Simultaneous transport of surface salts and water through unsaturated soils during infiltration and redistribution

Abstract

Certain concepts regarding the simultaneous transport of surface ‐salts and water under transient unsaturated flow conditions vere verified for three soils using laboratory soil columns. Treatments included different water application rates (i.e., continuous ponding and controlled rates) and different initial soil water contents. Calcium chloride, spread on the soil surface to simulate a salt‐affected soil or broadcasting of a fertilizer (or other additive), was leached with chloride free water (0.01 N CaSO₄). Salt and water profiles were determined by destructive sampling at 2 cm depth intervals at two stages: (i) immediately following infiltration and (ii) after Batching infiltration plus redistribution time.

Immediately following infiltration as well as after matching infiltration and redistribution time, chloride was leached more efficiently and to relatively deeper depths with slower than with faster rates of water application only in sandy and sandy loam soils. The results, thus, show that slower rates of water application nay not increase leaching efficiency over faster rates in heavy‐textured and sodic soils with very poor permeability. Regardless of water application rate, initial soil water content, redistribution time and soil type, salt front (i.e., salt peak) did not coincide with the water front but lagged behind it by a few to several centimetres. That is to say that salt peak did not occur at a depth above which total soil water storage in the profile equalled cumulative infiltration. The higher the initial soil water content, the deeper and more complete was the displacement of chloride during infiltration for a given quantity of water applied at different rates. This trend was not modified during post‐irrigation period in sandy soil, but it was entirely reversed in sandy loam soil.     

Nitrogen fertilizer leaching from cropped and irrigated sandy soil in Central Turkey

Pollution of ground water caused by excessive and uncontrolled use of nitrogen fertilizer is worrying. A recent example of such pollution has been observed in an agricultural basin in the province of Nevsehir, Turkey, where up to 900 kg ha^?1 nitrogen fertilizer is used for growing potatoes in sandy soils under irrigation. Using nitrogen fertilizer in amounts that guarantee large yields without polluting ground water is essential. We present results of field experiments and numerical simulations involving ¹⁵N-labelled nitrogen fertilizer leaching. In the field, we monitored the movement of water and the distributions of nitrogen species within the soil–water–plant continuum. The detailed dynamics of the nitrogen cycle within the system were simulated. Simulations included calibration and validation of the nitrogen version of the LEACHM model (LEACHN, version 3) and long-term applications of the model. The model’s predictions of nitrogen fluxes under long-term use of fertilizer and irrigation were analysed. Nearly half of the applied ammonium-N was converted to nitrate-N during the growing season. With increasing additions of N the rate of plant uptake declined, while leaching increased significantly, and the fraction of nitrogen remaining in the soil profile increased only moderately. In long-term applications, a significant fraction of the applied fertilizer tended to accumulate after the first year in soil as the residual nitrogen not taken up by the crop. Accumulated residual nitrogen is converted to nitrate-N and leached rapidly from the soil profile during the wet season following the harvest. To reduce leaching of the residual nitrate, the rates, frequencies and timings of fertilizer application and irrigation must be scheduled in accordance with the plant growth periods and the hydraulic regime of the soil.     

华北平原水浇玉米-小麦轮作农田硝态氮的淋失

Soil water deep drainage and nitrate (NO3^-) leaching losses below the root zone were investigated in a 1 ha wheatmaize rotation field under traditional agricultural management that local farmers generally follow in the North China Plain, using the soil water balance method and NO3-N concentration in suction samples. Water drainage, and NO3-N distribution and leaching losses exhibited pronounced spatial and temporal variability. Soil water deep drainage and NO3- N leaching loss mostly occurred during the summer maize growing season (rainy season), which coincided with irrigations and significant rainfall. On average, soil water deep drainage was 39 and 90 mm in the 1998/1999 and 1999/2000 cropping years, correspondingly, accounting for 10% and 19% of the total irrigation plus rainfall, respectively. The NO3-N leaching loss from soil and fertilizer N below the root zone ranged from 6 to 17 (averaging 12) and 30 to 84 (averaging 61) kg N ha^-1 in 1998/1999 and 1999/2000, correspondingly, equivalent to 1.4%-4.1% and 7.3%-20.3% of N fertilizer applied,respectively. The results indicated that water and fertilizer inputs could be greatly reduced, thus improving water and nutrient use efficiency in this region.     

