The Effect Of Straw Mulch Conservative Cultivation On Soil Nutrients And Crop Physio-biochemical Mechanisms

Straw mulch is a highly effective water-saving technology, which plays significant role in changing underlying surface properties and balance, regulating soil temperature and improving soil moisture status. The main objective of using straw mulch is to increase economic output, reduce water loss and improve the water use efficiency. It is widely used for successful crop production under water-limiting condition, leads to sustainable development, and is an important aspect of conservation tillage. Straw mulch could hold soil water, improve soil micro-climate, reduce soil erosion, adjust soil water fertilizer gas heat, which is conducive for crop growth, and increased photosynthesis. In the present study we evaluated the performance of straw mulch cultivation on soil nutrients dynamic changes in rapeseed and its possible role in physiological and biochemical responses in soybean under drought stress. Main results are as follows: 1. The effect of straw mulch conservative cultivation on soil nutrients, growth and yield components in rapeseedThe study aimed to investigate the growth, soil nutrient dynamic change and yield of rapeseed under straw mulch conservative cultivation. The research work was carried out at the experimental farm of Southwest University, which comprised of a set of 8 treatments viz.:①no straw mulch,②3750kg/hm2 rice straw mulch.③7500kg/hm2 rice straw mulch,④3750kg/hm2 maize straw mulch,⑤7500kg/hm2 maize straw,⑥7500kg/hm2 rice straw mulch no crop treat,⑦7500 kg/hm2 rice straw mulch+rottening agent and no crop treat.⑧7500 kg/hm2 Rice straw mulch+rottening agent. Soil sampling was carried out at various developmental stages of rapeseed from varying soil depths. The analysis of the soil nutrient dynamic change, growth and yield of rapeseed indicated that:(1) Under different straw mulch treatments the change of soil organic matter on 0-10cm and 10-20cm layer was similar, and the differences between the various levels of straw mulch were not significant. The treatment where rottening agent was used had significantly higher organic matter contents. The soil total N under straw mulch followed the "increased-decreased-increased" trend. whereas the alkali-hydro nitrogen contents followed the "down-up-down" trend. The soil total P in 0-10cm and 10-20cm soil layer were volatility elevated and soil available P layer were first increased then declined. The trend of total K in 0-10cm was" increase-decrease" and in 10-20cm soil layer was opposite. The readily-available potassium in 0-10cm and 10-20cm soil layer followed the same trends as of total potassium. The soil pH value in 0-10cm and 10-20cm soil layer was consistent, which followed the increasing trend as the crop grew.(2) When we investigating the soil nutrients after harvest under straw mulch, the experimental results revealed that application of straw mulch had non-significant effect on the soil organic matter accumulation; the total nitrogen with the straw mulch increased;the same level of maize straw mulch treatments have more pronounced effect on the accumulations of nitrogen than rice straw mulch treatments; the straw mulch treatments improved the soil total potassium; the impact of different straw mulch treatments on soil potassium was variable, the various rice straw mulch treatments resulted in better soil available phosphorus, total potassium and readily-available potassium than the effects of maize straw mulch treatments; the use of rottening agent had no effect on accumulation of soil organic matter and alkali-hydrolysable nitrogen, but it resulted in increased accumulation of total soil nitrogen and total phosphorus, in the case of non-crop the rottening agent increased the accumulation of soil potassium.(3) Straw mulching had a significant effect on promoting the vegetative and reproductive growth of rapeseed. In our study, straw mulching significantly improved the rapeseed plant height, number of branches per plant and inflorescence, whereas rottening agent significantly improved the vegetative growth. The effect rottening agent on reproductive growth was not considerable. Rottening agent produced significantly higher yield than the same level of straw mulch treatments. Within one type of straw the yield of rapeseed was continuously enhanced follow the quantity of straw mulch.2. Physio-biochemical response of soybean to straw mulch To investigate the influence of straw mulch on growth, gas exchange, chlorophyll contents, soluble protein, free proline, lipid peroxidation and the activities of antioxidative enzymes in soybean under drought stress, a pot experiment was carried out in rain-protected wire-house of Southwest University. Chongqing. China. Soybean