Effect of timing of a deficit-irrigation allocation on corn evapotranspiration, yield, water use efficiency and dry mass

Water regulations have decreased irrigation water supplies in Nebraska and some other areas of the USA Great Plains. When available water is not enough to meet crop water requirements during the entire growing cycle, it becomes critical to know the proper irrigation timing that would maximize yields and profits. This study evaluated the effect of timing of a deficit-irrigation allocation (150 mm) on crop evapotranspiration (ETc), yield, water use efficiency (WUE = yield/ETc), irrigation water use efficiency (IWUE = yield/irrigation), and dry mass (DM) of corn (Zea mays L.) irrigated with subsurface drip irrigation in the semiarid climate of North Platte, NE. During 2005 and 2006, a total of sixteen irrigation treatments (eight each year) were evaluated, which received different percentages of the water allocation during July, August, and September. During both years, all treatments resulted in no crop stress during the vegetative period and stress during the reproductive stages, which affected ETc, DM, yield, WUE and IWUE. Among treatments, ETc varied by 7.2 and 18.8%; yield by 17 and 33%; WUE by 12 and 22%, and IWUE by 18 and 33% in 2005 and 2006, respectively. Yield and WUE both increased linearly with ETc and with ETc/ETp (ETp = seasonal ETc with no water stress), and WUE increased linearly with yield. The yield response factor (ky) averaged 1.50 over the two seasons. Irrigation timing affected the DM of the plant, grain, and cob, but not that of the stover. It also affected the percent of DM partitioned to the grain (harvest index), which increased linearly with ETc and averaged 56.2% over the two seasons, but did not affect the percent allocated to the cob or stover. Irrigation applied in July had the highest positive coefficient of determination (R²) with yield. This high positive correlation decreased considerably for irrigation applied in August, and became negative for irrigation applied in September. The best positive correlation between the soil water deficit factor (Ks) and yield occurred during weeks 12-14 from crop emergence, during the “milk” and “dough” growth stages. Yield was poorly correlated to stress during weeks 15 and 16, and the correlation became negative after week 17. Dividing the 150 mm allocation about evenly among July, August and September was a good strategy resulting in the highest yields in 2005, but not in 2006. Applying a larger proportion of the allocation in July was a good strategy during both years, and the opposite resulted when applying a large proportion of the allocation in September. The different results obtained between years indicate that flexible irrigation scheduling techniques should be adopted, rather than relying on fixed timing strategies.     

Tomato nitrogen accumulation and fertilizer use efficiency on a sandy soil, as affected by nitrogen rate and irrigation scheduling

Tomato production systems in Florida are typically intensively managed with high inputs of fertilizer and irrigation and on sandy soils with low inherent water and nutrient retention capacities; potential nutrient leaching losses undermine the sustainability of such systems. The objectives of this 3-year field study were to evaluate the interaction between N-fertilizer rates and irrigation scheduling on crop N and P accumulation, N-fertilizer use efficiency (NUE) and NO₃-N leaching of tomato cultivated in a plastic mulched/drip irrigated production system in sandy soils. Experimental treatments were a factorial combination of three irrigation scheduling regimes and three N-rates (176, 220, and 330 kg ha⁻¹). Irrigation treatments included were: (1) surface drip irrigation (SUR) both the irrigation and fertigation line placed underneath the plastic mulch; (2) subsurface drip irrigation (SDI) where the irrigation drip was placed 0.15 m below the fertigation line which was located on top of the bed; and (3) TIME (conventional control) with the irrigation and fertigation lines placed as in SUR and irrigation applied once a day. Except for the TIME treatment all irrigation treatments were soil moisture sensor (SMS)-based with irrigation occurring at 10% volumetric water content. Five irrigation windows were scheduled daily and events were bypassed if the soil water content exceeded the established threshold. The use of SMS-based irrigation systems significantly reduced irrigation water use, volume percolated, and nitrate leaching. Based on soil electrical conductivity (EC) readings, there was no interaction between irrigation and N-rate treatments on the movement of fertilizer solutes. Total plant N accumulation for SUR and SDI was 12-37% higher than TIME. Plant P accumulation was not affected by either irrigation or N-rate treatments. The nitrogen use efficiency for SUR and SDI was on the order of 37-45%, 56-61%, and 61-68% for 2005, 2006 and 2007, respectively and significantly higher than for the conventional control system (TIME). Moreover, at the intermediate N-rate SUR and SDI systems reduced NO₃-N leaching to 5 and 35 kg ha⁻¹, while at the highest N-rate corresponding values were 7 and 56 kg N ha⁻¹. Use of N application rates above 220 kg ha⁻¹ did not result in fruit and/or shoot biomass nor N accumulation benefits, but substantially increased NO₃-N leaching for the control treatment, as detected by EC monitoring and by the lysimeters. It is concluded that appropriate use of SDI and/or sensor-based irrigation systems can sustain high yields while reducing irrigation application as well as reducing NO₃-N leaching in low water holding capacity soils.     