不同肥料运筹对夏玉米田间土壤氮素淋溶与挥发影响的原位研究

运用排水采集器法和通气法结合田间原位试验,研究了不同肥料运筹对夏玉米田间土壤氮素淋溶与挥发的影响。结果表明,在夏玉米生长季节,田间土壤水分淋溶体积达63.49～7.L/hm2,且表现与灌溉水量和降雨量正相关。与单施氮肥相比,有机肥配施氮肥在夏玉米生长发育前期易加剧水分的淋溶;氮素淋溶损失量明显高于氨挥发损失量,且二者均随施氮量的增加而升高;与单施氮肥相比,有机肥配施氮肥极显著地增大了氮素淋失量,减少氮素的氨挥发损失量,总体分析显示,有机肥配施氮肥极显著增大了氮素净损失量和氮素损失率;在夏玉米生长期内,施肥运筹的田间土壤淋溶水硝态氮浓度均呈现双峰趋势,以硝态氮形式淋失是田间土壤氮素淋失的主要形式,铵态氮浓度则呈现先升后降的趋势,铵态氮的累计淋失量很少。同时发现,大口期夏玉米生长旺盛,对氮素的需求强烈可以减少氮素的淋失和氨挥发损失,适量增加夏玉米大口期的追肥量,是提高氮肥利用效率的有效途径。     

华北平原农田裂缝对硝态氮淋溶的影响

土壤干缩开裂是常见的自然现象。目前关于土壤干缩开裂的研究主要集中于裂缝的最终形态特征,并且以室内试验为主。本研究通过室外大田试验,结合动态计算机图像分析及水氮运移模拟软件WHCNS,研究土壤干缩开裂的动力学过程、特征及其对农田水氮运移的影响。利用原位熔化石蜡浇筑得到了裂缝三维结构形态,借助三维激光扫描仪量化裂缝的几何特征,发现每平米裂缝平均长度为4.58m,裂缝上表面平均宽度为5.72 mm,平均深度为9.06 cm。基于三维扫描仪提取得到的裂缝几何参数,通过WHCNS仿真模拟,发现相较于无裂隙情况,裂隙的存在分别增加了传统施肥和优化施肥情况下97.40%和256.43%的硝态氮淋失量;与优化施肥模式相比,传统施肥模式更容易造成硝态氮的淋失风险。在模拟灌溉模式对硝态氮淋洗情况的影响时,其差异不明显;强降雨的设置同样增加了硝态氮的淋失风险,导致硝态氮的年均淋洗量增加83.61%。裂缝的存在严重影响农田作物对肥料的吸收和利用,通过优化施肥量、更改灌溉模式以及避免强降雨前施肥都可以减少肥料的损失。     

不同类型土壤引黄灌溉固碳效应的对比研究

通过在宁夏引黄灌区实地调查、采样与分析,研究5种类型土壤在不同灌溉耕作时间序列下土壤有机碳含量及碳密度的变化特征,对比分析不同类型土壤对引黄灌溉耕作固碳效应的差异。结果表明:灌溉耕作引起的土壤有机碳含量的变化因土壤类型的不同而存在差异;在相同的灌溉耕作时间下,5种类型土壤的有机碳密度大小顺序为:灌淤土>潮土>新积土>风沙土>淡灰钙土;与同类型未灌溉耕作的土壤比较,灌溉耕作使各类型土壤有机碳密度均有不同程度的增加,相同的灌溉耕作时间下土壤有机碳密度增幅排列次序为:风沙土>潮土>灌淤土>淡灰钙土>新积土。宁夏引黄灌区的土壤固碳效应因土壤类型的不同存在明显差异。     

