Rainfall Simulation Study Research Articles

Standards vary in studies using rainfall simulators to evaluate erosion

Rainfall simulators are often employed to measure erosion rates, in order to estimate stream loading of sediment and nutrients in California foothill watersheds. The rainfall simulator enables the precise application of artificial rain with controlled drop sizes, intensity and duration. In addition to rain factors such as drop energy and intensity, several soil- and cover-related factors affect erosion rates. While computational models have evolved to quantify erosion based on field measurements taken by rainfall simulators, there has not been a consensus on the methodology to be deployed, especially in forested and remote landscapes. In addition, it is challenging to apply study results from small plots to entire watersheds. To guide future fieldwork on sediment loading to water bodies, we review key concerns related to rainfall simulator studies.

Impact of tillage on runoff in long term no-till wheat systems

Adoption of no-till cropping systems continues to increase worldwide due to enhanced soil and water conservation, reduced inputs and maintained crop production. Soil compaction, particularly in grazed systems, can become a concern within no-till cropping systems and occasional tillage may be a method to relieve these concerns. However, there is no data within the US Southern Great Plains examining the impact of tilling long-term no-till wheat cropping systems and the potential subsequent impacts on runoff characteristics. The objective of this study was to evaluate the impact of tilling long term no-till wheat systems on runoff water quantity and quality. The study was conducted within a field that had been in no-till wheat with occasional grazing for seven years. Seven tillage treatments were evaluated, including: no-till, conventional till, and soil aeration using roller angles of 0°, 2.5°, 5°, 7.5°, and 10°. Rainfall simulation studies providing a 7cmh−1 storm event were conducted approximately three months after tillage. Results showed that conversion from no-till to conventional tillage increased runoff volume by 38%. Total sediment losses were at least 2.8 times greater from conventional till plots than no-till and aerated treatments. Nutrient concentrations were similar among tillage treatments. However, total P and ammonium-N loads in runoff water were significantly higher from conventional till plots compared with other tillage treatments. Aeration did not provide a consistent trend and generally provided no significant improvement in runoff characteristics compared with no-till. Initial results indicate no advantage of tilling long term no-till wheat systems in regard to runoff quality and quantity three months after tilling.

Erosion modelling for land management in the Tahoe basin, USA: scaling from plots to forest catchments

Land management and its effects on water quality are a concern where regulatory agencies work to establish sediment and/or nutrient loadings. Runoff and erosion measurement in the field and modelling at the catchment scale are often the only means of generating realistic data and results for subsequent analyses. As such, it is critical to link local-scale field measurements associated with the range of land uses or soil restoration efforts with the catchment-scale sediment loading. A distributed hydrological model with locally-derived, slope-dependent sediment yield (erodibility) equations developed from rainfall simulation (RS) studies at the 1-m2 scale across the Tahoe basin, USA, is employed to determine the runoff-dependent scaling factors (SFs) necessary to predict daily stream sediment loading from the forested uplands. Data from three “paired”, adjacent, west-shore Lake Tahoe tributary catchments are considered for the period 1994–2004 at time scales ranging from daily to annual. At all time scales, the SF was dependent on runoff (R), particularly at smaller values, but was readily simplified as an approximately inverse square-root function. Optimized SF–runoff regressions for each watershed were equivalent when modified by ratios of watershed area. As a result, a single daily SF–runoff equation was determined (through minimization of sediment load prediction errors) that could be successfully applied to all three watersheds with an accuracy consistent with the predictive error associated with any one of the watersheds alone. Sensitivity analyses indicated that sediment loading predictions were more sensitive to the SF–runoff equation coefficient rather than the exponent. Annual sediment load prediction errors of ˜30% might be expected for low or high runoff years. Editor D. Koutsoyiannis Citation Grismer, M.E., 2012. Erosion modelling for land management in the Tahoe basin, USA: scaling from plots to forest catchments. Hydrological Sciences Journal, 57 (5), 878–900.

