Utilization Of Rainfall And Its Simulation In Winter Wheat

With rapid social and economic development, shortage of water resources is becoming more andmore serious, and competition for limited agricultural water resources also is becoming more and morebitterly in China. Water consumption for irrigation is the majority of agricultural water resourcesconsumption and also occupies a very important position in whole social water resources utilization.However, water use efficiency and return is still relative low and water waste is still very common andserious. So that, development of water-saveing irrigation techniquies and irrigation management modelsis very helpful for relieving severe competition for water resources and ensuring national security ofgrain supply. With this background, it is necessary and urgent to study systematically the transformationand utilization of rainfall during crop growth period, to analyse factors related with rainfall utilizationand their affecting mechanisms, and simulate numerically the relationships between relavant factors andrainfall utilization. The research results may provide an important theoretical basis for estimatingeffective conversion level of rainfall during crop growing period and a helpful tool for designingoptimal irrigation schedule, which has theoretical and practical significance for improving the utilizationof limited agricultural water resources in China.Field experiments were conducted at Guangli Irrigaiton Experimental Station located in Qinyangcounty, Jiaozuo city, Henan province in2009-2011. Characteristics of canopy interception, surfacerunoff and soil infiltration during a rainfall, and soil surface evaporation and redistribution of soil waterafter the rainfall were investgated and studied in winter wheat season, The effcets of soil surfacemulching patterns and characteristics of rainfall on utilization of rainfall on winter wheat field were alsostudied. The main results are as followings:(1)The capacity of intercepting rainfall in winter wheat at plant and canopy level was measuredand factors affected the capacity were analyzed with wet-absorption method. The results showed thatintercepted rainfall amount(IRA) by a winter wheat plant was effected significantly by leaf number(P<0.05) before heading. The IRA by a plant with same leaf number varied significantly at differentgrowing stages (P<0.01). The IRA per plant increased linearly with leaf area, plant height and freshweight increasing, respectively. However, absorption rate decreased linearly with leaf area, plant heightand fresh weight increase. The IRA by the whole winter wheat canopy presented linear positivecorrelation with leaf area index (LAI), and aboveground biomass(AB) separately, but absorption rateexpressed a negative correlation with LAI and aboveground biomass. From jointing stage to maturity,IRA by winter wheat canopy increased slowly, and then decreased gradually. The peak value of IRA(1.28mm) occurred at heading stage. The IRA values varied significantly in different growing stages(P<0.01),Simulated rainfall experiment showed that water amount fell on interrow soil surface in winterwheat was positively correlated significantly with total rainfall (P<0.01), while the relationship betweencanopy interception and total rainfall fitted significantly a power function (P<0.01). There existed anegative exponential correlation between rainfall intensity and interrow throughfall percentage (P<0.01) and a negative power correlation between rainfall intensity and canopy interception percentage (P<0.01). The canopy interception under different rainfall intensities changed similarly with growing stages of winter wheat, while the time from starting of rainfall to reaching canopy interception capacity was longer with lower rainfall intensity. Rainfall intensity did not show significant influence on canopy interception capacity of winter wheat. Rainfall Interception decreased with the increase of rainfall intensity, and showing a significant negative correlation with rainfall intensity under a fixed rainfall amount. A mechanism model for simulating rainfall interception process of winter wheat canopy was developed, and relavent parameters were determined based on experimental data.A parameter, a, indicating evaporative capacity of rainfall intercepted by winter wheat canopy, was set to0.008. Simulated values fitted well to measured values, indicating that the model is suitable for estimating rainfall interception of winter wheat canopy.(2) The effects of rainfall intensity (RI), canopy coverage (expressed with Leaf area index, LAI) and initial water content of soil layer of0-40cm (θ4O) on surface runoff and water infiltration characteristics was investigated and analyzed with a simulated artificial rainfall experiment in winter wheat field. Results indicated that under other factors were fixed, the surface runoff intensity, cumulative runoff, infiltration rate and cumulative infiltration fitted obviously as negative exponent function, power function, power function, and logarithmic function of the rainfall duration(t)(P<0.01), respectivally The time that surface runoff began to be seen was advanced with RI increased and can be fitted well as a power function (P<0.01). Runoff intensity, accumulative runoff and runoff coefficient increased with RI increasing. As RI increasing, the time reached stable infiltration was advanced, and average infiltration rate, stable infiltration rate, and accumulative infiltration gradually increased, but rainfall storage coefficient decreased. As LAI decreasing, surface runoff appeared earlier and can be fitted significantly with a linear function (P<0.01). Runoff intensity, accumulative runoff and runoff coefficient decreased with LAI increasing. Average infiltration rate, stable infiltration rate, accumulative infiltration volume and rainfall storage coefficient increased with LAI increasing, and the time reached stable infiltration was postponed