对中国南方部分籼型杂交水稻纹枯病抗性的评价

由立枯丝核菌引起的水稻纹枯病是世界性的水稻严重病害之一,且在育种和生产上可利用的抗病种质极少,迫切需要发掘抗源。本研究鉴定了来自中国南方11个省(市、自治区)的166个籼型杂交稻组合对纹枯病菌的苗期抗性。未发现免疫或高抗的组合,但不同组合间的抗性差异极显著,平均病情指数符合正态分布N(5.27,0.68²),变化幅度为2.84~7.64。根据动态聚类分析,参试组合被划分为抗、中抗、中感、感和高感5级,分别占总数的1.20%、13.86%、36.14%、43.37%和5.42%。参试的大多数组合为感病,仅K优88和中优9801抗病,但其抗性还需在大田进行成株期验证。用Bayes法建立了各抗性级的判别函数,判别准确率达96.39%。根据综合病情指数,上述5级的组合分别占总数的1.20%、13.25%、63.25%、21.69%和0.60%。与动态聚类比较,两者极显著相关(r＝0.81,P<0.01),说明这两种方法均可用于水稻对纹枯病的抗性评价。但动态聚类法较适用于接种环境相对一致的苗期鉴定,而不能比较不同环境条件下的鉴定结果;综合病情指数法则不受时间、地点和批次的限制,更具实用性。通过这两种方法共筛选出26个抗或中抗的组合,它们之间的遗传距离为0.04~0.71;在遗传距离为0.36处,可将其中的22个组合聚为一簇,表明其遗传基础较窄。系谱追踪表明26个抗或中抗的杂交稻亲本亲缘关系较近。因此,在抗纹枯病育种中,需要拓宽抗病种质的遗传基础,培育聚合有数量抗性的材料或组合。     

地下调亏滴灌对紫花苜蓿耗水、产量和品质的影响

地下滴灌技术是最为节水的灌溉技术,为了推进地下滴灌技术在紫花苜蓿生产中的应用,2012年在甘肃武威开展了大田试验,通过对建植当年第2茬苜蓿不同生育期设置不同的亏水处理,研究了地下滴灌条件下调亏灌溉对紫花苜蓿耗水、产量和品质的影响。结果表明:随亏水程度的加重,紫花苜蓿的产量降低,耗水量减少,水分利用效率(WUE)提高,干重茎叶比降低,粗蛋白含量提高,粗蛋白产量降低;全生育期调亏,生育期间的耗水强度呈现现蕾期分枝期分枝前期的规律,并且随着亏水程度的增加,规律愈加明显;分枝期调亏的紫花苜蓿,在现蕾期复水后耗水强度有明显的补偿效应;与现蕾期调亏相比,分枝前期和分枝期调亏有利于降低茎叶比,提高粗蛋白质量分数和粗蛋白产量。该研究揭示了地下滴灌条件下不同调亏处理对紫花苜蓿耗水、产量和品质的影响,为干旱地区优质、高产、节水苜蓿的生产提供了试验依据。     

大豆对SMV数量(程度)抗性的综合分级方法研究

选用63个不同抗性类型的代表品种,进行接种大豆花叶病毒病,分析了品种发病率、病级、潜育期和病害扩展速度4个数量抗性组分的遗传变异特点,以4个组分为基础指标,对63个品种的程度抗性进行了聚类分析.发现在距离约为0.38时,63个品种被分成免疫、高抗、中抗、中间、中感和高感6种类型,在聚类分析的基础上建立了各抗性级别的判别函数;另外,利用发病率、病级和接种至最大病情的天数构建了度量数量抗性强弱的综合病情指数(SDI),提出各抗性级别的临界标准;并对同一批材料聚类和判别分析分级结果与综合病情指数分级结果进行了比较,结果显示两种方法可取得类似的分级效果,而综合病情指数是对感病对照的相对统计量,不受时间、地点和批次的限制,便于不同环境下品种抗性的鉴定以及品种间抗性的比较,且简单易行.因此,综合病情指数可作为对SMV数量抗性鉴定的分级指标.     