Reducing the risk of herbicide runoff in sugarcane farming through controlled traffic and early-banded application

The off-site transport of agricultural chemicals, such as herbicides, into freshwater and marine ecosystems is a world-wide concern. The adoption of farm management practices that minimise herbicide transport in rainfall-runoff is a priority for the Australian sugarcane industry, particularly in the coastal catchments draining into the World Heritage listed Great Barrier Reef (GBR) lagoon. In this study, residual herbicide runoff and infiltration were measured using a rainfall simulator in a replicated trial on a brown Chromosol with 90–100% cane trash blanket cover in the Mackay Whitsunday region, Queensland. Management treatments included conventional 1.5m spaced sugarcane beds with a single row of sugarcane (CONV) and 2m spaced, controlled traffic sugarcane beds with dual sugarcane rows (0.8m apart) (2mCT). The aim was to simulate the first rainfall event after the application of the photosynthesis inhibiting (PSII) herbicides ametryn, atrazine, diuron and hexazinone, by broadcast (100% coverage, on bed and furrow) and banding (50–60% coverage, on bed only) methods. These events included heavy rainfall 1day after herbicide application, considered a worst case scenario, or rainfall 21days after application. The 2mCT rows had significantly (P<0.05) less runoff (38%) and lower peak runoff rates (43%) than CONV rows for a rainfall average of 93mm at 100mmh−1 (1:20yr Average Return Interval). Additionally, final infiltration rates were higher in 2mCT rows than CONV rows, with 72 and 52mmh−1 respectively. This resulted in load reductions of 60, 55, 47, and 48% for ametryn, atrazine, diuron and hexazinone from 2mCT rows, respectively. Herbicide losses in runoff were also reduced by 32–42% when applications were banded rather than broadcast. When rainfall was experienced 1day after application, a large percentage of herbicides were washed off the cane trash. However, by day 21, concentrations of herbicide residues on cane trash were lower and more resistant to washoff, resulting in lower losses in runoff. Consequently, ametryn and atrazine event mean concentrations in runoff were approximately 8 fold lower at day 21 compared with day 1, whilst diuron and hexazinone were only 1.6–1.9 fold lower, suggesting longer persistence of these chemicals. Runoff collected at the end of the paddock in natural rainfall events indicated consistent though smaller treatment differences to the rainfall simulation study. Overall, it was the combination of early application, banding and controlled traffic that was most effective in reducing herbicide losses in runoff.

Transient Soil Surface Sealing and Infiltration Model for Bare Soil under Droplet Impact

The marked reduction in infiltration rate caused by formation of a soil surface seal due to water droplet impact on bare soil is a well known phenomenon but is rarely considered in infiltration models, especially under center-pivot irrigation. Water application rates under center-pivot irrigation commonly exceed the infiltration rate, especially near the end of the system lateral. This can lead to off-site runoff and erosion, but more importantly results in field-scale non-uniform water infiltration that can substantially reduce water use efficiency of these irrigation systems. The objective of this study was to develop a sealing soil infiltration model that considers transient soil seal formation on a 30 min or less time scale and can potentially be applied to center-pivot sprinkler irrigation systems. A sealing soil infiltration model was developed using an explicit finite difference solution scheme with a transient soil seal formation model, which is unique from other studies in that it explicitly uses droplet specific power as the driving factor for formation of a soil surface seal. The form of the transient seal formation model is also unique in that it is expressed as a rational function of specific power rather than an exponential decay function of droplet kinetic energy. The model was applied to published runoff data from two rainfall simulation studies with varying droplet kinetic energies and application rates on three soils. The sealing soil infiltration model represented the measured infiltration rates very well for all rainfall simulator tests. The transient soil seal formation model uses three parameters, one of which is an empirical parameter representing the susceptibility of the soil to aggregate breakdown that was constant for a given soil. A second model parameter, final saturated hydraulic conductivity of the surface seal, was well correlated to droplet specific power for a given soil. Application of the model to center-pivot irrigation will require the development of a model for estimating droplet specific power and application rate profiles from center-pivot sprinklers for a range of sprinkler designs, flow rates, operating pressures, spacings, and heights.