with LAI increasing. As RI increasing, the effects of LAI on surface runoff and infiltration during a rainfall process diminished. Under a stable RI and LAI, the time surface runoff appeared was advanced with the increase of θ40, and can be fitted well as a positive linear function (P<0.01), but there was little effects of initial moisture in soil layer of40-100cm on the time surface runoff appered. Runoff intensity, runoff volume and runoff coefficient increased with the increasing of θ40, but with a similar stable runoff intensity. Under fixed RI and LAI, the time that infiltration rate reached stable point was advanced, and infiltration rate, infiltration volume and rainfall storage coefficient decreased with the increasing of θ40, but with a similar stable infiltration rate.With multiple regression analysis, a numerical model describing the relationship among the time surface runoff appears and RI, LAI, θ40in winter wheat was established as: tp=2O.3O7ORI-1.0761LAI1.52O9θ0-1.1844 The practical use of the model showed that the modificated values fitted well with the measuredvalues.Runoff intensity, cumulative runoff volume, infiltration rate and cumulative infiltration volume canall be fitted as a function of t, RI, LAI and θ40, Respectively. The regression models for calculatingrunoff coefficient and rainfall storage coefficient were established respectively as:RC=0.19188+0.2282RI-0.00785LAI+0.009231θ₄0RSC=1.5754RI^-0.5437LAI^0.0430θ₄₀^-0.2339(3)Soil evaporation and soil water redistribution in winter wheat field under different rainfallsituations were explored with simulating6rainfall grades, from light rain to torrential rainfall. Resultsshowed that under similar meteorological conditions, soil evaporation varied with growing stages, buton a similar pattern for different rainfall grades. Both daily soil evaporation and cumulative evaporationcan be fitted well as a positive logarithmic function of the rainfall volume. The soil evaporation volumesin different rainfall grades in daytime was significantly different, but the differences in night time werenot obvious. The ratio of soil evaporation to rainfall (E/P) in winter wheat was fitted well as a negativepower function of rainfall. Correlating meteorological factors and soil evaporation showed that soilevaporation after a rain was signicantly correlative with sunshine hours,20cm Pan evaporation, dailymaximum temperature and mean temperature in winter wheat field (P<0.05or P<0.01), respectively.Effects of meteorological factors on soil evaporation increased with the rising of rainfall grades (rainfallvolume and rainfall intensity). The correlation between daily soil evaporation and water content in soillayer of0-100cm was very significant (P<0.01), and the correlation coefficients for each soil layers allincreased with rainfall grade rising.The higher a rainfall grade (rainfall volume and rainfall intensity) was, the deeper a soil profileinfluenced by soil water redistribution was, the larger soil water content change, and the longer the timeneeded to finish soil water redistribution was. Movement velocity of wetting front increased withrainfall grade rising, while final depth of wetting front reached also increased. In addition, with a fixedrainfall grade, wetting front movement velocity increased, but the time needed to finish soil waterredistribution shorted with the increasing of initial soil water content. The changing range of soilmoisture within0-100cm at reviving stage was smaller than those at jointing stage and grain fillingstage, showed the influence of crop root growth. The higher rainfall grade was, the greater the ratio ofrainfall volume to water stored finally in soil was. However, the transformation efficiency of mediumgrade rainfall to soil water was relatively higher.With HYDRUS-1D model, changes of soil water content in unsaturated zone caused by rainfall,evaporation and crop root water uptake was simulated. Results showed that simulated values fitted verywell to the measured valued in all rainfall situations in winter wheat field, and the model is a suitabletool of forecasting soil moisture in practical field water management.(4)Six mulching theatments, consisting of one plastic mulching (PM), four straw mulching(with1500,4500,7500, and10500kg/hm2, and labeled as SM15, SM45, SM75and SM105, respectively),and one no mulching(CK), was set in winter wheat field to study the effectes mulching models and rainfall characteristics on interraw soil surface evaporation, soil moisture distribution and soil waterstorage after a rainfall under simulated rainfall situation. Results indicated that the changing trends ofdaily soil evaporation and cumulative evaporation are very similar for all mulching treatments, but thedifferences of cumlative soil evaporation during a same period among six mulching treatments wereobvious, and ranged as SM105<SM75<PM<SM45<SM15<CK. Canopy structure of winter wheataffected significantly soil evaporation rate after a rain. Under same rainfall situation,(daily orcumulative) soil evaporation before jointing stage was significantly greater than that after the jointingstage for a same treatment. There were significant differences for soil moisture in0-100cm soil layeramong six treatments, and smallest for PM, and greatest for M105. For soil water storage after a rainfall,the results can be ranged as: SM105＞SM75＞SM45＞SM15＞CK＞PM. By canopy interceptionincreasing, soil moisture and soil water storage after jointing stage for six treatments were significantlylower than that before the jointing stage. Both rainfall infiltration depth and infiltration volume underrainfall intensity of60mm/h was significantly greater than that under rainfall intensity of40mm/h atsame mulching treatment and same rainfall duration. Compared those under rainfall intensity of60mm/h, the differences of soil water storage before and after jointing stage was more greater for all sixmulching treatments under rainfall intensity40mm/h.