Contamination of unfenced streams with P, sediments, and pathogenic bacteria from cattle (Bos taurus) activity may be affected by the availability of shade and alternative water sources. The objectives of this study were to evaluate water quality in two streams draining tall fescue (Festuca arundinacea Schreb.)-common bermudagrass (Cynodon dactylon L.) pastures with different shade distribution, and to quantify the effects of alternative water sources on stream water quality. For 3 yr, loads of dissolved reactive phosphorus (DRP), total phosphorus (TP), and total suspended solids (TSS) were measured during storm flow, and loads of DRP, TP, TSS, and Escherichia coli were measured every 14 d during base flow. We also used GPS collars to determine amount of time cattle spent in riparian areas. Our results showed that cattle-grazed pastures with unfenced streams contributed significant loads of DRP, TP, TSS, and E. coli to surface waters (p < 0.01). Time spent by cattle in riparian areas as well as storm flow loads of DRP, TP, and TSS were larger (p < 0.08) in the pasture with the smaller amount of nonriparian shade. Water trough availability decreased base flow loads of TSS and E. coli in both streams, and decreased time cattle spent in riparian areas in the pasture with the smaller amount of nonriparian shade (p < 0.08). Our results indicate that possible BMPs to reduce contamination from cattle-grazed pastures would be to develop or encourage nonriparian shade and to provide cattle with alternative water sources away from the stream.

Establish a common threshold in P saturation across a geographic diversity of soils.• Predict water-soluble P from soil P storage capacity to guide fertilizer strategies.• Relate runoff P concentration with soil P storage capacity. ABSTRACTLoss of legacy soil phosphorus (P) due to historical over-application of fertilizers and manures can result in eutrophication of water bodies. The soil P storage capacity (SPSC) has been proposed as a tool to estimate the capacity of humid region soils to act as either sinks or sources of P to runoff or leaching. The SPSC is based on a threshold molar ratio of extractable P/(Al+Fe), called the soil P saturation ratio (PSR), above which water-soluble P abruptly increases. Objectives were to (i) document consistency of the threshold PSR for a wide geographic range of acid soils, (ii) determine applicability of a SPSC vs. water-soluble P predictive equation to soils from various regions, and (iii) relate SPSC with water quality parameters. Surface samples were collected from acidic, humid-region soils encompassing multiple physiographic provinces of the United States. Water quality data, including dissolved reactive P and total P, were obtained from various study sites. Phosphorus, Fe, and Al in Mehlich 3 solutions were determined, and PSR and SPSC calculated. The threshold PSR based on 186 samples is 0.1, indicating a common threshold across the geographic range of this study. Phosphorus concentrations in runoff related closely with SPSC, PSR, and M3-P values of soils that were the source of the runoff. However, SPSC has the additional potential of estimating extent of legacy P loss at excessive concentrations for soils of eastern and central United States. Results support general applicability of PSR and SPSC for acid soils.Abbreviations: DRP, dissolved reactive phosphorus; ICP-OES, inductively coupled plasma-optical emission spectrometry; M3-Al, Mehlich 3-extractable aluminum; M3-Fe, Mehlich 3-extractable iron; M3-P, Mehlich 3-extractable phosphorus; PSR, phosphorus saturation ratio; SPSC, soil phosphorus storage capacity; STP, soil test phosphorus; TP, total phosphorus.

