| Northeast is one of the most important major grain production regions in China, as well as the highest yield potential area among the grain production regions of China. Sustainable food production in northeast will be benefit for Chinese food security and healthy development of the national economy. The black soil rgion of Northeast China is famous due to flat land, easy farming and high soil fertility. However, over-cultivation and inappropriate agronomic practices have resulted in soil fertility decline, severe soil erosion and soil productivity decreaseing, leading to a negative increasing of resources use efficient for a long time in this area. Recently, traditional rotation of maize and legumes has been replaced by continuous maize cropping with single fertilizer application based. Additionally,northeast is one of the most susceptible areas responding to global climate change, and spring drought and low temperature weather often occurred at this area in recent decades.The construction of corn production systems for the integrated goals of improving soil fertile and crop yield with enhanced response capacity of soil in the face of climate change,have become an important problem to solve in sustainable food production in northeast.Therefore, based on a long-term field experiment in Gongzhuling, Jilin province in northeast China, through the combination of in-situ monitoring and data analysis, we investigated the effects of cropping regimes under organic manure application on corn yield,soil chemical and physical properties and water-heat traits as well as the components and structure of soil microbes, also the greenhouse gas fluxes pattern and global warming potential (GWP) under different cropping regimes were comprehensive elevated. The cropping regimes in this long-term experiment included continuous maize cropping (CMC),maize-soybean rotation (MSR, two years maize planting followed one year soybean planting) and continuous soybean cropping (CSC). The present study will provide important theoretical and technological supporting for Black Soil degradation management and sustainable food production in northeast China.(1) Long-term chemical fertilizer application with organic manure amedments tend to incease maize yields under CMC and MSR treatments with grain yield among 11.2 and 11.3 t ha-1, and there were no significantly differences (P > 0.05) in yields between cropping regimes. There were also no significantly differences in yield components including total ear numbers, grains per spike and 100-kernel weight. No significant trends occurred in mean air temperature, maximum temperature, minimum temperatue, and rainfall over the corn growing season during 2004 to 2013. Moreover, there was no significant correlation between corn yield and climatic factors. It is indicated that organic fertilizer application could compensate the negative effect of long term continuous maize cropping on soil fertile, and ensure steady increase in maize yield. However, it is needed to reduce the risk of pest and disease in continuous maize cropping system by strength integrated pest management.(2) The results of soil samples analysis and water-heat localized observation showed that CMC treatment significantly decreased soil bulk density but increased soil porosity compared to MSR and CSC treatments (P < 0.05), where the decreased rates in soil bulk density of 0～10 cm soil were 12.9% and 19.8%, also 21.4% and 23.2% for 10～20 cm,23.9% and 29.2% for 20～30 cm, 20.3% and 25.2% for 30～40 cm, respectively. CMC treatment significantly increased soil water storage in May and June compared to the MSR and CSC treatments,especially for 0～10 cm soil layer with increased rates of 6.5% and 6.3%, 3.6% and 3.4%, respectively. Relative high soil water storage is benefit for the improvement of population quality under CMC treatment at early and late growing stages.Soil temperatures of 0～30 cm did not significantly differ between cropping regimes in the whole growing stage. The above results exhibited that continuous maize cropping under organic fertilizer combined with chemical fertilizer application could significantly improve soil structure and add soil water storage, and thereby stimulating the growth of crop during early growing period.(3) According to the results of the measurement and analysis of soil chemical characters, the contents of soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN) and available phosphorus (AP) of 0～100 cm soil reduced gradually from topsoil to bottom soil, but no obvious change in available potassium (AK) was observed in different soil layers. Through correlation analysis, we found that the content of SOC was extremely significant correlation with the contents of TN and AN (P< 0.01),indicating that high SOC content is benefit to improve soil N availability. After nearly 30 years of soil organic amendment, there has been a significant improvement in the contents of SOC, TN,AN, AP and AK of 0～20 cm soil under different treatments, the values of these indicators were the highest in CMC treatment among all treatments. Besides, CMC treatment had the highest amounts of soil aggregate (>2000 μm, ≥250-2000 μm, ≥53～250 μm, <53 μm) and easy oxidative organic carbon with high reactive, indicating that soil in CMC treatment is sensitive to the environment. However, the passive SOC was not significantly related with cropping regimes. Results above showed that continuous maize cropping combined with organic fertilizer application could improve soil nutrient condition and increase the accumulation of soil carbon and nitrogen that is benefit for soil cultivation, but with high sensitivity of its carbon sink to the environment, it is need to reduce the risk of mineralization of SOC by associating with reasonable agricultural practices.(4) The results of microbial culture experiments showed that the amounts of soil microorganism including bacteria and actinomyces declined sharply from topsoil to bottom soil, but there was no significant difference of the amount of fungi between soil layers. The amounts of bacteria, actinomyces and microorganism of CMC treatment were 28.2% and 44.6%, 5.3% and 14.6%, 25.4% and 41.0% higher than these of MSR and CSC treatments under 0～40 cm soil. For the microbial structure, the ratio of bacteria to microorganism in CMC treatment was significantly higher than other treatments, but the highest ratios of fungi and actinomyces to microorganism were occurred at CSC treatment. In addition, the amount of soil microorganism was closely related to soil bulk density and the contents of SOC, TN and AN. The coefficients of the amounts of soil bacteria and actinomyces with soil bulk density were -0.818 (P < 0.01) and -0.718 (P < 0.05), and with the contents of SOC, TN and AN were 0.784 and 0.770, 0.777 and 0.740, 0.755 and 0.699, all reaching significant level. These results suggested that continuous maize cropping combined with organic fertilizer application could improve soil physical and chemical characteristics simultaneous with adding the amounts of soil bacteria and actinomyces, but reasonable agricultural practices should be combined to enhance soil microbial diversity. The significantly correlation between soil microorganism and soil physical and chemical properties also exhibited that the distribution of the amount of soil microorganism could sensitively reflect the variation of soil quality and serve as a biological indicator in elevating soil quality.(5) The monitoring results of greenhouse gas emissions showed that there were remarkable seasonal CO2, N2O and CH4 fluxes pattern under three cropping regimes treatments. Cropping regimes had significant impacts on soil CO2 emission, the average C02 emissions during 2011 and 2012 were 5309.6, 4422.0 and 4869.0 kg/ha1 under the treatments of CMC, MSR and CSC, and corresponding N2O emissions were 1.4, 1.5 and 1.5 kg/ha1, respectively. The CO2 emissions of three cropping modes in 2011 were significantly higher than in 2012, but inverse results occurred in N2O emissions, which may relate to the varied climate conditions during these two years. Furthermore, the global warming potential under CMC, MSR and CSC were 398.5, 424.6 and 451.2 kg CO2-eq/ha1,respectively. Therefore from a greenhouse gas emissions mitigation point of view, the present study suggest that continuous maize cropping combined with organic fertilizer application should be used in Black Soil region of northeast China.(6) In general, there was no significant difference in corn yield between CMC and MSR under long-term organic manure application. Furthermore, CMC treatment could increase soil fertility and soil organic cabon content, as well as reduce GHG emission.Therefore, it is practical to apply the continuous maize cropping in black soil region of Northeast China. However, inorder to maintaian the cron sustainable production, the appropriate cultivation measurements should be applied to control the plant diseases and insect pests, reduce the risk of soil organic carbon mineralization and decomposition, and improve soil microbial diversity under contiuous maize cropping. |
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