Nitrogen leaching during sprinkler irrigation of a Dutch clay soil

Short-circuiting, which is vertical movement of free water through large continuous pores in an unsaturated soil matrix, was measured in the field in large columns from a cracked Dutch clay soil. The columns had been fertilized with chemical nitrogen fertilizer at a rate of 80 kg N ha^?1. Sprinkler irrigation (with an average intensity of 18 mm h^?1 and applied quantities varying from 8 mm to 22 mm) resulted in strong nitrogen leaching from the columns. Losses, which averaged 30%, resulted from mass-flow due to short-circuiting. Redox measurements suggested that no denitrification occurred. Application of only 6 mm of water slightly reduced nitrogen losses to approximately 15%. Losses could be reduced to 8% by applying the fertilizer to a wet soil surface which had just been sprinkled, and by sprinkling again the next day. In that way, the fertilizer grains dissolve and nitrogen diffuses into the surface soil, allowing less nitrogen movement along the soil surface towards the vertical cracks during the next sprinkling.     

Seasonal movement of salts in naturally structured saline-sodic clay soils

Seasonal changes in the distribution of salt and water in fields of both arable and grassland saline sodic clay soils were studied under temperate rainfed conditions. Leaching of the topsoils during winter rains was further investigated in soil columns. The field studies indicated the cyclical nature of leaching. During winter rains the water moving through the macropores uniformly leached salt from the soil profile to a depth of 1.2 m, but in late summer the salt content of the grassland and arable soils had increased again by 11% and 35% respectively compared with their early spring salinity levels. The results indicated that the salt leached in winter was mainly not lost, but leached below 1.2 m, only to rise again as the soil profile dried in the summer. The implications for managing and reclaiming these soils with gypsum are discussed.Undisturbed grassland topsoils were slow to release salt into the leaching water, maximum salt concentration in the leachate only being reached well into the winters rains. In disturbed arable soils the maximum leachate concentration was achieved shortly after leaching commenced. The changes in surface structure brought about by rainfall impact on bare restructured ploughlayer soils caused a significant decline in leaching efficiency (up to 40%).The observed pattern of leaching questions the validity of the basic assumptions used in most of the mathematical leaching models.     

Image processing-based study of soil porosity and its effect on water movement through Andosol intact columns

The soil pore network and marcoporosity are important factors affecting water and solute transport. The transfer of contaminants to water resources is of particular importance in the Valle de Bravo watershed as it provides 10% of the drinking water for the 20 million inhabitants of Mexico City. This watershed is composed mainly of Andosols with unique mineralogical and physical characteristics. Soil porosity is usually examined on thin sections, using various image analysis techniques. We propose a novel methodology combining image analysis and a displacement experiment to study relationships between soil structure and water tracer transport parameters. H₂¹⁸O displacement experiments were conducted through intact soil columns sampled at three depths from a representative cultivated Andosol profile. The soil structure and pore characteristics were obtained by image analysis on thin sections obtained from each column at the end of the displacement experiment. The total 2D porosity (for pores larger than 50 μm) varied from 80% of the total section area in the topsoil to around 60% in the subsoil. Tubular pores were the most abundant in the soil profile, but ploughing of the topsoil had destroyed sections of these pores and replaced them with packing pores. Water transport in the intact subsoil columns was always in physical non-equilibrium, showing the existence of preferential flow pathways. In the topsoil, one column out of three showed no preferential flow, demonstrating that soil ploughing also homogenised pore connections. Pore connectivity was larger in the ploughed topsoil than in their deeper soil horizon counterparts. Our methodology offers a 2D quantitative characterisation of the macroporous network at 50 μm resolution and the determination of water transport parameters on the same intact soil samples. 3D characterisation of soil porosity using X-ray computed tomography (CT) gives a better picture of pore connection but usually has lower spatial resolution and a larger cost.     

