Nitrogen and phosphorus status of soil and trophic state of lakes associated with forage-based beef cattle operations in Florida

Authors: Sigua, Gilbert; Williams, Mary - Mimi; Coleman, Samuel; STARKS, R. - SWFWMD

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2005
Publication Date: 1/10/2006
Citation: Sigua, G.C., Williams, M.J., Coleman, S.W., Starks, R. 2006. Nitrogen and phosphorus status of soil and trophic state of lakes associated with forage-based beef cattle operations in Florida. Journal of Environmental Quality. 35:240-252.

Interpretive Summary: In southeastern United States, particularly, Florida, the grazing areas have considerable variability in soils, climate, and growing season, which not only affect the types of forage that can be grown, but also overall environmental and biodiversity management. Beef cattle operations have been suggested as one of the major sources of non-point source P and N pollution that are contributing to the degradation of water quality in lakes, reservoirs, rivers, and ground water aquifers. Cattle manure contains appreciable amounts of N and P (0.6 and 0.2 %, respectively), and portions of these nutrients can be transported into receiving waters during severe rainstorms. Better understanding of soil P and other crop nutrient changes due to differing management systems should improve our understanding of P dynamics and nutrient cycling in the soil system and allow us to better predict potential impact on adjacent surface waters. These issues are critical and of increasing importance among environmentalists, ranchers, and public officials in the state. We hypothesized that properly managed livestock operations might not be major contributors to excess loads of P and other crop nutrients in surface water. To verify our hypothesis, we examined the levels of nutrients in water and soils that are associated with forage-based pastures in subtropical Florida. The objectives of the study were: (1) to assess the changes that have occurred in soil fertility levels in beef cattle pastures with rhizoma peanuts over a 15-year period (1988-2002); and (2) to examine the levels of nutrients in water and assess the trophic state of lakes associated with beef cattle operations in Central Florida. Overall, there was no spatial and temporal build up of soil P and other crop nutrients despite the annual application of fertilizers and daily in-field loading of animal waste. Water quality in lakes associated with cattle production was “good” (30-46 TSI) based upon the Florida Water Quality Standard. These findings indicate that properly managed livestock operations might not be major contributors to excess loads of nutrients (especially P) in surface water. Our results indicate that current fertilization recommendations for foraged-based beef cattle systems in Central Florida offer little potential for negatively impacting the environment, and that properly managed livestock operations based on forage-based beef cattle pastures should not be major contributors to excess loads of nutrients (especially P) in surface water. In fact, our results suggest current recommendation for P may be too low to adequately maintain forage growth. Periodic applications of additional P and other micronutrients may be necessary.

Technical Abstract: Forage-based livestock systems have been implicated as major contributors to deteriorating water quality, particularly for P in fertilizers and manures affecting surface and ground water quality. Little information exists regarding possible magnitudes of nutrient losses from pastures that are managed for both grazing and hay production and how this might impact adjacent bodies of water. We examined the changes that have occurred in soil fertility levels of rhizoma peanut- (Arachis glabrata) based beef cattle pastures (n = 4) from 1988 to 2002. These pastures were managed for grazing in spring followed by haying in late summer and were fertilized annually with P (39 kg P2O5 ha-1) and K (68 kg K2O ha-1). Additionally, we investigated trends in water quality parameters and trophic state index (TSI) of lakes (n = 3) associated with beef cattle operations from 1993 to 2002. Soil fertility levels showed a declining trend for crop nutrient levels, especially soil P (y = 142 - 11.2*years; r2 = 0.52**). Overall, there was no spatial and temporal build up of soil P and other crop nutrients despite the annual application of fertilizers and daily in-field loading of animal waste. Water quality in lakes associated with cattle production was “good” (30-46 TSI) based upon the Florida Water Quality Standard. These findings indicate that properly managed livestock operations might not be major contributors to excess loads of nutrients (especially P) in surface water.