Prediction of phosphorus requirements of Desmodium intortum cv. greenleaf using a phosphorus sorption index and extractable phosphorus

Abstract

The rates of applied phosphorus required for 90% maximum yield of Desmodiim intortum cv. Greenleaf were calculated from pot experiments using 24 fertilized and unfertilized soils from the Atherton Tableland, Queensland, Australia.

Phosphorus required was highly correlated (r² = 0.94) with the phosphorus sorbed (P sorbed) by the soils at a supernatant solution P concentration of 0.08 ppm. P sorbed was found to be a function of phosphorus buffer capacity at 0.08 ppm ("PBC") and phosphorus extractable by acid (0.005 M H₂S0₄) or bicarbonate (0.5 M NaHCO₃). PBC was highly correlated (r² = O.84) with a phosphorus sorption index ("PSI") derived from one addition of 500 μg P g^‐1 soil.

Combining PSI with acid or bicarbonate extractable P in a multiple regression equation allowed the estimation of phosphorus required with multiple correlation coefficients of R² = 0.80 and R² = 0.83 respectively.     

温带森林磷沉降-水系统输出-迁移动态特征及对土壤磷影响

采用对比和分析的方法,研究了黑龙江省带岭凉水国家级自然保护区温带森林生态系统磷沉降、溪流、河流和渗透水输出磷含量动态特征,以及磷沉降和水系统磷输出对红松人工林、落叶松人工林、椴树红松混交林、枫桦红松混交林和白桦次生林5种林型土壤全磷和有效磷的影响。结果表明,研究区域通过降雨产生的年磷沉降量约为0.888 kg hm-2,7月除红松人工林外,其他4个林型穿透雨磷浓度均高于大气降雨的磷浓度。7月枫桦红松林、8月白桦次生林和红松人工林A层土壤渗透水磷浓度低于林内雨磷浓度,表层土壤对穿透雨中磷有固定作用。在凉水自然保护区森林生态系统内,森林系统内小溪流、凉水河和凉水森林系统外永翠河水磷浓度均较林外降雨及穿透降雨磷浓度高,表现为永翠河水>土壤A层渗透水>凉水河>小溪>穿透雨>大气降雨。表明土壤中部分磷素通过地表径流和壤中流流出森林生态系统,并汇集于林中小溪,最后进入河流,造成磷在小溪和河流中的富集。大气磷沉降、森林水系统磷输出均与椴树红松林A0层土壤全磷含量呈显著负相关,与红松人工林B层土壤全磷含量呈极显著正相关,与落叶松人工林A0层土壤有效磷含量呈极显著正相关。     

Increased predicted losses of phosphorus to surface waters from soils with high Olsen-P concentrations

Abstract. Diffuse soluble reactive P (SRP) & total P (TP) loads from over 50 major river catchments in Northern Ireland were predicted using an export coefficient modelling approach. Phosphorus export coefficients for each CORINE land cover class, derived from satellite imagery, allowed the prediction of P loads from a breakdown of the CORINE land cover classes by catchment using a GIS. This approach was validated using observed P loads calculated from flow and concentration data. Mean measured Olsen-P concentrations in the soil A-horizon were also determined on a catchment basis. Plots of P loads to the watercourse versus Olsen-P concentrations in the soil showed a breakpoint around 22 mg Olsen- P l⁻¹ for both SRP & TP data. Below Olsen-P concentrations of 22 mg l⁻¹, SRP & TP losses were essentially independent of Olsen-P at 0.28 and 0.63 kg P ha⁻¹ yr⁻¹, respectively. Above Olsen-P concentrations of 22 mg l⁻¹, there was considerable spread in the P loss data. Nevertheless, significant upward trends in SRP and TP losses to watercourses were detected with increasing Olsen-P at a rate of approximately 0.5 and 1.0 kg P ha⁻¹ yr⁻¹, for SRP and TP respectively, for each 10 mg l⁻¹ increase in Olsen-P.     

