The influence of method and frequency of irrigation on soil aeration and some biochemical responses of apple trees

Summary The effect of various irrigation regimes on soil aeration was tested in a two-year experiment with 15 year-old apple trees growing in soil containing 67% clay. Irrigation was applied by sprinklers at four intervals ranging from 3 to 18 days and by trickle irrigation every 7 days. Each treatment received a total of 800–850 mm water from May until September. Irrigation by sprinkling at 7 day intervals appeared to be optimal for fruit growth. Less frequent irrigations resulted in smaller fruits; sprinkling at 3–4 day intervals, as well as trickle irrigation reduced the fruit growth rate in July. Leaves from plots irrigated once every 3–4 days had a low chlorophyll content and accumulated relatively large amounts of ethanol, particularly when grafted on the Khashabi rootstock, which is highly susceptible to damage caused by inadequate soil aeration. With increasing intervals between irrigations, the resistance of the leaf surface to the diffusion of water vapour measured prior to irrigation increased, and water loss relative to that from an evaporation pan decreased. Sprinkling at intervals of 14 days resulted in maximal, and at 3–4 days in minimal, air contents of the soil when calculated as averages for the total period of irrigation. The decrease in soil air content with very frequent irrigations was particularly marked in the upper soil layer; this same layer also had a relatively low air content near the emitters in trickle irrigation. After each irrigation, relatively large amounts of ethylene accumulated in the soil atmosphere, indicating inadequate soil aeration, particularly with sprinkling intervals of 3–4 days and at a depth of 30 cm. However, the influence of the irrigation treatments on the oxygen and carbon dioxide contents of the soil atmosphere was small and not consistent.     

Reclamation of saline organic soil

Summary Reclamation of saline, organic soils in the Sacramento-San Joaquin Delta of California was accomplished by both sprinkling and continuously ponding water on the soil surface. The reclamation data support the generalized guideline established for saline, organic soil.A 70% reduction in the average root zone salinity required 3 months under ponding, compared to 4 months under sprinkling. Although accurate measures of water application on the ponded trials were not possible, the limited data indicate that the amount of water required is about the same per unit depth of soil reclaimed for both ponding and sprinkling. Reclamation proceeded more quickly under the second ponding trial than for sprinkling or the first ponding trial because of improved subsurface drainage. With sprinklers, 70% of the salt was removed from the soil profile to a depth of 1.2 m after 850 mm of leaching water entered the profile. Reclamation by ponding required about the same quantity of water but the water required for leaching could be reduced significantly by improved drainage.     

喷灌条件下冬小麦的水肥利用特征研究

对喷灌条件下冬小麦对水肥的利用进行了研究,探讨了不同灌溉水量对冬小麦产量、耗水规律以及对土壤中硝态氮含量的影响,提出喷灌条件下冬小麦适宜的灌水定额。试验结果表明随着灌溉水量的增加,冬小麦消耗土壤水的份额逐渐减少,主要以消耗灌溉水为主;小麦生长期间对土壤中硝态氮的吸收随土壤深度的不同而有所区别;在3个灌溉水平下,随着灌水量的减少,灌溉水的利用效率逐渐升高,经济灌溉量为209.3 mm。     

Influence of vertical sand column and supplemental irrigation on barley yield in arid soils affected by surface crust

A field experiment was conducted during the 1996/1997 season at the University of Jordan Research Station near Al-Muwaqqar village to investigate the effects of sand columns, sand column spacing, soil ridges, and supplemental irrigation on soil water storage, redistribution, and barley yields. The experimental site represents a typical Jordanian arid environmental soil suffering from surface crust formation overlaying impermeable material. In the 600-mm-depth soil profile, soil water storage was improved significantly by 59%, 45%, and 38% in the 1-m, 2-m, and 3-m sand column spacing treatments, respectively, compared with soil water storage in the control treatment (no sand columns). Sand columns increased the moisture stored in all four soil layers (0–150, 150–300, 300–450, and 450–600 mm). Moisture stored in the 450–600 mm soil layer increased significantly by about 188%, 147%, 88%, and 29% in the 1-m, 2-m, 3-m, and 4-m sand column spacing treatments, respectively, compared with moisture stored in the same soil layer of the control treatment. Increasing soil water storage also increased barley consumptive use significantly from 130 mm in the control treatment to an average of about 185 mm in sand column treatments. Without supplemental irrigation, barley grain and straw yields were negligible and almost zero. Barley yields in the control treatment, with 167 mm supplemental irrigation were low, being 0.19 ton/ha and 1.09 ton/ha of barley grain and straw, respectively. Sand columns increased barley grain and straw yields significantly compared with the control treatment to a maximum of 0.68 ton/ha and 3.97 ton/ha, respectively, with the 1-m sand column spacing. Soil ridges perpendicular to the land slope had no significant effect on increasing soil water storage due to lateral runoff and loss along the ridge. In general, sand columns minimize surface runoff and evaporation by allowing water to infiltration through the strong surface crust. Sand columns act as a sink for surface water, enhance subsurface lateral water movement, and reduce the possibility of surface crust formation in the vicinity of the sand column opening by preventing surface ponding. Received: 3 October 1997     