Manure Composition and Incorporation Effects on Phosphorus in Runoff Following Corn Biomass Removal

Greater demand for corn ( L.) stover for bioenergy use may lead to increased corn production acreage with minimal surface residue cover, resulting in greater risk for soil erosion and phosphorus (P) losses in runoff. A rainfall simulation study was conducted to determine the effects of spring-applied dairy cow () manure (none, in-barn composted, and exterior walled-enclosure pit) with >200 g kg organic solids content following fall corn biomass removal with and without incorporation (chisel plow [CP] and no-till [NT]) on sediment and P in runoff. Runoff was collected from a 0.83-m area for 60 min following the onset of rainfall simulation (76 mm h), once in spring and once in fall. Runoff dissolved reactive P (DRP) and dissolved organic P (DOP) concentrations were positively correlated with manure P rate and were higher in NT compared with CP. Conversely, sediment and particulate P (PP) concentrations in runoff were inversely correlated with manure P rate (and manure solids) and were higher in CP compared with NT. Runoff volume where no manure was applied was higher in NT than in CP in spring but similar in fall. The addition of manure reduced runoff volumes by an average of 82% in NT and 42% in CP over spring and fall. Results from this study indicate that surface application of dairy manure with relatively high solids content may reduce sediment and PP losses in runoff without increasing the risk of increased DRP and DOP losses in the year of application where corn biomass is harvested.

Runoff and soil erosion from highway construction spoil deposits: A rainfall simulation study

To measure soil loss from these road construction spoils, 30 rainfall simulations involving five rainfall intensities were conducted to study runoff and soil erosion processes on a road in China. Twenty-five of the rainfall simulations were carried out on loose materials five different slopes. Another five rainfall simulations were conducted on compacted road materials with a slope of 30.6%. The results show that soil bulk density has a positive effect on runoff rate, and the effect of slope on runoff rate changes with rainfall intensity. Higher soil bulk density increases soil loss under low rainfall intensity, but decreases soil loss when rainfall intensity is high. Soil loss is positively related to slope, but the relationship differs from that in prior studied of croplands and disturbed lands. Equations for predicting soil erosion from loose materials and compacted road are developed.

Effects of grass and shrub cover on the critical unit stream power in overland flow

Improved knowledge of the effects of grass and shrub cover in overland flow can provide valuable information for soil and water conservation programs. Laboratory simulated rainfall studies were conducted to determine effects of grass and shrub on runoff and soil loss and to ascertain the relationship between the rate of soil loss and the unit stream power of runoff for a 20 o slope subjected to rainfall intensities of 45, 87, and 127 mm/h. The results indicated that the average runoff rates ranged from 4.2 to 73.1 mm/h for grass plots and from 9.3 to 58.2 mm/h for shrub plots. Runoff rates from shrub plots were less than those from grass plots for all but the 45 mm/h rainfall intensity regime. Average soil loss rates varied from 5.7 to 120.3 g/min.m 2 for grass plots and from 5.6 to 84.4 g/min.m 2 for shrub plots. Soil loss rates from shrub plots were generally lower than those from grass plots. Runoff and soil loss were strongly influenced by soil surface conditions due to the formation of erosion pits and rills. The rate of soil loss increased linearly with the unit stream power of runoff on both grass and shrub plots. Critical unit stream power values were 0.0127 m/s for grass plots and 0.0169 m/s for shrub plots. Shrub plots showed a greater stability to resist soil detachment and transport by surface flow than grass plots.

Livestock Manure Windrow Composting Runoff And Infiltration Characteristics from Laboratory Rainfall Simulations

