| The Huang-huai-hai Plain is one of the most important agricultural area in China and one of the seven major agricultural areas in China's 12th five-year plan.The development speed and prospect of agricultural production have significant influence on China's agriculture and economy.In Huang-huai-hai Plain,the low yield fields are the most widely distributed in the Huaibei Plain.The widely distributed calcic vertisols in Huaibei Plain is the main reason that the grain yield can not reach its potential.In order to improve the agricultural productivity of calcic vertisols,it is necessary to have a better understanding of material circulation and energy conversion in farmland system.Due to calcareous concretions(CCs)and soil cracks in the profile,structure of calcic vertisols is relatively complex.Hence,the quantification of soil moisture and nutrients is difficult.Field experiment is not able to meet the requirement.The Soil-Plant system model has obvious advantages in the quantitative description of complex soil processes,and it can also provide better management for higher yield in farmland.This research focus on the basic properties,water-nutrient dynamics and plant growth in typical calcic vertisols:Firstly,the distribution of soil nutrient,mechanical composition and calcareous concretions in calcic vertisol fields were mearsured to get a better understanding of low productivity of the fields;Secondly,the effect of CCs on soil water retention was studied quantitatively.Thirdly,the root zone water quality model(RZWQM)was used to explore the soil water-nitrient movement and plant growth of soil under the condition of straw mulching and soil cracks.The conclusions are as follows:(1)Soil nutrients and CCs appeared great variability in spatial,and the clay content distribution was relatively uniform.The contents of soil organic matter,available phosphorus,available potassium,total nitrogen and available nitrogen of calcic vertisols were relatively low,and the average value were 11.555 g kg-1,1.681 mg kg-1,77.351 mg kg-1,660.29 mg kg-1,and 64.171 mg kg-1 respectively.CCs begined to appear in the 20-40 cm soil layer,and the content increased with the deepening of soil depth,with a maximum content of 0.441 g g-1.The soil clay content in the test fields was more than 30%,which was classificated as silty clay loam(USDA).(2)CCs can maintain considerable water,and the saturated water contents of CCs of 2-5 mm,5-8 mm and 8-30 mm were 0.251,0.220 and 0.196 cm3 cm-3,respectively.The addition of CCs to soils significantly changed the water retention curve and pore distribution of soils.The soil available water contents(AWCs)of soil-CC mixtures decreased when CC content increased.To calculate the accurate AWC of soils contained CCs,a linear equation was proposed,in which CC content and CC water content were considered.Accounting calcareous concretion in calcic vertisol can improve the accuracy of soil hydraulic property estimation and lead to a better field water management.(3)Straw mulching can significantly improve the soil moisture content.During the test,water content of surface soil(0-20 cm)under straw mulching increased 0.010?0.019 cm3 cm-3.Compared with conventional croping,soil nitrate content under straw mulching was decreased and then increased.The wheat yield under straw mulching was significantly lower than that of conventional croping,with an average reduction of 547.3 kg ha-1,while the difference between maize yield under straw mulching and conventional croping was not significant.(4)The water-nitrogen movement of calcic vertisol under straw mulching and conventional croping was simulated by RZWQM,and the soil water and nitrogen balance was calculated by the model.RZWQM model can simulate the water-nitrogen movement and plant growth under conventional cropping,but cannot simulate the systemic impact of straw mulching on.plant diseases and insect pests.The Simulated crop yield under straw mulching was higher than the measured values.(5)The average annual soil evaporation under straw mulching decreased by 28.7?36.8 mm,compared with conventional cropping.The average annual transpiration under straw mulching increased by 18.9?21.0 mm.Meanwhile,straw mulching reduced surface runoff and increased deep seepage.Water use efficiency(WUE)was increased by 0.03?0.05 kg m-3.Straw mulching increased the amount of nitrogen uptake,nitrogen uptake and denitrification,thus reducing the nitrogen use efficiency(NUE)by 0.4 kg kg-1.(6)The distribution of macropores can greatly affect water and nitrogen balance in the soil.In the scenario crack only appeared in the' surface soil,the average annual surface runoff decreased by 14.9?32.6 mm,and the deep seepage increased by 9.5?21.1 mm,and the annual leaching of nitrogen increased by 2.8?5.2 kg ha-1.When the crack penetrates the soil profile,the average annual surface runoff decreased by 86.8?159.2 mm,the deep seepage increased by 78.4?139.0 mm,and the annual average leaching nitrogen increases by 23.9?31.5 kg ha-1.The existence of crack reduced WUE of calcic vertisols,and decreased by 0.01?0.04 kg m-3,reducing the NUE by-0.2-1.5 kg kg-1.This study investigated the main obstacle factors of agricultural production in calcic vertisols,analyzed the CC effect on soil water retention curve and AWC of calcic vertisols quantitatively,and discussed the impact of straw mulching and soil crack on water-nitrogen movement,plant growth,WUE,and NUE in calcic vertisols quantitatively.The results of this study can provide a theoretical basis for the improved utilization of calcic vertisols. |
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