Source areas of phosphorus transfer in an agricultural catchment,south-eastern Norway

Abstract

The strategy to mitigate phosphorus (P) losses in areas of arable cropping in Norway has focused on measures to reduce erosion. Risk assessment of erosion has formed the basis for implementation of the measures. The soil P content has increased during recent decades, motivating an evaluation of its effect on P transfer in the landscape. The present study describes the spatial variability of runoff P concentrations from an agricultural dominated catchment (4.5 km²), representative for agriculture in south-eastern Norway. The concentrations of suspended sediments (SS), total P (TP) and dissolved reactive P (DRP) in runoff from 22 subcatchments (0.3–263 ha) during one year (monthly and during runoff-events) were evaluated. Contributions from point sources were 38 kg TP yr^?1 compared to a total P loss of 685 kg yr^?1 from the whole catchment. During low flow, mean diffuse TP concentration in runoff from subcatchments varied from 28 to 382 µg l^?1. The mean low flow TP concentration was 39 µg l^?1 from the housing area (only diffuse runoff) and 33 µg l^?1 from the forested area. During high flow the highest diffuse TP concentration was measured in an area with high erosion risk and high soil P status. At the subcatchment level the transfer of SS varied from 25 to 175% of the whole catchment SS transfer. Correspondingly for TP, the transfer varied from 50 to 260% of the whole catchment TP transfer. For each of five agricultural subcatchments the slope of the relationship between TP and SS concentrations reflected the mean soil P status of the subcatchment. Erosion risk estimates were closely related to the SS concentration (R²=0.83). The study illustrates that soil P status in addition to soil erosion is an important factor for P transfer.     

Predicting the degree of phosphorus saturation using the ammonium acetate–EDTA soil test

As a result of the important role played by phosphorus (P) in surface water eutrophication, the susceptibility of soils to release P requires evaluation. The degree of phosphorus saturation, assessed by oxalate extraction (DPS_ox), has been used as an indicator. However, most laboratories do not include DPS_ox in routine soil tests because of cost and time. This study evaluates the suitability of the ammonium acetate extraction in the presence of EDTA (AAEDTA), the standard soil test P (STP) in Wallonia (Southern Belgium), to predict DPS_ox; we also compared it with the Mehlich 3 extraction. Ninety‐three topsoil samples were collected in agricultural soils throughout Wallonia. Good correlations were found between the AAEDTA and the Mehlich 3 methods for P, Fe and Al (r = 0.85, 0.77 and 0.86, respectively). An exponential relationship was found between P_AAEDTA and DPS_ox. Results of principal component analysis and regression demonstrated that STP can be used to predict DPS_ox (r = 0.93) after logarithmic transformation. Soil test Al was also a good indicator of the P sorption capacity (PSC_ox) of soils (r = 0.86). Including the clay fraction in regression equations only slightly improved the prediction of PSC_ox (r = 0.90), while other readily available data (such as pH or organic carbon) did not significantly improve either DPS_ox or PSC_ox predictions.     

Simple phosphorus saturation index to estimate risk of dissolved P in runoff from arable soils

Abstract. There is increasing evidence that phosphorus has been accumulating in the surface horizons of agricultural soils to the extent that some soils represent a potential diffuse source of pollution to surface waters. The relationships between equilibrium phosphorus concentration at zero sorption (EPC ₀) of soil and a number of soil physicochemical variables were investigated in the surface layers of arable and grassland agricultural soils sampled from the Thame catchment, England. Soil EPC₀ could be predicted from an equation including soil test (Olsen) P, soil phosphate sorption index (PSI) and organic matter content (OM) (R²=0.88; P <0.001) across a range of soil types and land use. The simple index Olsen P/PSI was found to be a good predictor of EPC₀ (R²=0.77; P <0.001) and readily desorbable (0.02 m KCl extractable) P (R²=0.73; P <0.001) across a range of soil types under arable having soil organic matter contents of <10%.     

施磷对苦麦菜生长及土壤磷素淋失的影响

利用网室土柱模拟试验, 研究了不同磷用量[0、0.05 g·kg^-1(土)、0.10 g·kg^-1(土)、0.20 g·kg^-1(土)]对苦麦菜产量、磷素吸收和利用及土壤磷淋失的影响。结果表明, 施磷显著增加苦麦菜产量、促进植株对磷的吸收。苦麦菜产量在低磷水平[0.05 g·kg^-1(土)]时最高, 为每个土柱186.29 g。随磷用量增加, 苦麦菜产量和磷肥利用率明显降低, 植株吸磷量无明显变化。施磷显著增加土壤磷淋失量, 且随磷用量增加, 不同形态磷淋失量均显著增加。同一磷处理颗粒磷淋失量高于溶解态磷。不同磷用量条件下土壤各形态磷的淋失率均低于0.1%。低量施磷条件下溶解态磷在施磷后第10 d 出现第1 次淋失高峰; 中量和高量施磷条件下溶解态磷在施磷后第10 d 和第40 d 分别出现2 次淋失高峰。土壤总磷和颗粒磷淋失高峰期在施磷后第40~50 d 出现。施肥后第60 d, 土壤总磷、溶解态磷和颗粒磷淋失浓度均明显降低。综合考虑苦麦菜产量、磷素吸收和利用及土壤磷淋失量等因素, 苦麦菜以0.05 g·kg^-1(土)的施磷量为佳。     

