Characteristics Of Water Consumption Of Female And Male Parents And Evapotranspiration Modeling Of Maize For Seed Production In An Arid Region Of Northwest China

Understanding the mechanism of water transfer and determining the estimating model of evapotranspiration (ET) in soil-crop ecosystem are focused intensively by the international water science researches. Since the shortage of water resources in northwest China, the comprehensive observations of water transfer to maize for seed production were conducted using eddy covariance systems, sap flow systems, automatic weather station and soil moisture sensors in 2012-2014 in an arid region of northwest China. The objectives of this study were to investigate the characteristics of water consumption of female and male parents and developed the estimated model to estimate the ET and its components. The main results are outlined as follow:(1) The difference of morphological and physiological parameters in the female and male parents were investigated, variation of sap flow and controlling factors in female and male parents were explored. During the vegetative growth stage, the female parent had higher sap flow rate than the male parent, with the maximum difference of daily sap flow rates in the female and male parents of 0.33 and 0.28 L d"1 in 2013 and 2014 respectively. Hourly sap flow rates in the female and male parents were highly correlated with net radiation, while daily sap flow rates in the female and male parents were highly correlated with net radiation, SWC, leaf area index, but not correlated with crop height. Moreover, daily sap flow rates in the male parents were positively correlated with stem diameter.(2) The parameters used to scale up sap flow of maize for seed production from per plant to the stands were determined, and the variation of ET was explored. The sap flow rate was scaled from per plant to the stands using leaf area, diameter and planting density. Methods scaling up sap flow rate based on planting density and diameter overestimated ET measured by eddy covariance systems (ETEC). The ET scaling up based on leaf area was close to ETEC. The total ET was 479.75、373.92 and 401.30 mm over the whole growth stage of maize in three seasons, and the total transpiration (Ts) was 424.75‘ 315.54 and 321.95mm. The transpiration of female parents was higher than that of male parents, accounted for 63-80% of the total ET. And the soil evaporation (E) was 55.00% 47.77 and 62.21 mm over the whole growth stage, accounting for 11%、13% and 16% of the total ET. The crop coefficient (Kc) showed an "S" curve over the whole growth stage, and was 0.78,0.79 and 0.73 in three seasons respectively.(3) The effect of planting density on Kc and ET were evaluated, a relatively simple and accurate method to calculate Kc and ET was developed. Results showed that higher planting density increased ET and Kc and decreased soil evaporation and evaporation coefficient within the planting densities of the experiments. We introduced a density ratio (Kdensity) that is a function of leaf area index (LAI) to account for the effect of planting density on Kc (Kdensity method).Compare to the Allen method considering an adjustment coefficient (Acm),the single and dual Kc methods considering a density coefficient (Kd), the Kdensity method had higher accuracy in estimating daily and Kc over the whole stage.(4) The aggregation method of the effective resistance of maize for seed production after considering the variation of fraction cover of the canopy and canopy resistance of female and male parents was proposed, the Penman-Monteith model (P-M model) based on effective resistance was used to estimate the daily ET of maize over the whole growing stage. Results show that when the fraction cover of the canopy (f)=1, the obtained rce by aggregating female and male canopy resistances in parallel, was closer to the measured rce (rcec) obtained by inverting P-M model based on effective resistance using the measured ET by eddy covariance system. When f<1, the obtained rce by aggregating female and male canopy resistances and soil resistance in parallel, weighed by fc, was significantly higher than rcec, but the obtained rce by female and male canopy resistances and soil resistance in parallel, weighed by leaf area index (LAI), was closer to rcec. Compared to the P-M model based on originally calculated method of canopy resistance, the P-M model based on effective resistance was closer to ETEc, especially the effective resistance by aggregating the plant and soil resistances in parallel, weighed by LAI.(5) The performance of crop coefficient approach considering female parents, male parents and soil components and multi-components model based on the radiation interception by neighboring plants in estimating ET and its components was evaluated. Compared to crop coefficient approach, the ET, transpiration of female and male parents (T) and E estimated by multi-components model were closer to the measured value, and the ET, T of female and male parents and E were higher than the measured value.