A Full-Scale Optimization of a Crop Spatial Planting Structure and its Associated Effects

Driven by the concept of agricultural sustainable development,crop planting structure optimization(CPSO)has become an effective measure to reduce regional crop water demand,ensure food security,and protect the environment.However,traditional optimization of crop planting structures often ignores the impact on regional food supply–demand relations and interprovincial food trading.Therefore,using a system analysis concept and taking virtual water output as the connecting point,this study proposes a theoretical CPSO framework based on a multi-aspect and full-scale evaluation index system.To this end,a water footprint(WF)simulation module denoted as soil and water assessment tool–water footprint(SWAT-WF)is constructed to simulate the amount and components of regional crop WFs.A multi-objective spatial CPSO model with the objectives of maximizing the regional economic water productivity(EWP),minimizing the blue water dependency(BWFrate),and minimizing the grey water footprint(GWFgrey)is established to achieve an optimal planting layout.Considering various benefits,a fullscale evaluation index system based on region,province,and country scales is constructed.Through an entropy weight technique for order preference by similarity to an ideal solution(TOPSIS)comprehensive evaluation model,the optimal plan is selected from a variety of CPSO plans.The proposed framework is then verified through a case study of the upper–middle reaches of the Heihe River Basin in Gansu province,China.By combining the theory of virtual water trading with system analysis,the optimal planting structure is found.While sacrificing reasonable regional economic benefits,the optimization of the planting structure significantly improves the regional water resource benefits and ecological benefits at different scales.

Influence of plastic film mulching and planting density on yield,leaf anatomy,and root characteristics of maize on the Loess Plateau

In rainfed areas of northwestern China,maize production is constrained mainly by low temperature during early growth and water limitation during the entire growth period.Plastic film mulching is commonly used to increase maize yield in this area,because it increases topsoil temperature and moisture content as well as water use efficiency.However,the physiological and anatomical bases of maize yield improvement with plastic film mulching are not well understood.The effects of plastic film mulching and planting density on maize yield,photosynthetic characteristics,respiration,leaf anatomy,and root growth were studied in a two-year field experiment conducted on the Loess Plateau of China in 2017 and 2018.The experiment used a split-split plot design with two mulching treatments(plastic film mulching and no mulching),two planting densities(7.5×104 and10.5×104 plants ha-1),and two maize cultivars,Zhengdan 958 and Xianyu 335.Compared with no mulching,plastic film mulching increased maize yields by 31.1%–46.4%in 2017 and3.6%–34.7%in 2018.Compared with low planting density,high planting density significantly increased and slightly reduced yields of both cultivars in the dry year 2017 and the rainy year 2018,respectively.Plastic film mulching increased photosynthesis and respiration as well as leaf stomatal density and aperture.Photosynthetic rate,dark respiration,and stomatal conductance and aperture were lower at high planting than at low planting density.Maize yield was positively correlated with photosynthesis,dark respiration,and stomatal aperture.Mulching increased root dry weight and length in the 0–20 cm soil layer and root activity at maturity.Overall,the changes in root growth and leaf anatomy resulted in increased photosynthesis and dark respiration,and the increased photosynthesis contributed to the increase in grain yield and biomass production under plastic film mulching conditions.Our results increase understanding of the physiological mechanisms by which plastic film mulching increases maize yield in water-and temperature-limited areas.

Effects of irrigation and nitrogen management on hybrid maize seed production in north-west China

Scientific irrigation and nitrogen management is important for agricultural production in arid areas. To quantify the effect of water and nitrogen management on yield components, biomass partitioning and harvest index(HI) of maize for seed production with plastic filmmulching, field experiments including different irrigation and N treatments were conducted in arid north-west China in 2013 and 2014. The results indicated that kernel number per plant(KN) was signi ficantly affected by irrigation and N treatments. However, 100-kernel weight was relatively stable. Reducing irrigation quantity signi ficantly increased stem partitioning index(PI_(stem)) and leaf partitioning index(PIl_(eaf)), and decreased ear partitioning index(PI_(ear)) at harvest, but lowering Nrate(from 500 to 100 kg N$hm^(–2))did not signi ficantly reduce PI_(stem), PI leaf, andPIl_(eaf) at harvest. HI was signi ficantly reduced by reducing irrigation quantity, but not by reducing Nrate. Linear relationships were found between KN, PI_(stem), PI leaf,PIl_(eaf) at harvest and HI and evapotranspiration(ET).