Windrow-composted livestock manure has been shown to be less hazardous to the environment compared to manure directly applied to cropland and other agricultural areas. Although offsite contaminant losses through runoff and leaching can occur during the composting process, these losses are suspected to increase under different compost moisture conditions and as composted materials mature. This research quantified the effects of windrow-composted livestock manure and straw bedding components on runoff and infiltration characteristics from laboratory rainfall simulations. Compost samples collected on three dates at approximately the beginning (day 0), middle (day 30), and end (day 60) of a June-July 2004 field research windrow composting period were used for this rainfall simulation study. Replicated compost windrow-shaped cross-section samples were constructed in a specially-designed Plexiglas container apparatus for viewing and recording infiltrated leachate wetting front position boundary movement from simulated rainfall events. Runoff and leachate samples were collected and analyzed for drainage volumes and concentrations and total mass losses of sediment, nitrate-nitrogen (NO3-N), and ortho-phosphorus (PO4-P) during and following rainfall simulation trials. Leachate wetting front position boundary movement was significantly lower for day 60 compost samples compared among day 0 and day 30 compost sample material. Drainage volume analysis results indicated significantly higher average runoff versus leachate volumes within all compost sampling dates, and runoff volumes were significantly higher among day 30 and day 60 compost samples compared to runoff volumes from day 0 compost samples. Average sediment, NO3-N, and PO4-P concentrations were significantly higher in leachate versus runoff within all compost sampling dates. Conversely, the total mass losses of these contaminants were significantly higher in runoff compared to leachate within all compost sampling dates. Results of this study suggest that biological and mechanical functions of the composting process reduced compost sample aggregates and increased compost bulk density. We hypothesize that these changes in compost material structure and porosity volume decreased infiltration and increased runoff sediment, NO3-N, and PO4-P losses during the second and final compost sampling stages of a field windrow composting period.

Effects of cattle, sheep and deer grazing on soil physical quality and losses of phosphorus and suspended sediment losses in surface runoff

Livestock grazing and treading is strongly linked to a decrease in freshwater quality and promotes eutrophication. A two-year field trial was carried out to investigate the influence cattle, sheep and deer have on soil physical quality and the loss of phosphorus (P) and suspended sediment (SS) in surface runoff. Surface runoff plots (4m long by 1m wide) were installed within areas designated as stock or ungrazed (control). Surface runoff was collected and analysed for concentrations and loads of P fractions (dissolved reactive P-DRP, dissolved unreactive P-DUP, total dissolved P-TDP, particulate P-PP and total P-TP) and SS. Grazed at equivalent stocking density, soil physical samples (macroporosity, bulk density, and saturated hydraulic conductivity Ksat) were taken after each grazing event (n=11). Soil physical data indicated differences between cattle, sheep and deer with cattle having greater negative effects. However, these differences had no impact on P and SS losses between stock types in surface runoff. Significant relationships showed that an increase in macroporosity, Ksat, and time (days) since grazing decreased concentrations and loads of P and SS losses. A separate rainfall simulation study also revealed that an increase in simulated cattle treading intensity increased the volume of surface runoff and SS losses. Most surface runoff (> 90%) occurred in winter when soil moisture was at or above field capacity. A seasonal effect was observed and showed that although the greatest P loads occurred in winter, the greatest P concentrations occurred in summer months, under infiltration-excess conditions. These summer losses could pose a risk to receiving waterways because increased light and warmth may induce an algal response compared to winter. While there is limited scope to manage for infiltration-excess surface runoff losses from pasture, with most runoff occurring in winter, these findings reinforce the use of mitigation strategies such as restricted or nil grazing in winter when soil moisture has reached field capacity to minimise P and SS loss to surface water, regardless of stock type.

Cob Removal Effect on Sediment and Runoff Nutrient Loss from a Silt Loam Soil

The cob fraction of corn (Zea mays L.) residue has been identified as a potential feedstock for ethanol production. However, the role of the cob in soil and water conservation is largely unknown. A rainfall simulator study was conducted in an irrigated corn field in Nebraska having replicated strips where corn residue was removed (6.0 ± 1.0 Mg ha−1 residue remaining, 49.5% cover) or retained (12.9 ± 1.0 Mg ha−1 residue remaining, 77% cover). Duplicate plots were installed in each strip and cobs were removed from one and retained in the other. Simulated rainfall was applied for 30 min at a mean rate of 83 mm h−1 to plots at antecedent moisture and 24 h later at near saturated soil moisture conditions. Time to initiate runoff, runoff and sediment loss, and water quality parameters were measured. Residue removal reduced the time to initiate runoff (195.9 ± 1.0 vs. 239.5 ± 4.8 s) and increased sediment loss (0.36 ± 0.02 Mg ha−1 vs. 0.27 ± 0.01 Mg ha−1). Cob removal reduced time to initiate runoff during the antecedent run but not during the saturated run. Residue removal and rainfall treatment (antecedent vs. saturated) affected runoff water quality parameters (NO3–N concentration, pH, soluble P concentration, and NO3–N loss). Cob removal did not affect runoff, sediment loss, runoff pH, NO3–N, NH4–N, or soluble P loss. Cob removal when adequate stover was retained did not negatively affect erosion and runoff nutrient loss at this site.