施磷对玉米吸磷量、产量和土壤磷含量的影响及其相关性

为了给玉米磷高效利用提供理论依据, 在低磷土壤(Olsen-P 4.9 mg·kg^-1)上, 通过田间试验, 研究了施磷0(T₀)、50 kg(P₂O₅)·hm^-2(T₁)、100 kg(P₂O₅)·hm^-2(T₂)、200 kg(P₂O₅)·hm^-2(T₃)、1 000 kg(P₂O₅)·hm^-2(T₄)对两个玉米品种"鲁单9002" (LD9002)、"先玉335"(XY335)的产量、磷素吸收利用及根际磷动态变化的影响。结果表明: 两玉米品种根际土、非根际土速效磷含量在不同生育时期都表现为T12O₅)·hm^-2的T₃处理非根际土转化为根际土土壤磷的量最大, 同时玉米生物量、产量、磷转移量也达到最高, 而施磷1 000 kg(P₂O₅)·hm^-2处理玉米生物量、产量与中磷水平相比没有显著增加, 但植株吸磷量较高。XY335的花后磷转移量小于LD9002。相关分析表明, LD9002根际土、非根际土速效磷含量与茎、叶吸磷量之间显著相关, 以播种后79 d与茎、叶磷浓度、吸磷量、生物量、产量之间的相关系数最高; 而XY335根际土、非根际土速效磷含量与茎、叶磷浓度之间显著相关, 在播种后47 d期间与茎、叶磷浓度、吸磷量、生物量、产量之间的相关性最好。因此, 在低磷土壤上, LD9002和XY335分别在播种后79 d和47 d时是植株对磷的敏感期, 可以通过测试根际土、非根际土速效磷含量来反映土壤的供磷状况; LD9002在79 d时最大吸磷量需要的根际土、非根际土速效磷含量分别为54.95 mg·kg^-1、32.99 mg·kg^-1, XY335品种在47 d时最大吸磷量需要的根际土、非根际土速效磷含量分别为51.24 mg·kg^-1、35.35 mg·kg^-1; 施磷量1 000 kg(P₂O₅)·hm^-2处理两品种玉米产量、生物量、磷积累量与施磷量100~200 kg(P₂O₅)·hm^-2处理没有显著差异。     

太湖湖积物及黄海潮间海积物中氮的反硝化及硝态氮还原成铵的研究

Denitrification and nitrate reduction to ammonium in Taihu Lake and Yellow Sea inter-tidal marine sediments were studied.The sediment samples were made slurry containing 150g dry matter per liter.Various of glucose-C to nitrate-N.Acetylene inhibition technique was applied to measure denitrification in the slurres,All samples were incubated anaerobically under argon atmosphere,Data showed that Taihu Lake sediment produced more N2O than marine sediment,Denitrification potential was higher in Taihu Lake sediment than in marine one,Glucose added increase denitrification activity but not the denitrification potential of the sediments.Dissimilatory nitrate reduction to ammonium seemed to occur in marine sediment,but not in freshwater one.When the marine sediment was treated with 25mmol L^-1 glucose,its denitrification potentail,as indicated by maximum N2O production by acetylene blockage,was lower than that treated with no or 2.5mmol L^-1 glucose.Acetylene was suspected to have inhibitory effect on dissimilatory nitrate reduction to ammonium.     

