Conservation management practices reduce non-point source pollution from grazed pastures.

Producers in Northwest Arkansas and globally need alternative management practices to ensure long-term sustainable and economical use of poultry litter, which is an abundant source of valuable carbon (C), nitrogen (N) and phosphorus (P). Project objectives were to measure the efficacy of conservation management practices (i.e., pasture aeration and subsurface litter incorporation) to reduce nutrient runoff compared to poultry litter surface applications from small watersheds under rainfed and grazed conditions. Watersheds (0.23 ha each) were assigned a treatment [pasture aeration, subsurface litter incorporation, or surface application of litter (positive control)] on a Leadvale (fine-silty, siliceous, thermic Typic Fragiudult) silt loam. Poultry litter was applied annually to each watershed from 2007-2012. Over the 4-yr study period, runoff loads of NO3-N, total nitrogen (TN), soluble reactive phosphorus (SRP), and total phosphorus (TP) varied per conservation practice (P ≤ 0.05). Specifically, average annual loads of NO3-N, TN, SRP, and TP loads were reduced 49, 42, 28, and 35% following pasture aeration and by 78, 72, 55, and 59% from subsurface applying poultry litter, relative to surface applications, respectively. Greatest annual N loads and runoff corresponded with surface poultry litter applications, followed by pasture aeration, with subsurface incorporation of poultry litter resulting in lowest (P ≤ 0.05) TN and NO3-N loads. Overall, subsurface incorporation of poultry litter and pasture aeration are two promising conservation practices for reducing non-point source pollution in watersheds with nutrient imbalances. Further work needs to be done on factors influencing the efficacy of these conservation practices under rainfed conditions, as well as the economic feasibility of these conservation agricultural practices.

Long-term effects of grazing management and buffer strips on phosphorus runoff from pastures fertilized with poultry litter.

Phosphorus (P) runoff from pastures can cause accelerated eutrophication of surface waters. However, few long-term studies have been conducted on the effects of best management practices, such as rotational grazing and/or buffer strips on P losses from pastures. The objective of this study was to evaluate the long-term effects of grazing management and buffer strips on P runoff from pastures receiving annual (5.6 Mg ha-1 ) poultry litter applications. A 14-yr study was conducted on 15 small watersheds (0.14 ha) with five treatments: hayed (H), continuously grazed (CG), rotationally grazed (R), rotationally grazed with an unfertilized buffer strip (RB), and rotationally grazed with an unfertilized fenced riparian buffer (RBR). Runoff samples were collected using automatic samplers during runoff events. Average annual runoff volumes from H (40 mm yr-1 ) and RBR (48 mm yr-1 ) were lower than CG and RB, which were both 65 mm yr-1 , and from R (67 mm yr-1 ). Rotational grazing alone did not reduce P loads compared with continuous grazing (1.88 and 1.71 kg P ha-1 for R and CG, respectively). However, compared with CG, total P losses from RB pastures were reduced 36% with unfertilized buffer strips (1.21 kg P ha-1 ), 60% in RBR watersheds with unfertilized fenced riparian buffer strips (0.74 kg P ha-1 ), and 49% by converting pastures to hayfields (0.97 kg P ha-1 ). Hence, the use of unfertilized buffer strips, unfertilized fenced riparian buffer strips, or converting pastures to hayfields are effective best management practices for reducing P runoff in U.S. pasture systems.

A Global Perspective on Integrated Strategies to Manage Soil Phosphorus Status for Eutrophication Control without Limiting Land Productivity.

Unnecessary accumulation of phosphorus (P) in agricultural soils continues to degrade water quality and linked ecosystem services. Managing both soil loss and soil P fertility status is therefore crucial for eutrophication control, but the relative environmental benefits of these two mitigation measures, and the timescales over which they occur, remain unclear. To support policies toward reduced P loadings from agricultural soils, we examined the impact of soil conservation and lowering of soil test P (STP) in different regions with intensive farming (Europe, the United States, and Australia). Relationships between STP and soluble reactive P concentrations in land runoff suggested that eutrophication control targets would be more achievable if STP concentrations were kept at or below the current recommended threshold values for fertilizer response. Simulations using the Annual P Loss Estimator (APLE) model in three contrasting catchments predicted total P losses ranging from 0.52 to 0.88 kg ha depending on soil P buffering and erosion vulnerability. Drawing down STP in all catchment soils to the threshold optimum for productivity reduced catchment P loss by between 18 and 40%, but this would take between 30 and 40+ years. In one catchment, STP drawdown was more effective in reducing P loss than erosion control, but combining both strategies was always the most effective and more rapid than erosion control alone. By accounting for both soil P buffering interactions and erosion vulnerability, the APLE model quickly provided reliable information on the magnitude and time frame of P loss reduction that can be realistically expected from soil and STP management. Greater precision in the sampling, analysis, and interpretation of STP, and more technical innovation to lower agronomic optimum STP concentrations on farms, is needed to foster long-term sustainable management of soil P fertility in the future.

Ammonia emission factors from broiler litter in barns, in storage, and after land application.

We measured NH3 emissions from litter in broiler houses, during storage, and after land application and conducted a mass balance of N in poultry houses. Four state-of-the-art tunnel-ventilated broiler houses in northwest Arkansas were equipped with NH3 sensors, anemometers, and data loggers to continuously record NH3 concentrations and ventilation for 1 yr. Gaseous fluxes of NH3, N2O, CH4, and CO2 from litter were measured. Nitrogen (N) inputs and outputs were quantified. Ammonia emissions during storage and after land application were measured. Ammonia emissions during the flock averaged approximately 15.2 kg per day-house (equivalent to 28.3 g NH3per bird marketed). Emissions between flocks equaled 9.09 g NH3 per bird. Hence, in-house NH3 emissions were 37.5 g NH3 per bird, or 14.5 g kg(-1) bird marketed (50-d-old birds). The mass balance study showed N inputs for the year to the four houses totaled 71,340 kg N, with inputs from bedding, chicks, and feed equal to 303, 602, and 70,435 kg, respectively (equivalent to 0.60, 1.19, and 139.56 g N per bird). Nitrogen outputs totaled 70,396 kg N. Annual N output from birds marketed, NH3 emissions, litter or cake, mortality, and NO2 emissions was 39,485, 15,571, 14,464, 635, and 241 kg N, respectively (equivalent to 78.2, 30.8, 28.7, 1.3, and 0.5 g N per bird). The percent N recovery for the N mass balance study was 98.8%. Ammonia emissions from stacked litter during a 16-d storage period were 172 g Mg(-1) litter, which is equivalent to 0.18 g NH3 per bird. Ammonia losses from poultry litter broadcast to pastures were 34 kg N ha (equivalent to 15% of total N applied or 7.91 g NH3 per bird). When the litter was incorporated into the pasture using a new knifing technique, NH3 losses were virtually zero. The total NH3 emission factor for broilers measured in this study, which includes losses in-house, during storage, and after land application, was 45.6 g NH3 per bird marketed.