Effect of antecedent soil water content and rainfall regime on microrelief changes

Surface microrelief substantially affects surface sealing, runoff, and soil erosion processes on bare soils. Yet, the stability of microrelief for different antecedent soil water contents and rainstorms is not well understood. This study investigates the effect of surface microrelief and antecedent water content on the decay of microrelief under different rainstorm regimes. Two different rainstorm regimes were studied in laboratory experiments: continuous rainfall for a total amount of 60 mm applied at 30 mm/h intensity, and intermittent rainfall consisting of five successive rainstorms of 12 mm each, again with an intensity of 30 mm/h and separated by one week drying cycles. Rough, medium, and fine microrelief surface conditions representing different degrees of seedbed preparation were studied for three soils at antecedent soil water contents of 2–4% and 14–20%. Before and after rainfall, digital elevation models determining the surface microrelief were developed using a laser scanner with 2 mm grid spacing. The specific surface area calculated from microrelief data was used as an index to characterize microrelief. Microrelief stability increased with increasing initial roughness and was much higher for the antecedent wet soils than for the dry soils. Microrelief stability for the continuous rainstorm regime was higher than for intermittent rainfall. Differences in microrelief stability were mostly attributed to different aggregate stabilities. Additionally, the higher stability for the rougher microrelief surfaces was attributed to the lower drop impact density and splash density on the surfaces with larger specific surface area. Aggregate slaking due to air escape and rapid wetting was found to be responsible for the low microrelief stability at initially dry conditions.     

Changes in microrelief and their effects on infiltration and erosion during simulated rainfall

The erosivity of soils under a given rainfall energy appears to vary greatly among soil orders, probably reflecting differences in clay composition and organic matter content. This study was conducted to quantify microrelief, infiltration, and sediment yield changes during three consecutive simulated rain events on a Udic Haploboroll and a Typic Hapludalf from Minnesota, and a Mollic Kandiudalf, and Typic Palehumult from Uganda. Air dry aggregates (< 5 mm) were packed in 19 1 containers tilted to a 5% slope and were subjected to three consecutive high energy rain storms (63 mm h⁻¹) for a duration of 1 h. Runoff and sediment were continuously monitored during a storm. Infiltration was measured by continued weighing of the soil and containers. An automated non-contact laser relief meter was used to measure changes in soil roughness initially and after each storm. Soil surface roughness decreased during the rain events indicating that aggregate breakdown was the dominant process in seal formation. For example, random roughness decreased form 5.9 to 4.0 mm on Barnes loam and from 9.7 to 6.9 mm on Renova silt loam with cumulative rainfall of 0 and 126 mm. These infiltration rates indicated that the Barnes Loam (Haploboroll) and Kabanyolo clay (Kandiudalf) were unstable soils while Kachwekano clay (Palehumult) and Renova silt loam (Hapludalf) were quite stable. Final infiltration rates after 3 consecutive rainfalls on Kachwekano clay (15 mm h⁻¹) and Renova silt loam (13 mm h⁻¹) [the stable aggregate soils] were significantly higher than those of Barnes loam (4 mm h⁻¹) and Kabanyolo clay (3 mm h⁻¹). For the two stable soils a high infiltration rate on a rough surface was maintained until aggregate breakdown occurred and runoff began. Sediment yield from Barnes loam (29 kg m⁻²) and Kabanyolo clay (28 kg m⁻²) was significantly greater than soil loss from Kachwekano clay (0 kg m⁻²) and Renova silt loam (6 kg m⁻²). The microrelief method to quantify aggregate stability is an improvement over wet sieving and other related measurements because of its rapidity and because the statistical quantification can be linked to physical processes.     

