomized plot design was used in the experiment with eight treatments. They were designed and laid out:(Tr1) no fertilizer (ck); (Tr2) N fertilizer alone (N); (Tr3) K fertilizer alone (K); (Tr4) NK; (Tr5) NPK; (Tr6) 2(NPK) (twice treatment); (Tr7) organic manure (OM); and (Tr8) NPK+OM. Each treatment was carried out in three plots. Except for the 2NPK and ck treatments, the same amounts of NPK chemical fertilizer were applied in each treatment:N, 90 kg urea-N·hm-2·a-1; P, 45 kg triple superphosphate-P·hm-2·a-1; K, 75 kg potassium chloride-K·hm-2·a-1; or pig manure at 22 500·kg·hm-2·a-1.The results showed that organic carbon of Tr8 was significantly greater (P=0.05) in the 0-20 cm topsoil of both upland and paddy soils than Tr1, Tr2, Tr3, Tr4, Tr5, Tr6, and Tr7. Black carbon ranged from 2.72 to 5.33 g·kg-1 in upland soil and from 9.01 to 10.60 g·kg-1 in paddy soil. In the upland soil Tr3 and Tr7 as well as Tr2 and Tr5 were not significantly different (P=0.05); whereas in paddy soil no treatments were significantly different (P=0.05). A significant correlation (P=0.05, r=0.72) in upland soil existed for organic carbon and black carbon, but in not paddy soil. Thus, co-application of organic and inorganic fertilizer was best for organic carbon in upland and paddy soils, and accumulation of organic carbon and black carbon was more favorable in paddy soil than upland soil.