| Straw is a very big resource in agriculture. As a big agricultural country, China has a very large straw output which is up to 700 million ton per year. In some middle and lower Yangtze districts where rice-wheat rotation exits, the exited ways of straw returning can not solve the problem caused by large amout of straw and limited time. Straw channel-buried returning is a new method that the straw is returned in the ditches and covered by soil. The ditches were digged distance by distance after harvest. By using this method, it is likely to get all the straw deeply buried with low costs and is good for carbon sink and soil cultivation. Our research is in order to establish a corresponding technical specification by studying on the effects of straw channel-buried returning.This study with field and pot experiment was mainly about:①The effect of straw channel-buried returning on the soil physical properties;②The effect of straw channel-buried returning on straw decomposition and rice field CO2 emission;③Function of Channel-buried straw intercepting and adsorbing nitrogen;④Preliminary research on rice-straw growth.The main conclusion were as follows:1. Straw channel-buried returning improved soil water and temperature obviously.After the rain stoped, in 3 days the straw channel reduced the waterlogging damage, which was similar with drainage ditch. The soil moisture was reduced more quikly where was nearer to the edge of straw channel and drain. After continuous rainfall, preferential order of the reducing waterlogging effect by different depth of channel is 30 cm>20 cm>40 cm>50 cm. The velocity of 30cm depth straw channel was about 71.4 mL/min, which is the biggest. The day and night temperature of straw upper soil layer was biger than that of CK, while the day and night temperature of underlayer soil is smaller than that of CK. Straw layer had the effect of insulation in the period of lower temperature. The soil bulk density on the ditch decreased by straw returning in the ditch, which increased after 3 seasons and still was 0.09 g/cm lower than that of CK. The soil bulk density of plough layer obviously decreased after multiple quaternary of straw channel-buried.2. Different depth of straw ditch and straw concentration ratio obviously affected the decomposition and rice field CO2 emission.The experiment was foused on the straw decomposition and rice field CO2 emission by nylon mesh bag method and static lye absorption in situ. The results showed that:the straw decomposition progress increased fristly and then decreased, as the depth of ditch increased. The decomposition progress of rice straw was quikest in 15 cm and 20 cm, while wheat straw was quikest in 25 cm and 30 cm. The treatments of more than 10 cm depth are all showed that the decomposition in the first season is quiker than it in the second. The lost weight of 50 cm depth treatment straw is the smallest in the second season, as the weight loss rate is only 1.85%. At the first time, the CO2 emission was lower as the depth of ditch increased, which would promote the soil carbon sink. The CO2 emission increased with the straw-buried increased, but the CO2 emission of per straw-buried decreased as the buried straw increased. It showed that increasing the buried straw concentration ratio can enhance the effect of soil carbon sink.3. Straw returning had obvious effect on reducing soil nitrogen loss.The test was ralyed on pot and indoor culture, and measured nitrogen content of soil, straw and soak. The result showed that:The wheat straw had the adsorption ability to nitrogen. When the content of nitrogen concentration was from 150 mg/L to 2400 mg/L, the nitrogen adsorption by 1 g straw was from 2.4 mg to 7.2 mg. The largest content of adsorption was 9 mg/g in theory, the straw layer formed in the soil intercepted some nitrogen. The intercepting nitrogen by 1 g straw was 0.852mg on the condition of normal fertilization(18 kg/mu pure nitrogen). It is concluded that straw returning reduced the loss of soil nitrogen.4. Reasonable depth and straw quantity had no negative effect on crop growth.The treatments of straw-buried depth with 10 cm,buried rice straw with 3 kg/m (or wheat straw with 1.5kg/m)and 4 kg/m(or wheat straw with 2kg/m) was bad to crop, whose emergence number, effective panicle number and grain number per spike was obviously smaller than those of CK. The treatments of the quantity of buried rice straw≤3 kg/m or 1.5k g/m wheat and depth of straw ditch≥20 cm had little effect on the growth of rice and wheat. Reasonable depth and straw quantity had no negative effect on crop growth. |
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