The Effect of Different Soybean Tillage Systems on Infiltrability and Erosion Susceptibility of an Oxisol in Paraná, Brazil

Measurements of infiltrability were carried out during the soybean vegetation period in three different tillage systems on an Oxisol, with the aim of estimating relative erosion susceptibility. The tillage systems studied were conventional tillage (disc plow), minimum tillage (chisel plow) and no-tillage. Infiltration was determined as the difference between rainfall applied with a portable rainfall simulator and runoff collected from mini-plots.
During all growth stages of the soybeans, infiltrability under no-tillage was higher than under conventional tillage. Minimum tillage took an intermediate position. Lowest overall infiltrability and consequently, highest relative erosion susceptibility was observed in the early growth stage after planting, in a wet year, when the degree of soil cover was also lowest. Infiltrability was mainly affected by degree of surface seal development as a result of natural rainfall energy the soil surface had received prior to measurements, as well as degree of soil cover. Highly significant correlations were found between the calculated sum of erosivity indices one month before measurement and the total infiltration. Differences in bulk density and macroporosity had hardly any effect on infiltrability.
The better performance of no-tillage in controlling erosion observed in Brazil can thus be explained by the higher degree of soil cover in comparison to the other tillage systems studied.     

Calculating Annual Pollution Load in Urban Runoff

Sampling and monitoring of surface runoff in Bengbu urban area were carried out during rainy seasons in 2009, and 40 rainfall samples from 7 sampling sites were analyzed. Discharge processes of runoff pollutants during rain events and relationships of the processes with rainfall characters were discussed. Then some aspects were analyzed, such as city surface pollutants, land style and system of drains, etc. Finally annual total quantity of runoff pollution from Bengbu urban area was calculated based the method.     

安徽省沿淮大豆种植区氮磷流失特征研究

为了探明沿淮地区大豆农民常规施肥种植过程中的氮磷流失情况,采用径流池法,通过2008—2012年野外径流小区试验,研究沿淮大豆种植区大豆生长季氮磷流失特征。5年监测结果表明:大豆种植季处于沿淮地区全年降雨旺盛时期,降雨量占全年降雨量的45.4%~73.27%;大豆生产季农田产流量表现为不施肥空白处理常规处理,不施肥空白处理大豆生长季径流量和产流系数分别为173.293~34.639 mm和8.27%~33.68%,常规施肥处理大豆生长季径流量和产流系数分别为175.366~30.347 mm和5.72%~34.08%;大豆种植生长季常规施肥处理总氮流失量为1.58~14.93 kg/hm2,总氮流失率为0.44%~5.66%,硝态氮流失比例为总氮的40.63%~64.59%,铵态氮流失比例为3.66%~18.16%;大豆种植生长季常规施肥处理总磷流失量为0.033~0.56 kg/hm2,常规施肥处理总磷流失率为0.17%~0.27%,可溶性磷流失比例为总磷的31.08%~53.31%。     

Soil surface densification under simulated high intensity rainfall

The formation of surface crusts in agricultural soils has adverse effects on seedling emergence and infiltration and causes excessive water loss by runoff. Changes in soil surface characteristics of Zamora soil were examined under high intensity (76.2 mm/hr) simulated rainstorms A hard, dense, several-cm-thick, consolidated layer developed on the soil surface upon drying. The thickness and bulk density of this layer were strongly related to rainfall duration. A strong exponential function was found between the thickness of the consolidated layer and the soil wetted depth. Soil surface strength was strongly correlated with rainfall duration and with the initial bulk density of the soil despite the marked change in the density of the consolidated layer. The largest changes in both strength and bulk density occurred within the first 10 min of the rainstorm. Mechanisms known to be responsible for crusting appear to partly hold for the densification process, but they do not adequately explain the deeper consolidation. Particle reorganization and close-packing associated with settling under saturated or near-saturated conditions appear to provide more logical mechanisms. The relative change in bulk density was inversely correlated with the initial soil bulk density. Measurements of soil strength with a small penetrometer probe indicated an agreement between surface strength and the cohesion of the consolidated layer as determined by a triaxial shear test. Temperature of drying had slight, but mostly inconsistent effects on the strength and density of the consolidated layer. Soil densification was also found to markedly decrease the infiltration rate. The physical properties of both the consolidated layer and the subsoil, however, appeared to control the infiltration process.     

