Water Absorption Of Root System And Water Productivity In Spring Wheat (Triticum Aestivum) Under Different Irrigation Regimes

In2012and2013, field experiment which selected the dryland wheat DX40asexperimental material and was conducted at Dingxi Arid Meteorology and EcologicalEnvironment Experimental Site. In order to provide a reliable theoretical basis formaking optimum irrigation system that guided by yield and water use efficiency, toput forward a reference for solving the agricultural contradiction between watersupply and demand. We studied the differences and reasons of spring wheat waterproductivity under different irrigation regimes, and created the one-dimension verticalnumerical model of the root water uptake to simulate the water absorptioncharacteristics and regularity by continuously monitoring the growth of crop, bareground evaporation, climate parameters and other related indicators. The researchbased on the theory of soil water dynamic. Our experiment comprised of fourtreatments respectively, as follows: irrigation at getting, jointing and filling stages(T1); irrigation at getting and filling stages (T2); irrigation at getting and jointingstages (T3); irrigation at getting stage (T4). Each treatments with three replications,arranged randomly.Two years irrigation experiment conclusions were made as follows:�'�Wheat roots distribution showed certain rules in soil and was influenced byirrigation regimes. On the whole, Root length density (RLD) of spring wheatdistributed as T-shaped in soil. In2012and2013, the average maximum RLDappeared in0-10cm soil profile, respectively were1.643and1.704, and the averageRLD were only0.088and0.099in90-100cm soil profile. Roots were mainlyconcentrated in the soil surface layer within the range of0to30cm, that more than75%of total roots. The tendency of RLD was exponential decline with soil depthincreased, the correlation coefficients was above0.928(P<0.05). At different growthperiods, the distribution of RLD and root dry weight density (DRWD), showeddifferences in different soil profile. In2013, compared with treatment T2and T4, thetotal RLD and DRWD of treatment T1and T3were higher in0-100cm soil profile after jointing period. RLD reached the maximum at filling period. So, we can see the importance of jointing stage irrigation to promote root growth. After filling period, the reduction values of total RLD showed a regulation that T1and T3were higher than T2and T4in0-30cm soil profile. And to some extent, the filling irrigation slowed down the root decline, especially the superficial roots.2. Absorption of spring wheat root on soil moisture was different due to differences in irrigation conditions. During two growth season, the total irrigation water presented a regulation as follow:T1>T2>T3>T4, but the soil water consumption percentage showed regulation of T1>T2>T3>T4and T1<T2<T3<T4at less than40cm soil layer and at more than80cm soil layer, respectively. So, the soil water consumption proportion consisted with root distribution; with the increased of total irrigation, the roots absorption and utilization on of upper soil water also increased. On the contrary, it would promote the absorption and utilization of deepsoil storage water.3. In order to guide the agricultural water saving work, the paper selected theFeddes model which improved by Luo Yi et al, in2000, to simulate the one-dimension vertical root water uptake. Through the establishment of reasonable one-dimension vertical model of root length density, soil water potential function and spring wheat transpiration rate function, we established a piecewise model of one-dimension vertical root water uptake, as follow:0.5242L(z)Tα(t)0<z<100.3359L(z)Tα(t)10<z<200.2153L(z)Tα(t)20<z<300.1380L(z)Tα(t)30<z<400.0885L(z)Tα(t)40<z<500.0567L(z)Tα(t)50<z<600.0363L(z)Tα(t)60<z<700.0233L(z)Tα(t)70<z<800.0149L(z)Tα(t)80<z<900.0096L(z)Tα(t)90<z<100Based on the one-dimensional soil moisture movement basic equations, we selected the soil moisture date on May25th,2012(jointing stage) and June30th,2012(filling stage) to verify the model that had established in this paper. Verificationresults showed that the maximum relative error were22.03%and15.50%,respectively, and the average relative error respectively were9.33%、6.59%, and thecorrelation coefficient could reach more than0.814(P<0.05). Consequently, theone-dimension vertical numerical model of the root water uptake could basicallyreflect the actual status of the spring wheat root water absorption in the Loess Plateauand could be used for simulating of spring wheat root water absorption regularity. Atthe same time, simulation results showed that root water absorption rate reached to themaximum in0-30cm soil layer, the root water absorption rate of filling stage washigher than jointing stage.�'�Irrigation regimes have significant influence on spring wheat growth andbiomass accumulation, and vegetative period was the main water sensitive period. Theplant height and leaf area of spring wheat in treatment T1and T3were significantlyhigher than that of treatment T2and T4. But no difference was detected between thetreatments T2and T4. However, there were no significant difference betweentreatment T2’s above-biomass and T3’s. From this, we can see irrigating at jointingstage play a key role to promote the spring wheat agronomic traits and above-biomass;May be due to more rainfall in the late growth period, irrigating at filling stage had nosignificant effect on promoting the growth of plant height and leaf area, neverthelessit can effectively promote the dry matter formation, especially under the drought andwater shortage conditions. The timely and effective supplementary water played asignificant role in compensation for the dry matter accumulation.�'�The water consumption, water use efficiency and yield of spring wheatwere all affected by the irrigation regimes. The total water consumption increasedwith the increasing of irrigation. Reduced irrigation can improve the utilization ofrainfall and soil water. Variation coefficient was about the percentage of the waterconsumption parts from the total. Viewed from the variation coefficient, in twogrowth season, soil water consumption (61.56%,62.15%) was higher than precipitation (14.76%,14.81%). Compared with precipitation, irrigation to controlwheat soil water consumption was more effective. When the quantity of irrigationincreased, the irrigation water utilization efficiency reduced significantly. The yield oftreatment T1and T3was higher than treatment T2and T4, but production water useefficiency observed as follows: T3>T4>T1>T2, so we can see the importance ofjointing stage irrigation to improve yield and water utilization efficiency in the samelevel of irrigation.�'�Root distribution and yield showed a correlation. The study found that theupper roots (0-30cm) showed positive correlation with spike grain number, and thecorrelation coefficient was0.929(P<0.05), however, it had no correlation with spikegrain weight,1000-grain-weight and yield; the middle roots (30-60cm) all had nocorrelation with spike grain number, spike grain weight,1000-grain-weight and yield;while the deep roots (60-100cm) showed positive correlation with spike grain number,spike grain weight,1000-grain-weight and yield, and the correlation coefficients allreached over0.929(P<0.05).