| Climate change, resulted from global warming, is one of the important issues that challenge the humankind. The global agriculture need to provide enough food to the increasing population and mitigate greenhouse gases emission. Therefore, it is urgent to enhance crop productivity and decrease greenhouse gases emission though suitable agricultural management practices, such as appropriate fertilization. The combination of chemical and organic fertilization has been evidenced to increase agriculture productivity. However, it is still unclear whether a co-benefit can be obtained either for soil carbon sequestration and greenhouse gases mitigation or for crop productivity improvement. It is still unclear that whether these benefits are universe and how long they can persist. A cross-site field experiment study was conducted to evaluate the effect of organics (crop straw, poultry manure and straw biochar) soil amendment on changes of soil organic carbon (SOC) storage, soil fertility, greenhouse gases emission and crop productivity in rice paddies. A meta-analysis was also done to investigate the changed of crop productivity with the amendment of biochar globally. We were trying to provide a scientific and technology base for the policy choose in mitigate climate change in Agriculture.The conclusions were as follows:1. A survey was conducted to evaluate the soil respiration rate influenced by different fertilization regime using an auto soil respiration monitor system. These six experimental sites are located in the South part of China, and had been practiced under different fertilization for nearly30years. The treatments at each site included:the control without any fertilizer amendment (CK), the amendment with chemical fertilizer (NPK), the combination of chemical fertilizer and crop straw, and the combination of chemical fertilizer and poultry manure (NPKOM). Among the six sites, rice growing under long-term no fertilization increased SOC with mean value of0.13g kg-1and mean annual increase rate of61.14mg kg-1a-1. Compared with the CK, long-term fertilization promoted the SOC accumulation at all sites, with mean values of3.64,5.12and6.10g kg-1for NPK, NPKStr, and NPKOM, respectively. The mean annual increase rates for the three treatments were136.10,195.66and225.27mg kg-1a-1. The average respiration rate under NPK at six sites was2.13μmol m-2s-1, which was significantly lower than the CK (2.57μmol m-2s-1). As expected, the amendment of crop straw and poultry manure increased soil respiration compared with the CK, with mean value of3.02and3.11μmol m-2s-1for NPKStr and NPKOM, respectively. The average microbial quoit of different sites was5.1under the CK, which higher than the other treatments.2. In order to evaluate to greenhouse gases emission under different fertilization regimes, we conducted greenhouse gases monitoring for one year including early rice, late rice and fallow period at two of the six sites mentioned above. Compared with the CK, the application of fertilizer increased soil fertility and rice productivity. The highest rice yield was observed under treatments with organic amendment at both sites. At Wangcheng, rice yield under organic amendment was1.8and1.1times of that under CK and NPK. Whereas, the rice yield under NPKOM was2.9and1.9times of that under CK and NPK at Jinxian. The greenhouse gases emission rate was higher at Wangcheng site than Jinxian within the whole year. At Wangcheng, no difference was observed among different treatments. However, the application of fertilizer increased methane and nitrous oxide emission compared with the control. The amendment of crop straw and poultry manure did not stimulate methane and nitrous oxide emission. At Jinxian, no difference was found among the treatments of CK, NK and NPK in terms the three greenhouse gases, but the amendment of poultry manure significantly promoted the emission of carbon dioxide, methane and nitrous oxide. The amount of greenhouse gas emission emitted at early rice, late rice and fallow period was different as a result of water management regimes, rice cultivation and fertilization. At Wangcheng, a great proportion of carbon dioxide was emited at fallow period while methane was emitted during the rice growing with higher emission rate at early rice. Nitrous oxide emission occurred at three periods with higher emission rate at late rice than early rice. At Jinxian, in contrast to Wangcheng, methane emission was higher at late than early rice while nitrous oxide was higher at early than late rice. There was also a considerable amount of N2O at fallow period at both sites. Although the amendment of organics increased the global warming potential compared with the control, the greenhouse gases emission intensity did not increased under treatments with straw and manure amendment due to the increase in rice yield.The emission patterns of three greenhouse gases were affected by water regimes and soil temperature. The emission peaks of carbon dioxide and nitrous oxide mainly occurred after the drainage of flooding water and in the fallow period; whereas, methane emission only occurred when the soil was flooded with water. The