Influence of a polyacrylamide soil conditioner on runoff generation and soil erosion: Field tests in Baringo District,Kenya

Following promising laboratory results the effect of low concentration applications of a polyacrylamide soil conditioner SEPARAN AP30 on soil properties was tested under field conditions in a severely degraded semi-arid region in northern Kenya. Tests of conditioner performance on tilled and undisturbed soils were carried out under simulated rainfall on crusting Eutric or Calcaric Fluvisols at two sites on alluviolacustrine flats adjacent to Lake Baringo. Tests were carried out in two series separated by up to six weeks of sunshine and natural rainfall, to determine the longevity and residual effects of conditioner application.Runoff generation and soil loss were significantly reduced on all runoff plots during the first rainfall simulation, but the most dramatic results occurred when conditioner application was combined with raking. This inhibited crust development and virtually eliminated runoff and soil loss. Under natural weathering, surface crust had developed on all plots before the second rainfall simulations. Some residual effects of the conditioner on infiltration rates were still noted, but the residual effect on soil loss was greatly diminished.The tests indicate that low concentration applications of SEPARAN are not useful on undisturbed soils, but can provide useful temporary reductions in sheet and rillwash hazard when combined with tillage and could be effectively combined with grass re-seeding for more permanent reclamation.     

土壤修复与覆盖防草布对台地柚园氮磷流失的影响

为促进果园生草栽培技术推广和做好果园土壤酸化治理工作,更好促进琯溪蜜柚生产的高质量发展,利用径流小区法,观测琯溪蜜柚果园土壤修复和覆盖防草布对果园土壤径流量和对氮、磷面源污染的控制效果差异。结果表明：（1）果园覆盖防草布可显著降低地表径流量,各次产流量为对照区的21.29%~86.29%;（2）施用沸石粉和白云石粉能够降低径流总氮和可溶性总氮的浓度及流失量,总氮流失量分别为对照（清耕）的64.16%和63.39%,可溶性总氮浓度为对照（清耕）的56.76%和57.65%,两者都有显著性降低。施用沸石粉和白云石粉可降低径流总磷和可溶总磷的浓度和流失量,但差异都不显著;施用沸石粉和白云石粉间的效果,差异不明显。（3）果园覆盖防草布能够显著降低径流总氮流失量和可溶性总氮浓度,可极显著降低年径流总磷和可溶总磷浓度,平均浓度分别为0.035 mg/L和0.006 mg/L,显著减少径流总磷11.54 g/hm²和极显著减少可溶总磷年流失量为2.02 g/hm²;果园生草栽培模式中配套覆盖防草布技术,可很好地解决生草栽培给生产带来的不便,并且可降低径流量和径流氮、磷浓度达到降低氮、磷流失量;土壤修复可降低径流氮、磷浓度达到降低氮磷流失量。     