地下滴灌土壤水分运动室内试验研究

通过室内试验,对地下滴灌土壤水分分布进行了直接观察分析。试验发现滴灌管壁的导水作用将对土壤水分分布也产生一定影响;地下滴灌3个方向上的湿润锋运移也均近似为时间平方根的线性函数;另外,滴头埋于地下后,其出流量将会受到周围土壤密实度的影响等。这些初步结论将对实际田间的地下滴灌技术的规划设计有一定参考应用价值。     

地下滴灌灌水器负压吸泥影响因素试验研究

为了探究引起地下滴灌系统灌水器负压吸泥的影响因素,通过对比试验,研究分析了土壤类型、单次灌水量、灌溉次数、灌水器类型、保水剂和灌水间隔等6个因素对灌水器负压吸泥的影响规律。结果表明,1流量可调式灌水器出水孔外部及内部存在负压吸泥并引起堵塞情况。外部出水孔有3个被堵塞的所占比例最多,为26.7%;泥沙分布主要集中在灌水器出水孔的内侧附近,有极少部分泥沙甚至可以越过内凸边缘,进入灌水器内圈。2压力补偿式灌水器抗负压吸泥的能力强于流量可调式灌水器,压力补偿式灌水器外部出水口及内部未发现有泥沙,而流量可调式灌水器外部出水口及内部有泥沙;灌水器在红壤土中比黄沙土中更容易出现负压吸泥情况,灌水器在红壤土中的内部泥沙量是黄沙土中的1.12~1.76倍。3灌溉方式(单次灌水量、灌溉次数、灌水间隔)对灌水器负压吸泥的影响显著。单次灌水量小的灌水器内部泥沙量较多,灌水器单次灌水量为170 m L内部泥沙量是250 m L的1.61~2.94倍;灌溉次数与负压吸泥量成正比,灌溉次数为16次的内部泥沙量是8次的3.48~5.41倍;在同一灌溉次数的条件下,灌水间隔长度与负压吸泥量成正比。4保水剂能够有效阻隔泥沙进入灌水器内部,在添加了保水剂的灌水器中,其内部未出现负压吸泥的现象。     

落叶松人工林林分极限密度确定方法的研究

为研究林分密度动态变化规律提供一个理论参考水平，且为合理经营森林提供一咱确定林分极限密度的较佳方法，本文对长白落叶松人工林为研究对象，在设置的３６块标准地上采用重复抽样的方法，每块标准地随机抽取２０个样方，在保证各样方株数分布为正态分布的前提下，引入顺序统计量分布的理论。采用抽象化的方法确定各标准地的林分极限密度。利用Ｒｅｉｎｅｋｅ公式ｌｎＮ－Ｋ＋     

The mean tree mass–stand density index relationship for forest stands in China

Most traditional studies of mean tree mass (MTM)– density relationships focus on crowded stands, without considering stands characterized with canopy gaps. We developed a model to estimate MTM of closed and unclosed forest stands based on stand density index (SDI). Data were obtained from eight forest stands in China to test the generality of this model. MTM was accurately expressed in terms of SDI by combining the equations for SDI and Yoda's model, and exponents of the MTM–SDI relationship ranged from –2.23 to 1.93. Compared with density, SDI is a better predictor of MTM, regardless of the degree of canopy closure in the stands.     

基于SDI校正指数的滨海平原盐渍化生态风险评价

为了研究滨海平原区土壤盐渍化风险情况，本研究以黄骅市为研究区，将Landsat 8夏季遥感影像获得的SDI（盐渍化植被监测指数）校正指数作为生态终点，采用相关性分析法筛选土壤生产潜力和土壤健康方面指标，最终选取含盐量、电导率及有机质、K⁺、Na⁺、Mg²⁺、SO₄^2-、Cl^-含量8个指标，借助SDI指数标准化校正的灰色关联度法构建盐渍化生态风险评价模型，对滨海平原区盐渍化生态风险进行定量评价及空间分析。结果表明：研究区内盐渍化生态风险值介于0.24~0.73，均值高达0.42，其中99.25%的区域处于中度及以上盐渍化生态风险水平，整体上土壤生态风险较高，呈现东部沿海高、西部平原低的趋势；盐渍化生态风险评价在空间上与土壤含盐量、土壤电导率较为相似，因此，土壤含盐量及电导率对盐渍化生态风险评价起主导作用。研究区内盐渍化生态风险及评价因子的空间分布可为生态环境、农业健康持续发展、地下水的限采禁采、土壤改良和盐渍化防治提供参考依据。