plants were supplied with varying wheat straw mulch treatments at true leaf stage viz:control (no straw mulch).3750 kg/hm2,7500 kg/hm2,11000 kg/hm2 and 14750 kg/hm2 and subjected to drought stress at blooming stage. An other pot experiment was carried out to investigate the response of soybean to varying type and different quantity of wheat and maize straw mulch treatments under water-deficit conditions, with following treatments: 11000kg/hm2 wheat straw mulch,14750 kg/hm2 wheat straw mulch,11000 kg/hm2 maize straw mulch and 14750kg/hm2 wheat straw mulch. The observations indicated that: Straw mulch promoted the cell elongation significantly which ultimately resulted in increased soybean plant height. The height of "Jin dou 21" was higher than the "xi dou 7". but between two varieties the increment of plant height under different mulch treatments was non-significant. Wheat straw and corn straw mulch both increased the number of soybean leaves per plant depending upon the type and quantity of straw mulch, but the effect of wheat straw mulch was more pronounced than maize straw mulch. Wheat straw mulch treatments enhanced the leaf area of soybean, the leaf area increased follow the quantity of straw mulch. The stem diameter of soybean plants grew following the amount of straw mulch applied.(2) Straw mulch significantly enhanced the photosynthesis (Pn), intercellular CO2 concentration (Ci), transpiration rate (E), stomatal conductance (Gs) and D-value (Ta-T1) (difference between air temperature and leaf temperature) over control treatment. All these gas exchange parameters were improved depending upon the quantity of wheat straw mulch; significantly highest Pn and E was observed in the treatment where wheat straw was applied at the rate of 11000kg/hm(3) The chlorophyll contents in soybean leaves altered noticeably during drought stress depending upon the type and the quantity of straw mulch. The observations indicated that chlorophyll contents proportionally decreased with the progression of drought stress but linearly increased with increase in straw mulch quantity.(4)Under varying levels of wheat straw, the contents of soluble protein in soybean continued to decline along with the prolongation of drought stress, but the straw mulch significantly alleviated the decrease of soluble protein content. The soluble protein increased with the drought stress under different type and amounts of straw mulch. The change of soluble protein content under drought stress was inconsistent and it was different because of types of straw mulch, crop varieties and stress time.(5) During drought stress in soybean, free proline content increased with the drought stress level. Straw mulch played an important role in drought-resistance of soybean by reducing the accumulation of proline content, but the amount of reducing was relevant to type and quantity of straw mulch.(6) The activities of Malondialdehyde (MDA) in leaves gradually increased as the water stress prolonged and decreased following the straw quantity in the treatments of different amount of wheat straw mulch. The contents of MDA changed with the progression of water stress. Wheat straw mulch led to drought ameliorating effect in drought-stressed soybean plants by decreasing the MDA contents which ultimately played a significant role in mitigation of lipid peroxidation on cell and crop.Under drought stress depending upon different type and quantity of straw mulch, the contents of MDA were increased at beginning of stress by following the amount of maize straw mulch and declined with the quantity of wheat straw mulch. In the middle of water deficit MDA content increased with the prolongation of drought, that the longer the plant suffered drought the greater lipid peroxidation damage. Straw mulch up to certain extent reduced the accumulation of MDA and the reduction was related to the quantity and type of straw mulch.(7) Straw mulch was able to enhance the activities of antioxidative system to mitigate the drought-induced oxidative damage in soybean plants. The effect of straw mulch on protective antioxidative system under slight drought conditions was significant. Superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were coordinated to play a positive role in soybean under drought stress depending upon soybean varieties, stress level, timing of stress and the different quantity of straw mulch.(8) Through the comprehensive evaluation it is clear that different amounts of wheat straw mulch contributed to drought resistance of "xi dou 7",11000 kg/hm2 got highest and control in worst. Among the different types and quantity of straw mulch the treatment of 14750 kg/hm2 maize straw mulch played a significant role in drought resistance, followed by 11000 kg/hm2 maize straw mulch in "jin dou 21"...