施灌沼肥对土壤氨挥发和氮素下渗规律的影响

为探讨施灌沼肥对土壤氨挥发和氮素下渗的影响,在室温条件下,采用土柱模拟试验,系统研究沼肥不同施用量和不同施用深度对土壤表面的NH3挥发及土壤垂直剖面上的总氮、NH+4-N、NO-3-N下渗的影响规律。结果表明:表施沼肥时,土壤表面的NH3挥发累积量和挥发的延续时间均随沼肥施用量的增加而增加;土壤垂直剖面上的含水率、总氮和NH+4-N均主要集中在表层土壤,而NO-3-N可迁移至较深层土壤。底施沼肥时,NH3挥发累积量随着沼肥施用深度的增加而减少,施用深度为10 cm时便可有效减少沼肥的NH3挥发损失;同时土壤垂直剖面上的含水率和总氮、NH+4-N、NO-3-N质量比的最高点均与沼肥施用深度呈显著正相关。     

不同施肥时序滴灌双点源交汇下土壤水氮分布研究

【目的】探究不同施肥时序下滴灌双点源交汇水、氮的运移规律和分布特征,为滴灌系统施肥装置的合理运行提供技术支撑。【方法】通过室内土槽试验,设置3个硝态氮质量浓度(300、600、900 mg/L)和3种施肥时序(1/2N-1/2W、1/4W-1/2N-1/4W、3/8W-1/2N-1/8W),分析了土壤湿润锋的运移以及水分、硝态氮在土体内的分布情况。【结果】交汇前湿润锋在水平和垂直方向上的运移距离与时间t符合幂函数关系,在交汇面垂直方向上的湿润锋运移距离与时间t可用二项式拟合。各处理的水分分布规律基本相同,随深度的增加,土壤含水率降低,从0～10 cm的30%～35%缓慢降低至10～15 cm土层的19%～25%。在交汇面上的土壤含水率不大于相同土层其他位置的含水率,但硝态氮量比相同土层其他位置的大。增加肥液质量浓度,土体内相同位置的硝态氮量增加。不同施肥时序下,硝态氮在点源交汇区域的内部和边缘的量存在差异。【结论】综合考虑硝态氮的分布规律和减少淋失,在点源交汇情况下,采用水-肥-水的施肥时序(即1/4W-1/2N-1/4W、3/8W-1/2N-1/8W)较肥-水的施肥时序(1/2N-1/2W)能减少硝态氮在点源交汇区域的边缘积累,控制氮肥的淋失。     

Interactive effects of soil salinity,fertility, and irrigation on field corn

Summary A line-source field experiment was conducted to study the interactive effects of four levels of soil salinity, five rates of applied nitrogen fertilizer and six levels of irrigation on the production of field corn (Zea mays L.). In general, increased levels of soil salinity and decreased irrigation reduced grain and stover (stems and other above-grand dry matter) yields. Increased quantities of irrigation, presumably through maintenance of high (less negative) total soil water potential, were effective in decreasing the effect of salinity, and as a result improved yield. The highest salinity level (9.6 mmho/cm) resulted in dry matter yield reductions of 41 and 93 percent of the maximum observed yield at the highest (479 mm) and lowest (210 mm) irrigation levels respectively, averaged over all fertility levels. Under the same conditions grain yield declined by 48 and 96 percent. Yield was not improved as a result of applying nitrogen. Main effects on yield of salinity (1% level), water (1% level) and nitrogen (5% level) were found. Interactive effects upon yield were demonstrated for salinity X nitrogen (1% level) and salinity X water (1% level) combinations. Nitrogen content of stover and grain rose with increased levels of soil salinity and nitrogen, and declined with increased irrigation. A salinity X nitrogen interaction effect was demonstrated for nitrogen content of the grain, and a salinity X water effect demonstrated for stover. Multiple regression equations for stover and grain yields as functions of salinity, fertility and irrigation were developed (R ² = 0.88 and 0.85 respectively).Utah Agricultural Experiment Station Journal Paper No. 2331Present address of the senior author: FAO, Addis Abeba, Ethiopia     