不同管理措施对三峡库区柑橘园土壤养分和径流氮磷流失的影响

综合考虑施肥管理方式和植物配置,本研究设置了常规施肥(CF)、常规施肥+生草覆盖(CF+GC)、常规施肥+生草覆盖+植物篱(CF+GC+PH)、水肥一体化(IWF)、水肥一体化+生草覆盖(IWF+GC)、水肥一体化+生草覆盖+植物篱(IWF+GC+PH)等管理措施,采用野外径流小区法,研究了不同管理措施对三峡库区柑橘园土壤养分及地表径流氮磷养分流失的影响。结果表明：水肥一体化柑橘园较常规施肥柑橘园土壤总氮(TN)和总磷(TP)平均高92.41%和32.45%,且配置生草覆盖和植物篱等可提高土壤总氮比例范围为17.30%~39.10%,但对总磷未见规律性影响。施肥方式以及配置生草覆盖和植物篱对土壤硝态氮(NO₃^—N)未表现出规律性影响,而配置生草覆盖和植物篱措施明显提升了铵态氮(NH₄⁺-N)含量。随着降雨量的增加,各处理地表径流量均呈逐渐增加趋势。相较常规施肥管理,水肥一体化管理可有效降低地表径流量,配置生草覆盖和植物篱措施均可进一步降低地表径流量,且以水肥一体化+生草覆盖+植物篱(IWF +GC+PH)削减地表径流效果最好。水肥一体化柑橘园地表径流中TN和NO₃^--N浓度相对较高,而TP和NH₄⁺-N浓度则相对较低。同时,配置植物措施可降低TN浓度比例为15.88%~37.55%,TP为23.48%~55.54%,NH₄⁺-N为14.11%~39.92%,NO₃^--N为25.34%~47.96%。综上可知,施肥方式、施肥时间、降雨强度、地表植被配置等差异均会影响土壤养分留存以及地表径流氮磷流失,建议未来三峡库区柑橘园管理应加大推广水肥一体化,减少肥料投入量,并配置水保型植物措施以降低养分流失水平。     

坡度对云南红壤径流中磷素浓度的影响研究

水体富营养化的发生与农田土壤中磷的淋失有密切的关系。采用模拟降雨试验研究了土壤坡度对地表径流和亚地表径流中磷素浓度的影响。结果表明：在0°—10°范围内,地表径流中总磷、水溶性磷和颗粒态磷浓度和亚地表径流中水溶性磷浓度都随土壤坡度的增加而增加。亚地表径流中总磷和颗粒态磷在坡度为15°时均有一定程度的下降,其下降机理将做下一步分析研究。     

The effects of soil organic matter content,rainfall duration and aggregate size on soil detachment

Soil detachment was measured using a factorial experiment involving five soils (with organic matter contents ranging from 1.23 to 5.64%), three rainfall durations (4, 12 and 20 mins) and two aggregate sizes (<2 mm and 2–5 mm). Detachment was described in terms of the direct effects and the first and second order interactions of these variables above.There were significant differences (P < 0.01) in the amount of soil detached between the study soils. The mean values of detachment generally declined with increasing soil organic matter content from 1.15 kg m⁻² in the G1 soil to 0.51 kg m⁻² in the G5 soil. For each soil, there were significant increases (P < 0.01) in detachment with increasing rainfall duration. Soil detachment was smaller for the larger aggregate size.The most significant interactions affecting soil detachment were between rainfall duration and aggregate size, organic matter content and aggregate size, and between organic content and rainfall duration in that order. These interactions were used to make inferences on the effect of organic matter on soil detachment.For each soil and aggregate size, power relationships were established to relate detachment to rainfall total kinetic energy and organic matter content.     

高速公路边坡不同乡土灌木建植模式的产流·产沙特征研究(英文)

[Objective] Indigenous plants with favorable water and soil conservation effects were screened for the shrub planting.[Method] Suining-Ziyang-Meishan Highway in the hilly areas of central Sichuan Province was taken for example,through sorting out plant species investigated in the route planning,3 indigenous shrub species(Neosinocalamus affinis,Vitex negundo and Coriaria nepalensis) and 3 indigenous herbaceous species(Setaria viridis,Miscanthus floridulus,Artemisia argyi) were selected.Rainfall simulation experiment was adopted to compare runoff and sediment yields of different combination modes and ratios under constant rainfall intensity(20 mm/min).[Result] Different combination modes under constant rainfall intensity all showed better water and soil conservation effects than that of control group did.For example,runoff appeared 1'-4'05"later,sediment yield reduced by 6.56-33.86 g respectively.Among all combination modes,runoff and sediment yield showed great difference after 20 min of constant rainfall,V.negundo+S.viridis had the lowest runoff(1,700 ml) and sediment yield(60.71 g);C nepalensis+A. argyi had the highest runoff(1,920 ml) and sediment yield(84.02 g).[Conclusion] Given the same planting conditions such as side slope and seeding quantity,and also the same planting techniques,in the hilly areas of central Sichuan Province,the combination of V.negundo and S.viridis can greatly improve the water and soil conservation capacity of highway.     

