Nitrate-N in Soil Solution from a Pastoral-Silvopastoral System Treated with Biosolids.

Fertilizer management is important to maximize nutrient-use efficiencies and reduce losses from grassland, especially on sandy soils. Both organic and inorganic fertilizers have been applied for increasing soil fertility and crop/forage productivity. Nutrients cycling in pastoral systems is different from that in cropping systems: the grazing animals are excreted back to the pasture most of the ingested nutrients. A research was initiated under a USDA-NRCS funded project to study land use alteration in urban-rural interface. Urban treatment facilities have been processing wastewater and producing biosolids that are suitable for using in nearby rural pastoral systems. While application of biosolids can improve forage quality and livestock performance, biosolids-treated sites have been also evoked as a source of pollution. Although studies have been carried out to clarify the acceptable rates for applying biosolids on grassland, the N-based rate is site specific and still challenging.

The objective of this study was to assess potential nutrient leaching by monitoring nitrate-Nconcentrations in soil solution from bahiagrass pasture plots fertilized with both inorganic and organic sources of nutrients. The study was conducted at the Florida A&M University Research and Extension Center, Quincy on Ultisols of the Orangeburg series. Soil solution was sampled from tension (suction cup) lysimeters randomly installed bellow the root zone of silvopastoral and pastoral plots. The samples were analyzed for pH, EC and nitrate-N; the results are discussed in relation to potential leaching and an attempt is made to find possible relationships and distribution patterns.

The nitrate-N concentrations in the soil solution varied greatly from 0 to a maximum of 30 mg L^-1 with the highest being recorded under the plots fertilized with biosolids. However, the mean concentrations were lower ranging from 0.08 to 5.71 mg L^-1. The nitrate-N concentrations were relatively low and constant for all the treatments during May-June but were higher during July-November for biosolids-treated plots. Occasionally nitrate-N was higher than the MPL of 11 mg L^-1, but the means were bellow the US drinking water quality standards.