不同尺寸蒸渗仪测定作物蒸散的田间试验研究

称重式蒸渗仪测定作物蒸散量（ET）是公认的一种标准测定方法。大型称重式蒸渗仪因单点独立安装而无法进行不同处理的重复试验,小型蒸渗仪则可解决该问题,但目前对于小尺寸蒸渗仪的适用性尚无统一结论。本文利用1m2（SL）、2m2（ML）和4m2（LL）3种不同面积的蒸渗仪在冬小麦（2012年11月21日播种,2013年6月20日收获）和水稻（2013年6月22日移栽,2013年10月28日收获）整个生长季进行连续蒸散量观测,筛选无有效降水日的数据进行对比分析。结果表明：（1）在冬小麦和水稻生长季内,SL（小）蒸渗仪所测蒸散量日内变化均表现出较大的变化幅度,ML（中）蒸渗仪所测蒸散量日内变化趋势均与LL（大）蒸渗仪所测一致,日内变化比较平稳;（2）ML蒸渗仪所测日蒸散量与LL所测结果的相关性最好（P<0.01）;（3）SL蒸渗仪所测水稻日平均蒸散量和蒸散总量与LL接近,所以可将SL蒸渗仪替代LL测定水稻日平均蒸散量和蒸散总量;ML所测冬小麦和水稻的日平均蒸散量及蒸散总量均比LL明显偏小,蒸散总量偏小主要由于拔节后较大的日蒸散量偏差导致。     

Environmental effects on soil NO concentrations and root N uptake in beech and spruce forests

This study aimed to investigate the shifts in net nitrogen (N) uptake and N compounds of fine roots over the vegetation period (i.e., spring, summer, autumn) and correlate this with NO concentration in the soil. Soil NO concentration was measured using gas lysimeters for collection and a chemiluminescence analyzer for quantification. Net N uptake by the roots was determined using the ¹⁵N enrichment technique. N pools were quantified using spectrophotometric techniques. Soil NO concentrations at beech and spruce forest sites were highest in spring (June), and lowest in winter (December). Total N of the roots was similar during the seasons and between the two years under study despite considerable variation of different N compounds. Net N uptake generally increased with higher N supply. Correlation analysis revealed a positive relationship between soil NO concentration and net N uptake only for spruce trees. This relationship seemed to be modulated by environmental factors and tree species.     

大型蒸渗仪的设计、建造与安装（英）

蒸渗仪是用来研究营养元素在农田中的运移的系统,本文系统描述了一种大型蒸渗仪的设计,建造与安装。试验采用湖北地区典型土壤类型黄棕壤与潮土,在华中农业大学校园内每种土壤安装16个大型蒸渗仪。蒸渗仪采用减少土柱的扰动的方法建造,并填充凡士林减少土壤水分的边缘流动。蒸渗仪采用外径630 mm高700 mm厚10 mm的PVC管作材料。土柱建成后安装在预制PVC底座上,底座中间有一圆孔外接淋失液收集装置。淋失液收集后用来测定淋失液离子含量。试验结果表明,相同土壤土柱之间淋失量差异不显著,没有检测到水分的边缘流动;同时建设效率高,费用低。     

微型蒸发器测量精度的影响因素试验

为优化微型蒸发器（MLS）的使用方式及提高测量精度,在15 d不更换筒内土体的情况下,采用田间试验的方法对影响其测量精度的多种因素进行了研究。结果表明：各处理精度均较高,最高达97.40%;内筒打孔与否对测量精度无显著影响;套筒打孔的处理比不打孔的处理精度更高,且孔洞适宜均匀分布,但数目不可过多,直径为3 mm时不宜超过36个;套筒封底会降低测量精度,内筒封底材料越薄、透气性能越好精度越高;内筒与套筒的间隔较小时精度更高。对露水进行的考察显示,夜间的露水会明显降低测量精度,当其凝结量大于土壤蒸发量时,无法利用MLS精确测出土壤蒸发量。测量精度随时间变化而相应改变,MLS刚装入土体后的前3 d土壤水分较大,精度比其后各日都低。在有适量水分补充的情况下,15 d不更换MLS筒内土体可行。     

Tomato Production and Soil Salt Distribution under Line-Source Trickle Irrigation1

Yield of red cherry tomatoes and soil salt distribution as affected by different amounts and salinities of irrigation water was studied in a field plot experiment during the summer of 1988 at Utah State University. Four different amounts of fresh water and two amounts of saline water were imposed with line source trickle irrigation on a sandy loam soil in lysimeters. Tomato yield and seasonal evapotranspiration increased in a linear fashion with increasing irrigation water. Tomato yields with fresh water (EC = 0.33 dS/m) were significantly higher than with saline (EC = 4.0 dS/m) water. There were no significant differences in seasonal evapotranspiration between the two salinity levels with two levels of deficit irrigation. Soil water depletion and availability decreased as the soil water salinity increased. Soil water salinities increased with both vertical and horizontal distance from trickle lines and reached a maximum at the bottom of the wetted area and between trickle lines.     

Effects of past and current crop management on soil microbial biomass and activity

Because soil biota is influenced by a number of factors, including land use and management techniques, changing management practices could have significant effects on the soil microbial properties and processes. An experiment was conducted to investigate differences in soil microbiological properties caused by long- and short-term management practices. Intact monolith lysimeters (0.2 m² surface area) were taken from two sites of the same soil type that had been under long-term organic or conventional crop management and were then subjected to the same 2.5-year crop rotation [winter barley (Hordeum vulgare L.), maize (Zea mais L.), lupin (Lupinus angustifolius L.), and rape (Brassica napus L. ssp. oleifera)] and two fertilizer regimes (following common organic and conventional practices). Soil samples were taken after crop harvest and analyzed for microbial biomass C and N, microbial activity (fluorescein diacetate hydrolysis, arginine deaminase activity, and dehydrogenase activity), and total C and N. The incorporation of the green manure stimulated growth and activity of the microbial communities in soils of both management histories. Soil microbial properties did not show any differences between organically and conventionally fertilized soils, indicating that crop rotation and plant type had a larger influence on the microbial biomass and enzyme activities than fertilization. Initial differences in microbial biomass declined, while the effects of farm management history were still evident in enzyme activities and total C and N. Links between enzyme activities and microbial biomass C varied depending on treatment, indicating differences in microbial community composition.     