Drought response of rice at different nitrogen levels using line source sprinkler system

Summary In rainfed rice, the nitrogen status of soil and plant is closely related to the moisture regime in the soil. The lower the soil moisture content, the lower the nitrogen use efficiency in the plants.In this study, the yield and growth responses of four rice cultivars to seven irrigation and three nitrogen levels were evaluated using the line source sprinkler system. Visual observations on the degree of drought reaction and measurement of leaf water potential (LWP) were also made.The effect of drought was least on the traditional variety Kinandang Patong and most on the modern variety IR 20. Increasing nitrogen levels from 0 (no nitrogen fertilizer) to 60 and 120 Kg N/ha increased the degree of water stress. This also resulted in decreased LWP especially when the total water applied was minimal. At all levels of nitrogen, Kinandang Patong had significantly higher LWP than IR 20. There was a curvilinear decrease in the number of days to heading and a linear increase in plant height and dry matter production with increase in total water applied.The yield-water-fertilizer relationships of the four cultivars revealed different production surfaces. The early-maturing IR 52 rice gave the highest grain yield at 120 kg N/ha and with maximum water application of 850 mm. Without nitrogen fertilizer application, Kinandang Patong gave the highest predicted yield with 550 mm of water applied. At 120 kg N/ha and 550 mm of water, IR 36 was superior in yield to other rices tested.Results suggest that in areas of uncertain moisture supply, nitrogen application rate should be reduced from that normally used for irrigated rice.     

Movement of water in restructured saline and sodic clay topsoils under a rainfall simulator

The nature of water movement through freely draining saturated and field moist aggregates of saline sodic clay topsoil was studied using 200 mm long columns filled with soil aggregates. Water containing tritium as a tracer was supplied either by means of rainfall simulator or directly to the surface of the soil under a negative pressure head of 500 Pa.The proportion of macropore and micropore flow was elucidated. The micropores of the aggregates were shown to convey very little water (0.013 mm h⁻) and hence, even at low rainfall intensities water was expected to move down through the macropores. In practice, at a low water application rate of 0.6 mm h⁻ drainage did not begin from the base of the column until the aggregates had become fully saturated due to mobile water in the macropores being continuously absorbed into the micropores. The results, however, indicated that extensive rapid bypassing does occur at medium and high rainfall intensities ( > 2.3 mm ⁻) , with the result that a large proportion of the water falling on the unsaturated plough layers of clay soils is drained before the topsoil becomes saturated.The soil absorbed water continuously during the application of the equivalent of a wetter than average winter's rain (400 mm), the rate of absorption being directly proportional to the amount of salt leached.Tritium, used as a tracer, was found to be preferentially absorbed by the clay during the leaching process, the concentration in the soil water rising to 1.8 times that of the applied tritiated water.     

Seasonal variations in nitrate leaching in structured clay soils under mixed land use

Nitrate leaching was studied for 2 years in a structured clay soil (Evesham series) under grass, winter wheat and spring barley at N fertilizer inputs of 135–144 kg ha^?1 year^?1. Measurements of soil water to 2 m depth by neutron probe showed that the year could be divided into well defined periods of deficit, separated by a period when the soil was at its winter mean water content. Soil water potentials showed very little gradient for water flow below 1 m, and a persistent convergent zero flux plane at 40–60 cm depth during the autumn wetting-up period (September—November).Nitrate concentration in the drainage increased with discharge rates up to 3–6 mm day^?1. Mean nitrate concentrations were generally highest during intermittent drain-flow in the autumn. Of the total N leached over the 2 years, 23 to 28% (5–7 kg N ha^?1) was lost during this period. The remainder (13–25 kg N ha^?1) was leached during winter and virtually no N was lost in the following spring-early summer. This seasonal pattern of N leaching was interpreted in terms of intermittent flow during rainfall of nitrate-rich water from surface layers, which bypassed the relatively dry soil matrix at 40–60 cm, but was intercepted by natural and artificial drainage channels. Implications for the prediction of N leaching loss based on the concept of excess winter rainfall are discussed. When predicting the start of N leaching in structured clay soils, the soil water status should be assessed from measurements of water potential rather than water content.     