不同淋洗方式下滨海沙性盐渍土改良效果

选择对滨海沙性盐渍土进行室内土柱模拟淋洗试验,采用连续淋洗与间歇淋洗2种方式比较不同淋洗方式下沙性盐渍土的改良效果。结果表明,淋出液矿化度随着体积变化急剧下降,直至稳定于很低的水平,连续淋洗与间歇淋洗淋出液矿化度分别从233.8,327.4g/L稳定至2.5,2.2g/L。间歇淋洗单位水量淋洗的盐分要高于连续淋洗。淋出液的各离子随体积变化趋势与矿化度变化相似;淋洗结束后土壤盐分变化显示,随着用水量的增加,淋洗效率逐渐降低,15,20,25,30cm水量下连续淋洗的淋洗效率分别为2.87,2.40,1.98,1.67g/ml;间歇淋洗的淋洗效率为3.10,2.48,2.00,1.68g/ml,间歇淋洗的淋洗效率始终要高于连续淋洗;由于各离子溶脱淋洗速率不同,改变了土壤中盐分离子组成,土壤由原来以Na+-Cl-型转变为以Ca2+-SO24-型。根据淋洗过程中土壤盐分变化与用水量之间的关系拟合出的淋洗曲线效果较好,相关系数分别为0.968和0.970。淋洗试验表明,间歇淋洗具有更高的淋洗效率,节水潜力要高于连续淋洗,由此得出的淋洗曲线可用于指导大田沙性盐渍土改良应用。     

A simple laboratory infiltration method for measuring the tendency of soils to crust

Abstract. Rainfall simulation experiments give an indication of the tendency of soils to crust or seal but are time-consuming and require several kilograms of soil per sample. We developed a laboratory infiltration method that is less time-consuming than rainfall simulation and uses less than 40 g of soil. The method involves the leaching of an agitated 1:5 soil/water suspension through a packed soil column, which simulates the crusting process. The preparation of a dispersed soil suspension is a key feature of the method as it simulates disturbance of a soil surface by rain. This laboratory infiltration method was performed on sandy, granite-derived soils from annually burnt as well as unburnt plots in the Kruger National Park, South Africa and gave results which correlated strongly with results from rainfall simulation experiments on the same soils. We suggest that this new method may be useful for assessing the effect of different land management practices on the tendency of soils to crust.     

A modified physical-based water-retention model for continuous soil moisture estimation during infiltration: experiments on saline and non-saline soils

ABSTRACT

Water infiltration is an issue of vital concern to farmland irrigation. Besides, a soil-water evaluation during infiltration benefits irrigation determination and salt leaching, which has still not been well revealed through a physical-based model regarding continuous soil-water estimation. We conducted one-dimensional infiltration on non-saline loam soil and saline sandy loam soil to propose a modified water-retention model which was expected to estimate continuous soil-water changes during infiltration. Results indicated that for the non-saline soil and the saline soil with different salinities, the modified water-retention model can be established based on the vertical one-dimensional algebraic model and the Kostiakov model. But different from the traditional vertical one-dimensional algebraic model, the new established model can be adopted for calculating and predicting continuous water content during infiltration at any duration, with higher accuracy than using HYDRUS, due to direct parameter acquisition from the observed infiltration data rather than indirect acquisition from soil water characteristic curve. The established potential relationship between soil moisture and cumulative infiltration promotes the development of precise agriculture.     

