| In China, arid regions account for>70%of total land area, taking up43%of the totalagricultural area, and are essential for its agricultural production. However, yield gaps, i.e.,the differences between potential and actual yields, are greater than50%in drylands regions.Continuous growth of the human population and the decline cultivated farmland will call for asignificant increase in crop yields per unit area. In addition, increasing temperatures anddeclining precipitation in semi-arid regions are likely to reduce yields of maize, wheat, rice,and other primary crops within the next two decades, and will be a huge challenge to China’sdrylands farm in the21st century. Hence, it is imperative for food security over the next fewdecades that we improve our understanding of the physiological mechanism of crop yieldrising, and continuing to improve rain-fed drylands agriculture with optimised watermanagement is a key priority to guarantee food security and eco-development sustainability.This study focused on the Loess Plateau, a typical semi-arid monsoon climate region, inwhich dryland farming is dominated by monoculture cropping systems. The applicability ofthe Hybrid-Maize model was tested using data from a twoe-year field experiment; and usedthe crop model to establish the high yield and high resource use efficiency （double-high）cultivation system of drylands maize production; and to determine the physiologicalmechanism contributing to yield improvement; as well as to assess tmaize productivityresponse to climate change and propose adaptive crop management strategies. This researchcould be helpful for water management strategies in maize production in semi-arid regions.The main results were showed as follow:（1） In this study, a new module for plastic film mulching in Hybrid-Maize model wasdeveloped to simulate maize growth development and grain yield of drylands farm. Theperformance of this modified Hybrid-Maize model was reasonably good in terms of biomassand grain dry matter. The Hybrid-Maize model can be used to simulate the yield potential ofmaize well under optimum irrigation, rainfed, and plastic film mulching conditions.（2） After modification the Hybrid-Maize model was used to simulate the yield potentialof maize in Changwu region over the last50years. The yields potential were14.1t ha-1under no water limited condition,12.7t ha-1under water limited conditions,15t ha-1under plasticfilm mulching conditions, respectively. We use the Hybrid-Maize model to guide the optimizestructure of drylands maize cultivation systems: to adjust variety, sowing date, plantspopulation, and the management for water and nutrition of soil; and established the high yieldand high resource use efficiency cultivation system that integrated atmospheric resource–crop community–soil environment system management.3-years field tests indicated that,maize yield of the cultivation system have reached100%of yield potential, the nitrogen useefficiency was reached61kg kg-1, the water use efficiency was reached35kg ha-1mm-1.（3） The mulch practices could significantly improve cumulative topsoil temperature andsoil moisture, thereby synchronising larger leaf area index （LAI） and greater radiationinterception with earlier development and rapid plant growth during the early VS stage.Consequently, these mulching practices are effective at improving the amounts ofaccumulated dry matter, leading to significantly greater final biomass, grain yield, and wateruse efficiency （WUE）. Compared to conventional gravel mulching, plastic film mulchingcould be more effective to increase the topsoil temperatures and the conservation of availablesoil water in spring. Additionally, this technique represents a more effective approach toimproving spring-sown maize yield in semi-arid regions.（4） Mulching treatments markedly accelerated plant growth and flowering, whichdirectly resulted in a longer grain-filling period. The robust plants and better growthenvironment during flowering increased the number of kernels. The prolonged growth periodsallowed greater resource interception and use efficiency of both heat and solar radiation,thereby inducing greater assimilation and translocation for grain growth and resulting inhigher final kernel weight. We concluded that the mulching treatments improved grain yieldsas a direct consequence of earlier flowering.（5） The mulching removed （RM） compared to the plastic film mulching （FM） treatmentincreased maize biomass, harvest index, and grain yields values with delayed crop senescenceresulted in greater photosynthetic assimilation during the grain filling period. Either greatersource capacity from the significantly higher LAI and photosynthetic rate, or stronger sinkcapacity due to more kernel numbers and larger kernel volume expansion contributed togreater dry matter accumulation to the grain. In comparison to the FM treatment, the RMpractice can increase grain yields further, thus should be considered in the semiarid monsoonclimate region where rain is sufficient during the reproductive stage of maize.（6） Climatic warming has increased significantly since the1980s on the Loess Plateau,meanwhile the solar radiation and precipitation declined. These climate trends may lead to thereduction in yield potential and induced the serious water deficits. The warming trends have significant reduced the crop growth duration, induced68.7%of the total yield potentialdeclined, was the most important factor in the reduction in yield potential. Notably, the risingminimum temperature was mainly reason for climate warms and the most important factor inthe reduction in yield potential, while the rising maximum temperature may be the mainlyreason for the serious water deficits. In addition, the declining solar radiation decreasedavailable energy of assimilates for plant growth, induced24.6%of the total yield potentialdeclined, was the secondary factor in the reduction in yield potential. The annual fluctuationsand decline trends of precipitation will aggravate the water deficits across the Loess Plateau.（7） The magnitude of warming, since the1980s, may lead to a reduction in growthduration, yield potential and water use efficiency （WUE） if maize varieties remainedunchanged. We suggest the adapted later maturing cultivars, based on the increases incumulative temperatures for the period April–September in each of the decades in all studyregions. The adapted varieties allowed the longer growth duration, increasing yields potential,and higher WUE, and will be an effective way to fit within the warming environment. Inaddition, continuing to develop water harvesting techniques （e.g., plastic film mulching） willhelp to offset decreasing rainfall, and to guarantee food security and sustainability in aridregions.In a word, our results have confirmed the feasibility that used the Hybrid-Maize model toguide the optimizing of maize production system, improved our understanding of thephysiological mechanism of crop yield rising, assessed the potential impacts of climatechange, and proposed the adaptation strategies to mitigate the negative impacts. This researchcould be helpful for improve crop production in semi-arid regions. |
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