The effect of timing on the redistribution of water-applied nitrogen in a sandy soil

Selection of the time period when liquid N fertilizer is introduced during an irrigation (timing), can potentially lead to more accurate placement of N in the root zone of perennial crops. The effect of four timing treatments, T1, T2, T3 and T4 the four quarters of a water application on in situ redistribution of ammonium nitrate at two water application rates (23 and 58 mm) was investigated. Irrespective of applied water quantity, soil ammonium-N content decreased with depth from the soil surface. Retarding the timing from T1 to T4 resulted in a significant increase in ammonium-N content in the uppermost 50 mm depth increment at both water application rates. In all timing treatments, the negatively charged nitrate ion moved to greater depths than its positively charged counterpart. These differences were greater where 58 vs. 23 mm of water was applied. Except for the T3 and T4 treatments at the 23 mm level, peak soil nitrate concentrations appeared below the soil surface. Retarding the timing at the 58 mm level gave rise to consecutive nitrate peaks between the surface and the 500 mm depth. A less distinct trend was also apparent where 23 mm was applied. Evidence for preferential movement of N in a uniform course sandy profile is also presented.     

氮肥溶液磁化灌溉下土壤入渗特征和水氮迁移规律研究

为探明不同浓度氮肥溶液磁化前后土壤入渗特征和水氮迁移规律,采用恒定磁场强度300 mT对质量浓度分别为0、0.4、0.7、1.1 g/L的硝酸钾溶液进行磁化处理,以未磁化处理为对照,测定各处理溶液的电导率、pH值、溶氧量、表面张力、累积入渗量、湿润锋运移距离和入渗后不同土壤剖面水氮迁移分布。试验结果表明：磁化处理溶液溶氧量显著提高,电导率和表面张力显著减小,并随溶液浓度变化有显著影响,但对pH值无显著影响。氮肥溶液磁化入渗增大了相同入渗时间内的湿润锋运移距离和累积入渗量,Philip、Green-Ampt、一维代数入渗模型拟合所得参数土壤吸渗率S、饱和导水率K_s以及有效土壤水扩散率■均增大,湿润峰处的土壤水吸力S_f、土壤水分特征曲线和非饱和导水率综合形状系数m均减小,增渗效果随氮肥溶液浓度增大而增大。磁化氮肥溶液可提高土壤持水能力,且随溶液浓度增大持水能力增强,一维代数入渗公式可较好描述不同磁场强度下各浓度溶液土壤入渗结束时的土壤含水率分布情况。氮肥溶液和磁化作用对土壤硝态氮含量的影响呈显著正相关关系,二者共同作用下,磁化高浓度溶液硝态氮含量...     

Effects of sand column, furrow and supplemental irrigation on agricultural production in an arid environment

The effects of supplemental irrigation, sand columns and blocked furrows on soil water distribution and barley yield were studied on arid soils affected by surface crusts. The sand columns were 50 mm diameter, 600 mm deep, and filled with sand of 0.375 mm mean diameter. The blocked furrows were trenches about 250 mm deep, 300 mm wide, and 6 m long established perpendicular to the slope direction. Sand column and furrow treatments significantly increased soil water storage compared with natural or control treatments. Soil water storage significantly increased by about 210% and 230% near the center of the sand column and the furrow treatments, respectively, relative to the control treatment. For sand column treatments, soil water storage decreased linearly with distance from the center of the sand column to about 2.5 m, while for the furrow treatment soil water storage decreased logarithmically to a distance of about 1.0 m, beyond which the soil water storage was not significantly different from the natural or control treatments. The furrow and sand column treatments significantly increased the water application efficiency, seasonal consumptive use and barley grain and straw yields compared with natural and control treatments. Increasing furrow spacing increased the catchment area and consequently crop production per furrow, but decreased crop production per unit total (cultivated and catchment) area. Decreasing sand column spacing reduced surface runoff and increased soil water storage and consequently barley grain and straw yields. Supplemental irrigation is essential for grain production in limited rainfall areas. Soil management is also required to overcome the problems of the soil surface crusting and the low permeability of subsurface soil layers for maximum rainwater efficiency, and for optimal crop production with minimum supplemental irrigation water. Where agricultural land is not limited, furrowed soil surfaces appear to be the most suitable technique for barley grain production. Sand columns with sprinkler irrigation might be more suitable for growing barley as forage crop where agricultural land is limited. Received: 19 October 1998     