Estimating Dissolved Reactive Phosphorus Concentration in Surface Runoff Water from Major Ontario Soils

Phosphorus (P) loss from agricultural land in surface runoff can contribute to eutrophication of surface water. This study was conducted to evaluate a range of environmental and agronomic soil P tests as indicators of potential soil surface runoff dissolved reactive P (DRP) losses from Ontario soils. The soil samples (0- to 20-cm depth) were collected from six soil series in Ontario, with 10 sites each to provide a wide range of soil test P (STP) values. Rainfall simulation studies were conducted following the USEPA National P Research Project protocol. The average DRP concentration (DRP30) in runoff water collected over 30 min after the start of runoff increased (p < 0.001) in either a linear or curvilinear manner with increases in levels of various STPs and estimates of degree of soil P saturation (DPS). Among the 16 measurements of STPs and DPSs assessed, DPS(M3) 2 (Mehlich-3 P/[Mehlich-3 Al + Fe]) (r2 = 0.90), DPS(M3)-3 (Mehlich-3 P/Mehlich-3 Al) (r2 = 0.89), and water-extractable P (WEP) (r2 = 0.89) had the strongest overall relationship with runoff DRP30 across all six soil series. The DPS(M3)-2 and DPS(M3)-3 were equally accurate in predicting runoff DRP30 loss. However, DPS(M3)-3 was preferred as its prediction of DRP30 was soil pH insensitive and simpler in analytical procedure, ifa DPS approach is adopted.

Source Water Effects on Runoff Amount and Phosphorus Concentration under Simulated Rainfall

Frequently, well water is used instead of rainwater to perform rainfall simulations to study P and soil loss in cropping systems. This study was conducted to determine whether the source water used in simulated rainfall studies affects runoff amount and P and sediment concentrations. Rainfall simulation and natural runoff studies were conducted in a corn (Zea mays L.) and alfalfa (Medicago sativa L.) field on a Tama silt loam (fine‐silty, mixed, superactive, mesic Typic Argiudoll) in spring and fall 2004. No significant differences in runoff composition were found between the well and deionized (DI) source waters in the spring rainfall simulation study in corn. The fall rain simulation in alfalfa showed significantly higher runoff volumes and dissolved reactive P (DRP) concentrations with DI water than with well water. Soil water‐extractable P (WEP) measurements showed that rain and DI water extracted similar amounts of P, while well water extracted less P. Using the same source waters in WEP procedures and in rainfall simulations yielded good relationships (r2 = 0.73) between simulated rain runoff DRP and soil WEP concentrations. Natural runoff DRP concentrations measured in the same field treatments as those used in the simulated rainfall studies were much greater than those found in simulated rainfall runoff, but the relative field treatment effects on runoff P concentrations were the same. These results emphasize that simulated rainfall data can provide a relative comparison of treatment effects on runoff composition, but results from simulated rainfall experiments are not likely to duplicate natural runoff composition, regardless of the source water used.

Modifying Broiler Diets with Phytase and Vitamin D Metabolite (25‐OH D3): Impact on Phosphorus in Litter, Amended Soils, and Runoff

