The Establishment Of Soil Moisture Model And The Effect Of Water Stress On Matter Accumulation And Yield Of Soybean

Soybean is one of the most important oil crops, which is sensitive to water. Studying on theeffect of water stress duration and levels of irrigation on soybean are profound implications fordesign of irrigation, increasing yield, water saving and drought-resistance.This work was conducted from2010to2012with frame tests. The irrigation was conducted inglass shed. Irrigation amount is determined by the mean rainfall in Harbin from1995to2009. Thevarieties of experiment include SN14, NF18, HN60and HN48. The time series models and statisticmodels are established. And the effect of periodic water stress and irrigation levels on plant height,accumulation of dry matter, nitrogen, phosphorus, potassium and yield of soybean are researched.The results show that:Irrigation amount and water stress duration affect soil moisture content. Irrigation amountinfluence the peak of soil moisture content, which can be formulated by logistic model. With theirrigation amount increasing, the soil moisure content approach to37%gradually. Water stressduration influence the trend of soil moisture content, which can be formulated by exponentialdecay model. As24days water stress duration, soil moisture content drop7%on average. Withwater stress duration increasing, soil moisure content fall and approach to13%gradually.Three models are created as follows.（1）Time series model of soil moisture content isexponential decay model and soil moisture content are spliced by the time-difference correlationanalysis. The model is S=23.786e-^0.041T+13, T∈[T0,T0+ΔT], which is significantly tested.This model can be used to predict soil moisture content after T days duration to judge the trendof soil moisture content after rainfall or irrigation in order to provide irrigation decision referenceafter certain duration of water stress.（2）The relationship of irrigation amount and peak of soilmoisture content can be formulated by logistic model asS=37/1+1.1e^-0.60w01+1.48e0.60W, significantly tested.This model can be used to predict peak of soil moisture content under certain rainfall or irrigationamount, combined withT=1/0.041In S-13/23.786and time series model to form regressionequations about the effect of irrigation amount and water stress duration. The regression equationscan be used to predict soil moisture content after T days water stress.（3）Establish statisticmodels about effect of water stress duration on soil moisture content. The relationship of irrigationamount and peak of soil moisture content can be expressed by two-dimension normal distribution with coefficient0.485. According to the two models above, the probability of soil moisture contentreach certain value when the rainfall or irrigation is W and water stress duration is T can becalculated. The result of statistic models is more effective than deterministic model.Water stress effect on plant height of soybean. Long-term water stress restrain the growth ofplant height at seedling and flowering-podding period in SN14, mild water stress don’t affect theplant height. Long-term water stress restrains the growth of5th-8th nodes of soybean at seedlingperiod. Long-term water stress restrains the growth of6th-15th nodes of soybean atflowering-podding period. Irrigation levels effect on plant height differently by varieties. Lowerlevels of irrigation restrain the plant height of SN14and NF18, but HN60is insensitive.There is significant effect of water stress on accumulation of dry matter, nitrogen, phosphorusand potassium of soybean. Long-term water stress restrain accumulation of dry matter, nitrogen,phosphorus, potassium at seedling, flowering-podding and podding-seed filling periods. The ruleof irrigation levels effect on accumulation of dry matter, nitrogen, phosphorus and potassium ofSN14, NF18, HN60are the same. Higher the level of irrigation comes to higher accumulation ofdry matter, nitrogen, phosphorus and potassium of soybean. Longer water stress duration andlower the level of irrigation comes to lower accumulation of dry matter, nitrogen, phosphorus andpotassium of soybean at flowering-podding and podding-seed filling periods.The effect of water stress on yield of soybean is different because of growth stages. The mildwater stress can not reduce the yield of soybean, but long-term water stress reduces the yield ofsoybean at seedling period in SN14and HN48. Soybean yield present a single peak curve withwater stress duration increasing at flowering-podding period in SN14. Soybean yield decreasedwith water stress duration increasing at flowering-podding period in HN48. Both moderate waterstress and severe water stress can reduce yield of SN14and HN48. Soybean yield decreased withwater stress duration increasing at podding-seed filling period in SN14and HN48, the yield of18days and24days duration decreases significantly in SN14. Longer water stress duration and lowerirrigation level comes to greater effect on soybean yield at podding-seed filling period. Bothmoderate water stress and severe water stress can reduce yield of soybean.