The effect of microorganisms,salinity and turbidity on hydraulic conductivity of irrigation channel soil

The introduction of polysaccharide producing benthic algae and bacteria could provide a low cost technique for seepage control in irrigation channels. The ability of algae and bacteria to produce polysaccharides proved to be successful in reducing the hydraulic conductivity of irrigation channel soil. Hydraulic conductivity was reduced to less than 22% of its original value within a month of inoculating soil columns with algae. Chlorophyll and polysaccharide concentrations in irrigation channel soil were measured in order to assess the growth of algae and extent of polysaccharide production, and their correlation with hydraulic conductivity of channel soil. Increases in polysaccharide occurred in the top layer (0–5 mm) of the soil column. The reduction of hydraulic conductivity was highly correlated with the amount of polysaccharides produced (r ² = 0.92). Hydraulic conductivity decreased with increasing algal and bacterial numbers. The first few millimetres of the soil core where microbial activity was concentrated, seemed effective in controlling seepage. Incorporation of extra nitrate and phosphate into algal medium did not increase the production of polysaccharides by algae in channel soil. The effect of salinity and turbidity of irrigation channel water on channel seepage was studied by measuring the effects on hydraulic conductivity of channel soils. When the electrical conductivity (EC) of the water increased above a threshold value, the hydraulic conductivity increased because of the flocculating effects on clay particles in channel soils. A relationship between sodium adsorption ratio (SAR) and EC of the channel water was established which indicated 15% increase in channel seepage due to increases in salinity. Increasing the turbidity of irrigation water (by increasing the concentration of dispersed clay) resulted in lowering the hydraulic conductivity of the channel soil due to the sealing of soil pores by dispersed clay particles. When the turbidity of the water was 10 g clay l^–1, the hydraulic conductivity was reduced by 100%. An increase in clay concentration above 1 g l^–1 resulted in significant reduction in hydraulic conductivity. Soil bowl experiments indicated that clay sealing with a coating of hydrophobic polymer on the surface could also effectively prevent seepage of saline water.     

鄂尔多斯景观格局演变与景观生态网络优化研究

以鄂尔多斯市为典型研究区，以2000、2005、2010、2015、2018年研究区景观格局数据和气象水文数据为研究素材，基于复杂网络理论、景观生态学和GIS空间分析技术，定量研究鄂尔多斯市景观格局的时空演变规律，并探究各级子流域的水源涵养深度，再将研究区景观格局演变数据和生态水文数据与由多个决定景观特征的因子构建的景观生态网络进行耦合分析，为研究区景观格局优化及生态环境建设提供参考。结果表明：在研究期内鄂尔多斯市的耕地不断减少，林地、草地、水域和建设用地均有一定程度的增加；景观演变主要是耕地、林地和水域之间的转化，林地、水体的景观演变最为剧烈，耕地、草地和建设用地相对平稳；鄂尔多斯地区整体水源涵养能力偏低，相对而言，东部地区的水源涵养能力高于西部地区，随着时间的推移，水源涵养深度高值逐渐南移；构建的鄂尔多斯市景观生态网络共342个生态节点、402条生态廊道，基于度低者优先的增边策略增加了119条廊道；优化后的网络连通度和连通鲁棒性均明显提升，网络中生态流更为畅通。     

Deep percolation during prolonged ponding of a swelling soil,and the effect of gypsum treatment

A sodic clay soil (a Vertisol) was instrumented from a 5 m deep pit to avoid the problems of preferential cracking around surface installations. Infiltration rates and changes in water content and vertical swelling at a number of depths in the soil profile were measured during prolonged ponding (139 and 160 days on separate plots). Essentially no deep percolation in one plot contrasted with a substantial amount (6.6 mm day^?1) in the second, gypsum-treated plot, with obvious consequences for changes in ground-water level. A method of calculating deep percolation is presented which takes into account the effects of swelling.     

