Effects of moisture and septoria tritici blotch stresses on wheat yields under semi-arid conditions: A Simulation study

The effects of Septoria tritici blotch on spring wheat were incorporated into a crop growth simulator and the model was then used to evaluate the interrelationships between moisture and disease stresses on wheat yields under semi-arid conditions. Simulation experiments revealed that moisture availability plays a role in determining the relationship between disease and yield. In a season when precipitation was distributed evenly, a non-diseased crop yielded more than diseased crops. Yield reductions in diseased crops were related to the severity of epidemics; the relationship between disease and yield was inverse and linear. In a season when water was scarce during the stage of kernel-filling, crops with mild or moderate disease epidemics (apparent infection rate of a logistic model,r, of 0.025 or 0.05 per unit) yielded more than the non-diseased crop. The yield of the crop with a severe epidemic (r of 0.1 per unit) was reduced substantially and the relationship between disease and yield was parabolic. The parabolic relationship was linearized when additional precipitation was simulated in the model.     

基于同化叶面积指数和条件植被温度指数的冬小麦单产估测

应用数据同化方法将遥感信息与作物生长模型融合,是估测区域作物产量的重要方法之一。以2008—2014年越冬后的冬小麦为研究对象,选择与作物长势、产量及水分胁迫信息密切相关的叶面积指数(LAI)和条件植被温度指数(VTCI),采用粒子滤波算法对CERES-Wheat模型模拟和遥感数据观测的LAI和VTCI实施同化,分别基于观测LAI和VTCI、同化LAI和VTCI构建冬小麦单产估测模型。结果表明,同化LAI变化趋势更加符合关中平原冬小麦的实际生长状况,同化VTCI能更好地反映冬小麦的水分胁迫程度。应用观测LAI和VTCI构建的估产模型决定系数为0.402,而单独应用LAI或VTCI单变量构建的估产模型决定系数分别为0.279和0.339,说明应用LAI和VTCI双变量构建的估产模型的精度优于单独应用LAI或VTCI单变量的精度。相比于观测LAI和VTCI构建的估产模型,基于同化LAI和VTCI构建的估产模型的决定系数从0.402提高到0.547。表明基于同化LAI和VTCI构建的估产模型的精度明显提高。     

Rainfall,evapotranspiration, and soil moisture as herbage production predictors for Wyoming rangelands

Rangelands are an important ecosystem in the western US, and herbage and livestock production are important issues throughout the western states. Making stocking rate decisions early in the growing season is difficult because of high variation in annual herbage production. In this study, regression analysis was used to relate herbage biomass to monthly and growing season predicator variables (rainfall, actual evapotranspiration, and soil moisture) using data collected from fifteen Wyoming rangeland sites. Both predictor and response variables were scaled before regression to correct for different physical and environmental conditions between sites. Growing season precipitation was the strongest predictor of herbage biomass production (r² = 0.79), followed by growing season actual evapotranspiration (r² = 0.69), and growing season profile-average soil water content (r² = 0.59). April profile-average (0–90 cm) and April surface (0–30 cm) soil moisture also predicted herbage biomass (r² = 0.53–0.54), indicating that early growing season soil moisture can be used to inform stocking rate and grazing management decisions as it provides information at the onset of the growing season.     

基于标准化降水指数SPI的泾惠渠灌区干旱演变对冬小麦气候产量的影响

为了研究干旱变化对于作物产量的影响机制,以泾惠渠灌区为例,选用标准化降水指数SPI作为干旱评判指标,采用Mann-Kendall趋势检验、最大熵谱分析等方法分析了灌区干旱的变化特征,以及干旱演变下冬小麦气候产量的变化规律。研究表明:(1)灌区冬小麦实际产量呈显著增加趋势(Z=7.6482),气候产量呈不明显减少趋势(Z=-0.5686);(2)灌区总体干旱化趋势明显(通过了99%的显著性检验),这种趋势在春、夏、秋三季都达到了显著水平;(3)干旱存在16 a的年代际周期波动,4~5 a的年际周期;(4)播种前7—9月份和播种后的10、11月的干旱情况对于冬小麦气候产量的影响最大,是影响作物气候产量的关键期;(5)SPI3-9与冬小麦气候产量关系最密切,可以解释46.21%的产量变异;(6)随着干旱的年代际周期变化,SPI3-9与冬小麦气候产量之间的相关系数从0.44上升至0.74,干旱对于冬小麦气候产量的影响有增强的趋势。     

