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Cropland best management practice recommendations often combine tillage and nutrient application improvements to reduce nutrient losses with surface runoff. This study used the Soil and Water Assessment Tool (SWAT) model to evaluate nutrient runoff yields from conventional-till and no-till management practices with surface and deep-banded fertilizer application in a sorghum-soybean rotation. The model was calibrated for three field plots (0.39 to 1.46 ha) with different combinations of practices and validated for three field plots (0.40 to 0.56 ha) during 2001 to 2004. Daily performance of the calibrated SWAT model in simulating total N for all treatments was satisfactory for median-based Nash-Sutcliffe model efficiency (Ef* of 0.54 to 0.64), good to very good for percent bias (PBIAS of 31% to 7%), and satisfactory to good for median-based root mean square error to observations standard deviation ratio (RSR* of 0.72 to 0.62). Performance was slightly lower and more variable for total P calibration (Ef* of 0.42 to 0.62, PBIAS of-48% to 2%, and RSR* of 0.76 to 0.62). Monthly statistics improved for total P runoff yield compared to daily performance, but changed little for total N runoff yields, probably due to the stronger influence of outliers in the N data. Based on validation results, SWAT was more robust in simulating total N runoff yields from the treatment with less soil disturbance (NT/SB) and total P for the two treatments with more soil disturbance (NT/DB and TILL). A major concern was that SWAT predicted greater annual average total N runoff yields for no-till treatments than for tilled treatments, which was contrary to measured values at the study site. This reinforces a fundamental research issue that tillage system effects on nutrient losses are still very much uncertain and thus may not be properly modeled. The SWAT model generally underpredicted monthly total N yields for all treatments in the higher-precipitation months of May and June and overpredicted total N and total P yields from September through November. Calibration for N and P resulted in identical calibration parameters for NPERCO (1.0), RSDCO (0.05), BIOMIX (0.2), PPERCO (10), PHOSKD (175), and UBP (50) regardless of tillage practice or fertilizer application method. Together with results that calibrated parameters for runoff (CN, Ksat, AWC) and erosion (Cmin) differed among the treatments, this study found that differences in nutrient yields among tillage and fertilizer management may be adequately modeled with SWAT by calibrating runoff and sediment yields only, and that further calibration of nutrient parameters may not improve model results. [ABSTRACT FROM AUTHOR]

Soil erosion from agricultural lands and the subsequent transport of sediment and sediment-bound nutrients (particularly P) are serious problems contributing to surface water pollution and threatening agricultural sustainability. Raindrop impact on bare soil destabilizes soil aggregates and leads to surface sealing, increasing runoff volumes and soil loss. Surface-applied polyacrylamide (PAM) decreases soil erosion by stabilizing the soil structure and reducing surface sealing. Previous research has shown that surface-applied PAM reduces erosion at relatively high application rates (20 to 80 kg ha-l). The purpose of this study was to evaluate the effectiveness and longevity of a new liquid/emulsion PAM formulation to reduce runoff, sediment, and P loss from rainfed agricultural fields. The formulation was applied using a hand sprayer at a low PAM rate of 5 kg ha-1 (13,333 L of solution ha-1). Plot-scale field rainfall simulations (75 mm ha-1) were conducted on individual test plots at three test intervals (rainfall simulated 2 days, 3 weeks, and 10 weeks after DAM application) on two soil types (Ashdale silt loam and Plano silt loam). The new polymer formulation, Soil Net EM-1000-50, reduced runoff volumes an average of 100% at the 2-day test interval, 59% at the 3-week test interval, and 55% at the 10-week test interval. Overall, larger rainfall depths were applied to treatment plots prior to runoff generation compared to controls. The most significant differences were observed at the 2-day test interval, when an average of 141 mm of rainfall was applied to the PAM-treated plots before runoff started, compared to 82 mm for the controls. These runoff reductions are not only important in terms of erosion but may also enhance water supply through increased infiltration. Sediment loss was reduced an average of 100% at the 2-day test interval, 80% at the 3-week test interval, and 74% at the 10-week test interval. Phosphorus loss was reduced an average of 100% at the 2-day test interval, 75% at the 3-week test interval, and 83% at the 10-week test interval. The polymer treatment was more effective on the Ashdale silt loam, which had received manure during the two years preceding the rainfall simulations. Manure application was the primary difference between the two soils (manure was not applied to the Plano silt loam), suggesting that the PAM treatment reacts more favorably to manured soils. The low cost of this new PAM technology (approx. $25 ha-1) coupled with its success in reducing runoff, sediment, and P loss over a 10-week period, make EM-1000-50 an attractive and economically feasible management practice for agricultural producers in rainfed regions. [ABSTRACT FROM AUTHOR]

Growing urbanization has led to increasing concern and emphasis on better construction site stormwater management. The objectives of this study were to determine the effectiveness of using compost rather than conventional hydroseeding or topsoil to reduce erosion from disturbed soils. The runoff rates, interrill erosion rates, and interrill erodibility factors from five compost and two control treatments (hydroseeding and topsoil) were compared. Compost treatments followed Texas Department of Transportation (TxDOT) specifications for compost applied as an erosion control at 1.3 and 5 cm depths. Rainfall simulation was used to apply a storm of 92 mm h-1. Surface runoff was collected after 5 min of rainfall (first-flush) and during the last 30 min of rainfall (steady-state). The first-flush mean runoff from the 5 cm depth general-use compost treatment was significantly higher than that of all other treatments. The other treatments (50% woodchips and 50% compost blend at 1.3 and 5 cm depths) and hydroseeding had significantly lower runoff and erosion rates compared to topsoil and compost manufactured topsoil at first-flush and steady-state. Furthermore, there were no performance differences between 1.3 and 5 cm compost applications at first-flush or steady-state. The TxDOT specification for erosion control compost depth might be able to be reduced from 5 to 1.3 cm. [ABSTRACT FROM AUTHOR]