京津冀地区耕地质量空间分布分形机制研究

为了进一步推进京津冀耕地规划统筹和协调配置,实施耕地质量空间管制与全面提升机制,保障京津冀协同发展的耕地资源需求,采用GIS技术、分形理论、灰色关联度分析相结合的方法,系统研究京津冀耕地质量空间分布分形特征及其机制。主要结论为:京津冀耕地质量在空间上呈现规律分布的态势,具有南北差异明显、南高北低、区域边缘低、中间高的特征;分形理论可以用于京津冀耕地质量空间分布的结构特征研究,分形特征反映了京津冀耕地质量类型的空间形态复杂性和空间占据度。京津冀高等地空间结构最简单,形态最稳定,空间占据度在自然质量水平上最高,在经济质量水平上最低;中等地的空间结构和稳定性居中,但空间占据度最大;低等地空间结构复杂度、空间形态稳定性和空间占据度与高等地完全相反。影响京津冀耕地质量分形特征的主要因素是光温/气候等自然条件,农业生产条件和社会经济条件在此基础上进一步扰动了其分形特征。     

Grapevine cv. ‘Riesling’ water use in the northeastern United States

Vine water use was measured in a Vitis vinifera cv. Riesling vineyard located in New York. Vines were fully irrigated and were trained via vertical shoot positioning giving a narrow curtain intercepting about 30% of the incident light during the sunlight hours. Vine water use was estimated on six vines by sap flow gauges directly calibrated with whole canopy transpiration measurements. The regression analysis between estimates of transpiration showed that there were large differences between vines in the calibration values obtained. Sap flow monitoring started late in June, about 2 weeks after bloom, when the canopy already filled the trellis system, and continued until October. Results showed that vine water use during most of the summer days was between 1.0 and 2.0 mm day⁻¹, with peak values around 2.5 mm. The basal (e.g. vine transpiration/reference evapotranspiration) crop coefficient (K _cb) varied somewhat between days, but it was quite stable during the whole season. Averaged over the entire experimental period, the K _cb was 0.49. Some of the day-to-day variation in the K _cb was negatively related with daily average air vapour pressure deficit. This suggests that reference evapotranspiration models on grass may not be fully accurate for vines under these experimental conditions.     

保水剂底施对沙子剖面水分和硝态氮运移的影响研究

【目的】解决沙土地区漏水漏肥的核心问题,建立保水防渗漏新技术体系,促进沙土地区农业可持续发展。【方法】基于保水剂的吸水保肥等物理化学特点,以保水剂和土壤混合物底施为技术方法,选用聚丙烯酸钠和壤土为材料,采用沙柱模拟试验,研究了不同施用厚度的保水剂-土壤混合物对剖面水分运移及硝态氮淋洗的影响。【结果】聚丙烯酸钠在壤土中的质量分数为1%时,可以对水分有效截流;混合物底施,以0.9～1.5 cm厚度为最佳;淋溶试验表明硝态氮主要集中在表层和保水剂层,占比为87.2%,有效防止了硝态氮的下移。【结论】保水剂壤土混合物底施,可以起到显著的水分养分截流作用,本试验中聚丙烯酸钠质量分数1%及1 cm厚度时,可获得较好效果。     

The transport of chloride and non-diffusible solutes through soil

Summary The mean velocity at which water flowed through large undisturbed cores of soil was determined from the breakthrough of surface-applied Cl^–, using a transfer function based on the normal distribution of the logarithm of cumulative drainage. For soils ranging in texture from sandy loam to silty clay loam, mean pore water velocities varied from 7 to 30 cm h^–1 for an input rate of 2 cm h^–1. Antibiotic-resistant Escherichia coli applied to the soil surface appeared to be transported through large pores only (> 10–15 m diameter), and the relative concentration in the effluent (C/C₀) did not change significantly with effluent volume. Mean C/C₀ values for E. coli in these soils, which ranged from 0.003 to 0.94, could be predicted from the mean pore water velocity derived from Cl^– transport.     

玉米深松全层施肥精量播种机关键部件的设计

设计一种玉米深松全层施肥精量播种机,该机具进地一次可完成深松、全层施肥、精量播种、覆土和镇压等多项作业。同时,在介绍整机的基础上,对深松铲和可调全层施肥装置进行了研究设计。通过试验得出:当导肥槽与地面的角度为55°、导肥管与竖直方向的角度不超过45°时,全层施肥效果较好;通过调整施肥调整片,可以达到最佳的全层施肥效果。     

