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Assessment of the contribution percentage of inherent soil productivity of cultivated land in China
WANG Shi-chao, WANG Jin-zhou, ZHAO Ya-wen, REN Yi, XU Ming-gang, ZHANG Shu-xiang, LU Chang-ai
2019, 18 (11): 2619-2627.   DOI: 10.1016/S2095-3119(18)62152-5
Abstract103)      PDF in ScienceDirect      
The contribution percentage of inherent soil productivity (CPISP) refers to the ratio of crop yields under no-fertilization versus under conventional fertilization with the same field management.  CPISP is a comprehensive measure of soil fertility.  This study used 1 086 on-farm trials (from 1984–2013) and 27 long-term field experiments (from 1979–2013) to quantify changes in CPISP.  Here, we present CPISP3 values, which reflect the CPISP states during the first three years after site establishment, for a series of sites at different locations in China collected in 1984–1990 (the 1980s), 1996–2000 (the 1990s), and 2004–2013 (the 2000s).  The results showed that the average CPISP3 value for three crops (wheat, rice, and maize) was 53.8%.  Historically, the CPISP3 in the 1990s (57.5%) was much higher than those in the 1980s (50.3%), and the 2000s (52.0%) (P≤0.05).  Long-term no-fertilization caused CPISP levels to gradually decline and then stabilize; for example, in a mono-cropping system with irrigation, the CPISP values in Northwest and Northeast China declined by 4.5 and 4.0%, respectively, each year for the first ten years, but subsequently, the CPISP values stabilized.  In contrast, the CPISP for upland crops in double-cropping systems continued to decrease at a rate of 1.1% per year.  The CPISP for upland-paddy cropping decreased very slowly (0.07% per year), whereas the CPISP for paddy cropping decreased sharply (3.1% per year, on average) for the first two years and then remained steady during the following years.  Therefore, upland crops in double-cropping systems consume the most inherent soil productivity, whereas paddy fields are favourable for maintaining a high level of CPISP.  Overall, our results demonstrate a need to further improve China’s CPISP3 values to meet growing productivity demands. 
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The efficiency of long-term straw return to sequester organic carbon in Northeast China's cropland
WANG Shi-chao, ZHAO Ya-wen, WANG Jin-zhou, ZHU Ping, CUI Xian, HAN Xiao-zeng, XU Ming-gang, LU Chang-ai
2018, 17 (2): 436-448.   DOI: 10.1016/S2095-3119(17)61739-8
Abstract761)      PDF in ScienceDirect      
Black soil is one of the most precious soil resources on earth because it has abundant carbon stocks and a relatively high production capacity.  However, decreasing organic matter after land reclamation, and the effects of long-term inputs of organic carbon have made it less fertile black soil in Northeast China.  Straw return could be an effective method for improving soil organic carbon (SOC) sequestration in black soils.  The objective of this study was to evaluate whether straw return effectively increases SOC sequestration.  Long-term field experiments were conducted at three sites in Northeast China with varying latitudes and SOC densities.  Study plots were subjected to three treatments: no fertilization (CK); inorganic fertilization (NPK); and NPK plus straw return (NPKS).  The results showed that the SOC stocks resulting from NPKS treatment were 4.0 and 5.7% higher than those from NPK treatment at two sites, but straw return did not significantly affect the SOC stocks at the third site.  Furthermore, at higher SOC densities, the NPKS treatment resulted in significantly higher soil carbon sequestration rates (CSR) than the NPK treatment.  The equilibrium value of the CSR for the NPKS treatment equated to cultivation times of 17, 11, and 8 years at the different sites.  Straw return did not significantly increase the SOC stocks in regions with low SOC densities, but did enhance the C pool in regions with high SOC densities.  These results show that there is strong regional variation in the effects of straw return on the SOC stocks in black soil in Northeast China.  Additional cultivations and fertilization practices should be used when straw return is considered as an approach for the long-term improvement of the soil organic carbon pool.
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