| Straw is an important renewable organic resource for improving soil fertility,which contains rich nutrients such as carbon,nitrogen,phosphorus and potassium.With the increased awareness of environment,returning straw to field is now gradually applied among farmers.Protected vegetable production has been affected by soil compaction and salinization caused by excess application of chemical fertilizer and lack of rain leaching.Previous studies have investigated that paddy-upland rotation could improve soil property.Cultivated aquatic vegetable in protected shallow-water filed mulched with rice straw.The study showed that the decomposition rate of race straw cut into two halves in spring and summer were 75.33%and 89.11%,respectively,which were significantly higher than the rate of 49.11%for 5-8 cm rice straw segments in autumn reported.In this study,half-cut wheat straw was mulched on the surface of shallow-water rotation field for water spinach and watercress cultivation in both high-and low-temperature seasons.The research was to investigate the decomposition rate of wheat straw in different seasons and for different mulch amount,and the effects on vegetable yields and quality,and soil properties.Meanwhile,the impacts of decomposition microorganism on wheat straw decomposition rate were studied.The main results were as follows:1.In summer and autumn,2015,500 kg/mu(0.75 kg/m2)wheat straw was applied on the surface of shallow-water field for water spinach cultivation.The highest electrical conductivity value of soil surface solution was 907 μS·cm-1,the lowest redox potential value was-362 mv,and the decomposition rate after 80 days was 57.7%.The yields of water spinach of the first two harvest times after treatment were lower than control,but the difference was not significant.The yields of latter two treatment times were significantly higher than control,and the total yields of water spinach after treatments were significantly higher than control.The nitrogen,phosphorus and potassium contents of water spinach were significantly higher than control,and the VC and total phenol content were higher as well.As for the soil properties,the phosphorus content increased,while the nitrogen and potassium contents decreased,and the organic matter content increased.This result suggested that the high temperature and humidity environment in poly tunnel(green house)accelerated the decomposition of wheat straw and was beneficial for improving vegetable yields and soil properties.2.In autumn and winter,2015,500 kg/mu(0.75 kg/m2)wheat straw was applied on the surface of shallow-water field for watercress cultivation.The highest electrical conductivity value of soil surface solution was 645 μS·cm-1,the lowest redox potential value was-191 mv,and the decomposition rate after 131 days was 50.1%.The yields of watercress were significantly higher than control.The nitrogen,phosphorus,potassium and VC contents,and the DPPH radical scavenging activity were significantly higher than control.As for the soil properties,the nitrogen,phosphorus and organic matter contents were increased.The decomposition rate of wheat straw decreased in low temperature seasons,but it remained at a relatively high rate in protected environment.3.In spring,summer and autumn,2016,1000 kg/mu(1.5 kg/m2)wheat straw was applied on the surface of shallow-water field for water spinach cultivation.The highest electrical conductivity value of soil surface solution was 1595 μS·cm-1,the lowest redox potential value was-384 mv,and the decomposition rate after 170 days was 68.6%.The yields of water spinach after treatment were significantly higher than control(except for the first harvest time),and the total yields of water spinach were 5.5%higher than control.The result suggested that expending decomposition time could increase decomposition rate and adding mulching amount could improve yields.The nitrogen,phosphorus,potassium and organic matter contents and the soil enzyme activities significantly increased,while the nitrate nitrogen content decreased.This suggested that increasing wheat straw mulching amount was beneficial for improving soil properties.4.In spring and summer,2017,500 kg/mu(0.75 kg/m2)wheat straw was applied on the surface of shallow-water field for water spinach cultivation.The decomposition rate after 123 days was 55.8%and the yields were significantly higher than control.After four treatment periods,the total wheat straw mulching amount reached 2500 kg/mu(3.75 kg/m2).The nitrogen,phosphorus,potassium and organic matter contents and the soil enzyme activities significantly increased,while the nitrate nitrogen content decreased.It could be concluded that successive application of wheat straw mulch significantly improved soil properties.5.In spring and summer,2017,500 kg/mu(0.75 kg/m2)wheat straw was applied on the surface of shallow-water field for water spinach cultivation and decomposition microorganism was added.The decomposition rate after 123 days was 68.3%,which was higher than the field without decomposition microorganism application by 12.5%.The soil enzyme activities significantly increased,among which the phosphatase activity significantly rose.This demonstrated that the decomposition microorganism facilitated soil enzyme activities and the demonstration rate of wheat straw increased as a result.In the environment of protected aquatic vegetable fields,the whole wheat straw mulch demonstration rate was significantly higher than the rate of 5-8 cm rice straw segments provided by Dai Zhigang,while it was lower than the rice straw decomposition rate reported by Yan Wuwei.Higher temperature,longer mulching time and application of decomposition microorganism could increase decomposition rate.The nutrients provided by wheat straw decomposition not only increased the yields and the quality of aquatic vegetables,but significantly improved the properties of soil,which is a sustainable way for better developing protected vegetable cultivation. |