Alternate partial root-zone irrigation with high irrigation frequency improves root growth and reduces unproductive water loss by apple trees in arid north-west China

Alternate partial root-zone irrigation(APRI)can improve water use efficiency in arid areas. However,the effectiveness and outcomes of different frequencies of APRI on water uptake capacity and physiological water use have not been reported. A two-year field experiment was conducted with two irrigation amounts(400 and500 mm) and three irrigation methods(conventional irrigation, APRI with high and low frequencies). Root length density, stomatal conductance, photosynthetic rate,transpiration rate, leaf water use efficiency, midday stem and leaf water potentials were measured. The results show that in comparison with conventional irrigation, APRI with high frequency significantly increased root length density and decreased water potentials and stomatal conductance.No differences in the above indicators between the two APRI frequencies were detected. A significantly positive relationship between stomatal conductance and root length density was found under APRI. Overall, alternate partial root-zone irrigation with high frequency has a great potential to promote root growth, expand water uptake capacity and reduce unproductive water loss in the arid apple production area.

Quantitative analysis of irrigation water productivity in the middle reaches of Heihe River Basin, Northwest China

With the growing shortage of surface water resources,it is of great significance for improving the irrigation water productivity(IWP)to ensure the water and food security.The contribution of the driving factors of the IWP and the rational regulation of the input factors of agricultural production is required.In this paper,118 and 80 sampling points were selected in Pingchuan and Liaoquan irrigation districts(PLID,the spacing of sampling point is approximately 1 km)and the middle reaches of the Heihe River basin(MHRB,the spacing of sampling point is approximately 10 km),respectively.Soil characteristics and management measures near the sampling points were obtained.Results showed that the average value of the IWP in MHRB was 1.67 kg/m3,with a moderate heterogeneity in the space.The main driving factors of IWP were irrigation,fertilization and planting density.On the PLID,the contribution rates of soil factors and management measures to IWP were 20.6%and 35.2%,respectively,and the contribution of soil factors to IWP increased to 43.8%in the MHRB,while the contribution rate of management measures decreased to 24.8%.It shows that in a small irrigation districts,from the perspective of farmers,the improvement of IWP should be mainly controlled by management measures,while in the large area of watershed scale,the spatial differences in soil factors also need to be considered by the government management departments,when they want to increase IWP through regulating management measures.

Marginal land bioethanol production of sweet sorghum based on limited water resources in Northwest China

Sweet sorghum is considered a leading non-grain candidate for bioethanol production due to its low input requirement,good tolerance,high biomass potential,and high sugar content.However,insufficient studies have been conducted on the spatial distribution of sweet sorghum-based bioethanol production potential considering the water resources limitation.We presented a multi-factor analysis method not only considering terrain,meteorology,soil,and crop natural growth habits but also considering the local water resource to explore the available marginal land suitable for sweet sorghum cultivation and assess the bioethanol production potential in Northwest China.The results showed that 4.63×10^(7)hm^(2)available marginal land was suitable for sweet sorghum planting.Considering the constraint of local water resources,2.76×10^(6)hm^(2)available marginal land was suitable for sweet sorghum planting,accounting for 4.7%of the total available marginal land.And 1.23×10^(10)L bioethanol could be produced on it.Moreover,for these districts under low water stress levels,9.79×10^(5)hm^(2)available marginal land in Gannan Tibet AP and Longnan of Gansu and Hulun Buir of Inner Mongolia was considered a priority to develop sweet sorghum-based bioethanol,and 5.56×10^(9)L bioethanol could be produced in these districts,which can satisfy the 1.54%biofuel goal for 2050 of China.