黄土塬区降水变化条件下冬小麦田土壤水分消耗与补给

通过人工实时降水分配试验,研究了黄土塬区冬小麦田3种降水条件:正常降水(R_(CK))、降水增加1/3(R_(+1/3))和降水减少1/3(R_(-1/3))下,土壤水分变化速率、消耗深度以及水量平衡状态。结果表明:R_(CK)和R_(-1/3)处理0~3.8 m土层土壤储水量以91.85 mm·a~(-1)和109.39 mm·a~(-1)的速度下降,而R_(+1/3)处理土壤储水量在0~3.0 m深度以48.94 mm·a~(-1)的速度减少,而在深层(3.0~3.8 m)土壤水以17.39 mm·a~(-1)的速度增加;降水增加使得土壤水分的补给次数增多,减少了土壤水分的时空变异;当土壤底墒充足且生育期降水量较多时,各降水处理土壤水分的消耗深度较浅,反之,则较深;在休闲期,降水的转化效率与生长季土壤水的消耗率呈现极显著的指数相关。     

内蒙古皇甫川流域作物生长期气候旬变异特征及其对作物产量效应分析

皇甫川流域地处我国北方半干旱区,作物生产对气候变化具有明显的脆弱性。利用该流域1961—2000年生长季(5~9月)的降水、气温数据、农作物播种面积和产量数据,深入分析作物生产对旬尺度降水、气温变异的响应。研究表明,排除社会经济因素影响,皇甫川流域农作物生产对旬尺度降水、气温变异有明显响应,但不同农作物的响应程度不同,同一种农作物对不同旬的响应亦不同;8月上旬降水量的丰缺对糜黍、玉米、薯类和谷子等农作物的气候产量有明显正效应,6月下旬和7月上旬降水量的多少对高粱的气候产量有决定性的影响;5月中旬最高气温和7、8月份各旬平均气温、最低气温和最高气温的升高,都可能使农作物的气候产量不同程度降低。因此,加强生态环境建设特别是生长季(尤其是7、8月份)旱作区的田间管理,降低农业生产对气候变化的敏感性,显得尤为重要和必要。     

Critical period of weed control in transplanted chilli pepper

Summary Field experiments were conducted from 1991 to 1993 to determine the critical period of weed control in chilli pepper. The maximum weed-infested period ranged between 0.7 and 3.2 weeks after transplanting (WAT) at a 5% yield loss level. To prevent losses in total and marketable yields, weeds should be removed 2.1 or 0.9 WAT respectively. The end of the critical period decreased as the predetermined yield loss level increased from 2.5% to 10%. The minimum weed-free period ranged between 6.7 and 15.3 WAT at a 5% yield loss level depending on crop yield category. The chilli pepper crop required an average of 12.2 weeks of weed-free maintenance to avoid losses above 5%. Using a 5% yield loss level, the duration of the critical period of weed control was 14 weeks in 1991 and 11.2 weeks in 1993, but was shortened to 5.1 weeks in 1992. The results suggest that weeds must be controlled during the first half of the crop's growing season in order to prevent yield losses.     

The effect of timing of fungicide applications on control of frogeye leaf spot and grain yield of soybeans

Soybean cultivar Samsoy 1, and the breeding lines TGx 849-313D and TGx 996-26E, grown in a field with a heavy epidemic of frogeye leaf spot caused byCercospora sojina, were treated with double foliar applications of the fungicide benomyl. The treatments were made using four application schedules at six different growth stages, starting from V₃ (fully developed leaves, beginning with trifoliate nodes) to R₅ (beginning seed_, to determine the effect of the fungucide timing on frogeye leaf spot severity, soybean grain yield and grain quality. Generally, applications at R₁ (beginning bloom) and R₃ (beginning pod) significantly (P<-0.05) reduced disease severity in the 2 susceptible genotypes, Samsoy 1 and TGx 849-313D. Plot yields of these genotypes were also significantly greater than the untreated controls when the fungicide applications were made at R₁ and R₃. There was no significant difference in diseave severity or grain yield, between the untreated control and the different times of application, on the resistant genotype TGx 996-26E. Improved seed germination and lower levels of seed infection byC. sojina occurred for all fungicide timings in the susceptible genotypes. The results suggest that fungicide spraying initiated at R₁ and followed up at R₃ is most effective in frogeye leaf spot control and can also result in higher grain yields, than applications made earlier or later in the season. Control of frogeye leaf spot, however, is best achieved by growing resistant cultivars.     

