The Research On Evolution Mechanism Of Layered Mulching Straw And Its Decomposition Rate Regulation Methods

Straw layered mulch has many effects on orchard soil,such as reserve water,heat preservation,inhibit weeds and improve soil organic matter.The thickness of the mulch layer affects mulch effects to some extent.The straw decomposition rate determines the timeliness of mulch effects when the thickness is constant.Therefore,it is of great significance to study the evolution of straw mulching layer and the regulation method of decomposition rate for determining the working time and period of mechanized straw mulch in orchard.Wheat straw,corn straw,soybean straw and mushroom residue were been selected as mulch materials,decomposition accelerator,antiseptic agent and urea as additives,simulate straw layered mulching in outdoor containers for 365d.Study straw layer evolution regularity and the method of regulate straw's decomposition rates through analysis the straw mass,thickness,nutrient,organic components,gas release and microstructure.Establish a model for predicting straw's decomposition rates through temperature and moisture.Combining the actual needs of orchards determine reasonable mulch time and period.The results are as follows:?1?The rot of the mulch layer is fast in the early stage and slow in the late stage and layered mulch delays straw decomposition.The decomposition rate of straw and mushroom residue was up to 2.67-3.63 g/?d·kg?on 10d,after gradually reduced to an average of 1.59g/?d·kg?.The average cumulative decomposing rate was 56.93%at the end of the test?365d?.The decreasing rate of the thickness of straw and residue layer reached the maximum 0.040mm/?d·cm?and 0.049 mm/?d·cm?at 150d and 10d respectively.The average thickness reduction percentage was 79.73%in the end.The changes of the decomposition rate and thickness of the three kinds of straws and mushroom residue with time can expressed by equations,the R² were>0.9603 and 0.9677,respectively.?2?The rapid release period of nutrients for straw was initial 30d and the order of cumulative release rate was K>N>P,the cumulative release rates of N,P,K were 72.28%,63.22%,and 80.71%at the end of the test,respectively.Straw organic components rapid decomposed in the first 30 days.At the end of the test,the accumulated decomposition rates of cellulose,hemicellulose,and lignin were 77.76%,85.22,and 56.02%,respectively.The CO₂ release of the coating increases first and then decreases,straw and mushroom residue slag peak at 60d and 120d respectively.The amount of CH₄ released fluctuates,peaking at45d and 150d respectively.The stalk's microstructure gradually appeared holes with decomposition,and loose structure was the main reason for the change of the thickness of the straw layer.?3?The decomposition accelerator and antiseptic agent accelerating and delaying the rot decomposition process respectively in the initial stage of the experiment.The average decomposition rate of straw add decomposition accelerator or antiseptic agent were 3.62g/?d·kg?or 1.99 g/?d·kg?in 10d.The rate of decline of the thickness of the straw layer treated by the decomposition accelerator is higher than that of the antiseptic agent by 0.014mm/?d·cm?.The release of CO₂ and CH₄ showed a higher level of decomposition accelerator added in the early stage and a higher addition of antiseptic agent at a later stage.?4?The multi-regression equations with add antiseptic agent and urea affecting the straw layer decomposition rate and thickness decrease rate are both significant,the R² were 0.9521and 0.9986.The multi-regression equations with add decomposition accelerator and urea affecting the straw layer decomposition rate and thickness decrease rate are both significant,the R² were 0.9758 and 0.9979.?5?Taking the decomposition time,layer temperature,and layer water content as independent variables,the mass decomposition rate and thickness decrease rate of straw as dependent variables to establish multivariate quadratic regression equations.The models are significant and the R² were>0.823 and 0.808,respectively.The decomposing rate and thickness decreasing rate model of the overburden layer were tested respectively.The R²between the predicted value and the measured value were>0.993 and 0.974,respectively.The standard errors were<0.023 and 0.043,respectively.?6?The orchard straw mulch timing and cycle time were determined take Shaanxi as an example.Direct mulch use wheat straw after harvest in June,and use corn straw and soybean straw after harvest direct secondary mulch in October.Twice a year mulch is optimal technology of straw layered mulch in orchard.The thickness of the first mulch from 15cm to the second mulch is predicted to>8.6±0.4cm,and the thickness of the second mulch from15cm to the first mulch in the following year is predicted to>6.6±2.2cm.The decomposition rate of the mulch layer can be regulated by additives,and predicted by temperature and moisture.This paper can provide theoretical basis for the timing and cycle of mechanized layered mulch of orchard straw.