The growth and nitrogen economy of rice under sprinkler and flood irrigation in South East Australia

Summary Dry-seeded rice (Oryza sativa L., cv. Calrose) was subjected to 4 irrigation treatments — continuous flood (CF) and sprinkler irrigation at frequencies of one (S1 W), two (S2W) and three (S3W) applications per week — commencing 37 d after 50% emergence (DAE). The amount of water applied was calculated to replace water lost by pan evaporation. Urea (120 kg N ha^–1) was applied in a 1:1 split 36 and 84 DAE, and there were also unfertilized controls for each irrigation treatment. Amounts of nitrate (NO ₃ ^– ) in the soil were very low throughout the growing season in all treatments, despite regular periods of draining which lasted for up to 7 d in SlW. In all irrigation treatments, the majority of the fertilizer nitrogen (N) was located in the top 20 mm of soil. After each application of fertilizer, levels of mineral N in CF declined rapidly, while levels in S3W and S1W remained high for 1–2 weeks longer. The poor growth of sprinkler-irrigated rice was not due to lower amounts of mineral N in the soil. The greater persistence of fertilizer N in the sprinkler-irrigated treatments was probably due to reduced root activity near the soil surface because of frequent periods of soil drying in between irrigations. Net mineralization of soil N in the unfertilized sprinkler-irrigated treatments was reduced by about half compared with CF.On average, the quantity of water applied (1.2–1.4 × EP) to the sprinkler-irrigated treatments appeared to be sufficient to meet the evapotranspiration demands of the crop, except possibly around flowering time. However, the plants may have suffered from moisture stress in between irrigations. Soil matric potential data at 100 mm suggested little water stress in the sprinkler-irrigated treatments during the vegetative stage, consistent with the similar tiller and panicle densities in all irrigation treatments. However, the crop was stunted and yellow and leaf rolling was observed in the sprinkler-irrigated treatments during this period. Soil matric potential data at 100 mm indicated considerable water stress in S1W beyond the commencement of anthesis, and in S2W during grain filling, consistent with the reduced floret fertility and grain weight in those treatments.     

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.     

水炭运筹对寒地黑土区稻田土壤肥料氮素残留的影响

为揭示水炭运筹下肥料氮素在稻田土壤中的残留情况,采用田间小区试验与微区试验相结合的方法,应用15N示踪技术,以传统淹水灌溉作为对比,研究水分管理模式和生物炭施用量二因素全面试验构成的不同水炭运筹模式下水稻收获后基肥、蘖肥、穗肥和肥料整体在稻田土壤中的残留情况,以及各阶段施用的肥料氮素残留在不同深度土层的分布规律。试验结果表明,稻作浅湿干灌溉模式不同生物炭施用水平下施用的氮肥在稻田土壤中的总残留率为28.16%~34.42%,其中基肥、蘖肥和穗肥氮素的残留率分别为27.53%~41.35%、34.32%~43.50%和11.58%~25.67%。当生物炭施加量在0~12.5 t/hm^2时,水稻收获后两种灌溉模式下基肥和蘖肥氮素在土壤中的残留量均随着生物炭施入量的增加而增大,而穗肥氮素在土壤中的残留量随生物炭施入量的增加而减小,相同生物炭施用水平下稻作浅湿干灌溉模式各阶段肥料氮素在土壤中的残留率显著高于传统淹水灌溉(P<0.05),且两种灌溉模式肥料氮素在相同土层深度中的残留量差异显著(P<0.05),不同生物炭施用水平下稻作浅湿干灌溉模式各阶段施用的氮肥在稻田0~20 cm土层中的残留量均高于传统淹水灌溉,而在40~60 cm土层的残留量均低于传统淹水灌溉;施加25 t/hm^2生物炭时,对稻作浅湿干灌溉模式的基肥、蘖肥和穗肥氮素在稻田土壤中的残留产生负效应。合理的水炭运筹模式能够增加耕层土壤(0~20 cm)肥料氮素残留量,减少肥料氮素损失,抑制肥料氮素向深层土壤运移,降低残留在土壤中的肥料氮素对稻田生态环境造成污染的风险。     

Removal of nitrogen and phosphorus from untreated milking-shed wastes after application to permanent pasture

Wastewaters from a milking shed serving 320 cows were sprinkler irrigated onto drained permanent pasture. Estimates of the amounts of nitrogen (N) and phosphorus (P) applied to the pasture and leaving in subsurface drainage water have been prepared and compared to soil N and P data obtained after 3 years of field operation.The pasture disposal site received between 960–1280 kg N ha^?1 year^?1 130–180 kg P ha^?1 year^?1. Approximately 90% of the P applied could be accounted for in the top 5 cm of the pasture soil. In contrast, only 15% of the N-applied could be accounted for and there was no evidence that the pasture soil was able to serve as a storage medium for nitrogen. We consider that it is likely that large amounts of N were lost from the soil—plant system involving gaseous mechanisms, e.g. denitrification.     