Early assessment of the yield loss in rice due to the brown planthopper using a hyperspectral remote sensing method

The brown planthopper (BPH) is an important pest in rice. Rice losses due to BPH's damage are often more than 10% of yield. Assessments on loss rates from BPH are now basically dependent on experiential indices. However, early assessments on rice yield losses using hyperspectral data are still rare. In this study, reflectance from rice canopy was measured in net cages after different densities of BPH release. Results showed that reflectance in the near-infrared region (750–1000 nm) from milk grain stage, and in 400–531 nm and 567–705 nm from mature grain stage was closely related to BPH density. These spectral indices: red-edge parameters (λ_r, Dλ_r, Sλ_r), ratio of the maximal reflectance in green (490–560 nm) to minimal reflectance (640–740 nm) in red (R_GREEN/R_RED), ratio of the near-infrared peak (R_NIR) to R_RED, normalized difference vegetation index between R_NIR and R_RED and soil-adjusted vegetation index (SAVI) from both milk and mature grain stages, indicated BPH densities well. As expected, rate of loss in rice grain was higher with increasing BPH density. SAVI, Dλ_r, Sλ_r and reflectance at 760 nm (R₇₆₀) from milk grain stage were significantly correlated with rates of loss in panicle, and 1000-grain weight and multiple-linear regression models for detecting loss rate were established. The hyperspectral reflectance from rice at milk grain stage can be used to assess rice yield losses due to BPH and improve management policies.     

半干旱区春小麦水分与产量关系及其影响因素分析

水分是影响半干旱雨养作物生长、发育及产量形成最重要的环境因素。以中国西北半干旱区田间试验为基础,收集长期观测资料和文献数据,分析春小麦产量与水分之间的关系及其环境影响因素,揭示不同环境条件下春小麦水分限制特征和调控机制。研究表明：半干旱区常规管理水平下,雨养春小麦产量与水分间的关系相对稳定,然而播前土壤储水影响生育期降水与春小麦产量间的关系,不同播前土壤储水条件下,每增加1 mm降水量,春小麦产量的增加量分别为21.3 kg·hm^-2和16.8 kg·hm^-2。生育期大气干湿条件（潜在蒸发量与降水的差值）对播前土壤储水与春小麦产量间的关系也有影响,其中大气较为干燥时（潜在蒸发量与降水的差值大于425 mm）,产量与土壤水分间关系斜率为22.9 kg·hm^-2·mm^-1,大气较为湿润时（潜在蒸发量与降水的差值小于425 mm）,斜率为20.1 kg·hm^-2·mm^-1。相较生育期降水,播前土壤储水对春小麦产量更具有决定性作用。半干旱雨养春小麦的气候年型由播前土壤储水和生育期大气干湿条件共同决定。增加播前土壤水分储量、在生育期的特定阶段灌溉均会改变小麦耗水量与产量之间的关系,并最终导致小麦水分利用效率发生变化。大气干湿条件和灌溉条件共同导致中国西北不同地区春小麦边界函数存在差异。     

Assessing the response of dryland barley yield to climate variability in semi-arid regions,Iran

Precipitation and temperature are the most abiotic factors that greatly impact the yield of crop, particularly in dryland. Barley, as the main cereal is predominantly cultivated in dryland and the livelihood of smallholders depends on the production of this crop, particularly in arid and semi-arid regions. This study aimed to investigate the response of the grain yield of dryland barley to temperature and precipitation variations at annual, seasonal and monthly scales in seven counties of East and West Azerbaijan provinces in northwestern Iran during 1991-2010. Humidity index (HI) was calculated and its relationship with dryland barley yield was evaluated at annual and monthly scales. The results showed that the minimum, maximum and mean temperatures increased by 0.19°C/a, 0.11°C/a and 0.10°C/a, respectively, while annual precipitation decreased by 0.80 mm/a during 1991-2010. Climate in study area has become drier by 0.22/a in annual HI during the study period. Negative effects of increasing temperature on the grain yield of dryland barley were more severe than the positive effects of increasing precipitation. Besides, weather variations in April and May were related more to the grain yield of dryland barley than those in other months. The grain yield of dryland barley was more drastically affected by the variation of annual minimum temperature comparing with other weather variables. Furthermore, our findings illustrated that the grain yield of dryland barley increased by 0.01 t/hm² for each unit increase in annual HI during 1991-2010. Finally, any increase in the monthly HI led to crop yield improvement in the study area, particularly in the drier counties, i.e., Myaneh, Tabriz and Khoy in Iran.     