Adding phytase and 25- hydroxycholecalciferol (25-OH D(3)) to broiler diets has been shown effective at reducing total P concentrations in broiler litter. This study was conducted to determine the impact of field application of broiler litter from modified diets on P solubility in litter-amended soils and P losses in runoff. Five broiler diets and their resulting litters were evaluated: a high P diet, a low P diet, each of those basal diets with phytase added, and a low P diet with phytase and 25-OH D(3) added. A field study was initiated at two sites with each of the five broiler litters and a commercial P fertilizer (triple superphosphate [TSP]) applied at the same total P rate (150 kg P ha(-1)) and a control where no P was applied. Soil P was monitored over time at two depths (0-5 cm and 0-15 cm) soils were collected in the spring and fall to perform rainfall simulation studies. Broiler litter or TSP application increased soil water-soluble P and Mehlich 3-P concentrations relative to the control, however there were no consistent differences detected between litter treatments. Results from the rainfall simulation experiments indicate that diet modification with phytase or 25-OH D(3) does not increase the potential for P losses in runoff from amended soils relative to traditional diets. Moreover, broiler diet modification to reduce excreted P could be a potentially effective method for reducing watershed scale P surpluses in areas of intensive broiler production, without raising concerns over soluble P losses from litter-amended soils.

Rainfall Sequence Effects on Phosphorus Loss in Surface Runoff from Pastures that Received Poultry Litter Application

Land application of poultry litter to pasture elevates the concentration of phosphorus in surface runoff, and it is becoming an increasing problem in sensitive water bodies. The objectives of this study were to assess the effects of soil test phosphorus (STP), surface application of poultry litter, rainfall/runoff sequences, and time after litter application on dissolved reactive phosphorus (DRP) in surface runoff from pasture in a greenhouse experiment using rainfall simulation. Treatment factors were poultry litter at a rate of 0.0 and 6.7 Mg ha-1, low and high STP, and three rainfall/runoff sequences (RRS). The latter refers to runoff-producing rainfall events starting from day 1, day 4, and day 7 after litter application. The study also included a rainfall simulation study of pasture field plots to investigate the effects of poultry litter and time after application on DRP in surface runoff, which was used to corroborate the greenhouse study. In both studies, runoff samples were taken at the end of 30 min of continuous runoff. Treatment effects on DRP concentrations in surface runoff were analyzed using ANOVA procedures using an alpha = 0.05. For the greenhouse study, poultry litter application, RRS, and time after litter application were found to have a highly significant effect on DRP concentration in surface runoff. Poultry litter had a significant effect on DRP concentrations in surface runoff until 18 days after litter application compared to the controls. Between 18 and 32 days after litter application, the effect on DRP became insignificant for any level of STP or rainfall sequence. A rainfall event without runoff reduced DRP concentration in the first surface runoff events by more than 50%. For the field plot study, DRP decreased rapidly with time, thereby corroborating the greenhouse study. The effect of poultry litter on DRP became statistically insignificant sometime between 35 and 161 days after application.

Simulated rainfall study for transport of veterinary antibiotics – mass balance analysis

Occurrence of human and veterinary antibiotics has been reported in various environmental compartments. Yet, there is a lack of information verifying the transport mechanisms from source to environment, particularly the transport of veterinary antibiotics as a non-point source pollutant. A rainfall simulation study was conducted to address surface runoff as a possible transport mechanism of veterinary antibiotics introduced in the field and mass balance was calculated with supplementary surface and depth soil measurement. Seven veterinary antibiotics that are the most abundantly used in agriculture for therapeutic and non-therapeutic (growth-promotion) purposes were examined in this study, including tetracycline (TC), chlortetracycline (CTC), sulfathiazole (STZ), sulfamethazine (SMZ), erythromycin (ETM), tylosin (TYL), and monensin (MNS). Runoff in aqueous and sediment phases was collected every 5 min for 1 h with varied rainfall intensity and additional surface (0–2 cm) and depth (2–30 cm) soil samples were collected after rainfall simulation for mass balance analysis. Quantification of antibiotic concentration in all collected samples was based on solid phase extraction (SPE) followed by measurement with high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). MNS showed the highest concentration in runoff aqueous samples (0.22 mg plot −1), while ETM showed the highest concentration in runoff sediment samples (0.08 mg plot −1). The highest concentration of each applied antibiotic in surface soil samples occurred at different locations. This result might indicate the mobility of these compounds in surface soil varies due to different physicochemical properties among the antibiotics. Further, the analysis results showed that all of the subject antibiotics had penetrated into the subsurface; yet, no residuals were found for STZ, suggesting this compound might have penetrated even deeper into the soil. These results indicate that aqueous or sediment erosion control might reduce the transport of veterinary antibiotics in the environment.

