Soil water resources use limit in the loess plateau of China

Soil water is a key factor limiting plant growth in water-limited regions. Without limit of soil water used by plants, soil degradation in the form of soil desiccation is easy to take place in the perennial forestland and grassland with too higher density or productivity. Soil water resources use limit (SWRUL) is the lowest control limit of soil water resources which is used by plants in those regions. It can be defined as soil water storage within the maximum infiltration depth in which all of soil layers belong to dried soil layers. In this paper, after detailed discussion of characteristics of water resources and the relationship between soil water and plant growth in the Loess Plateau, the definition, quantitative method, and practical applications of SWRUL are introduced. Henceforth, we should strengthen the study of SWRUL and have a better understanding of soil water resources. All those are of great importance for designing effective restoration project and sustainable management of soil water resources in water- limited regions in the future.

California Simulation of Evapotranspiration of Applied Water and Agricultural Energy Use in California

The California Simulation of Evapotranspiration of Applied Water （CaI-SIMETAW） model is a new tool developed by the California Department of Water Resources and the University of California, Davis to perform daily soil water balance and determine crop evapotranspiration （ETo）, evapotranspiration of applied water （ETaw）, and applied water （AW） for use in California water resources planning. ETaw is a seasonal estimate of the water needed to irrigate a crop assuming 100% irrigation efficiency. The model accounts for soils, crop coefficients, rooting depths, seepage, etc. that influence crop water balance. It provides spatial soil and climate information and it uses historical crop and land-use category information to provide seasonal water balance estimates by combinations of detailed analysis unit and county （DAU/County） over Califomia. The result is a large data base of ETc and ETaw that will be used to update information in the new California Water Plan （CWP）. The application uses the daily climate data, i.e., maximum （Tx） and minimum （Tn） temperature and precipitation （Pcp）, which were derived from monthly USDA-NRCS PRISM data （PRISM Group 2011） and daily US National Climate Data Center （NCDC） climate station data to cover California on a 4 kmx4 km change grid spacing. The application uses daily weather data to determine reference evapotranspiration （ETo）, using the Hargreaves-Samani （HS） equation （Hargreaves and Samani 1982, 1985）. Because the HS equation is based on temperature only, ETo from the HS equation were compared with CIMIS ETo at the same locations using available CIMIS data to determine correction factors to estimate CIMIS ETo from the HS ETo to account for spatial climate differences. CaI-SIMETAW also employs near real-time reference evapotranspiration （ETo） information from Spatial CIMIS, which is a model that combines weather station data and remote sensing to provide a grid of ETo information. A second database containing the available soil water holding capacity and soil depth information for all of California was also developed from the USDA-NRCS SSURGO database. The Cal-SIMETAW program also has the ability to generate daily weather data from monthly mean values for use in studying climate change scenarios and their possible impacts on water demand in the state. The key objective of this project is to improve the accuracy of water use estimates for the California Water Plan （CWP）, which provides a comprehensive report on water supply, demand, and management in California. In this paper, we will discuss the model and how it determines ETaw for use in water resources planning.

Reducing water and nitrogen inputs combined with plastic mulched ridge-furrow irrigation improves soil water and salt status in arid saline areas,China

Plastic mulched ridge-furrow irrigation is a useful method to improve crop productivity and decrease salt accumulation in arid saline areas.However,inappropriate irrigation and fertilizer practices may result in ecological and environmental problems.In order to improve the resource use efficiency in these areas,we investigated the effects of different irrigation amounts(400(I1),300(I2)and 200(I3)mm)and nitrogen application rates(300(F1)and 150(F2)kg N/hm^(2))on water consumption,salt variation and resource use efficiency of spring maize(Zea mays L.)in the Hetao Irrigation District(HID)of Northwest China in 2017 and 2018.Result showed that soil water contents were 0.2%-8.9%and 13.9%-18.1%lower for I2 and I3 than for I1,respectively,but that was slightly higher for F2 than for F1.Soil salt contents were 7.8%-23.5%and 48.5%-48.9%lower for I2 than for I1 and I3,but that was 1.6%-5.5%higher for F1 than for F2.Less salt leaching at the early growth stage(from sowing to six-leaf stage)and higher salt accumulation at the peak growth stage(from six-leaf to tasseling stage and from grain-filling to maturity stage)resulted in a higher soil salt content for I3 than for I1 and I2.Grain yields for I1 and I2 were significantly higher than that for I3 and irrigation water use efficiency for I2 was 14.7%-34.0%higher than that for I1.Compared with F1,F2 increased the partial factor productivity(PFP)of nitrogen fertilizer by more than 80%.PFP was not significantly different between I1F2 and I2F2,but significantly higher than those of other treatments.Considering the goal of saving water and nitrogen resources,and ensuring food security,we recommended the combination of I2F2 to ensure the sustainable development of agriculture in the HID and other similar arid saline areas.