Deforestation effects on soil degradation and rehabilitation in western Nigeria. IV. Hydrology and water quality

Hydrological and water-quality measurements were made on a 44·3 ha watershed under forest cover and following deforestation and conversion to an agricultural land-use. Under secondary tropical rainforest, water yield ranged from 2·2 per cent to 3·1 per cent of annual rainfall. Deforestation of 7 per cent of the watershed area increased water yield to 7·0 per cent of annual rainfall. Baseflow increased with deforestation, and increased progressively with time after deforestation. It was 5·1 per cent of annual rainfall in 1979, 15·1 per cent in 1980, 16·4 per cent in 1981 and 17·9 per cent in 1982. In comparison, surface flow was 4·5 per cent in 1979 and 6·2 per cent in 1980, but decreased to 2·3 per cent in 1981 and 2·4 per cent in 1982. Total water yield following deforestation and conversion to agricultural land-use ranged from 9·6 per cent to 21·3 per cent of the annual rainfall received. The dry season flow decreased with time as the dry season progressed, but increased over the years following deforestation. Surface runoff during the rainy season depended on ground cover and soil quality. The extent and severity of soil degradation affected the dynamics of surface flow. Because of actively growing crops, plant nutrient concentrations in surface runoff were low. Forested lysimeters had higher seepage losses than cropped lysimeters, and the water-use efficiency was 1·9–3·6 kg ha⁻¹ mm⁻¹ for cowpeas compared with 6·1–11·0 kg ha⁻¹ mm⁻¹ for maize. The delivery ratio was high immediately after deforestation and decreased to a steady value of about 3·2 per cent within 7 years. The data show five distinct phases of soil degradation in relation to generation of surface runoff. © 1997 John Wiley & Sons, Ltd.     

LG-I型称量式蒸渗仪自动监测系统

为了方便有效地测定植物的蒸散,同时也为水分利用研究提供测试精度高、稳定性好的简单易用的仪器,开发研制了LG-Ⅰ大型自动称量式蒸渗仪监测系统。此系统采用自行研制的高精度弹簧、高精度SQC-A500 kg悬臂梁传感器、垂直升降调整支架和计算机软件控制处理程序。该仪器应用结果表明：与国内使用的同类蒸渗仪相比,其具有测试精度高、性能稳定、重复性好的特点,仪器最大绝对误差为±25 g（相当于0.012 mm水柱）,最大相对误差0.7%,完全可以满足实际应用的技术要求。此系统的测定值较好地反映了植物在短时段内的土壤水分蒸散变化情况,是一种比较方便实用的测定盆栽植物蒸散的仪器。     

Nitrogen Leaching Of Spring Wheat Genotypes (Triticum Aestivum L.) Varying In Nitrogen-Related Traits

Efficient use of nitrogen (N) by wheat crop and hence prevention of possible contamination of ground and surface waters by nitrates has aroused environmental concerns. The present study was conducted in drainage lysimeters for three years (1998–2000) to identify whether spring wheat genotypes (Triticum aestivum L.) that differ in N-related traits differ in N leaching and to relate parameters of N use efficiency (NUE) with parameters of N leaching. For this reason two spring wheat cultivars (‘Albis’ and ‘Toronit’) and an experimental line (‘L94491’) were grown under low (20 kg N ha^?1) and ample N supply (270 kg N ha^?1). The genotypes varied in parameters of NUE but not in N leaching. Grain yield of the high-protein line (‘L94491’) was, on average, 11% lower than that of ‘Toronit’ but among genotypes had significantly higher N in the grain (%), grain N yield, and N harvest index. Nitrogen lost through leaching was considerably low (0.42–0.52 g m^?2) mainly due to low volume of percolating water or the ability of the genotypes to efficiently exploit soil mineral N. There were no clear relationships between N-related genotype traits and N leaching, but across all treatments significantly negative correlations between volume of leachate and the amount of N in the total biomass and grain N yield existed.     

Determining fertilizer phosphorus requirement of upland rice

Abstract

Assessing the fertilizer phosphorus requirement (FPR) of crops is an important component of research for efficient and rational use of fertilizers. Soil and plant tests are used to determine the FPR of crops. Two methods were evaluated for determining the FPR of upland rice grown on an Ultisol in the humid forest zone of Cote d'Ivoire. The first method used a simple model based on P uptake using the equation: FPR=(Up‐U0)/PRF, where Up is P uptake at a given yield, Uo is P uptake from unfertilized soil, and PRF is the P recovery fraction of applied P. The parameters, U0, Up, and FPR were determined in field experiments for the rice cultivars grown on an Ultisol under rainfed upland conditions. The second method was based on the P applied, P uptake, and grain yield relationships for upland rice. First, P uptake at a given rice yield was determined from the relationship between total P uptake and grain yield. The amount of fertilizer P applied for the given P uptake and grain yield was then, determined from the relationship between P applied and P uptake. There was a good agreement between the observed values of FPR and the predicted values of FPR determined by the two methods. The results suggest that the simple model based on P uptake can be utilized for determining the fertilizer P requirements of crops.