天鹅湖潟湖表层沉积物磷的吸附容量及潜在释磷风险

研究了天鹅湖潟湖表层沉积物对磷的吸附容量,分析了沉积物磷吸附指数(PSI)、磷吸附饱和度(DPS)及由这两个指标构成的磷释放风险指数(ERI),预测了不同区域沉积物磷的潜在释放风险。结果表明,沉积物的PSI变化范围为7.44~28.53 mg L/100 gμmol,湖北部和中部沉积物的PSI值较高;DPS与PSI的变化趋势相反,变幅为0.85%~4.99%,表现为湖南部和中部沉积物的DPS高于北部。沉积物的PSI与磷的理论吸附容量(Qmax)呈极显著正相关(P0.01),而DPS与沉积物各理化参数间的相关性较差。有机质(OM)、活性铝(Alox)和粘粒是表层沉积物对磷持留的主要影响因素。此外,天鹅湖潟湖表层沉积物的ERI变化范围为2.93%~44.70%,磷释放诱发富营养化的风险处于中度范围,其中东南部发生富营养化的风险较高     

Inhibition of phosphorus sorption to goethite, gibbsite, and kaolin by fresh and decomposed organic matter

The direct effects of dissolved organic matter (DOM) on the sorption of orthophosphate onto gibbsite, goethite, and kaolin were examined using a one-point phosphorus sorption index and the linear Tempkin isotherm model. DOM extracted from fresh and decomposed agricultural residues, as well as model organic and humic acids, were used. Changes in the chemical and sorptive characteristics of the DOM in the absence and presence of added orthophosphate (50 mg l⁻¹) were also determined. For residue-derived materials, DOM sorption to all minerals correlated well with percent hydrophobicity, apparent molecular weight, and phenolic acidity in the absence of added orthophosphate. Sorption of DOM to goethite and gibbsite was significantly decreased in the presence of added P. The correlation coefficient values of percent hydrophobicity, apparent molecular weight, and phenolic acidity to sorption also declined in the presence of added P. Thus, the addition of P substantially lowered fractionation of DOM after sorption to goethite and gibbsite. In contrast, few significant P sorption-induced differences were observed in the kaolin system. According to one-point P sorption results, DOM in the form of Aldrich humic acid, oxalate, and decomposed clover and corn residue, significantly inhibited P sorption to goethite at concentrations of 50 and 200 mg total soluble carbon (C_TS l⁻¹). Phosphorus sorption to gibbsite was significantly inhibited by 50 mg C_TS l⁻¹ derived from decomposed corn residue, fresh dairy manure residue, and oxalate solution. At 200 mg C_TS l⁻¹, all DOM solutions were found to inhibit P sorption to gibbsite. This study suggests that DOM inhibition of P sorption depends on the chemical properties of both the sorbent and the DOM itself. In general, DOM from decomposed organic materials inhibited P sorption to a greater extent than did DOM derived from fresh materials. This stronger inhibition highlights the importance of microbial processes in the release of soluble soil P, a key determinant of P availability to plants.     

Soil cultivation effects on sediment and phosphorus mobilization in surface runoff from three contrasting soil types in England

To encourage the adoption of best management practices in a priority catchment (Hampshire Avon) in south-west England suffering from diffuse pollution, field demonstration areas were established over a 2-year period on three major soil types (a Chalk soil with an 8° slope, a Greensand soil on a 5° slope and an underdrained Clay soil with a 1° slope). Within each demonstration area, three replicate runoff plots measuring 15 m long and 2 m wide and each containing a tramline were established to monitor the effectiveness of cultivation date (early versus late) and cultivation method (traditional versus reduced) on suspended sediment and P mobilization in surface runoff. Reduced cultivation consisted of heavy discing (5–8 cm depth) instead of ploughing (20–25 cm depth). Soil cultivation effects were variable and site specific depending on weather, inherent soil susceptibility to structural degradation and management. Surface sealing of the Greensand soil, tramline compaction on the Chalk soil and direction of drilling on the Clay soil were key contributing factors. Late cultivation increased surface runoff up to 5-fold and mobilization of sediment and P by up to an order of magnitude compared to early drilling using traditional cultivation techniques. Concentrations of sediment and P in runoff from the Greensand and Chalk soils were consistently lower when the soil was minimally tilled than ploughed, even though a range of soil physical measurements indicated greater soil consolidation where the soil was not inverted. The benefits of reduced cultivation were attributed to better surface cover and a firmer surface for tractor wheelings. Early drilling, timeliness of cultivation to avoid soil compaction, better tramline management and reduced cultivation techniques would help reduce agriculture's impact on water quality in the catchment area.     