旱塬区新增耕地质量和粮食产能影响因素分析——以占补平衡项目为例

为揭示渭北旱塬区耕地占补平衡项目对粮食产能的影响,以冬小麦和春玉米为量化标准,采用Logistic回归模型,对典型的渭北旱塬区千阳县2017年占补平衡项目新增耕地粮食产能影响因素进行研究;同时,对项目实施前后新增耕地土壤理化性质变化进行分析.结果表明:通过占补平衡项目实施使新增耕地等级提升了1—2个等级,且新增耕地中水浇地面积占比越大,新增耕地等别越高,单位面积上水浇地较旱地的粮食产能提高率增加25%.随着项目实施年限增加,土壤理化性质不断得到改善,总孔隙度、大团聚体、水稳性团聚体和微团聚体均显著变大(P<0.05),土壤结构破坏率显著减小(P<0.05),抗侵蚀能力显著提高(P<0.05).土壤有机质质量比显著提高(P<0.05),土壤养分状况不断改善.新增耕地的面积、等别、基础设施、单位面积投资、年限等因素均与粮食产能之间呈现不同程度的正相关关系;各因素对新增耕地粮食产能影响程度,按因素排序由大到小表现为等别,面积,基础设施,年限,投资.     

Changes in hydraulic conductivity of soils varying in calcite content under cycles of irrigation with saline-sodic and simulated rain water

Soil infiltration problems occur as a result of alternating irrigation with saline-sodic waters and monsoon rainfall. Hydraulic conductivity (K) and related soil properties of a non-calcareous (CaCO₃ 0.8%) and a calcareous soil (25.7%) having similar textural constituents were monitored. The soils were subjected to six consecutive cycles of irrigation with saline waters (SW) of sodium adsorption ratio (SAR), 10, 20 or 30 (mmol/l)^1/2, but of similar electrolyte concentration (EC; 80 mEq/l), and each followed by simulated rain water (SRW) (electrical conductivity <0.02 dS/m). Results are presented in terms of relative K i.e. K _r=K _sw/K _tw where K _tw is steady state K measured separately under application with tap water (ECw 0.54 dS/m, SAR 0.9). For irrigation with SW alone, K _r values were reduced to 0.95, 0.79 and 0.70 at SAR of 10, 20 and 30, respectively, in non-calcareous soil. The corresponding values of 0.95, 0.87 and 0.79 were slightly higher in calcareous soil. Severe reductions in K _r were observed in both the soils when subjected to alternate use of SW and SRW (K _r=0.22, 0.03 and 0.02 in non-calcareous, and 0.57, 0.17 and 0.07 in calcareous soil). About half of the reductions in K _r were reversible when SW was subsequently applied. Depth distributions of salinity, pH, dispersible clay and hydraulic head indicate that disaggregation and dispersion of surface soil was the cause of reduced K with SRW, whereas “washed in” sub-soil became restrictive and controlled the K values with SW under alternations of SW and SRW. Salt release (<1 mEq/l) was insufficient to avoid dispersion and sustain K even in the calcareous soil. For evaluating the infiltration hazard of saline-sodic water, measurements of stabilized K values after consecutive cycles of SW and SRW should serve as a better diagnostic criteria under monsoonal climates than threshold EC–SAR combinations. Received: 8 June 1998     

Cation exchange,hydrolysis and clay movement during the displacement of saline solutions from soils by water

Deterioration of soil physical conditions occurs when rain or irrigation water displaces soluble salts during reclamation and subsequent management of salinesodic soils. Damage, which depends primarily on the presence of exchangeable Na⁺, appears to be ameliorated during leaching by exchange of Ca²⁺ and Mg²⁺ for Na⁺ and loss of exchangeable Na⁺ by hydrolysis. The extent of these processes has been measured by leaching columns of repacked soil with water after preparation with Na⁺ and Ca²⁺ or Na⁺ and Mg²⁺ as the exchangeable cations and high or low (1 or 0.1 mol_cl^–1) initial salinities. Structural deterioration was monitored by changes in flow rate, and soil properties were measured both initially and after cutting the leached columns into layers. Preliminary studies established reliable methods for measuring exchangeable cations and cation exchange capacity in the saline soils. In a sandy loam (Na-Ca system), clay dispersion and movement occurred particularly in the upper layers as measured both by decreases in CEC and by the amount of clay in the leachate. Cation exchange and hydrolysis of exchangeable Na⁺ during leaching reduced the exchangeable Na⁺ percentage, although cation exchange was restricted to columns with high initial salinity. In a clay textured soil (Na-Ca system) there was negligible clay movement, and cation exchange and hydrolysis occurred in columns with both high and low initial salinities: cation exchange may have been encouraged by diffusion limited preferential release of Na⁺ from aggregates during by-pass flow. In the sandy loam (Na-Mg system) Mg²⁺ increased the preference of the soil for exchangeable Na⁺ compared to the Na-Ca system. There was no cation exchange even in columns with high initial salinity. The amounts of clay movement and hydrolysis were similar in the two systems. Conditions conductive to cation exchange are a high initial salinity, a Na-Ca rather than a Na-Mg system and, possibly, restricted release of the divalent cation from within soil aggregates. Attempts to model these changes are complicated by difficulties in predicting the effects of hydrolysis and by-pass flow.     

