Effects Of Wetted Percentage On Soil Water Distribution And Growth And Physiological Index Of Maize

Drip irrigation is one of the most widely used irrigation methods, it belongs to local irrigation. Dripper discharge and design wetted percentage are two important design parameters in drip irrigation system, the selection of its specifications will affect the size of wetted body after irrigation, and then affect the growth of crops. On the basis of previous studies, this article according to the technical specification for micro irrigation used two kinds of dripper discharge and three kinds of design wetted percentage, conducted drip experimental study on soil water infiltration in a condition of bare soil, and used Hydrus-3D software to simulate. By studied the effect of different drip discharges and design wetting ratios on the soil water distribution characteristics, the characteristics of the actual wetting body were evaluated, assessed the actual wetted body character- rustics and analyzed the law of effective wetted body and chose one drip discharge whose infiltration effect is better. Then still chose three design wetted ratios of infiltration study as the control level, the wetting ratio of T1、T2�'� T3 are 80%、60%、40%, planted summer maize using drip irrigation whose size of emitter is determined by infiltration test. This article analyzed the law of stem diameter changes, leaf temperature and sap flow in the condition of drip irrigation, studied the method to determine the soil water availability and sensitive position to water deficit based on the physiological index, the main results are as follows:(1) When the design wetted ratio is same, the moisture content of the same position in the wet body becomes larger as the drip discharge increased after the irrigation, with the water redistributed, the smaller the average water content of the large emitter discharge; In order to achieve a larger wetted body, we can choose a larger drip discharge. Selected 65% and 70% field capacity as the low limit of effective water content, and found that within 24 h of irrigating ended, the effective wetting ratio all were about 1/2 of design wetting percentage; after 48 h, the effective wetted volume is decreased, and the volume of water is smaller than 1/2 of design wetting percentage.(2)The test conditions were simulated by Hydrus-3D software, and the relative error between the simulated and measured water content of the observation points were less than 10%, the relative error of the measured and simulated wetted ratio is 4.75%~11.78%, it shows that the model can be used to simulate the actual infiltration characteristics; Used the established model to simulate the characteristics of wetted body when wetting ratio was 40%、 50%、60%、70%、80% and the dripper discharge respectively 2L/ h、3L/h、4L / h、5L / h, and analyzed the simulation results of wetted body characteristics. Conclusions that increasing the design of wet ratio, the growth rate of wetting front in the vertical direction is greater than the horizontal direction, in the wetting of the average moisture content will increase. However, when increased dripper discharge, wetting front in the horizontal direction is larger than the vertical direction. Therefore, in order to reach a wide range of moist, you can choose appropriate large dripper discharge.(3) Research the law of stem diameter variations of three treatments in an irrigation cycle, which were found that the stem diameter shrinkage during the day, the diameter recovery expansion in night, and the stem diameter growth of T2 was the fastest, the stem diameter of T1 and T3 increased slowly, so when the design wetted ratio is 60% of three treatments is more conducive to crop stem diameter growth; The maximum daily shrinkage(MDS) of T2 treatment was the largest in three treatments, which showed that when the design wetted percentage is 60%, it is easy to diagnosis the water status using maximum daily shrinkage; The correlation analysis between maximum daily shrinkage(MDS), daily mean air temperature(T), relative humidity(RH), daily total radiation(RS) and vapor pressure deficiency(VPD)was carried out.(4) Research the law of leaf-air temperature of three treatments in the irrigation period, found the daily variation of leaf-air temperature was a single peak curve distribution, the daytime leaf- air temperature difference is positive and night leaf – air temperature difference is negative mostly; According to the change situation of the leaf-air temperature between the before and after irrigation with the soil moisture, it can be seen that leaf-air temperature of T2 treatment was the most sensitive to soil moisture; From small to large, change range of leaf-air temperature were seven leaf stage, jointing stage and filling stage; Leaf-air temperature(ΔT), vapor pressure deficiency(VPD) and total radiation(RS) was performed using multiple linear regression, and compared the measured and simulated leaf-air temperature changes with time. It was found that the trends were very similar.(5) Diurnal variation of sap flow was analyzed in cloudy and sunny weather conditions, and found that the law was same; in addition to T3 treatment whose water deficit was serious, sap flow rate in sunny day is greater than cloudy day; in the same irrigation period, sap flow rate variation with time of T1 and T3 treatments were analyzed, found the stem flow rate of T3 has been greater than T1 throughout the irrigation cycle, and reflected the water consumption rate of T3 treatment was higher than T1 indirectly, the water for plant growth is less, and it was not conducive to the growth of crops, reduced the water use efficiency.(6) The change situation of maximum daily shrinkage(MDS) with the average water content was analyzed in a same irrigation period, founded that with moisture content decreased, MDS decreased first and then increased, and the analysis showed that the low limit of the effective moisture was 58%~67% field capacity; Through analyze the correlation between the leaf-air temperature and layered soil moisture, it is concluded that leaf-air temperature of T1 and T2 treatment is more sensitive to soil moisture of 30 ~ 40 cm, but the correlation coefficient with the soil moisture rate of T1 treatment was greater than T2, T3 treatment was sensitive to 20 ~ 30 cm soil moisture rate.