Cropping system effects of maize on infiltration,runoff and erosion on loess soils in South-Limbourg (The Netherlands): A comparison of two rainfall events

Two natural rainfall events are compared to evaluate the effects of three cropping systems of silage maize on soil moisture content, infiltration, runoff and erosion. Both rainfall events took place in early summer. One was a low intensity event with 27.6 mm of rain in 9 hours, and the other a high intensity event with 33.4 mm in 42 minutes. Cropping systems were:

• 1.(I) a spring tilled system (conventional),
• 2.(II) an autumn and spring tilled system with summer barley as spring cover crop, and
• 3.(III) an autumn tilled system with winter rye as winter cover crop and direct drilling of silage maize.

During the low intensity event, soil moisture content of the top 5 cm rose to field capacity on all three cropping systems. No runoff was generated. During the high intensity event, soil moisture content rose to field capacity on the two spring tilled cropping systems but was only slightly raised in the direct drill system, in spite of 17.7 mm of infiltrated rain. Runoff coefficients of the high intensity event were 41.7% (conventional system), 14.9% (autumn and spring tilled system) and 47.0% (direct drill system). The direct drill system showed a severely slaked soil surface in early summer, caused by winter rain.The response to rainfall of soil moisture content is ascribed to:

• 1.(I) a predominance of matrix infiltration on all cropping systems during the low intensity event and on the spring tilled systems during the high intensity event, and
• 2.(II) a predominance of infiltration via continuous macropores, open to the surface (of biologic origin), by-passing the soil matrix, on the direct drill system during the high intensity event.

The presence of continuous, vertical macropores on the direct drill system explains its surprisingly high infiltration capacity, considering its strongly slaked appearance. The smooth soil surface of the direct drill cropping system may have delayed infiltration during the flooded stage of the high intensity event by not providing vent points for the escape of soil air. Soil loss from the direct drill system during the high intensity event was only 15.6% of that from the conventional system. This is ascribed to low detachment rates of soil material by drop impact and/or overland flow, due to the presence of winter rye remains and, especially, the relatively high soil surface shear strength of the direct drill cropping system in early summer.     

青海省海北州水分资源变化的初步研究

为了给农业生产提供精细化的预报服务产品。本研究基于1961—2015 年降水、河流径流量、最大冻土深度等资料,利用气候诊断方法,对海北州地区水分资源的变化特征进行初步研究。结果表明：1981—2010 年年降水量比1971—2000 年、1961—1990 年分别增加11.6 mm和13.3 mm。≥25.0 mm降水出现的站次1990s、2000s 均偏多。年平均降水变率（相对湿度）基本呈弱的增大（减小）趋势。年干燥度指数呈极其显著的减小趋势,1960s、1970s、1990s 相对偏大,1980s 和2000s 相对偏小。年平均最大冻土深度呈极显著的减小趋势。布哈河和沙柳河年平均流量总体呈微弱的增大趋势,青海湖年平均水位呈极其显著的下降趋势,青海湖年平均水位变差呈十分显著的增加趋势,年降水量和平均流量是影响年平均水位变差的最关键因素。     

