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Background: Differences in cropping systems and their impacts on plant growth and carbon (C) uptake as well as soil C release pose a major challenge in projecting agroecosystem C balance. Methods: A four-year (2012-2015) field experiment was conducted to examine crop C uptake and soil respiration in two conventional (wheat-cotton and wheat-maize) and two legume-based (wheat-soybean and alfalfa-maize) double-season cropping systems in North China Plain. Results: During the 4 experimental years, crop C uptake was greater in the two conventional systems than the two legume-based systems. However, soil respiration was higher in the two systems with C (i.e. maize) than C crops (i.e. cotton and soybean) planted in summer. As consequences, cropland C balance was positive in the two conventional cropping systems, with greater value in the wheat-maize comparing to wheat-cotton system. However, the two legume-based cropping systems showed negative cropland C balance. Conclusions: Our findings indicate that, although more CO-C is emitted in maize-related cropping systems, the conventional agricultural activities may sequestrate more C in comparison with the legume-based farming in North China Plain due to higher C uptake, and highlight the importance of management strategy in improving agroecosystem C storage. [ABSTRACT FROM AUTHOR]

Changes in field management and climate will alter soil organic carbon (SOC) and nitrogen (SN) cycling in the coming decades. This study is to quantify the effects of various fertilisation strategies and climate change scenarios on crop yield, and soil C and N cycling by the end of this century. Data from a long-term experiment with a winter-wheat ( Triticum aestivium L.) and summer maize ( Zea mays L.) rotation in Northern China was used to calibrate and validate the SPACSYS model. Five fertiliser practices were used: control (CK); combined mineral nitrogen, phosphorus and potassium (NPK); NPK plus manure (NPKM); high application rate of NPK fertilisers plus manure (hNPKM) and NPK with straw incorporation (NPKS). Crop yields, and SOC and SN stocks by 2100 were predicted under four climate scenarios (Baseline, RCP2.6, RCP4.5 and RCP4.5). Results showed that the SPACSYS model can adequately simulate the dynamics of SOC and SN stocks and the yields of winter wheat and summer maize. An application of NPK plus manure or straw not only enhanced crop yield, but also substantially increased SOC and SN stocks. The predictions showed the positive effects of fertilisation and climate change on crop yields and SOC stocks compared with those under the baseline. However, SN stock under the RCP8.5 decreased by 3–14% by 2100 for various fertilisation strategies compared with that under the baseline. On the other hand, mineral fertiliser plus manure led to a higher soil respiration rate and nitrogen losses through leaching and surface runoff under all the climate scenarios. Therefore, application of mineral fertilisers plus manure could enhance crop productivity and sustain soil fertility but cause more carbon emitted to the atmosphere and nitrogen losses. More attention should be paid on optimising fertilisation in order to increase crop productivity while minimising environmental risks. [ABSTRACT FROM AUTHOR]

The aim of the study is to analyze the effects of different fertilization of organic and inorganic fertilizers on soil organic carbon (SOC) sequestration and crop yields after a 22 years long-term field experiment. The crop yields and SOC were investigated from 1981 to 2003 in Dry-Land Farming Research Institute of Hebei Academy of Agricultural and Forestry Sciences, Hebei Province, China. The dominant cropping systems are winter wheat–summer corn rotation. There were totally sixteen treatments applied to both wheat and corn seasons: inorganic fertilizers as main plots and corn stalks as subplots and the main plots and subplots all have four levels. The results revealed: after 22 years, mixed application of inorganic fertilizers and crop residuals, the SOC and crop yields substantially increased. Higher fertilizer application rates resulted in greater crop yields improvement. In 2002–2003, wheat and corn for the highest fertilizer inputs had the highest yield level, 6400 kg ha −1 and 8600 kg ha −1 , respectively. However, the SOC decreased as the excessive inorganic fertilizer input and increased with the rising application of corn stalks. The treatment of the second-highest inorganic fertilizer and the highest corn stalks had the highest SOC concentration (8.64 g C kg −1 ). Pearson correlation analysis shows that corn and winter wheat yields and the mineralization amount of SOC have significant correlation with SOC at p < 0.05 level. [ABSTRACT FROM AUTHOR]