垄膜沟灌对旱区农田土壤盐分及硝态氮运移特征的影响

引黄水量的执行性削减加剧了河套灌区农业水资源的紧缺程度及土壤次生盐渍化问题。采取合理的节水灌溉模式对缓解河套灌区农业用水紧张、改良盐渍化土壤、营造适宜作物生长的土壤环境具有重要意义。为明晰垄膜沟灌对河套灌区土壤盐分及硝态氮运移特征的影响及调控效果,通过4次田间沟灌试验,对比研究了高水、中水、低水及高肥、低肥6个组合处理条件下土壤盐分以及土壤硝态氮的变化特征。结果表明:垄膜沟灌条件下灌水量对土壤全盐量的影响高于施肥量,中水处理土壤全盐量始终维持在一个适宜且稳定的水平。灌水量和施肥量对土壤硝态氮含量均有不同程度的影响,中、低水处理后期硝态氮的淋溶显著低于高水处理。垄膜沟灌种植模式下中水低肥处理增加了土壤水分的有效性,抑制了土壤反盐,减少了垄上硝态氮的淋溶,在节水节肥的基础上为作物的生长发育提供了一个适宜的土壤环境,利于生物量的累积及最终产量的形成,在一定程度上解决了河套灌区引黄灌溉配额减少与漫灌洗盐方式严重浪费水资源之间的矛盾,为当地垄膜沟灌技术的推广提供了一定的理论依据与技术支撑。     

咸水安全利用农田调控技术措施研究进展

淡水资源短缺已经成为全球性的问题,开发利用地下咸水资源,发展农业灌溉已成为各国关注的焦点问题。微咸水或咸水代替部分淡水进行农业灌溉,在一定程度上可缓解淡水资源的不足,但咸水和微咸水灌溉带来的土壤积盐和作物减产等问题始终是研究的重点和难点。本文从咸水或微咸水灌溉带来的潜在土壤盐渍化危害入手,就如何应对咸水和微咸水灌溉带来的次生盐渍化问题,通过总结前人大量的研究成果,分析了减轻土壤盐渍化对作物危害的各种途径,从微咸水灌溉和咸水灌溉两个层面就优化农田管理农艺措施、生物措施、水利工程措施等方面进行概述。重点介绍了咸水或微咸水灌溉对土壤微环境的影响,优化田间管理农业措施(如合理的灌溉制度和灌溉方式、覆盖、深耕等),土壤中施入有机物质(如植物秸秆、有机肥、绿肥、生物质炭等)和无机土壤改良剂(如石膏、沸石等)、施用根际促生菌肥、种植盐土植物和耐盐作物品种等,以及咸水结冰灌溉、暗管排盐等水利工程措施,这些都是降低咸水灌溉带来的土壤盐害行之有效的方法。以微咸水或咸水补灌为核心,结合雨水资源利用,通过种植耐盐植物品种、增施土壤微生物肥、土壤调理剂等措施提高土壤缓冲能力,配套垄作和地膜覆盖等降低土壤蒸发措施,抑制土壤盐分表层积聚,配套秸秆还田和土壤耕作技术,提高土壤蓄雨淋盐和养分快速提升,集成微咸水安全高效灌溉技术模式,制定规范化的技术应用规程,有机地结合各种改良措施,可有效控制咸水和微咸水灌区土壤次生盐渍化,达到咸水资源的高效安全可持续利用,提升水资源保障能力。     

Differential hydrological response of biological topsoil crusts along a rainfall gradient in a sandy arid area: Northern Negev desert,Israel

Drylands are regarded as highly sensitive to climatic change. The putative positive relationship between average annual rainfall and runoff, assumed for areas between 100 and 300 mm ignores the fact that climatic change in drylands is not limited to climatic factors alone, but is often accompanied by a parallel change in surface properties. Data on rainfall, runoff and soil moisture regime were collected at five monitoring sites in a sandy area, along a rainfall gradient from 86 to 160 mm. Despite the uniform sandy substratum the frequency and magnitude of runoff declined with increasing annual rainfall. Under wetter conditions a thick topsoil biological crust develops. This crust is able to absorb and retain large rain amounts, limiting the depth to which water can penetrate, and therefore water availability for the perennial vegetation. In the drier area, the thin crust can absorb only limited rain amounts, resulting in surface runoff and deeper water infiltration at run-on areas. Our findings demonstrate the important role played by different types of biological soil crusts along the rainfall gradient considered, and question the generally held belief that higher rainfall necessarily leads to deeper water infiltration in sandy arid areas; and higher water availability for the perennial vegetation.     