Minimizing runoff losses from grasslands may benefit the producer and abate potential eutrophication of aquatic systems. This study was conducted to evaluate the effects of fertilizer source and soil aeration on the volume and quality of runoff from grassed plots. Sixteen tall fescue [Festuca arundinacea Schreb.]–bermudagrass [Cynodon dactylon L.] plots were established on Altavista sandy‐loam soil (fine‐loamy, mixed, semiactive, thermic Aquic Hapludults) in Georgia, USA. Two fertilizer sources (inorganic fertilizer [IF] and broiler litter [BL]) and two aeration treatments (aerated and nonaerated) were factorially combined to generate four experimental treatments. Broiler litter was applied at 1765 kg dry matter ha−1 and IF was applied to match nutrient rates applied with BL (36 kg available N ha−1, 39 kg P ha−1, 60 kg K ha−1). Simulated rainfall was applied immediately after fertilizer application and 1 mo later. Runoff samples were analyzed for dissolved reactive phosphorus (DRP), total Kjeldahl phosphorus (TKP), and ammonium (NH4–N). In the first runoff event, plots fertilized with IF lost more TKP than plots fertilized with BL (3.4 vs. 1.1 kg P ha−1). In contrast, plots fertilized with BL lost more NH4–N than plots fertilized with IF (1.4 vs. 0.6 kg N ha−1). These results support the use of different weighting factors for BL and IF when assessing their potential for contaminating surface runoff. Aeration numerically reduced runoff volume by 27%, though not significantly, in the first runoff event (P = 0.16), but did not affect runoff volume 1 mo later. Aeration did not affect the mass losses of DRP, TKN, and NH4–N. These results indicate that aeration of hayed grasslands on these soils would not be expected to significantly affect the volume and quality of surface runoff.

Pesticide runoff research relies heavily on rainfall simulation experiments. Most are conducted at a constant intensity, i.e., at a fixed rainfall rate; however, large differences in natural rainfall intensity is common. To assess implications we quantified runoff of two herbicides, fluometuron and pendimethalin, and applied preemergence after planting cotton on Tifton loamy sand. Rainfall at constant and variable intensity patterns representative of late spring thunderstorms in the Atlantic Coastal Plain region of Georgia (USA) were simulated on 6-m2 plots under strip- (ST) and conventional-tillage (CT) management. The variable pattern produced significantly higher runoff rates of both compounds from CT but not ST plots. However, on an event-basis, runoff totals (% applied) were not significantly different, with one exception: fluometuron runoff from CT plots. There was about 25% more fluometuron runoff with the variable versus the constant intensity pattern (P = 0.10). Study results suggest that conduct of simulations using variable intensity storm patterns may provide more representative rainfall simulation-based estimates of pesticide runoff and that the greatest impacts will be observed with CT. The study also found significantly more fluometuron in runoff from ST than CT plots. Further work is needed to determine whether this behavior may be generalized to other active ingredients with similar properties [low K(oc) (organic carbon partition coefficient) approximately 100 mL g(-1); high water solubility approximately 100 mg L(-1)]. If so, it should be considered when making tillage-specific herbicide recommendations to reduce runoff potential.

Vadas, Peter A., William E. Jokela, Dory H. Franklin, and Dinku M. Endale, 2011. The Effect of Rain and Runoff When Assessing Timing of Manure Application and Dissolved Phosphorus Loss in Runoff. Journal of the American Water Resources Association (JAWRA) 47(4):877‐886. DOI: 10.1111/j.1752‐1688.2011.00561.x Abstract:  A significant pathway of nonpoint source, agricultural phosphorus (P) transport is surface runoff, to which surface‐applied manure can contribute. Increasing the time between manure application and the first rain‐runoff event is proposed as a practice to reduce runoff P loss. Few studies have investigated this aspect of manure P loss in runoff, with mixed results. Studies observing a decrease in runoff P as the time between application and the first rain‐runoff attribute the decrease to adsorption of manure P by soil and manure drying effects, but do not consider the effect of storm hydrology on runoff P. We ran the manure P runoff model SurPhos with data from nine published studies that investigated the effect of time between application and the first rain event on runoff P. SurPhos successfully simulated the experimental conditions in the studies and predicted runoff P loss. Simulation results suggest soil adsorption of manure P is not the dominant mechanism that will significantly decrease manure P availability to runoff. Rather, regardless of when the first rain‐runoff event occurs, storm hydrology will significantly affect manure P loss in runoff. Although model scenarios indicate that increasing the time between manure application and the first rain‐runoff event will typically decrease P loss in runoff, runoff P could be equal to or greater 30 days after application than the day after application if a more intense rain and runoff event occurs at the latter date.