Simulated For Soil Water Dynamics Based On Stem Flow And Root Fractal Characteristics Of Seed-maize

The Hexi corridor of Gansu, which is characterized by rich solar heat resource and well natural isolation conditions, has developed into one of the national largest seed-maize production base. In recent years, because of the underground water level decline and river water water decreasing, water shortage has become a bottleneck in the development of seed-maize industry. The study on dynamics and simulation in seed-maize field under alternate furrow irrigation is of great importance for seed-maize water efficient cultivation and the development of water-saving agriculture.This paper mainly studied the water transfer mechanisms and quantitative simulation of seed-maize field using soil moisture profile meters, soil moisture content monitoring system, stem sap flow meters and automatic weather station. The experiments were conducted at Shiyanghe Experimental Station for Water-saving in Agriculture and Ecology, China Agricultural University in 2012-2014. The main results are outlined as follow:(1) The order of stem flow of different irrigation methods was:conventional furrow irrigation> alternate furrow irrigation> border irrigation. The stem flow fluctuation range was 80.8-884.0 mL d"1, 47.1-786.5 mL d"1 and 38.5-629.1 mL d"1, respectively, under conventional furrow irrigation, alternate furrow irrigation and border irrigation. And the average daily stem flow was 498.1 mL d-1,455.7 mL d-1 and 337.7 mL d"1, respectively.(2) On hourly scale, the main influence factors of south side female parent and male parent were Rs, RH, and VPD, and they were Rs and VPD for north female parent during the heading stage. Rs was the main driving factor of seed-maize stem flow during the filling stage and maturity stage. Ta, RH and VPD also had significant influence on the north side female parent and male parent during the maturity stage. On daily scale, Rs and Ta were the key effect factors of SFP stem flow, but the main driving factor was Rs for NFP and MP.(3) Changes in stem sap flow consistently lagged behind changes in Rs and preceded variation of VPD, Ta and RH both on hourly and daily scales. The order of stem flow time lag of different growth stages was:maturity stage> filling stage> heading stage. The lag time of male parent stem flow to Rs was significant longer than female parent. The time lag of male parent stem flow was 30min,60min and 75min, respectively, duirig heading stage, filling stage and maturity stage. While the time lag of female parent was 15min,30min and 45min. The time of male parent stem flow preceding VPD, Ta and RH were shorter than female parent. The stem flow can be better simulated by ARIMAX model. The slope of simulated and measured stem flow of female parent and male parent was 1.021 and 1.059, respectively. The determine coefficient was 0.928 and 0.871, respectively.(4) The root of seed-mazie under furrow irrigation centralized in the depth between 0-80cm, and the roots accounted for over 90% of total roots. The root system distribution of the plants on both sides of the ridge is asymmetric. The change of root length density in horizontal and vertical direction was cubic function and Gaussian function, respectively. There was a logarithmic relationship between fractal dimension and root length density. The fractal dimension had the same seasonal characteristics as the root lenth density. Roots in the area, where root length density is greater than 0.2 cm cm-3, have obvious fractal characteristics. The horizontal and vertical changes of fractal dimension were quadratic function.(5) The soil water content was estimated using RD model and FD model, and the simulated soil water content agreed well with the measured value in vertical direction. At 80-120 cm soil layer, the deviation of soil water content form RD model was lager, where the capacity of root water uptake is underestimated. Compared to the RD model, the simulation effect of FD model is better. In different growth stage, FD model can accurate simulate soil water content of 20 cm,40 cm,60 cm and 80 cm depth in the wet and dry area under plastic mulch condition. The root mean square error was only 0.001-0.013 cm3cm-3, and the relative root mean square error was less than 6%.