A comparison of surface applied granulated biosolids and poultry litter in terms of risk to runoff water quality on turf farms in Western Sydney, Australia

A simulated rainfall study was carried out on couch ( Cynodon dactylon cv) turf on a Haplic Lixisol soil at Camden in South Western Sydney, Australia, to compare surface applications of a new granulated biosolids product with poultry litter (the current turf farm practice) in terms of runoff water quality impacts. The granulated biosolids were surface applied to the turf at a total N loading of 240 kg N ha −1, equivalent to the current turf farm practice of applying 18.9 m 3 ha −1 of poultry litter. One week after the application of the organic fertiliser treatments, simulated rainfall was applied to each plot at an intensity of 90 mm h −1 for a period of 0.5 h, and all runoff water was collected and analysed for a range of important water quality parameters. The most significant result from this study was the finding that runoff water samples from the poultry litter treatment plots were found to contain 10 times more total P (12.3 mg l −1 compared to 1.2 mg l −1) and dissolved P (8.3 mg l −1 compared to 0.6 mg l −1) than that found in the runoff water samples from the biosolid treatment. The relationship between application total P loading (TPA) and runoff water total P concentration (RO-P) was significantly ( P < 0.05) different between the biosolids (RO-P:TPA ratio = 0.01) and poultry litter (RO-P:TPA ratio = 0.16) products, reflecting the importance of the chemical nature of the applied P in addition to the total loading. The phosphorus in the poultry litter was much more easily mobilised and transported in runoff than the biosolids P. For surface applications of these organic wastes, bicarbonate extractable P loading provided a better indication of runoff P contamination risk in the first flush of runoff, than total P loading. The runoff from the biosolid treatment plots also had lower levels of NH 4-N and salinity than the poultry litter plots, although both treatments had moderate levels of dissolved organic carbon in their runoff. Heavy metal levels in the runoff were below guideline limits for both organic amendments, while runoff pathogen levels were highly variable. Our findings highlight the potential benefits of using granulated biosolids as an alternative surface applied organic N fertiliser on turf farms for its lower risk to surface water quality as compared to poultry litter, the current practice.

Effects of different soil management practices on total P and Olsen-P sediment loss: A field rainfall simulation study

Field rainfall simulations were conducted in 2002 and 2005 to study the effects of different soil management practices on the total phosphorous (TP) and Olsen-P losses by soil erosion and redistribution along a 15 m long slope in Luoyang, Henan province, China. Field plots were set up in 2001 and included the following soil management practices: subsoiling with mulch (SSM), no-till with mulch (NTM), reduced tillage (RT), and a conventional tillage control (CT). The results showed that there were no significant differences in TP and Olsen-P content in the sediment load between different plots after 6 years uniform tillage practices. The enrichment of TP and Olsen-P at the lower slope showed a clear redistribution along the slope. Effects of tillage practices on the temporal pattern of the enrichment ratio (ER) of TP and Olsen-P was not uniform. ER TP values were initially high and diminished after a short period of time and leveled to the end of the rainfall test in CT and RT plots, but remained ≥ 1. The ER of Olsen-P at the end of rainfall simulation showed a significant difference when compared to the initial stage, 0.78 to 1.60, respectively. However, the temporal loss rate of TP and Olsen-P showed a similar pattern because it was more depending on the sediment loss rate than on the concentration in the sediment. SSM resulted in 96% less TP and Olsen-P erosion loss compared to CT in 2002. Also, SSM showed the highest reduction in TP and Olsen-P loss after 4 years consistent practice. RT reduced TP and Olsen-P loss by 30%, although the runoff reduction was not significant. NTM was the best alternative with respect to TP and Olsen-P conservation, when considering its lower operational costs.