花生复合系统土壤水分动态与平衡特征研究

花生复合系统是促进低丘红壤区农业水分资源综合利用的重要耕作方式,其在不同时段水分动态、水分平衡和利用过程差异值得进一步探索。土壤表层采用15 bar的先进负压计监测,结合定位法于2001—2003年监测收集了花生生长季花生复合系统、花生单作田间土壤水分、地表径流、降雨资料,分析了花生复合系统对土壤水分动态、降雨影响和水分平衡各要素的影响。分析表明,土壤10 cm与 60 cm水分单作花生地与复合系统在雨季无明显差异,但受降雨过程影响。旱季单作花生10 cm水势降到最低值-344.0 kPa,复合系统水势最低值为-50.6 kPa,60 cm单作花生地水势数值也低于复合系统花生地,旱季复合系统能减少土壤表层的蒸发。3年土壤水分周期动态可分为3个阶段,即水分盈余期、水分消耗期、水分稳定期。花生复合系统旱季表现出较强的耗水作用,2001年7月贮水量减少108.8 mm,2002年8月贮水量减少111.7 mm,2003年7月贮水量减少105.5 mm。花生复合系统平均渗漏量低于花生单作62.2 mm,平均贮水量变化低于花生单作41.8 mm。桔树与花生作物在旱季水分利用方面没有明显的竞争作用,花生复合系统系统的表土水分保持作用和生态效应明显。     

Einfluß von Bodenbearbeitung, Kulturart und Zwischenfruchtanbau auf den Bodenabtrag und den Oberflachenwasserabfluß

The effects of different soil tillage systems, crop rotations and short time cover crops on soil losses and runoff
Soil and water losses were carried out from 1979 to 1986 on a pseudogley-parabrownearth of the farm Ihinger Hof throughout the growth period of green maize and sugar-beet, both planted by plough and rotary hoe. From 1983 to 1986 the effect of short time soil cover crops (October—Dezember) were also studied.
The soil losses under rotary hoe were significantly lower in comparison to plough, but the differences in runoff between the tillage treatments were not significant. Under sugar-beet the erosion caused by rainfall was less than under maize. From the short time soil cover crops, the legume mixtures were found to have the best influence on soil and water conservation, and on the maize growth as well. There was no relationship between runoff or rainfall amount and soil losses. The soil losses correlated strongly to EI₃₀-indices, and this means that the USLE equation of W ischmeier and S mith (1965) can be applied in our experimental Farm in Ihinger Hof.     

Effect of Rainfall Collecting with Ridge and Furrow on Soil Moisture and Root Growth of Corn in Semiarid Northwest China

A plastic‐covered ridge and furrow farming of rainfall collecting (RC) system were designed to increase water availability to corn for improving and stabilizing agricultural production in the semiarid Loess region of northwest China. This system comprised two elements: the ridge mulched by plastic film that acts as a rainfall harvesting zone and the furrow as a planting zone. To adopt this system for large‐scale use in the semiarid region and bring it into full play, it is necessary to test the appropriate rainfall range for RC farming. A field study (using corn as an indicator crop) combined with rainfall simulation was conducted to determine the effect of RC on soil moisture, root characteristic parameters and the yield of corn under three different rainfall levels (230, 340 and 440 mm) during the growing seasons of 2006 and 2007. The results indicated that with the rainfalls ranging within 230–440 mm, the soil moisture at 0–100 cm depth for RC system in furrows was significantly higher (P < 0.05) than that of conventional flat (CF for control) practice. At 100–200 cm soil depth, there was no significant difference (P > 0.05) between soil moisture in the RC₂₃₀ plots and in the CF₂₃₀ plots during the corn growing seasons, while the soil moisture both in the RC₃₄₀ and RC₄₄₀ plots were significantly higher (P < 0.05) than those in the CF₃₄₀ and CF₄₄₀ plots. The root length, root surface area, root volume and root dry weight for RC₂₃₀ and RC₃₄₀ plots all significantly increased (P < 0.05) compared with CF₂₃₀ and CF₃₄₀ plots, but these root characteristic parameters at 440 mm rainfall slightly decreased compared with those of CF practice. Compared with the CF_230–440 pattern, the increasing amplitude of grain yield under the RC_230–440 pattern diminished with the rainfall increase and there was no obvious yield‐incrementing effect (P > 0.05) between two patterns at 440 mm rainfall in 2006. In comparison with these two farming practices, the RC system not only improved soil moisture of dry farmland, but also promoted the development of corn root systems when the rainfall ranged between 230 and 440 mm. Thus, it could be concluded that the optimal upper rainfall limit for the RC system is below 440 mm in the experiment. For corn, the adoption of the RC practice in the 230–440 mm rainfall area will make the system more effective during the whole growth period and offer a sound opportunity for sustainable farming in semiarid areas.     

