Effect of Split Nitrogen Application on Growth and Yield of Wheat (T. aestivum L.) Genotypes with Different N-Assimilation Potential

A field experiment was conducted with different nitrogen regimes to assess the growth and yield performance of wheat genotypes which differ in nitrate assimilation potential. Genotypic differences in biomass accumulation were observed at different growth stages. The nitrogen treatment had little effect on biomass accumulation at early stages of growth, while at later stages of growth there was enhanced biomass accumulation when N was applied in more than two splits. On an average, genotypes with high nitrate reductase activity (the 'HNR' genotypes) accumulated 14.2 % more biomass than the genotypes with low nitrate reductase activity ('LNR' genotypes) when an extra dose (40 kg N ha⁻¹) of nitrogen was given at the time of anthesis. The application of nitrogen in more than two splits increased grain yield of both 'HNR' and 'LNR' genotypes mainly by increasing grain weight per ear. The application of an extra dose of nitrogen (40 kg N ha⁻¹) at the time of anthesis increased grain yield of 'HNR' genotypes by 38.5 % as compared to 'LNR' genotypes.     

The effects of stubble burning and tillage on soil carbon sequestration and crop productivity in southeastern Australia

Abstract. In Australia, stubble burning and tillage are two of the major processes responsible for the decline of soil organic carbon concentration in cropped soils, and the resulting soil degradation. However, the relative importance of these two practices in influencing the soil organic carbon concentration and the long-term impact on soil quality and productivity are not clear. The effects of stubble burning as practised by farmers in southeastern Australia were evaluated in two field trials, one of 19 years duration, the other of 5 years. Conventional tillage (three tillage passes) led to greater loss of soil organic carbon than stubble burning. Loss of total soil organic carbon attributed to stubble burning in the 0–10 cm layer was estimated to be 1.75 t C ha⁻¹ over the period of the 19-year trial, equivalent to 29% of that lost due to tillage. In the 5-year trial, no change in soil organic carbon due to stubble burning was detectable. Changes in soil quality associated with stubble burning detected in the longer trial included a reduction in macro-aggregate stability, and increases in pH and exchangeable K⁺. Only the latter two were detected in the shorter trial. A higher mean wheat yield (average 0.15 t ha⁻¹) following stubble burning was observed in the 19-year trial but not in the 5-year trial. Research to monitor the longer term effects of stubble burning is needed, and to identify conditions where loss of soil organic carbon is minimized.     

我国南方草地资源现状及其发展前景

根据我国南方地区自然资源特点、草地类型、利用现状等,总结、分析了南方草地资源的优势、发展潜力和目前所面临的实际问题,并有针对性地提出了不同类型草地资源草产业发展模式。     

标准校正法测定土壤中的全氟

为了探讨不同测定方法对土壤全氟测定结果的准确性,采用标准加入法对标准土样的全氟含量进行测定,并对分析结果和普通测量法的分析结果进行对比,指出了空白电位值对测定结果的影响,通过精确度计算、t检验以及回收率试验证明,标准校正法能消除空白电极电位漂移对分析结果产生的影响,提高了分析结果的精密度和准确度.     

辽宁省水稻新品种产量及产量结构与环境效应的方差分析

以辽宁省2004～2005年中晚熟水稻区试参试品种为试材,分析了水稻品种在不同试点的产量和产量结构的差异,方差分析表明:水稻品种产量的变化主要受环境效应影响,年份×地点互作效应是影响产量的主要随机因素。每穴穗数、每穗总粒数、成粒率、千粒重都与产量有显著线性效应,每穴穗数和每穗总粒数对产量的直接作用较大,每穗总粒数通过每穴穗数对产量表现为显著负向作用。     

甘蓝型油菜减氮增效潜力评价及种质资源筛选

为培育具有高潜力的减肥增效油菜品种,以不同甘蓝型油菜种质资源为材料,通过两年三点的田间肥效试验,研究了它们对氮肥的响应特征及节氮增产潜力.以产量平均值为分界线将供试材料划分为4种类型:低氮高效型、双高效型、双低效型和高氮高效型.在高氮条件下,双高效型和高氮高效型材料具有16.96％～36.50％的节氮潜力和21.57％...     

微分及其在理论力学中的应用

微分有两个含义:1.对于与时间有关的函数(称之为动态函数)f而言,微分df表示在无限小的时间dt内函数f的增加量,即df=f(t dt)-f(t);2.对于与时间无关的函数(称之为静态函数)g而言,微分dg表示g的微小部分,所有dg之和等于g。时间的微分即时间的增加量dt总是恒大于0的正实数。函数f的增加量df与时间的增加量dt之比称为函数f的增加率,而非变化率。函数f的减小量-df与时间的增加量dt之比称为函数f的减小率。变化率包括增加率与减小率两种情况。质点所受到的合外力等于它的动量的增加率。作用力与反作用力互为对偶力。保守力与势能梯度互为对偶矢量。势能定理即势能的减小量等于保守力所作的功。     

基于MaxEnt模型的柑橘木虱在西南地区潜在分布模拟

本研究应用生态位软件MaxEnt和地理信息系统软件ArcGIS预测柑橘木虱在西南地区的潜在地理分布范围,筛选影响柑橘木虱分布的关键变量。结果表明柑橘木虱在西南地区高适生区主要位于西藏东南部、四川中东部、重庆大部、贵州大部和云南中北部,总面积为52.03万km 2,占西南地区总面积的23.89%。影响柑橘木虱分布的关键变量为最冷月最低温度、最冷季度平均温度、最湿季度降水量、最暖季度降水量、最暖季度平均温度和最暖月最高温度。本研究不仅模拟了柑橘木虱在西南地区的潜在地理分布,更为该虫的分布与环境变量之间关系的研究提供了理论参考。     

封育草地与弃耕地土壤碳氮固持及固持速率动态

研究植被恢复对土壤碳氮动态的影响,对了解陆地生态系统碳氮循环,应对全球温室效应具有重要意义。本研究以黄土高原丘陵区封育草地和弃耕地为对象,分别以放牧草地和农田为参照,对比分析了封育14年草地和弃耕地0~300 cm土层土壤有机碳(SOC)和土壤全氮(STN)储量、固持量及固持速率。结果表明,封育草地和弃耕地显著增加SOC储量,并且二者封育14年后SOC储量相同;在0~200 cm土壤中,封育14年草地与弃耕地STN储量相对于对照并无增加,0~300 cm土壤中,封育14年草地STN储量显著高于弃耕地(P<0.05);弃耕地SOC固持及固持速率显著高于封育草地,封育14年弃耕地SOC固持主要发生在0~140 cm表层土壤;0~100 cm土壤弃耕地STN固持及固持速率显著高于封育草地,0~300 cm土壤弃耕地STN固持及固持速率显著低于封育草地。以上结果表明,封育和弃耕均可显著提高土壤碳储量,并未明显提升土壤氮储量,弃耕地有较高的SOC固持量及固持速率。