太湖、巢湖、龙感湖沉积物中磷的地球化学形态

A sequential extraction method for the fractionation of phosphorus （P） in lake sediments was used to analyze phos- phorus fractions of sediments taken from three large, shallow. eutrophic freshwater lakes of China-Talhu Lake. Chaohu Lake, and Long.an Lake. All three lakes are located in the lower reaches of the Changjiang River （Yangtze River）. In Taihu Lake and Chaohu Lake, algae blooms occurred every year, while Longgan Lake was a macrophyte-dominated lake. Results showed that exchangeable phosphorus fractions were much higher in the eutrophic lake sediments than in the macrophyte-flourishing lake sediment. Also, the ratio of Fe：P in the sediments of the algae-predomlnant lakes was generally much lower than that in the macrophyte-predominant lakes. Thus, the geochemical fractions of phosphorus in sediments had a closer relationship with the type of aquatic vegetation.     

上海郊区河流沉积物N、P释放的初步研究

A laboratory study was conducted to observe the release of nitrogen and phosphorus from the sedimentsunder both anaerobic and aerobic conditions. The samples used were five creek sediments and a fish-pondsediment (as a comparison) obtained from suburban Shanghai. High loads of nitrogen and phosphoruswere found in the creek sediments. Total nitrogen of the sediments ranged from 1.17 to 5.95 g kg^-1; totalphosphorus from 608.63 to 2 033.95 mg kg^-1. Making up more than 90% of the total nitrogen, organicnitrogen was the dominant nitrogen fraction in the sediments; where as inorganic phosphorus was the dominant phosphorus fraction, which made up more than 85 percent of the total phosphorus. Cabound phosphorus fraction dominated inorganic phosphorus, which occupied more than 50% of the total. A large amount of ammonium was released from the sediments under both aerobic and anaerobic conditions, and the anaerobic releases were slightly greater than the aerobic. In addition, ammonium contents in the aerobic waters decreased sharply after reaching the peaks because of strong nitrification, compared with the relatively maintained ammonium peaks in the anaerobic waters. Anaerobic phosphate releases were much greater than the aerobic and the released ortho-phosphate was mainly from Fe-bound phosphorus. Ammonium and ortho-phosphate releases from the sample of the dredged creek were the lowest, showing that creek dredging could effectively remove contaminants from the surface of sediments and weaken the release potentials of nitrogen and phosphorus. Ammonium and ortho-phosphate releases from the fish-pond sediment were greater than those from the creek sediments though its total nitrogen and phosphorus were not the highest, which was probably due to the larger amount of biologically degraded organic matter in the fish-pond sediment.     

磷肥和有机肥对不同磷水平土壤磷吸附-解吸的影响

采用培养试验结合Langmuir吸附等温方程进行拟合求出吸附、解吸的相关参数的方法,研究了磷肥和有机肥对不同磷水平土壤磷吸附和解吸特性的影响。结果表明,随土壤磷水平和磷肥和有机肥用量的增加,土壤最大吸磷量、土壤磷最大缓冲能力显著降低;土壤易解吸磷和土壤磷的解吸率显著增加。土壤易解吸磷和土壤磷的解吸率与土壤Olsen-P呈显著正相关;土壤最大吸磷量、土壤磷最大缓冲容量与土壤Olsen-P呈显著负相关。单位量磷肥所增加的土壤易解吸磷随着磷肥用量和土壤磷水平的增加而增大;土壤磷水平和磷用量是影响土壤磷最大吸磷量和土壤磷最大缓冲能力的重要因素。     

