Water quality effects of repeated annual poultry litter application

Excerpt

This study, which is one component of a broader, long-term project on the environmental and agro-economic impacts of land applying poultry litter off-site of animal production operations, was designed to determine the water quality effects of repeated annual poultry litter application. To date, more than eight years of data have been collected from ten field-scale cropland and pasture watersheds. On cropland, increasing litter rates from 0.0 to 13.4 Mg ha⁻¹ (0 to 6 ton ac⁻¹), with corresponding decreases in supplemental inorganic nitrogen, increased soluble phosphorus concentrations in runoff but reduced extreme high nitrate-nitrogen concentrations. On pasture, increasing litter rates increased both soluble phosphorus and nitrate-nitrogen concentrations in runoff because litter was the only nutrient source. Following seven annual litter applications, soluble phosphorus concentrations in runoff were strongly correlated with phosphorus levels in the soil on both land uses; however, the dynamic interactions of rainfall, runoff, vegetation condition, soil nutrient levels, and fertilizer application limited consistent, long-term trends in nitrogen and phosphorus runoff. In addition to these and other issues of scientific interest, the present study produced several practical outcomes.

First, combining inorganic and organic fertilizers can be an effective fertilization strategy on farms and ranches. With this strategy, organic fertilizers…