Effects of long-term full straw return on yield and potassium response in wheat-maize rotation

The effect of long-term straw return on crop yield, soil potassium（K） content, soil organic matter, and crop response to K from both straw and chemical K fertilizer（K_2SO_4） were investigated in a fixed site field experiment for winter wheat-summer maize rotation in 6 years for 12 seasons. The field experiment was located in northern part of North China Plain with a sandy soil in relatively low yield potential. Two factors, straw return and chemical K fertilizer, were studied with two levels in each factor. Field split design was employed, with two straw treatments, full straw return of previous crop（St） and no straw return, in main plots, and two chemical K fertilizer treatments, 0 and 60 kg K2 O ha^（–1）, as sub-plots. The results showed that straw return significantly increased yields of winter wheat and summer maize by 16.5 and 13.2% in average, respectively, and the positive effect of straw return to crop yield showed more effective in lower yield season. Straw return significantly increased K absorption by the crops, with significant increase in straw part. In treatment with straw return, the K content in crop straw increased by 15.9 and 21.8% in wheat and maize, respectively, compared with no straw return treatment. But, straw return had little effect on K content in grain of the crops. Straw return had significant influences on total K uptake by wheat and maize plants, with an increase of 32.7 and 30.9%, respectively. There was a significant correlation between crop yield and K uptake by the plant. To produce 100 kg grain, the wheat and maize plants absorbed 3.26 and 2.24 kg K2 O, respectively. The contents of soil available K and soil organic matter were significantly affected by the straw return with an increase of 6.07 and 23.0%, respectively, compared to no straw return treatment. K_2SO_4 application in rate of 60 kg K2 O ha^（–1） showed no significant effect on wheat and maize yield, K content in crop straw, total K uptake by the crops, soil available K content, and soil organic matter. The apparent K utilization rate（percentage of applied K absorbed by the crop in the season） showed difference for wheat and maize with different K sources. In wheat season, the K utilization rate from K_2SO_4 was higher than that from straw, while in maize season, the K utilization rate from straw was higher than that from chemical fertilizer. In the whole wheat-maize rotation system, the K absorption efficiency by the two crops from straw was higher than that from K_2SO_4.

Methane emissions from rice fields under continuous straw return in the middle-lower reaches of the Yangtze River

A three-year experiment was conducted in the middle-lower reaches of the Yangtze River in China to study the influence of continuous wheat straw return during the rice season and continuous rice straw return in wheat on methane （CH 4 ） emissions from rice fields in which, the rice-wheat rotation system is the most dominant planting pattern. The field experiment was initiated in October 2009 and has continued since the wheat-growing season of that year. The analyses for the present study were conducted in the second （2011） and third （2012） rice growing seasons. Four treatments, namely, the continuous return of wheat straw and rice straw in every season （WR）, of rice straw but no wheat straw return （R）, of wheat straw but no rice straw return （W） and a control with no straw return （CK）, were laid out in a randomized split-plot design. The total seasonal CH 4 emissions ranged from 107.4 to 491.7 kg/ha （2011） and 160.3 to 909.6 kg/ha （2012）. The increase in CH 4 emissions for treatments WR and W were 289% and 230% in the second year and 185% and 225% in the third year, respectively, in relation to CK. We observed less methane emissions in the treatment R than in CK by 14%-43%, but not statistically significant. Treatment R could increase rice productivity while no more CH 4 emission occurs. The difference in the total CH 4 emissions mainly related to a difference in the methane flux rate during the first 30-35 days after transplant in the rice growing season, which was caused by the amount of dissolved oxygen in paddy water and the amount of reducible soil materials.