水分和磷对苗期玉米根系形态和磷吸收的耦合效应

水分亏缺和土壤缺磷已经成为玉米(Zea mays L.)生产的主要限制性因素,但水分和磷如何调节玉米根系形态和磷吸收尚不完全清楚。本研究采用盆栽土培试验,设置4个水分梯度[田间持水量的35%(W1)、55%(W2)、75%(W3)和100%(W4)]和2个磷处理[高磷:205 mg(P)·kg~(-1);低磷:11 mg(P)·kg~(-1)],探究水分和磷对苗期玉米根系生长和磷吸收的耦合效应。结果表明:(1)不管土壤磷供应如何,玉米苗干重、根干重、总根长和根表面积随水分供应强度的增加呈现先增加后降低的趋势,土壤有效磷含量也表现出相似的变化趋势,根质量比和平均根直径随水分供应强度的增加呈现下降的趋势,植株磷含量和磷累积量随水分供应强度的增加呈现稳定增加的趋势;(2)水分亏缺(W1)和过量供应(W4)均不利于玉米根系生长和干物质累积,水分亏缺(W1)抑制玉米对土壤磷素的获取,水分过量供应(W4)引起土壤磷素的奢侈吸收(W4),轻度的水分胁迫(W2)能够促进玉米根系的生长和干物质累积,减少对土壤磷的奢侈吸收,充足的水分供应(W3)能够促进玉米根系的生长、干物质累积和土壤磷素的吸收;(3)磷供应显著增加了玉米苗干重、根干重(W4除外)、总根长、根表面积、植株磷含量(W4除外)和磷累积量,但降低了玉米的根质量比。(4)两因素方差分析结果表明,水分对苗干重、根干重、根质量比、总根长、根表面积、平均根直径、植株磷含量、植株磷累积量和土壤有效磷含量的相对贡献分别为45.94%、36.71%、67.95%、59.63%、58.34%、81.86%、24.75%、35.66%和3.00%,磷对这些参数的相对贡献分别为34.78%、21.19%、14.84%、9.22%、9.21%、1.56%、35.54%、49.75%和94.40%,可见水分是控制玉米根系形态和干物质累积的关键因子,磷是控制玉米地上磷吸收和土壤有效磷含量的关键因子。总体来说,低磷条件下玉米根系对土壤磷的获取偏向于以根形态为主导的适应策略,高磷条件下玉米根系对土壤磷的获取偏向于以根生理吸收为主导的适应策略。水分和磷之间较好的耦合能够促进玉米根系生长、干物质累积,减少对土壤磷素的奢侈吸收。     

Sediment and phosphorus delivery from field to river via land drains in England and Wales. A risk assessment using field and national databases

Abstract. As measures to reduce point source inputs of phosphorus (P) to water have been introduced, the effect of diffuse P has become more evident. Land drains can act as an effective conduit for transfer of sediment and sediment P from agricultural land to surface waters. This article describes the development of a national risk map, identifying areas of agricultural land in England and Wales that are most likely to be prone to such losses. The map is based on data obtained from a variety of sources, including field studies, laboratory-based rainfall simulation experiments and secondary sources. From these studies, eight factors relating to soil HOST class, rainfall, soil moisture deficit, land use and the type and condition of land drains were identified as influential in the process of sediment and sediment P transfer. Each factor was weighted to provide an estimate of risk and the combined total was used to plot a national risk estimate at a resolution of 25 km². The exercise suggests that large areas of England and Wales may be at risk of subsurface sediment and sediment P transfer from agricultural land to rivers. The scale of the map is insufficient for planning at the farm level, but further work incorporating similar data and principles could make it more applicable to potential end-users on the ground.     

Rainfall effects on erosion of earthworm casts and phosphorus transfers by water runoff

 We investigated whether, under a temperate climate and in a maize crop, earthworm casts could contribute to soil erosion and further favour the exportation of phosphorus by runoff waters. Recording of casts was made in compacted (wheel-tracks) and non-compacted inter-rows, for a 2-month period in spring. To assess the rainfall impact on cast evolution, half of the observation sites were protected against rain splash by a nylon mesh placed above the soil surface. The water runoff was collected and analysed for sediment contents and phosphorus concentration. The mean annual production of surface casts was calculated to be 34 kg (dry weight) year^–1 kg^–1 earthworm (fresh weight). Synchronization between cast erosion and rainfall events was shown under natural conditions (unprotected sites). The erosion rate was 4 times greater over rainy periods than dry ones, reaching 80% of cast numbers. It appeared that not the runoff effect but the splash effect, due to the kinetics of the drops, disrupted casts. Newly formed casts disappeared first, with the erosion rate decreasing twofold for casts more than 10 days old. Cast erosion and runoff, as well as worm casting activity, were greater under compacted sites than under non-compacted sites, indicating an influence of earthworms on soil erosion from compacted soils. The total phosphorus content was similar in casts and uningested soil (0.80 mg phosphorus g^–1). Potential phosphorus losses from cast erosion was calculated to reach 25–49 mg phosphorus m^–2 per rainfall event depending on soil compaction. The amounts of particulate phosphorus recovered in water runoff after each rainfall event varied from 1 mg to 11 mg phosphorus. These results are compared and discussed. Received: 20 October 1998