近30 a来黑龙江省气候变化及其对玉米产量的影响

基于全球气候变化,以黑龙江省为例,在收集1980-2009年气象站点农业气象资料的基础上,运用线性倾向率方法,分析了近30 a来黑龙江省玉米生长季和3个主要生育阶段的气候变化特征;在此基础上分析了玉米气象产量与不同生育阶段气候要素的相关性。结果表明：平均、最高和最低温度指标从时间变化来看,在各个生育阶段都表现为升高趋势,从空间变化来看,温度升高趋势基本表现为从东到西的增加趋势;日照时数和参考作物蒸散量的变化从时间上来看,除在播种-苗期表现为减少趋势外,在其他生育阶段都表现为增加趋势;从空间上来看,其变化幅度在各个生育阶段基本上表现为从西南向东北递增的趋势;降水量时间上主要表现为减少趋势,空间变化趋势则不明显。相关分析表明：穗期和花粒期的最低温度与玉米的气象产量呈正相关关系,花粒期的最高温度与玉米的气象产量呈负相关关系。     

Effects of variation in rainfall on rainfed crop yields and water use in dryland farming areas in China

Crop production in the dryland farming areas of northern China is constrained by low and variable rainfall. This article presents the analysis of the relationships between variations in rainfall and yields of winter wheat and spring maize. The analysis is based on data from both several short-term and our ongoing long-term field experiments in dryland farming research projects in Tunliu, Linfen, Shouyang, and Luoyang. Grain yields of wheat and maize ranged from 1,548 to 5,169 and from 2,612 to 8,789 kg ha^-1 respectively, with differences up to above 200% (between dry and wet years). Wheat yields are sensitive to growing season rainfall but also correlated to water use (ET), whereas maize yields are sensitive to the critical time of water supply (especially June rainfall) but not correlated to ET. The ratio of grain yields to soil water at sowing is an important indicator, showing close relationships between yields and soil water-related ratio within the rainfed crops site. Comparison between the indices of water use efficiency (WUE) and precipitation use efficiency (PUE) suggests that the index WUE is more grain-related indicator than the PUE used for assessing rainfed crop water use by both maize and wheat. The index PUE should be used in caution, especially for wheat crops in dry years. Our results indicate that options to alleviate crop moisture stress must be tailored to the rainfall pattern. This holds especially for conservation tillage with response nutrient management practices that aim at enhancing water use efficiency.     

The critical period of weed control in double-cropped soybean

Double-cropped soybean after winter cereals is the most common soybean production system in the eastern Mediterranean region of Turkey. Weeds are among the main obstacles to double-cropped soybean. A study was conducted in 2002 and 2003 to determine the critical period of weed control (CPWC) for double-cropped soybean. The treatments consisted of either allowing weeds to infest the crop for increasing durations after sowing, or maintaining plots weed-free for increasing durations after sowing. The Gompertz and logistic equations were fitted to relative yields representing the critical weed-free period and the critical time of weed removal, respectively. Johnsongrass (Sorghum halepense), common cocklebur (Xanthium strumarium) and field bindweed (Convolvulus arvensis) were the dominant weeds. For 5% crop loss level, the CPWC was almost all season long, whereas it was from V1 to R6-R7 growth stages for 10% yield loss level. These findings indicate that pre-sowing or pre-emergence control methods should be applied in the region to avoid greater crop losses.     

Estimating relative crop yield loss resulting from herbicide damage using crop ground cover or rated stunting, with maize and sethoxydim as a case study

The research goal was to determine whether crop damage from herbicides measured early in the growing season soon after treatment could be used to estimate relative crop yield loss. Percentage stunting was rated visually and percentage crop ground cover (i.e. percentage of the ground surface covered by vegetation) was determined from video photographs taken 2–4 weeks after sethoxydim-susceptible maize ( Zea mays L.) was sprayed with sethoxydim at various rates plus crop oil concentrate. Averaged over 3 years, relative percentage maize yield was a negative sigmoidal function of relative sethoxydim rates from 0.065× to 0.5×, where the 1× rate was 420 g a.i. ha⁻¹ ( r ² = 0.80). Relative maize yield was positively linearly related to percentage crop ground cover and negatively linearly related to rated percentage stunting averaged over 3 years. Linear regression models of relative maize yield vs. percentage maize ground cover explained only slightly more data variability ( r ² = 0.86) than did rated stunting ( r ² = 0.82) over 3 years. The advantages and disadvantages of rated stunting and crop ground cover as scientific measurements are discussed.     

