Effects of long-term repeated mineral and organic fertilizer applications on soil organic carbon and total nitrogen in a semi-arid cropland

To meet and the ever increasing need for food and mitigation of global climate changes, plenty of fertilizers have been used to increase crop yield in China, especially in semi-arid regions. In this study, we investigated the impacts of long-term fertilization on wheat yields, soil organic carbon (SOC) and soil nitrogen (N) in the semi-arid Loess Plateau, China. One fallow and eight winter wheat-wheat (Triticum aestivum L.) rotation cropping plots were selected for the field experiment from 1984 to 2010 in the semi-arid Loess Plateau, China. hi total we conducted eight fertilization treatments including no fertilizer, mineral nitrogen fertilizer (N), mineral phosphate (P), cattle manure (M), N + P, N + M, P + M and N + P+ M. In 2010, we collected three replicate soil samples from each plot to the depth of 100 cm from soil surface. Meanwhile, soil bulk density, SOC. total N, and mineral N (ammonium and nitrate), wheat grain and aboveground biomass yields in each plot were measured. We found that mineral fertilizers, especially those applied together with cattle manure, increased winter wheat grain and aboveground biomass yields dramatically. Moreover, wheat biomass was found to have significant correlation with SOC and soil total N in the 0-20 cm soil layer. We also found that SOC and soil N were highest in the topsoil layers (0-30 cm) than other layers and declined to the depth of 50 cm with insignificant changes from 50 to 100 cm in all treatments. Compared to the data in 1984, fertilizer application increased surface soil SOC content, especially for the N + P + M treatment after 26 years cropping and fertilization. However, changes in soil total N and mineral N differed from SOC with decreasing N in mineral-fertilized and fallow plots but increasing N in the M-fertilized plots. (C) 2012 Elsevier B.V. All rights reserved.