基于宜耕性评价的耕地利用效率分区与提升路径

在宜耕性的基础上,为合理提高耕地利用效率、加强生态文明建设和资源可持续利用,以原阳县为例,综合考虑耕地利用效率与宜耕性评价结果,对耕地利用效率进行分区,提出各区域耕地利用效率提升路径。结果表明：从耕地利用效率来看,原阳县耕地利用整体水平不高,其综合效率均值为0.837,纯技术效率和规模效率均有较大的提升空间;从宜耕性评价结果来看,原阳县耕地的适宜宜耕区、基本适宜宜耕区、低适宜宜耕区、流域保护区面积分别占耕地总面积的37.84%、41.36%、19.09%、1.71%,整体宜耕性较强。叠加组合耕地利用效率和宜耕性评价结果,将原阳县耕地利用效率分为保持区、提升区、调整区、保护区。从可持续利用和生态保护角度考虑,结合差异化的整治措施,保持区宜耕性和耕地利用效率均较高,应以维持现有耕地利用效率、延伸耕地的生态和经济价值为重点;提升区宜耕性强、耕地利用效率较低,应通过规模化经营最大限度地提高其有效利用效率;调整区宜耕性差,不宜提升耕地利用效率,应发展生态农业或设施水培农业,在提高耕地经济效益的同时,缓解耕地与生态保护压力;保护区内耕地应逐步退出,充分发挥其湿地功能与生态功能。本研究可为耕地资源的可持续利用提供决策参考。     

黄土丘陵区退耕还林土壤不同大小颗粒固碳过程与速率

为揭示黄土丘陵区退耕还林土壤固碳过程及其变化机制,采用物理分组法探讨了安塞纸坊沟退耕15~45 a刺槐与柠条林地土壤砂粒、粉粒、黏粒截存有机碳的效应与速率。结果表明,对比坡耕地,两种退耕林地土壤颗粒结合碳含量均随退耕年限延长显著增加,并且表层0~10 cm土壤增幅最高,10~60 cm各土层增幅基本接近。退耕15~45 a期间,刺槐与柠条林0~20 cm土层均以粉粒碳密度增速最高,分别达0.21、0.11 Mg/(hm2·a),砂粒碳和黏粒碳增速相近,平均分别为0.13、0.06 Mg/(hm2·a)。同样的变化发生在0~60 cm土层,但各颗粒碳密度增速为0~20 cm土层的1.6~2.5倍。按此增速到退耕45 a时柠条林地砂粒碳、粉粒碳、黏粒碳相比坡耕地分别增大了2.6、1.1、0.8倍,刺槐林地则分别增大了8.3、2.2、2.8倍,并且对总有机碳累积贡献的平均比率为:砂粒碳(23%)等于黏粒碳(26%)且均小于粉粒碳(51%)。此外碳库管理指数比碳库活度与土壤总有机碳库变化有更显著的线性相关性。综上分析,该区域退耕刺槐林比柠条林土壤有更强的固碳效应,两种林地均以粉粒碳为主要固碳组分,以砂粒碳周转速率最快。     

基于SWAT模型的金华江上游土地利用变化对径流影响的研究

流域内土地利用变化对水文循环有着重要影响.本文通过在金华江上游建立SWAT模型,模拟了不同土地利用情景下流域径流的变化特点,结果表明:SWAT模型模拟精度高,其中验证期Ens=0.85,R2=0.85,Re=0.07,可以模拟及分析流域水文对土地利用变化的响应;在该流域内,林地有减少径流量的作用而草地和耕地相反;保护耕地使流域内农业产量增加但也使径流量增加,且增加量集中在雨季.     

