| Water shortage is the main factor that restrains grain productivity on the dryland in theLoess Plateau area. Therefore, making fullest use of limited water resources to increase grainyield is of great importance for sustainable development of this area’s agriculture. Basing onthe established researches, we made the following assumptions:1) the spatial and temporaldistribution of spring maize’s root system on the dryland was closely connected with thefarming land’s water management, furthermore, the aboveground had much impact on theroot system.2) The best water management model of farming land was to make water,nutrients and root system reach space coupling so as to raise grain yield and the highefficiency of them. In this study, the two-year continuous field experiment was conductedthorough three-dimension collection and scanning of root system method, and five watermanagement measures was under close inspection, which were irrigation at the jointing stage,irrigation at both the jointing stage and the filling stage, rainfed farming, film mulching, andstraw mulching, to study their impacts on the spatial and temporal distribution of the springmaize’s root system on the dryland. The researches aimed to verify the above assumptions.And the following main results were obtained:(1) Although PEG can be used as penetrant to promote grain growth, because itcomprised impurities such as sodium and phosphorus that can be absorbed by crop roots,which curbed crop growth. And choosing PEG as penetrant exited the disadvantages. Thus thebetter method to conduct the research on spring maize in the dryland was choose natural fieldconditons.(2) Root length density of the spring maize showed the trend of initial increase and laterdecreased during the growth period, produced the peaks of once irrigation, straw mulchingand rainfed farming during the tasseling stage, and peaks of twice irrigation and filmmulching during the milking stage. It was obvious that better hydrothermal condition helpedto postpone root system’ aging and delay the peak of root length density. As the period wasfurthered, the above measures all led to the root/shoot ratio’s decline with the lowest atharvest. The low root/shoot ratio after film mulching during the heading stage reduced grain yield due to plant lodging. The proper timing of lifting mulching during the later period couldmaintain root system activeness, improved the distribution of photosynthetic product androot/shoot ratio, restrained plant lodging ratio, and furthermore, enhanced grain productivity.(3) The utilization rates of the accumulated temperatures of five water managementmodels of spring maize in dryland indicated as follows: irrigation once> straw mulching>film mulching> irrigation twice> rainfed farming. Irrigation at the jointing stage couldcoordinate soil water and heat demand and promoted the utilization rate of the accumulatedtemperatures with the water and heat reaching coupling. The soil temperature was positivelycorrelated to root coefficient during seedling stage and heading stage. That is to say, raisedtemperature could increase root radius, volume and length density. And it was negativelycorrelated to root coefficient during the jointing stage, milking stage and wax ripeness stagebut without clear conclusion.(4) Irrigation at the jointing stage led to high grain yield and water utilization rate ofkernel, which was an ideal model of limited water irrigation of spring maize in dryland field.Irrigation at the jointing stage clearly enhanced dry matters’ contribution rate of kernel. Butirrigation at the seed filling stage decreased the dry matters’ contribution rate of kernel, whilefilm mulching could promote the contribution rate of kernel‘s assimilation of dry matters.Root radius at vegetative growth period was positively correlated with the canopy growthratio of the spring maize, while negatively correlated at the reproductive stage.(5) Among the plant organs, the leaves’ N nutrient translocation efficiency was highest.Straw mulching and once irrigation could enhance the potential of the leaves’ N translocationto kernel. Grain production efficiency of N among varied water management models showedas follows: once irrigation> rainfed farming> film mulching> supplemental irrigation, whileonce irrigation could cause highest grain production efficiency. But nitrogen harvest indexshowed as follows: film mulching> straw mulching> irrigation once> irrigation twice>rainfed farming. Although the yield rate caused by each unit of N’s forming by film mulchingwas not high, but the kernel’s N concentration formed by each unit was highest. As it seemedthat irrigation once was the best choice among all the five types of water management withconsideration with yield; but with kernel’s N concentration under consideration, filmmulching was the best choice.In general, NAE, NPE and NGPE was positively correlated to the indexes of the rootsystem, and negatively correlated to the wax ripeness. Irrigation once could improve NAE,NPE and NGPE through adjusting the root’s growth at the milking stage so as to synchronizethe root’s spatial distribution and N productivity. There was no clear showing of root lengthdensity’s correlation with NAE, NGPE and NPE, but obvious correlation with NHI that was root length density influences N’s translocation process to kernel above the ground, yetinfluenced little of N’s absorption, biomass and grain yield.(6) Compared to no film mulching, film mulching during the summer fallow time couldpromote mineralization, the absorption rate of mineralized N by crops and deceased nitrateleaching, which could enhance the surface nutrition of next spring’s maize during the seedingstage; straw mulching during summer fallow period could lead to the N’s accumulatedincrease of90.0kg/ha in0-100cm soil layer. The loss of N during the period in dryland by thefive water management types was: rainfed farming> once irrigation> film mulching> strawmulching> irrigation twice.(7) As the two-year field experiment showed, the spring maize yields of the variouskinds of water managemet models showed, once irrigation> film mulching> strawmulching> rainfed farming, among which the first two yields were highly superior to the restthree models.(8) Through film mulching, the moisture of topsoil and root going out of the surface canbe improved, furthermore, it was likely to reach the spatial coupling of water, nutrients androot system so as to heighten the grain yield and water utilization rate, which is best drylandfarming land water management model. |
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