Summer cover crop impacts on soil percolation and nitrogen leaching from a winter corn field

The impacts of a leguminous summer cover crop (sunn hemp; Crotalaria juncea) on nitrogen leaching from a corn (Zea mays L.) field was evaluated by direct measurements of soil water content and nitrogen balance components, complemented by direct and inverse modeling as an exploratory tool to better understand water flow and nitrogen balances in the soil. Water and nitrogen inputs and outputs were measured during winter corn production in an experimental field located in the south Miami-Dade basin in southern Florida (USA). Data from the last two seasons (2001-2002 and 2002-2003) of a 4-year study are presented. The field was divided into six 0.13 ha plots. One-half of the plots were rotated with sunn hemp (CC plots) during the summer while the remaining plots were kept fallow (NC plots). Sweet corn management was uniform on all plots and followed grower recommended practices. A numerical model (WAVE) for describing water and agrochemical movement in the soil was used to simulate water and nitrogen balances in both types of plots during the corn seasons. The hydrodynamic component of WAVE was calibrated with soil water data collected continuously at three depths, which resulted in accurate soil water content predictions (coefficients of efficiency of 0.85 and 0.91 for CC and NC plots, respectively). Measured components of the nitrogen balance (corn yields, estimated nitrogen uptake, and soil organic nitrogen) were used to positively assess the quality of the nitrogen simulation results. Results of the modeled water balance indicate that using sunn hemp as a cover crop improved the soil physical conditions (increase in soil water retention) and subsequently enhanced actual crop evapotranspiration and reduced soil drainage. However, nitrogen simulation results suggest that, although corn nitrogen uptake and yields were slightly higher in the CC plots than in the NC plots, there were net increases of soil N content that resulted in increased N leaching to the shallow aquifer. Therefore, the use of sunn hemp as cover crop should be coupled with reductions in N fertilizer applied to the winter crop to account for the net increase in soil N content.     

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.     

施肥对采煤塌陷复垦土壤团聚体组成及其碳、氮分布的影响

【目的】研究施肥对采煤塌陷复垦土壤团聚体组成及其碳、氮分布的影响,为改善采煤塌陷复垦土壤的物理团粒结构与化学性质,促进复垦土壤碳氮循环与利用提供一定理论基础。【方法】以山西省晋城市采煤塌陷复垦区土壤为研究对象,在常规灌溉条件下,以不施肥处理为对照(CK),研究了有机肥、无机肥、有机无机肥配施3种施肥处理对0～20、20～40 cm土层团聚体组成及碳、氮分布的影响。【结果】与CK相比,有机肥处理显著增加了土壤>2mm和1～2 mm粒级团聚体量,降低了0.053～0.25 mm和<0.053 mm粒级微团聚体量,单施化肥较有机肥处理提高了微团聚体量。单施有机肥、有机无机肥配施处理土壤的平均质量直径(MWD)、几何平均直径(GMD)显著高于单施化肥处理,分形维数(D)低于化肥处理。有机肥处理土壤有机碳、全氮量最高,有机无机肥处理配施次之,单施化肥处理显著低于有机肥处理;土壤有机碳、全氮主要分布在>2 mm、1～2 mm、0.25～1 mm粒级大团聚体,显著高于0.053～0.25 mm、<0.053 mm粒级小团聚体;有机肥处理、有机无机肥配施处理土壤>2 mm、1～2 mm、0.25～1 mm粒级团聚体中的有机碳、全氮量要显著高于单施无机肥处理的。各施肥处理土壤1～2 mm、0.25～1 mm粒级团聚体有机碳、全氮贡献率较高,显著高于其余粒级。有机肥、有机无机配施处理各级团聚体(除0.053～0.25 mm外)的C/N值显著高于CK,而单施化肥处理与CK差异不显著。【结论】不同施肥处理(尤其是有机肥)提高了复垦土壤大团聚体量,增强了团聚体稳定性,提高了团聚体有机碳、全氮量。