华北平原大气降水对土壤淋洗脱盐的影响

华北平原属季节性干旱半湿润太平洋季风气候区,降水量500-600 mm,年际和年内降水分布不均,旱涝盐碱灾害并存,成为农业生产可持续发展的主要制约因素。降水量74%集中在雨季,对土壤发生淋洗脱盐作用。一般在雨季7-8月份降水量超过300 mm,土体表现为脱盐。次降水量超过25 mm,根层土壤发生淋洗脱盐。海河平原自1964年逐年开挖骨干排水河道,使海河五大河流水系都有了自己的入海尾闾, 在排洪排涝的同时也排走了大量的盐分。20世纪60年代末,开始大规模开发利用地下水,井灌的同时降低了地下水位,起到井排作用,减少了潜水蒸发,增大了降雨入渗,加强了降雨淋洗脱盐作用,并引河水回灌补源,淡化了地下水。华北平原控制了灌区土壤次生盐碱化,而且大面积盐碱地得到改良。     

降雨入渗对黄土斜坡土体含水率时空分布特性的影响

为了对降雨入渗引起黄土斜坡土体含水率的变化有较深入的了解,在陕西省延安市宝塔山选取了一个典型的黄土自然斜坡进行土体含水率和降雨联合监测。监测结果表明,斜坡土体中的含水率对降雨入渗的响应具有时间上的滞后性与空间上的差异性。当日降雨量达到10mm或10d累计降雨量达到70mm时,降雨入渗对土体含水率的影响深度小于1.0m;当日降雨量达到50mm或10d累计降雨量达到140mm时,降雨入渗对土体含水率的影响深度小于2.0m。同时,当小时降雨量达到10.4mm时,降雨入渗至0.2m的入渗速率为0.04m/h,由0.2m入渗至1.0m的入渗速率为0.033m/h,降雨入渗速率随着土层深度的增加而减小。     

Effect of leaching events on the fate of polyhalite nutrient minerals used for crop fertilization

Abstract

Polyhalite is a natural mineral containing potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) and is proposed as a fertilizer source for these essential nutrients. Application of polyhalite is expected to be most relevant in soils where the availability of these nutrients is low: in sandy soils, in highly leached soils, or in areas where crops are irrigated by water with low content of these nutrients or are rain-fed. A controlled lysimeter experiment investigated the efficacy of surface applied polyhalite as a fertilizer supplying K, Ca, Mg and S compared to soluble sulfate salts in two soils (sandy and loamy) with or without simulated rain leaching events through two cycles of cropping. In the first cycle, carrot response and nutrient uptake, transport, and loss through leaching were studied, while in the second cycle the residual effect of the fertilizer was considered on maize without additional fertilizer application or leaching. Polyhalite plus rain led to increased carrot yield due to augmented Ca uptake in sandy soil. In both soils, polyhalite behaved as a prolonged availability fertilizer with more nutrients retained in the top soil layer and not leached below the root zone. The treatments did not affect maize growth or nutrient uptake except for lower K and S uptake in soils where rain had been simulated for the previous crop. We conclude that polyhalite shows potential as a commercial fertilizer to supply K, Ca, Mg, and S nutrients under conditions of dryland agriculture where occasionally leaching by rainfall occurs.     

有机肥配施保水剂对紫色土水分入渗及氮素淋溶的影响

以有机肥、保水剂(聚丙烯酰胺PAM、高分子吸水树脂SAP和沃特)为供试材料,通过室内土柱模拟试验,研究有机肥配施保水剂对紫色黏土水分入渗及氮素淋溶的影响。结果表明:有机肥配施保水剂可有效增加土壤的保水保肥能力,是控制土壤水分和养分淋失的有效措施。单施有机肥和有机肥配施保水剂均降低了湿润锋运移深度和入渗速率。与对照相比,单施有机肥和有机肥配施保水剂处理的湿润锋运移深度降低了33.33%～46.49%,入渗速率降低了22.73%～31.82%,累计淋溶液体积降低了1.25%～6.78%。施用有机肥有一定增肥保肥能力,但随淋洗次数增加保肥能力逐渐降低,与对照相比,在持续淋溶条件下单施有机肥的硝态氮和全氮累计损失率分别升高了12.00%,17.51%。有机肥配施保水剂可有效减少氮素淋失量,降低氮素淋失率,提高土壤保肥能力。与施用有机肥相比,有机肥配施保水剂硝态氮损失率降低了35.49%～78.46%,全氮损失率降低了35.53%～71.85%,其中有机肥配施PAM处理保水保肥效果最好。     