Validating economic and environmental sustainability of a short-term summer forage legume in dryland wheat cropping systems in south-west Queensland

The present study set out to test the hypothesis through field and simulation studies that the incorporation of short-term summer legumes, particularly annual legume lablab (Lablab purpureus cv. Highworth), in a fallow–wheat cropping system will improve the overall economic and environmental benefits in south-west Queensland. Replicated, large plot experiments were established at five commercial properties by using their machineries, and two smaller plot experiments were established at two intensively researched sites (Roma and St George). A detailed study on various other biennial and perennial summer forage legumes in rotation with wheat and influenced by phosphorus (P) supply (10 and 40 kg P/ha) was also carried out at the two research sites. The other legumes were lucerne (Medicago sativa), butterfly pea (Clitoria ternatea) and burgundy bean (Macroptilium bracteatum). After legumes, spring wheat (Triticum aestivum) was sown into the legume stubble. The annual lablab produced the highest forage yield, whereas germination, establishment and production of other biennial and perennial legumes were poor, particularly in the red soil at St George. At the commercial sites, only lablab–wheat rotations were experimented, with an increased supply of P in subsurface soil (20 kg P/ha). The lablab grown at the commercial sites yielded between 3 and 6 t/ha forage yield over 2–3 month periods, whereas the following wheat crop with no applied fertiliser yielded between 0.5 to 2.5 t/ha. The wheat following lablab yielded 30% less, on average, than the wheat in a fallow plot, and the profitability of wheat following lablab was slightly higher than that of the wheat following fallow because of greater costs associated with fallow management. The profitability of the lablab–wheat phase was determined after accounting for the input costs and additional costs associated with the management of fallow and in-crop herbicide applications for a fallow–wheat system. The economic and environmental benefits of forage lablab and wheat cropping were also assessed through simulations over a long-term climatic pattern by using economic (PreCAPS) and biophysical (Agricultural Production Systems Simulation, APSIM) decision support models. Analysis of the long-term rainfall pattern (70% in summer and 30% in winter) and simulation studies indicated that ~50% time a wheat crop would not be planted or would fail to produce a profitable crop (grain yield less than 1 t/ha) because of less and unreliable rainfall in winter. Whereas forage lablab in summer would produce a profitable crop, with a forage yield of more than 3 t/ha, ~90% times. Only 14 wheat crops (of 26 growing seasons, i.e. 54%) were profitable, compared with 22 forage lablab (of 25 seasons, i.e. 90%). An opportunistic double-cropping of lablab in summer and wheat in winter is also viable and profitable in 50% of the years. Simulation studies also indicated that an opportunistic lablab–wheat cropping can reduce the potential runoff + drainage by more than 40% in the Roma region, leading to improved economic and environmental benefits.

A rainfall simulation study on the relationships between soil test P versus dissolved and potentially bioavailable particulate phosphorus forms in runoff

Runoff from clayey soils often contains abundant particulate phoshorus (PP), part of which may solubilize in surface waters. Monitoring losses of potentially bioavailable forms of PP is expensive, calling for other ways to predict them. Such predictions could be based on soil loss and available soil P indices, e.g., agronomic P status. To study correlations between P pools in runoff versus soil P saturation (by Mehlich 3 extraction; DPSM3) and acetate soil test P (PAc), 15 clayey soils of south Finland were subjected to laboratory rainfall simulation. Runoff from these simulations was analyzed for concentrations of suspended soil (TSS), dissolved molybdate-reactive P (DRP), total P (TP), and, as normalized to soil loss, potentially bioavailable forms of PP: desorbable (anion exchange resin-extractable, AER-PP/TSS) and redox-labile PP (bicarbonate- dithionite-extractable, BD-PP/TSS). Correlation coefficients (r2) between DPSM3 and DRP, AER-PP/ TSS, and BD-PP/TSS equaled 0.92, 0.77, and 0.45, respectively. Runoff P forms were also correlated to soil PAc with r2 values of 0.84, 0.56, and 0.58 for DRP, AER-PP/TSS, and BD-PP/TSS, respectively. Prediction of soil loss-normalized concentrations of potentially bioavailable PP by the agronomic PAc test was considered possible. However, such predictions have a high degree of uncertainty, evidenced by comparison to published field data. Acceptably accurate predictive equations would require a large material as a basis for their construction, and soils should probably also be grouped according to other soil properties that would account for variation in P sorption capacity.;