emission rate of carbon dioxide and nitrous oxide increases exponentially with the increase in soil temperature at5cm. While methane emission increased with soil temperature linearly with soil temperature.3. A new experiment was established at Guanghan, Sichuan province. The objectives were to evaluate the influence of biochar amendment on rice production, soil improvement and greenhouse gases emission. Biochar amendment increased soil pH, organic carbon and available K concentration, with no influence on soil total N and available P, but decreased soil bulk density. The activity of invertase was also promoted with the amendment of biochar. There was a significant interaction effect of biochar and N fertilizer on soil microbial biomass carbon. In the absence of N fertilizer, the soil microbial biomass carbon decreased with the increase in biochar amended amount. However, the soil microbial biomass carbon increased with the increase in biochar amended amount in the presence of N fertilizer.Biochar addition did not affect the yield of rice grain and biomass, but it significantly decreased N uptake and increased Si uptake. Nitrogen uptake by grain and rice straw by rice harvest was decreased by16.9%and28.8%respectively under biochar application rate of40t ha-1. The promotion of Si by rice was resulted from the input of Si with biochar and the elevation of soil pH. The average increase of Si in rice straw was264%compared with the control.The amendment of biochar significantly decreased nitrous oxide emission, with emission factor decreased by53.7%under40t ha-1, while, the emission of methane and carbon dioxide were not affected by biochar addition. The global warming potential (GWP) and greenhouse gases emission intensity was also decreased correspondingly with biochar during the whole rice growing season.4. We investigated the potential of greenhouse gases mitigation potential of biochar amendment into agricultural soils and its sustainability. The biochar effects was analyszed on crop yield, SOC concentration and greenhouse gases emission by comparing the effects between paddy rice and dry cropland. The results showed that the amendment of biochar consistly and significantly increased crop yield in dry croplands, but without any effect on rice yield. The average increase in dry cropland yield was8.5%. Biochar addition increased SOC concentration by24.7%and48.3%for20and40t ha-1, respectively. However, soil respiration was no affected by biochar addition. The amendment of biochar, either in rice paddies or in dry croplands, consistently and significantly decreased N2O emission. The decrease in N2O was propotinaly related with biochar application rate in rice paddies; whereas, there was no difference in N2O mitigation between application rate of20and40t ha-1for dry croplands. Biochar decreased the greenhouse gases emission intensity (GHGI) in both systems.5. A meta-analysis was conducted to access the effect of biochar soil amendment on crop productivity including yield and above ground biomass. And we were also trying to obtain the key factors that influence crop productivity response to biochar addition. By summarizing the leteratures released before April1st,2013using a meta-analysis, we found that biochar soil amendment increased crop yield and above ground biomass by8.4%and12.4%, respectively. The response of crop productivity to biochar addition was regulated by many factors including soil texture, pH, biochar feedstock and crop types. Higher crop productivity can be obtained when biochar was applied to soils with sandy and clay textures and soils with low pH. The crop productivity increased by29.0%,16.0%,30.2%and14.8%for sandy, clay, strong acid and acid soils, respectively. The amendment of manure biochar increased crop productivity by28.3%, which was2to3times of those other biochar feedstocks. The best response of crop productivity was found for vegetables and beans and the yield increase was30.3%and28.6%, respectively. It is very interesting that biochar increased crop productivity by10.6%for dry land crops which was significantly higher than that for rice paddies (5.6%). Besides, there were some other factors that influence crop productivity response to biochar addition. These factors included pyrolyzing temperature of biochar and experimental types. The results from pot studies may overestimate the yield increase than in field studies.In conclusion, long-term different organics amendment significantly increased rice yield and SOC accumulation. Although the combination of chemical fertilizer and organics promoted the global warming potential in rice paddy, it did not increase greenhouse gases emission intensity due to the increase in rice yield. It is a good way to treat crop straw by converting it to biochar through pyrolysis and then applied to soil. Biochar could increase SOC content in a very short time and decrease nitrous oxide emission during crop growing period. Therefore, biochar production and amendment in agricultural soils would be an efficient way to utilize organic waste, improve soil fertility and mitigate greenhouse gases emission in agriculture. |
PDF Full Text Request