Leaching of spring—applied fertilizer nitrogen: measurement and simulation

Abstract. The leaching of spring-applied fertilizer nitrogen was measured by soil sampling on three soils widely used for spring cropping: a loamy sand, a sandy loam and a sandy silt loam. Soils were fallow during the experiment. Results were compared with simulations obtained with a computer leaching model. The model differentiated well between soil types, and predicted mineral nitrogen remaining in the top 30, 60 or 90 cm with reasonable precision. It tended to over-estimate the rate of nitrification of ammonium from ammonium nitrate fertilizers. The causes of occasional large discrepancies between sampling and measurement are discussed.     

成垄压实耕作施肥机械的改进设计(简报)

基于土壤大孔隙流理论、垄沟微型集雨理论和阻水层理论提出的成垄压实耕作施肥方法,能够有效地达到集雨保肥的作用,而推行该耕作措施的关键是加强其配套农机具的研制.在国外相关研究的基础上改进设计了成垄压实耕作施肥机械.该设计合理.一机多用.具有结构紧凑、调整方便等特点.采用改进后的平底箭铲式施肥开沟器能够阻断土壤中大孔隙流的连续性,在垄底形成一致密的施肥带,减少了氮肥在土壤中随大孔隙流的淋溶迁移.利用单圆盘起垄覆盖施肥带,并采用仿垄形加压式镇压器对垄面进行镇压,通过改变弹力来实现镇压力的调整,形成不同紧实度的水分运动障碍层.达到集雨保肥的作用.     

灌溉方式及腐植酸用量对温室内土壤Cd迁移的影响

目前,我国温室大棚栽培面积呈逐年递增趋势。与露地栽培相比,温室大棚栽培肥料用量大,土壤表层养分含量高,土壤污染严重,直接影响农产品的品质和栽培经济效益。采用温室内土柱模拟试验,研究了不同灌溉方式以及腐植酸用量下土壤Cd的迁移转化行为。结果表明,添加腐植酸促进表层土壤Cd2＋向下迁移,该迁移行为与灌溉方式、腐植酸添加量关系密切,随腐植酸用量的增大,灌溉淋出的Cd2＋量逐渐增加。与常规灌溉相比,滴灌使Cd2＋多存在于土壤的表层,通过减少Cd2＋的淋滤量而减轻对地下水安全的威胁。     

Concentration Profile of Nitrogen and Phosphorus in Leachate of a Paddy Plot during the Rice Cultivation Period in Southern Korea

Abstract

The relationships between nitrogen (N) and phosphorus (P) concentrations in surface flooding water and those in the leachate of various soil depths were monitored, and temporal variation of leaching losses of N and P from a paddy plot during rice cultivation was estimated under the conditions of southern Korea. Even flooded conditions nitrification in subsurface soil was identified, but nitrate concentrations in leachate were less than 10 mg/L, the standard drinking water nitrate concentration set by the World Health Organization (WHO). The NO₃‐N and ortho‐P concentrations in the leachate were generally higher than those in the surface flooding water. Field data implied that leaching losses would not be accurately estimated under the flooded conditions of the paddy field when using the N and P concentrations of surface flooding water and infiltration depth. The leaching losses of NO₃‐N from paddy fields were high immediately after fertilization. The study results suggested that proper fertilization and irrigation strategies are required to reduce leaching losses of NO₃‐N from paddy fields.