干旱区棉花水分胁迫指数对滴灌均匀系数和灌水量的响应

为了修订和完善滴灌均匀系数的设计与评价标准,在新疆干旱区研究了滴灌均匀系数和灌水量对作物水分胁迫指数（CWSI）的影响。供试作物为棉花,试验中滴灌均匀系数（C_u）设置0.65（C1）、0.78（C2）和0.94（C3）三个水平,灌水量设置充分灌水量的50%、75%和100%三个水平。结果表明：棉花冠层温度和CWSI表现出随灌水量增加而降低的趋势;冠层温度和CWSI均匀系数的变化范围分别为0.91～0.98和0.65～0.91,均随滴灌均匀系数增加而增大;灌水量对冠层温度和CWSI均值的影响达到极显著水平（α=0.01）,滴灌均匀系数对冠层温度和CWSI均匀系数的影响达到显著水平（α=0.05）或极显著水平。CWSI与皮棉产量呈显著或极显著的负相关关系;滴灌均匀系数越低,水分亏缺引起的减产幅度越小。     

基于作物水分盈亏指数的昆明水稻生长季干旱特征及成因分析

基于昆明站点1952—2013年逐日气象观测资料,根据联合国粮农组织1998年推荐的PenmanMonteith公式计算了昆明站近62 a来逐日的参考作物蒸腾量、水稻生育期需水量,利用Mann-Kendall趋势检验法研究作物需水量变化规律,同时根据水稻的水分亏缺指数(CWDI),采用通径分析方法研究各气象因子对水分亏缺指数的影响。结果表明:近62年来昆明地区平均旬需水量为32.55 mm;水稻生长季内干旱分布明显不均匀,随着生长季的推进,干旱级别从轻旱到重旱,干旱发生最严重时期是黄熟生育阶段,在整个水稻生长季内,水稻水分盈亏指数均值为38.07%,表明水稻处于重旱状态;在水稻生育期变异系数研究中,水分盈亏指数变异系数均较小,在返青、分蘖、拔节、抽穗、乳熟和黄熟六个阶段中,变异系数分别为1.8%、1.9%、1.3%、1.1%、0.8%、和0.8%,表明昆明地区近年干旱等级变化较小;影响水分盈亏指数最大正相关因素为日照,最大负相关因素为水汽压。     

AquaCrop作物模型在黄土塬区夏玉米生产中的适用性评价

为评价Aqua Crop作物模型在黄土塬区的适用性,基于Hsiao等人推荐的玉米参数对模型参数进行调试及验证。在陕西长武地区模拟2003、2004、2005、2007、2008、2010年玉米生育期内生物量、蒸发蒸腾量的变化过程及收获时产量、地上部生物量,将模拟值与收集到的实测值进行对比、分析。结果表明,这6年模拟产量与实测产量间的校正决定系数(Adj)R2为0.9270,相对误差在-2.479至11.182之间;模拟地上部生物量与实测地上部生物量间的Adj.R2为0.7842,模型对产量的模拟效果优于对生物量的模拟;2005年和2008年模拟蒸散量与实测蒸散量间的Adj.R2分别为0.6229和0.7973。模拟效果较好,对黄土塬区夏玉米水分优化管理模拟有重要意义。     

Effects of Cultivation after Planting on Yields of Seed Cotton

Abstract

Experiments carried out over several seasons showed that, on a soil prone to crusting, cultivations after the establishment of a cotton crop only increased yields in a season of low rainfall. This yield increase appeared to have been due to enhanced entry into the soil of the limited effective rainfall. In one season of high rainfall, deep cultivation significantly reduced yields.     

东北地区玉米大豆水分利用效率研究

利用大安和朝阳玉米研究站点、呼玛和锦州大豆研究站点近20 a作物产量、发育期及土壤水分实测资料,同时结合分期播种试验资料,研究了玉米大豆产量水分利用效率(WUE_g)对降水、温度的响应特征,分析了两种作物产量水分利用效率与群落水平水分利用效率(WUE_b)的关系。结果表明:大安和朝阳站点玉米WUE_g分别为1.75±0.47 kg·m~(-3)和1.98±0.72 kg·m~(-3),呼玛和锦州站点大豆WUE_g分别为0.63±0.35 kg·m~(-3)和0.55±0.18kg·m~(-3);玉米站点WUE_g与播种—成熟期间的降水量和ET均呈显著的二次曲线关系(P0.05),WUE_g与温度关系不明显;大豆WUE_g与播种至成熟期间的降水量呈现显著的负相关关系;历史资料分析结果表明,随着生育期期间平均气温的增加,大豆WUE_g升高;在大安和朝阳站点,取得高水分利用效率与获得高产所消耗的水量(即ET)并不一致,表明对于存在干旱胁迫的半干旱和半湿润区,有效的利用水(Effective use of water,EUW)而不是一味追求水分利用效率(WUE)是提高产量的有效途径,植物消耗的水量(ET)往往是决定作物产量的重要因素。