Effects of land use patterns on slope soil water in the semiarid Loess Plateau,China

Land use patterns(LUPs)are the form in which various land use types are combined spatially,evidently impacting soil water.However,the influence mechanism by which LUPs form remains unclear.In this study,the soil water content(SWC)in the 0–160-cm soil depth was observed in shrubland(SL),mature forestland(MF),grassland(GL)and young forestland(YF)sites on four slopes with different LUPs in the Yangjuangou catchment of the Chinese Loess Plateau.The SWC in SL-YF-SL(13.28%)was significantly greater than that in YF-MF(9.93%),MF-GL-YF(10.38%)and SL-MF(10.83%)and was temporally stable during the study period.The spatial distribution of SWC along the slope differed among the four LUPs.Vegetation characteristics and soil texture mainly determined the spatial variations in SWC in the shallow soil layers(0–40 cm),while topographic factors were the determinants in the deep soil layers(60–160 cm)as well as in the entire soil profile(0–160 cm).The significance of SWC differences among the various land use patterns increased with decreasing precipitation during the growing seasons.YF-MF(77.8 mm)and SL-YF-GL(73.9 mm)required more rainwater than SL-MF(68.2 mm)and MF-GL-MF(67.5 mm)to compensate for the loss of soil water on the monthly scale during the rainy season.Therefore,vegetation restoration should consider land use patterns on hillslopes for soil water conservation.

黄土丘陵半干旱区柠条林密度对土壤水分和柠条生长的影响

研究密度对土壤水分和植物生长的影响对森林植被恢复和生态建设具有重要的意义。以黄土丘陵半干旱区人工柠条为研究对象,对相同立地条件下不同密度柠条林生长与林地土壤水分进行了长期定位观测和分析。研究表明,1—5年生柠条不同密度林地土壤水资源量差异显著,从第3年开始,土壤水资源量随着密度增加而增加;10—12年生柠条密度越低土壤水资源量越高(Treatment4除外,T4),不同密度之间水资源量差异不显著。1—3年生柠条密度越高会促进其株高生长;从第四年开始,柠条密度过高会抑制其株高生长;1—5年生柠条密度越高基径生长越快,不同密度生长差异不显著;10—12年生密度过高(Treatment1,T1)或过低(T4)均会抑制柠条株高与基径生长。在柠条播种后第5年,高密度试验小区(T1和Treatment2,T2)柠条林地最大入渗深度土壤水资源量降到水资源利用限度,此时需要依据土壤水分植被承载力通过平茬来降低林分密度,以达到减少土壤水分消耗和可持续利用土壤水资源之目的。

黄土丘陵区撂荒坡地土壤水分特征曲线及水分常数的垂直变异

为探索黄土丘陵区不同深度土壤的持水和供水特性,选择典型多年撂荒坡地,分层取0-400cm纵深剖面原状土样测其主要土壤理化指标和土壤水分特征曲线,分析其土壤水分特征曲线及主要水分常数的垂直变化规律。结果表明:研究区各土层土壤水分特征曲线可用Gardner幂函数方程进行很好地拟合。方程中的参数a、b均表现出先减少后增加的垂直变化规律,极小值分别出现在160cm和120cm土深处;由方程推得的各水分常数的垂直变化规律与之相似,极小值也位于160cm土深处。土壤的持水和供水能力以0-40cm和240-400cm土层较强,中间土层较弱。土壤物理性粘粒含量、有机质含量、粘粒含量以及容重是影响上述垂直变异性的主要因子。本区土壤水资源利用限度等于0-290cm范围内各土层土壤含水量降至凋萎系数时的土壤水资源残留量,为222.84mm。

