Effect Of No-till With Straw Cover On Soil Organic Carbon In Dry Land

The change of soil total organic carbon, sodium pyrophosphate—extractable carbon, hot water—extractable carbohydrates, hydrolysable carbohydrate, oxidizible carbon in soil for two years had been studied through the experiment of no－till with straw cover in Dingxi where is the typical semiarid area. 1. No－till with straw cover (NTS) can improve soil total organic carbon, especially on the surface. it is 7.83g/kg in 0～5㎝ layer which has the highest content in all treatments, the average content is 6.95 g/kg. The total organic carbon in 0～5㎝, 5～10㎝, 10～30㎝, 0～30㎝ layer after harvest is more 20.28%, 58.41%, 53.80% and 44.16% than what is before sowing. Soil total organic carbon was negatively correlated with depth of soil, is not significant difference among soil layers in NTS. The total organic carbon in NTS is extremely significant difference in 0～5㎝ layer with conventional tillage with no straw(T), conventional tillage with straw incorporated(TS),no－till with plastic mulch(NTP)before sowing.2. NTS can stable the physics and chemistry character of soil. The content of sodium pyrophosphate—extractable carbon were respectively 2.14g/kg, 2.07g/kg, before sowing and after harvest. The rate of Sodium pyrophosphate—extractable carbon in total organic carbon is 23.70%～52.05％ before sowing and 15.73％～29.81％ after harvest, relate with the tillage method, sample time and soil condition. The content of sodium pyrophosphate—extractable carbon is not significant difference between layer and treatment not only before sowing but also after harvest in NTS.3. NTS can improve the content of hot water—extractable carbohydrate on surface. The content of hot water—extractable carbohydrate in NTS is the highest in all treatments before sowing, which is 271.56mg/kg. The content of hot water—extractable carbohydrate after harvest is more 44.515 mg/kg than before sowing. The hot water—extractable carbohydrate in NTS is extremely significant difference in 10～30㎝ layer with NTP. The rate of hot water—extractable carbohydrate in hydrolysable carbohydrate is decrease with the depth of soil, which is 12.74％, 9.90％, 9.39％ in 0～5cm,5～10cm,10～30cm layer before sowing and 15.46％, 13.28％, 11.78％ after harvest. The rate of hot water—extractable carbohydrate in hydrolysable carbohydrate before sowing is more 2.78％ than after harvest.4. The content of hydrolysable carbohydrate is steady. The content of hydrolysable carbohydrate after harvest is less 0.020％, 0.003％, 0.001％than before sowing in the three layers. The hydrolysable carbohydrate in NTS is significant difference in 5～10㎝ layer with NT. The rate of hydrolysable carbohydrate in total organic carbon is 15.78％～23.47％ before sowing and 10.02％～17.40％ after harvest.5. According as the content of oxidizible carbon and its regularity, we can study the change of soil organic carbon. NTS is benefit of the accumulation of organic carbon. The content of oxidizible carbon is the highest in 0～5㎝ and 5～10㎝ layer, is the lowest in 10～30㎝layer.