Simulation Of Water Transmission For Transplanted Cotton Following Wheat Harvest Under Different Irrigation Methods

Winter wheat and cotton are the main two crops a year grown in the Middle and Lower Reaches of the Yellow River.In recent years,the competition for cultivated land between winter wheat and cotton has become increasingly serious and the level of agricultural mechanization has been continuously improved.Traditional intercropping pattern for winter wheat and cotton has become more unsuitable for the development of modern agricultural.Developing transplanted cotton following wheat harvest is an important way to realize the mechanization for the production of winter wheat,to solve the shortage of growth time for direct-seeded cotton following wheat harvest,and to ensure a good harvest of winter wheat and cotton.However,transplanted cotton is very different from direct-seeded cotton in growth development and water requirement.Therefore,the simulation of water transmission for transplanted cotton following wheat harvest is of great significance for determining the relationship between water transport and conversion in cotton field,revealing the water saving mechanism and water transmission characteristics for different irrigation methods,and determining the suitable irrigation method and schedule for transplanted cotton following wheat harvest.A field experiment was conducted during2013-2016 to analyse the dynamic mechanism of water transport and simulate the water transport in cotton field when using border irrigation(BI),surface drip irrigation(SDI)and micro-sprinkling hose irrigation(MHI).The main results and conclusions are as follows:(1)The evapotranspiration of transplanted cotton following wheat harvest and its main influencing factors under different irrigation methods were revealed,and the crop coefficients(K_C)in different growth periods of transplanted cotton following wheat harvest were calculated.Compared with BI and MHI,SDI decreased the evapotranspiration by 19%and 10%.This is mainly due to the reduction of soil evaporation(E)in the SDI treatment.The K_Cs in seedling stage,bud stage,flowering stage,boll opening stage and the whole growth period of transplanted cotton following wheat harvest in the BI treatment were 0.80,0.87,1.12,0.83 and 0.92,respectively;the K_Cs in the SDI treatment were 0.57,0.73,0.96,0.67 and 0.74,respectively;and the K_Cs in the MHI treatment were 0.72,0.83,1.02,0.71 and0.83,respectively.(2)The SIMDualKc and S-W models were adjusted to simulate the E and the transpiration(T)in the transplanted cotton field under different irrigation methods.By calculating the parameters of SIMDualKc model and the resistances of the S-W model,the E and T in the transplanted cotton field under different irrigation methods were calculated by these two models.The results showed the changes of E and T calculated by the two models were approximately coincident,and compared with the measured values,the accuracy of the S-W model was better than the SIMDualKc model.This is mainly due to the neglect of water supply from the lower soil layer to the surface soil layer in SIMDualKc model,resulting in the underestimate of E.(3)The differences of the root systems between direct-seeded and transplanted cotton were investigated,and the growth model parameters for the root system of transplanted cotton following wheat harvest under different irrigation methods were determined.Soil core method and Minirhizotrons were used to analysis the effects of irrigation methods on root system of transplanted cotton following wheat harvest.SDI increased the root length density(RLD),root surface area density(RSAD)and root biomass density(RBD)in the 0-to 30-cm soil layer compared with BI and MHI.The average RLD,RSAD,root tip number density(RTND)and root diameter(RD)were all the highest in the SDI treatment.The values in the BI treatment were the lowest,and the values in the MHI treatment were between them.Compared with soil core method,the Minirhizotrons was easy to underestimate the root density in the surface soil layer.A linear regression model can be used to modify the underestimation of the Minirhizotrons.The growth model parameters of the cotton root system were determined based on the data obtained by Minirhizotrons.(4)HYDRUS-2D model with the root growth parameters could simulate the soil water movement under different irrigation methods accurately.Based on the experimental data of E,T and root growth of transplanted cotton following wheat harvest,the relative parameters for the two-dimensional basic soil water movement equatio in the transplanted cotton field were determined.The HYDRUS-2D model was used to simulate the dynamic change of soil water content(SWC)under different irrigation methods.The model evaluation indicators of MAE,RMSE and d_l in the BI treatment are 0.014,0.020 and 0.94,respectively;the indicators in the SDI treatment are 0.017,0.025 and 0.92,respectively;and the indicators in the MHI treatment are 0.82,0.013,0.019 and 0.94,respectively.All the model evaluation indicators indicated that the HYDRUS-2D model with the root growth parameters could simulate the soil water movement under different irrigation methods accurately.