河南省潮土区主要粮食生产潜力研究

为探讨河南省的粮食生产潜力,发掘限制粮食产量的限制因子,以通许和延津2个县的潮土区试验为例,在对试验区的光、温、水、土诸要素分析的基础上,计算出河南省潮土区粮食的光合生产潜力、光温生产潜力、气候生产潜力。结果表明,河南潮土区粮食生产潜力为15 535-21 927kg/hm2,粮食生产潜力指数在0.21-0.67。进一步分析出限制粮食产量的主要限制因子为水分,其次为温度和土壤,并提出了提高粮食产量的方法。

水资源紧缺地区土壤水分植被承载力论述

在详细论述土壤水资源概念发展和土壤水分植被承载力研究尺度的基础上,介绍土壤水分植被承载力量化模型,包括经典的承载力模型、种群增长通用模型、密度-土壤水分模型和基于物理过程的土壤水分植被承载力模型,述评土壤水分植被承载力研究现状,提出今后应在完善土壤水分植被承载力理论的同时,加强水资源紧缺地区土壤水分与植物生长的野外长期定位研究,从不同时空尺度确定不同植物群落的土壤水分承载力。

土壤水资源利用限度评价

在水资源紧缺地区,大部分地区的土壤水分主要来源于天然降雨,随着人工林生长,林地土壤水资源下降,当人工林发展到超过植物对土壤水资源的利用限度时,在林地最大土壤水分补给深度以下出现的土壤层将会成为不可逆转的土壤干层。这种现象不利于土壤水资源的可持续利用和森林植被的恢复、更新。土壤水资源利用限度理论的提出将使不可逆转的土壤退化防治变为积极的土壤水资源的可持续利用。在生产中应充分认识并掌握这个规律,设法避免人工林草植被对土壤水资源的过度利用。

基于logistic模型评估黑龙江农业生态系统水土资源利用与变化

水土资源是农业生态系统发展的两大关键资源,影响农业生态系统的可持续发展。【目的】探究黑龙江农业生态系统的变化和发展对水土资源利用的影响。【方法】利用Logistic模型和RMSE分析模型,在当前农业科技管理水平下,对黑龙江农业生态系统中作物用水量、种植面积等指标进行评估预测。【结果】该农业生态系统粮食作物种植总面积极值约为1.43×10~7hm^2,农业水资源供应极值约为3.16×10~8m^3,水稻单产极值约为7 030 kg/hm^2,粮食作物单产极值约为5 275 kg/hm^2,粮食作物总产量极值可达7.53×107 t。同时,利用该模型对水资源灌溉总量、作物种植总面积、作物单产等指标的模拟值与统计值的拟合分析可知,决定系数R2最小为0.89,最大为0.98,均方根误差RMSE均小于10%,达到了0.01水平下的极显著相关关系。【结论】Logistic模型能够较好地模拟20年间黑龙江农业生态系统水土资源利用与趋势变化。

黄土丘陵半干旱区土壤水资源利用限度

以柠条为对象,采用中子水分仪对黄土丘陵半干旱区人工植被恢复过程中土壤水分与植物生长进行长期定位观测.结果表明:撂荒地播种后,随着时间推移,植物群落保持水土能力增强,根系吸收利用水分的土层深度增加、土壤含水量下降.林地土壤出现干层,且干层土壤的深度和厚度逐年增加.植物对土壤水资源的利用限度为干层土壤深度等于最大补给深度时的土壤储水量.在黄土丘陵半干旱区人工柠条林地土壤水资源利用限度是0～290cm土层的土壤储水量为249.4mm.当人工林地土壤水资源接近或等于土壤水资源利用限度时,需要采取措施降低土壤水分消耗,或增加土壤水分补给,维持根系吸收利用水资源的相对稳定.