A scaling based estimation of soil unsaturated hydraulic properties at a field scale

This paper deals with the prediction of the soil water retention h(S) and the soil unsaturated hydraulic conductivity K(S) functions of a clay-loam soil at a field scale (1 ha) where the variable S represents water saturation. The Van Genuchten model and the corresponding Mualem-Van Genuchten model were used to predict h(S) and K(S) functions respectively. The field data (tensiometric and neutron probe measurements) used in this study were provided by the soil water balance (four neutron sites, 0.35 to 1.55 m soil layer) of a soybean crop over a 78 days growing season. The advantages of the scaling approach for describing the field variability of the h(S) function were confirmed. The scaling approach accounted for 73% of the field variability of the soil matrix potential. A simple procedure was proposed in order to predict the K(S) function using scaling theory. This was done by simultaneously applying a ``zero flux method' and ``deep flux method' to compute the soil water balance and fit the saturated hydraulic conductivitiy (K _sat), the only unknown parameter in K(S). Received: 15 November 1995     

植被恢复类型对土壤物理性质的影响研究

应用空间代替时间的方法研究了盐池县天然草地、人工封育草地、撂荒地、退耕还草地、固定沙地5种不同植被恢复类型的土壤物理性质和水分变化。结果表明,灌草结合的人工封育草地、退耕还林地和固定沙地在降低土壤密度方面优于草本为主的天然草地和撂荒地。不同植被恢复类型的土壤孔隙度差异显著,根系垂直分布较好的植被对深层土壤有较好的改良作用。封育、退耕还林等人工植被恢复措施能够降低土壤密度,增加孔隙度,改善土壤结构和物理性状,但在改良土壤质地方面还需要时间的累积。不同植被恢复类型的土壤水分变化迥异,这与土壤密度、孔隙度和质地等物理性质以及植被类型和分布密切相关。     

Effect of water quality on soil structure and infiltration under furrow irrigation

The quality of irrigation water has the potential to significantly affect soil structural properties, infiltration and irrigation application efficiency. While the effect of electrolyte concentration (as indicated by the electrical conductivity EC) and sodium adsorption ratio (SAR) have been studied under laboratory conditions, the effect on soil profile structural properties and irrigation performance have not been widely investigated under field conditions. In this paper, water with three different levels of sodium (SAR = 0.9, 10 and 30) was applied as alternative treatments to a clay loam soil. The application of 238–261 mm of medium- to high-SAR water was found to reduce aggregate stability, increase the bulk density of both the surface crust and underlying soil, and reduce the total depth of infiltration and final infiltration rate. Where low-SAR water was used, there was no significant (P<0.05) difference in final infiltration rate after the first four irrigations. However, where moderate- and high-SAR water was applied after the first four irrigations with the low EC-SAR water, the final infiltration rate was found to decrease on each of the successive irrigation events. For the moderate- and high-SAR treatments, this suggests that a steady-state equilibrium had not been reached within that part of the soil profile impeding infiltration. It is proposed that the initial reduction in infiltration is related to the physical processes of slaking leading to the development of an apedal, hardsetting surface soil layer. Similarly, it is proposed that the subsequent increase in bulk density and decline in infiltration where moderate and high EC-SAR water is applied is due to an increase in clay tactoid swelling reducing the size of the conducting micropores, dispersion blocking pores, and/or an increase in the thickness of the apedal surface layer. The reduction in infiltration associated with the use of high-SAR irrigation water was found to reduce the performance of the irrigations, with the application efficiency of the final irrigation decreasing from 40% where the low-SAR water was used, to 21% where the high-SAR water was applied. The implications for surface irrigating with water containing high sodium levels are discussed.Communicated by A. Kassam