团粒结构对黄绵土溅蚀速率和结皮形成的影响研究

为弄清团粒结构在土壤结皮形成过程所起的作用,笔者通过人工模拟降雨溅蚀试验,测定土壤溅蚀速率,同时采样制作土壤切片,分析不同直径团粒对黄绵土溅蚀速率和结皮形成的影响。结果表明：0.15 mm≤D＜2.0 mm和D＜0.038 mm的团粒土壤较易形成结皮,在降雨历时5 min时,土壤表面有结皮形成,随着降雨的继续,土壤表面结皮形成趋于完善;而中度直径0.038 mm≤D＜0.15 mm的团粒土壤不易形成结皮,在降雨历时5 min时,土壤表面都没有结皮形成。在团粒直径范围是0.105 mm≤D＜0.22 mm,随着土壤团粒直径的减小,土壤的溅蚀速率逐渐增加,直径位于0.096~0.15 mm之间的团粒结构土壤的溅蚀速率达到最大,随后,随着土壤团粒直径的减小,土壤溅蚀速率逐渐降低。     

滇池流域农田土壤氮污染负荷影响因素研究

采取模拟试验的方法,研究了在人工降雨和自然降雨条件下,坡度、土壤质地、地表覆盖状况以及施肥方式对坡地农田径流中氮素污染负荷的影响。结果表明：随着坡度的增加,农田土壤径流中氮的浓度和氮的输出量都增加;在人工模拟降雨和自然降雨条件下,土壤径流中氮的浓度变化趋势相同,都随着质地的变粗而减少;和裸地相比,种植小麦能明显减少土壤径流中氮的浓度和输出量,氮的流失量减少范围在11.80~238.46kg/hm2之间;相同施肥量条件下,面施氮肥时土壤径流中氮的浓度和输出量比穴施时明显增加。     

Polysaccharide and salt effects on infiltration and soil erosion. A rainfall simulation study

Seals forming at the soil surface during rainstorms reduce water penetration and increase runoff in many arid and semi-arid regions. The effect of surface application of an anionic polysaccharide (designated F-Ac), synthesized by the filamentous cyanobacterium Anabaenopsis circularis PCC 6720, on infiltration rate (IR), runoff and erosion of three soils during simulated rainstorms, was studied. The interaction between F-Ac and electrolyte concentration at the soil surface was studied by using distilled water (DW) or tap water (TW) or by spreading phosphogypsum (PG) on the soil surface. F-Ac added at the rate of 3.4 kg ha⁻¹ together with PG at the rate of 5 t ha⁻¹ was the most efficient treatment in improving infiltration and reducing runoff and erosion. This treatment reduced runoff, from the three soils studied, from 65–80% in the control to 14–24%. Soil loss was reduced from 3.6–4.5 Mg ha⁻¹ in the control to 0.5–1.3 Mg ha⁻¹ in the treated soils. DW treatment, singly and in combination with F-Ac, was quite inefficient in preventing seal formation and in reducing runoff and soil loss. Adding F-Ac with TW maintained final IR and runoff levels intermediate between those of F-Ac with PG and those of F-Ac with DW. Electrolytes in the soil surface which flocculated soil clay, enhanced the beneficial effect of F-Ac on aggregate stability and thus greatly reduced water and soil losses. The efficacy of F-Ac as a stabilizing agent (i.e., soil conditioner) wore out during three consecutive storms of 60 mm each.