LINKING CROP WATER PRODUCTIVITY TO SOIL PHYSICAL,CHEMICAL AND MICROBIAL PROPERTIES

Agriculture uses a large proportion of global and regional water resources.Due to the rapid increase of population in the world,the increasing competition for water resources has led to an urgent need in increasing crop water productivity for agricultural sustainability.As the medium for crop growth,soils and their properties are important in affecting crop water productivity.This review examines the effects of soil physical,chemical,and microbial properties on crop water productivity and the quantitative relationships between them.A comprehensive view of these relationships may provide important insights for soil and water management in arable land for agriculture in the future.

Effect of a new antitranspirant on the physiology and water use efficiency of soybean under different irrigation rates in an arid region

Antitranspirants are exogenous substances applied to leaves to reduce luxury transpiration by regulating stomatal conductance to increase water use efficiency(WUE). A cheap and environmentally-friendly antitranspirant, FZ, was newly developed, extracted mainly from Alhagi sparsifolia. Its effects on soybean water use were investigated in a field experiment using the locally-used irrigation rate and a low irrigation rate(The lower and upper limit of irrigation is 40%–70% of field capacity). Foliar application of FZ and measurement of leaf physiological characteristics, final biomass, seed yield and water use efficiency were carried out during the pod bearing and pod filling stages of drip-irrigated soybean with film-mulching. Under the low irrigation rate, leaf stomatal conductance(gs) and transpiration rate(Tr)decreased significantly by 7 d after spraying, but photosynthesis(Pn) and instantaneous water use efficiency(WUE_(in)) were not significantly affec ted. The stomatal frequency, stomatal aperture, gs, Tr and Pn decreased by 1 d after spraying, without significantly increasing WUE_(in).However, applying FZ during the pod bearing and pod filling stages did not significantly affect the final biomass,water consumption, seed yield and WUE of soybean.Under the locally-used irrigation rate, applying FZ increased the activities of superoxide dismutase and peroxidase in the leaves by 38% and 33%, respectively,but did not significantly affect gs, Tr, Pn, stomatal aperture and stomatal frequency. Applying FZ three times during pod bearing and pod filling stages enhanced seed yield and WUE by 24% and 21%, respectively, but did not significantly affect the final biomass and water consumption. Therefore, seed yield and WUE of soybean were significantly increased by foliar application of FZ during the pod bearing and pod filling stages under the locally-used irrigation rate in arid region, but applying FZ did not have a positive effect on water use efficiency of soybean under a low irrigation rate.

PLANT DENSITY,IRRIGATION AND NITROGEN MANAGEMENT:THREE MAJOR PRACTICES IN CLOSING YIELD GAPS FOR AGRICULTURAL SUSTAINABILITY IN NORTH-WEST CHINA

Agriculture faces the dual challenges of food security and environmental sustainability.Here,we investigate current maize production at the field scale,analyze the yield gaps and impacting factors,and recommend measures for sustainably closing yield gaps.An experiment was conducted on a 3.9-ha maize seed production field in arid north-west China,managed with border and drip irrigation,respectively,in 2015 and 2016.The relative yield reached 70%in both years.However,drip irrigation saved 227 mm irrigation water during a drier growing season compared with traditional border irrigation,accounting for 44%of the maize evapotranspiration(ET).Yield variability under drip irrigation was12.1%,lower than the 18.8%under border irrigation.Boundary line analysis indicates that a relative yield increase of 8%to 10%might be obtained by optimizing the yield-limiting factors.Plant density and soil available water content and available nitrogen were the three major factors involved.In conclusion,closing yield gaps with agricultural sustainability may be realized by optimizing agronomic,irrigation and fertilizer management,using water-saving irrigation methods and using site-specific management.