Study On Regulation Mechanism Of Soil Water-Heat-Salt Transfer And Crop Growth With Surface Mulching In The Salinizated Soil

In order to investigate the coordinate regulation mechanism of water-heat-salt on saline soil with different mulching method in cold-drought-salt irrigation district and the response relationship between crop growth conditions and ground cover, this research made the whole period (the freezing and thawing period and the growth period of maize) experiment and the growth period of sunflower experiment in Inner Mongolia Hetao irrigation district. The experiment set 8 treatments of crushing straw mulching. The mulching quantity of them are:1.2 kg·m-2(F1.2),0.9 kg·m-2(F0.9),0.6 kg·m-2(F0.6),0.3 kg-m"2(F0.3), YZ, KZ, DM and CK. Adopt the coupling method of field observation and lab analysis, mechanism research and model simulation. It is aimed at revealing the regulating effect of different mulching method on movement of soil water, salt and heat, crop growth and development and yield comprehensively. The main research results are as follows:1. The mulching experiment of whole period(1) After the autumn irrigation, the freezing and thawing characteristics of each treatment existed differences. The maximum frozen depth of straw mulching was less than 4～26cm of CK. The beginning frozen time lagged for 0-12d. The thawing time lagged for 0～21d. The maximum frozen depth of plastic film mulching (DM) was less than 26cm of CK. The beginning frozen time lagged for 14d. The surface thawing dates lagged behind CK for 6d. Through building the quantitative relation between the frozen depth of saline soil and negative accumulated temperature of air temperature, the freezing process of seasonal frozen soil could be decided by the negative accumulated temperature of air temperature.(2) The straw mulching stabilized the soil temperature fluctuation effectively. And the temperature range in the entire section of plastic film mulching (DM) was significantly larger than the temperature range of straw mulching and CK. The order of mean soil temperature in 0-120cm section was DM>CK>straw mulching. The overburden could restrain the invalid evaporation of perched water in early ablation and the salt amount in earth surface. Under the action of temperature gradient in frozen period, the water of bottom non-frozen layer moved upward to the frozen layer. The soil salt moved to the upside with water.(3) Based on the soil water, salt and heat of spring maize sowing date after freezing and thawing period, consider the influence of different mulching on the autumn irrigation comprehensively. The treatments of mulching made the soil water content in 0-20cm layer higher, which made the suitable sowing date of spring maize delay. Compared with CK, the mulching treatments decreased the soil salt content in 0～10cm and 0-40cm layer. The inhibitory effect of salt of straw mulching was better than the plastic film mulching. The inhibitory effect of salt of the whole stalk mulching was the best. Compared with CK, the plastic film mulching made suitable sowing date of spring maize 7 days earlier. And the straw mulching lagged behind CK for 6-7d.(4) The water-salt stress and low temperature were the main obstacle factors for germination of maize seed in salinity land. The emergence rates of YZ, F0.9, F1.2 and F0.6 were higher than the DM, F0.3, CK and straw mulching treatments significantly. Except for F0.3, they were higher than DM significantly. Compared with CK, mulching treatments increased the grain yield significantly. The rate of growth of YZ was highest. The higher emergence rate and mean grain weight were the main reasons of the increase of maize yield. The increase extent of biomass by mulching was less than the increase extent of grain yield, which made the economic coefficient of mulching treatments higher than the CK.(5) The defect of autumn irrigation and drainage system in Hetao irrigation district made the influencing factor that influenced migration and transformation of nutrients in freezing and thawing period was not merely the seasonal freezing and thawing cycle. For the arable layer of 0-40cm after autumn irrigation, the soil whole effect of nutrient, available nutrient and organic matter were all increased than before. In the freezing and thawing period, nutrients were in the process of leaching, migration and transformation.2. The mulching experiment of sunflower growth period(1) After the 2-year mulching experiment, make the double ring infiltration testing in the original sunflower land. Through the independent sample T-test, the analog data of Philip, Kostiakov and Horton model had no significant difference with measured data. These 3 models could be applied easily for simulating the infiltration process of no-till stubble land with different mulching.(2) The mulching mainly restrained the soil evaporation in early growth period. And it also promoted the evapotranspirtion intensity of sunflower in later growth period. The inhibitory evapotranspirtion effect of DM, F1.2 and YZ was significance. In wet year, the soil water storage and preservation effects of treatment F1.2, F0.9 and YZ were better than DM. In median water year, the soil water storage and preservation effect of DM was better than straw mulching. In the treatments of crushing mulching, the water storage and preservation effect enhanced with the increase of mulching amount. In the treatments of whole stalk mulching, the moisture conservation effect of YZ was better than KZ.(3) The decrease extent of salt content with mild or moderate mulching in median water year was larger than the decrease extent in wet year. Therefore, the median water year was more conducive to restrain salt accumulation by mulching. In wet year, the decrease extent of salt with moderate mulching treatments was larger than the mild mulching treatments. The inhibitory action for salt accumulation of moderate mulching was stronger than the mild mulching.(4) Covering treatment can improve the yield of sunflower compared with CK. For mild salinization soil, the yield of straw mulching treatment F0.6 and YZ were higher than other treatments and increase production effect is obvious in wet year and median water year. For moderate salinization soil, YZ and DM treatment yield is significantly higher than the rest of the covers in wet year; the yield of F 1.2 and DM treatment was the highest of all in median water year.(5) For mild salinization test field, water use efficiency (WUE) of F0.6 is the largest of all treatments in wet year; the covering treatments’WUE is significantly higher than CK in median water year and water use efficiency of F1.2,F0.9,F0.6,YZ are much higher than other treatments. For moderate salinization test field, YZ, F1.2 have higher water use efficiency and it is increases with the cover size in crushed straw mulching treatment.3. Simulating studies on water,heat,and salt movement in freezing and thawing soil with straw mulchUsing SHAW model simulation analysis on the water movement rule of freezing and thawing soil water-heat-salt.SHAW model has high precision for simulation of soil temperature variation under straw mulching and its simulation of shallow soil temperature accuracy is inferior to deep soil. For soil moisture simulation, the change rule of moisture profile was simulated successful due to achieve the soil conditions of saturated moisture content, but the simulation value is smaller than the measured values and the simulation for moisture effect is not good, the moisture content of the upper soil layer simulation has large deviation while the lower soil layer soil moisture content simulation values is more close to the measured values. For soil salt simulation, the simulation accuracy of F1.2 was slightly higher than that of YZ. Within 0～120 cm profile, the 1 precision was low overall simulation for soil salt.4. The optimal way for covering and the selection of mulching quantityFull coverage (freezing and thawing and maize growth period):YZ was the best of all,F1.2and F0.9 did better in smash of straw mulching treatment with comprehensive consideration of salt control, water content holding, temperature, fattening effects in different coverage ways; Sunflower growth period covered:For mild salinization field, YZ is the best and the best crushing straw mulching quantity between 0.6 kg·m-2 and 0.9 kg·m-2 considering soil water storage and preservation, the decrease of salinization and the increase of net income conditions. For moderate salinization field, DM is still the most effective mulching method.