Evaluation of the Phosphorus Source Component in the Phosphorus Index for Pastures

Abstract

A phosphorus (P) index for pastures was developed to write nutrient management plans that determine how much P can be applied to a given field. The objectives of this study were to (i) evaluate and compare the P index for pastures, particularly the P source component, and an environmental threshold soil test P level by conducting rainfall simulations on contrasting soils under various management scenarios; and (ii) evaluate the P index for pastures on field-scale watersheds. Poultry litter was applied to 12 small plots on each of six farms based on either an environmental threshold soil test P level or on the P index for pastures, and P runoff was evaluated using rainfall simulators. The P index was also evaluated from two small (0.405 ha) watersheds that had been fertilized annually with poultry litter since 1995. Results from the small plot study showed that soil test P alone was a poor predictor of P concentrations in runoff water following poultry litter applications. The relationship between P in runoff and the amount of soluble P applied was highly significant. Furthermore, P concentrations in runoff from plots with and without litter applications were significantly correlated to P index values. Studies on pastures receiving natural rainfall and annual poultry litter applications indicated that the P index for pastures predicted P loss accurately without calibration (y = 1.16x - 0.23, r(2) = 0.83). These data indicate that the P index for pastures can accurately assess the risk of P loss from fields receiving poultry litter applications in Arkansas and provide a more realistic risk assessment than threshold soil test P levels.

Nutrient losses from manure and fertilizer applications as impacted by time to first runoff event

“…Soil test P levels have been shown to be a factor controlling P losses if no fertilizers have been recently applied (DeLaune et al, 2004b;Schroeder et al, 2004b). Following the surface application of fertilizer or manure, the amount of soluble P applied can be the most important factor controlling P concentrations in runoff (DeLaune et al, 2004a;Smith et al, 2004a, b).…”

“…Relatively fewer studies have compared the impact of fertilizers on water quality with that of manures from different species (Gaudreau et al, 2002;Kleinmann et al, 2002;Daverede et al, 2004;DeLaune et al, 2004b;Tarkalson and Mikkelsen, 2004), or how the duration between application of different fertilizer sources and a runoff event will affect the concentrations of nutrients in runoff (DeLaune et al, 2004b;van Es et al, 2006). The objectives of this study were to identify the impact of the duration between fertilizer or manure application and first rainfall-runoff event on P and N concentrations in runoff, and to compare the effects of the fertilizer source on nutrient losses.…”

Spatial Model Assessment of P Transport from Soils to Waterways in an Eastern Mediterranean Watershed

“…Some attributes and factors are specific to site and/or climate; for example, in Nordic areas a freezing attribute was added to account for residual frozen plants in the field [19]. Delaune et al [22] developed an index for pastures in Arkansas, USA, where a multiplication parameter was used to include all of the source, transport and rain attributes. The Natural Resources Conservation Service [23] included soil erosion, runoff, soil P and the amount and method of P addition to the soils.…”

“…First, we tested the Arkansas model [22] which was originally designed for pastures and might therefore provide a good solution for our land-use applications (94% being used for cattle grazing, see Figure 1c) with minimal modifications. The values of the model's attributes and a list of the modifications installed in the model to fit the climate and land-use conditions of the study area are summarized in Table 2.…”

“…Soil-erosion classes were determined according to the RUSLE equation (see below) and the runoff categories were assigned values according to the slope angle and vertical hydraulic conductivity following the soil survey manual [34]. For further details of the computation of the P index in the Arkansas model see DeLaune et al [22]. (1) soil test was changed to water-extractable P; (2) grazing density was used as an indicator for added P; (3) changes in precipitation depth; and (4) no best management option was included.…”