Effect Of Straw Carbonization Returning On Nitrogen Utilization And Rice Yield In The Rice Paddies

Biochar has high stability and greater adsorption capacity. Research has demonstrated that biochar has the potential to improve soil fertility and enhance soil C sequestration and reducing GHG emissions and increase agricultural yield. Now as a common way of incorporation used widely, straw directly returning to field has also been advocated as a potential way of increasing soil fertility and improving crop yields has been recognized. For a special climate conditions in northeast China, such as a low temperatures in winter and annual accumulated temperature is low, there are few researchs about the effects of different straw incorporation methods on greenhouse gas emissions,. N utilization and yield of rice. 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 N utilization, N2O emissions,soil fertility and rice growth. The treatment was performed with five levels:Straw application rate:0 t-hm-2(CK),Straw returning directly:5.05 thm-2(S), Straw carbonization returning rate:1.78 t-hm-2(B1), Straw carbonization returning rate:14.8 t·hm-2(B2), Straw carbonization returning rate:29.6 t-hm-2(B3). The N fertilizer included two levels:0 kg N-hm-2(N0) and 210 kg N-hm-2(N).A super rice variety Shenyang 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 soil fertility shows:Whether or not applying N fertilizer, straw returning directly and straw carbonization returning both can increase the total N content in soil significantly, and the effect of straw carbonization returning with N fertilizer is more pronounced; The trend is mainly decided by the content of nitrate-N, and the change of ammonium-N concentration is not obvious. The alkali-hydrolyzable nitrogen content in soil is increased more obviously without N fertilizer than with N fertilizer applying. The activity of soil urease is reduced significantly with straw returning directly amendment, but not impacted obviously with straw carbonization returning.Two straw incorporation methods both can increase the the utilization rate of N fertilizer, especially straw carbonization returning is more obviously. Whether or not applying N fertilizer, nitrogen uptake of rice is not impacted significantly under the straw returning directly amendment, with the increasing biochar application, nitrogen uptake of rice is increased slightly without N fertilizer, but significantly with N fertilizer. Both of the two straw incorporation methods can reduce soil bulk density, and increase soil porosity and pH.2、 The comparison study of the effects of different straw incorporation methods to N2O emission shows:N2O emission is promoted significantly in the rice paddies with N fertilizer, especially under the condition of straw returning directly. With the increasing biochar application, N2O emission is reduced gradually in rice paddies, however in conditions of not applying N fertilizer, the variance whether interaction or comparison is not obvious, and the absolute value is markedly lower than that in conditions of applying N fertilizer. N2O emission is not changed with no applying N fertilizer after transplanting, even always maintain a lower level. But it is changed obviously with N fertilizer applied, two peak values appeare in 30-45d and 75-94d after transplanting approximately and the valley value appears in 60d after transplanting.3、Compared to the effect of straw returned modes in matter production, photosynthesis characteristics and yield formation, the results shows that:In 2013, dry matter accumulation of overground don’t have obvious difference between Nitrogen levels, amount of straw returning and returning methods, and regularity is poor. Under the condition of no nitrogen applied in 2014, dry matter accumulation of overground have slightly reduced in straw returning directly, but dry matter accumulation of overground are obvious increased with the increasing biochar application; under the condition of nitrogen applied in 2014, dry matter accumulation of overground are both increased with the amount of straw returning in straw returning directly and straw carbonization returning amendments. The plant height, tillering and relative content of chlorophyll were all increased in straw carbonization returning. Under the condition of nitrogen applied, Net Photosynthetic Rate, transpiration speed, Inter-cellular CO2 Concentration stomatal conductance are improved in both straw returning methods, but there is no obvious difference or no apparent rule in no nitrogen applied treaments. Under the condition of nitrogen applied,the yield of straw returning directly is obvious higher than CK, and is higher than other treatments but has no obvious difference. The yield has no obvious difference in straw returning modes and amount of returning under no nitrogen applied.