Simulation Of Root Distribution In Two Paddy Rice Cultivars Under Water Stress

In this paper,two rice varieties(Liangyoupeijiu and Ningjing 001) are taking as experimental crops in the pot experiment and field experiment.The two types of rice are treated to irrigation and drought stress conditions in this experiment.During the whole growth stages,the soil surface remain 2 cm water layer in the irrigation condition,while at the beginning of the each four growing stages(tillering stage,jointing-booting stage,heading to flowering and filling stage), moisture is controlled until the continuous soil water loss to the wilt point in the drought stress treatment.The root distribution model and the effect of water deficit on the roots growth are studied in this paper.The correlation between roots and above ground part of rice is analysis. Then,models of dry weight and volume of the rice root under the irrigation water deficit stress are established,respectively.1.The dry weight and the volume are the important index to reflect the root growth of the rice.In this study,we find that the root volume is smaller along the distance from the taproot horizontally while the volume decreases along the depth vertically.The dry weight and volume are different between two rice varieties.The dry weight and volume of Liangyoupeijiu is higher than that of the Ninjing 001.The dry weight and volume of the individual rice species show differences during the different growth stages.The general trend is that the dry weight and volume increase from the tillering stage,reach the highest value after heading to flowering and decreases since then.2.The power function model of the two-dimensional spatial root distribution is best to explain the rice root distribution in soil.The distribution model R(x,z)= A·e^{(B·x+C·z)} is obtained from the experiment.The model can explain the two-dimension distribution of the root during the four growing stages.The model is also tested by the pot data and R²ï¼ž0.85,RMSE＜0.1. The application value is presented by this relative accurate model.3.The dry weight and the volume of the root show a significant correlation with the above ground index of the rice.4.Water deficit can affect the root growth of the two rice species.The variation of dry weight and the volume of Liangyoupeijiu is much greater than that of Ningjing 001.The water deficit affects the Liangyoupeijiu greater than that on Ningjing 001.Water deficit also show different effects on the individual species during the different growth stages under different drought conditions.The result shows that water deficit affect the rice growth easily in the tillering stages and heading to flowering.Mild drought stress can promote the root development in the vegetative growth,while the severe drought stress can impede the vegetative and reproductive growth both.The severe drought stress can also accelerate the root decay in the post reproductive period.5.Considering water stress,a model on two-dimensional spatial distribution of root system is simulated,the equation is:R(x,z,θ)=A·e^{(B·x+C·z)}·f(θ).f(θ) is drought stress factor, and 0＜f(θ)＜1 between the wilt point and threshold soil water content.The model is also tested with the pot experimental data.The R²is greater than 0.80,and RMSE less than 0.1.It shows the simulated values are well agreement with observed values and model can give accurate predicted value.