Soil-surface nutrient distributions in grazed pastures of North Carolina

Abstract

Soil nutrient distribution in perennial pastures is likely affected by livestock activities, but detailed spatial patterns on a diversity of farms have not been widely investigated. Livestock management variables, such as placement of drinking water sources, fencing, and winter hay-feeding stations, as well as pasture utilization through seasonal stocking, could affect nutrient distribution despite attempts at uniform application of fertilizers. We sampled perennial pasture portions of three research station farms in North Carolina on a 40 m grid in 2016. Twenty-two soil variables were measured, including routine soil testing of pH, cation exchange capacity, and extractable phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg), as well as nonroutine testing of sand concentration, total and particulate organic carbon (C) and nitrogen (N), and soil-test biological activity. Large statistical variations in nearly all variables occurred within a location. Severely deficient and heavily excessive levels of soil-test P and K were observed on the same farm and sometimes on the same paddock. Soil-test biological activity and total soil N also varied spatially within locations. High nutrient concentrations and soil-test biological activity were congregated in zones of several pastures, which could be related to historical winter hay-feeding and permanent drinking water locations. At the Piedmont location with recent winter hay feeding, both organic and inorganic indicators generally corresponded to the same enrichment zones. At the Coastal Plain location with abandonment of some historical feeding locations, soil-test P remained high near feeding stations, but soil-test K and total soil N became more uniformly distributed due to leaching and/or decomposition dynamics over time. We suggest that both organic and inorganic soil testing indicators should be measured to make nutrient recommendations for better resource utilization. Livestock managers are encouraged to sample pastures in expected zones of nutrient differentiation so that nutrients can be used efficiently and environmental threats can be mitigated.