Effect Of Different Straw Returnning On Carbon And Nitrogen Sequestration And Rice Growth And Development

Nowadays, climate warming and food crisis are the main problems in the world. Recent studies have shown that biochar has high stability and greater adsorption capacity. Research has demonstrated that biochar has the potential to enhance soil C sequestration and reducing GHG emissions and improve soil fertility and increase agricultural yield. Biochar has the important role in the soil, climate and environment system. While another common way such as returning straw to field has also been advocated as a potential way of improving crop yields and increasing soil fertility has been recognized. For a special climate conditions in northeast China, such as a low temperatures in winter and annual accumulated temperature is low, it is a problem which kind of returning way is more suitable in the northeast China. Long-term impacts of straw-derived biochar on GHG emissions, as well as soil carbon sequestration in Northeast China are poorly understood. In addition, there is a lack of field reports on carbon stability, particularly in comparison with straw amendments. A field experiment was performed with different ways of returning straw and different applications rates with or without N fertilisation in rice paddies, which for two consecutive years, and analyzes the effect of the soil carbon storage, GHG emissions, soil fertility and rice growth. The treatment was performed with five levels:Straw application rate:0 t-hm"2; Straw returning directly:5.05 t·hm"2; Straw carbonization returning rates (biochar):1.78 t·hm-2,14.8 t·hm-2 and 29.6 t·hm-2. The N fertilizer included two levels:0 kgN·hm-2 and 210 kgN·hm-2. A super rice variety Shennong 265 was cultivated with permanent flooding. The main results were as follows:1. The comparison study of the different ways of returning straw to the variations of soil carbon and nitrogen content. The results showed that straw-derived biochar and straw incorporation are all significantly increased the soil total C content, specially returning straw carbonization without N fertilizer is more obvious, which was significant increased 6.31% compare to returning directly. Straw-derived biochar and straw incorporation have increased the soil total N content of 0-60 cm top layer. Straw returning directly significantly higher than CK under the condition of applying N fertilizer. and straw-derived biochar are slightly higher than the straw returning directly, which is significantly higher than CK without applying N fertilizer. Both straw returning ways have a tendency to increase the utilization rate of N fertilizer. The N fertilizer utilization rate were 55.99%,46.59%å'Œ44.08% in straw-derived biochar, straw returning directly and CK, respectively. On the whole, different ways of returning straw to the soil are all reduced the soil bulk density, increased total porosity and improved pH.2. The effect of different straw returned to paddy on GHG emissions had close relationship with nitrogen level. Whether applied N fertilizer, straw incorporation has significantly increased CH4 emissions relative to the control and biochar treatment, especially without N fertilizer. There are not particularly obvious difference between biochar amendment and the control. The accumulated CH4 emissions under the conditions of straw returning directly were about 3 times and 9 times compared with control with or without N fertilizer, respectively. The straw returning directly had significantly higher than the control and biochar treatment on the accumulated N2O emissions under N addition. There are no significant differences between the different ways of returning straw under the no nitrogen fertilizer. Whether or not applying N fertilizer, the accumulated N2O emissions under the biochar amendment had no significant difference with control. The different ways of returning straw had no significant influence of the accumulated CO2 emissions. The estimated seasonal gross global warming potentials (GWP) under the straw returning directly is significantly higher than biochar amendment and the control, which is 1.85 times of biochar amendment in the increasing temperature effect in a short time (20 years).3. The results of dry weights showed that the two returning ways are both improve the aboveground dry matter accumulation with N fertilizer. Straw incorporation increased by 8.42% compared with the control (P> 0.05); the equivalent straw carbonization amendment increased by 11.57% compared with the control (P< 0.01). Under no N fertilizer conditions, biochar amendment was increased of the accumulation of dry matter, but there was no significant difference between three kinds of way of returning straw about aboveground dry matter accumulation. The two ways of returning straw to soil are all improved rice yield with N fertilizer, but did not reach significant level. And under the condition of no N fertilizer, the two straw returning ways are both no significant difference in rice yield.4. In this study, the effect of two large amount biochar applications on soil C and N indicate that soil total C content increased significantly with the increasing biochar application with N fertilizer. The two treatments also greatly improve the soil total C content without N fertilizer, but with 29.6 t·hm-2 biochar had no significant level. The large biochar amendment significantly increased the soil total N content and utilization rate of N fertilizer with or without N fertilizer, and the differences between the two applications were small. The accumulated CH4 and N2O emissions have significant decreased with increasing the amount of biochar addition with N feitilizer. The accumulated CO2 emissions have significantly increased with 14.8 t-hm"2 biochar addition under N fertilization, but there had no significant difference between the two amount biochar application and control without N fertilizer. Comprehensive analysis results show that the GWP and GHGI with 29.6 t·hm-2 biochar addition are minimal with N fertilizer, but there are improved the greenhouse effect without N fertilizer under two amount of biochar applications. Like previous paper, there has reduced soil bulk density, increase total porosity and pH, and the range significantly increased compare with the straw returning ways.5. The photosynthesis and rice yield determination results showed that the two large amounts of biochar applications have improved the net photosynthetic rate, intercellular CO2 concentration, stomatal conductance and transpiration rate with N fertilizer, but they has no difference or to reduced under the no N fertilizer. The two amounts of biochar applications have significantly improved the aboveground dry weight relative to the control with or without N fertilizer. The two biochar applications were significant increased grain yield compared with the control with N fertilizer. The rice yield of two amounts of biochar application rates were higher 4.83% and 8.15% compared with the control with N fertilizer. The main reason of the increased yield maybe of the spike number had significantly increased, and the spike grain number has also increased.