Soil Phosphorus, Cattle Stocking Rates, and Water Quality in Subtropical Pastures in Florida, USA

Abstract

Minimizing nonpoint source nutrient pollution is important to the sustainability of grazing lands. Increased nutrient loads have reduced water quality in Lake Okeechobee in south Florida, prompting establishment of a Total Maximum Daily Load (TMDL) that will require large reductions in phosphorus (P) runoff into the lake. A significant portion of this reduction must come from beef cattle ranches, the major land use in the region. A large-scale research project, consisting of a 420-ha array of 8 improved summer and 8 semi-improved winter pastures, was established from 1998-2003 to investigate the influence of beef cattle stocking rate on nutrient loads in surface runoff. Each pasture type had two replicates of four different cattle stocking rates including a control with no cattle and stocked pastures with low, medium, and high stocking rates (1.3, 1.0, 0.6 ha AU À1 [animal unit] in summer pastures; 2.1, 1.6, and 0.9 ha AU À1 in winter pastures). Cattle stocking rate did not affect nutrient concentrations or loads in surface runoff during the study period. Average annual P discharges were 1.71 kg ha À1 from summer pastures and 0.25 kg ha À1 from winter pastures. Average total P concentrations in runoff were 0.63 mg L À1 for summer pastures and 0.15 mg L À1 for winter pastures. Differences in runoff P were related to differences in soil P test results, a difference believed to be due to prior fertilization practices. Our findings show that reducing cattle stocking rates on beef cattle pastures is not an effective practice for reducing nutrient loads, and that accumulation of P in soil from historical fertilization has an overriding influence on P loads in surface runoff. Results indicate that reducing the overall volume of surface discharges would be a more effective strategy than altering cattle stocking practices to reduce nonpoint runoff of P from cattle pastures in this region.

The cow-calf industry and water quality in South Florida, USA: a review

“…This is further supported by Capece et al (2007), who observed significant variability in P loads and runoff P concentrations as affected by rainfall. During a 6-year study, the authors observed significant differences (up to threefold greater) in P loads during the years of excessive rainfall compared to periods of extreme drought conditions.…”

“…However, because of the extensive acreage occupied by improved pastures (36%) compared to other land uses such as urban (3%), Hiscock et al (2003) concluded that improved pastures were still the major contributor of P imports. Similarly to Boggess et al (1995), Hiscock et al (2003) assumed a mean annual runoff P concentration for each land use; however estimates for improved pastures were twofold greater (0.45 mg L -1 ) than data reported by Allen (1988) (0.19 mg L -1 ), and 30% less than observed by Capece et al (2007) (0.63 mg L -1 ). The inconsistency associated with runoff P concentrations reported in the literature further indicates a major limitation in using estimates rather than actual data measured for each specific site.…”

Monitoring runoff from cattle-grazed pastures for a phosphorus loss quantification tool

“…There has been significant research conducted to monitor N and P loss in runoff from grazed pastures (Edwards et al, 2000;Halliwell et al, 2000;Nash et al, 2000;O'reagain et al, 2005;Haan et al, 2006;Owens and Shipitalo, 2006;Capece et al, 2007;McDowell et al, 2007;Dougherty et al, 2008). However, considerably less pasture runoff research has been conducted compared to nutrient loss from cultivated cropland, and most of it has been conducted in Australia, New Zealand, and the United Kingdom.…”

“…However, considerably less pasture runoff research has been conducted compared to nutrient loss from cultivated cropland, and most of it has been conducted in Australia, New Zealand, and the United Kingdom. In the U.S., only limited field-scale, natural precipitation, pasture runoff research have been conducted where the major source of nutrient addition is through grazing animals (Olness et al, 1975;Menzel et al, 1978;Chichester et al, 1979;Schepers and Francis, 1982;Owens and Shipitalo, 2006;Capece et al, 2007). The reason for this is unclear.…”

Aspects of northern bobwhite ecology on south Florida US pastureland

“…The ranch separated cattle into multiple herds (depending on season) that were rotated on regular intervals, rarely grazing >50 % of the herbage in a given paddock. The objective of the grazing systems was to reduce stress on the native grass species and legumes within pastures, reduce the probability of invasive exotic species occupation [e.g., cogon grass (Imperata cylindica) and tropical soda apple (Solanum viarum)], and limit fertilizer inputs (Capece et al 2007). Annually, a moderate amount of bahia grass sod was removed for commercial sale.…”