Sigua G C, Williams M J, Coleman S W, Starks R
USDA-ARS, Subtropical Agricultural Research Station, Brooksville, FL 34601, USA.
J Environ Qual. 2006 Jan 5;35(1):240-52. doi: 10.2134/jeq2005.0246. Print 2006 Jan-Feb.
Forage-based livestock systems have been implicated as major contributors to deteriorating water quality, particularly for phosphorus (P) from commercial 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 these might impact adjacent bodies of water. We examined the changes that have occurred in soil fertility levels of rhizoma peanut (Arachis glabrata Benth.)-based beef cattle pastures (n = 4) in Florida 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. Overall, there was no spatial or temporal buildup of soil P and other crop nutrients despite the annual application of fertilizers and daily in-field loading of animal waste. In fact, soil fertility levels showed a declining trend for crop nutrient levels, especially soil P (y = 146.57 - 8.14 x year; r2= 0.75), even though the fields had a history of P fertilization and the cattle were rotated into the legume fields. Our results indicate that when nutrients are not applied in excess, cow-calf systems are slight exporters of P, K, Ca, and Mg through removal of cut hay. Water quality in lakes associated with cattle production was "good" (30-46 TSI) based on the Florida Water Quality Standard. These findings indicate that properly managed livestock operations may not be major contributors to excess loads of nutrients (especially P) in surface water.
以草料为基础的畜牧系统被认为是水质恶化的主要因素，特别是来自商业肥料和粪便中的磷（P），影响地表水和地下水水质。关于用于放牧和干草生产的牧场养分流失的可能规模以及这些流失如何影响邻近水体的信息很少。我们研究了1988年至2002年佛罗里达州以根茎花生（Arachis glabrata Benth.）为基础的肉牛牧场（n = 4）土壤肥力水平的变化。这些牧场春季用于放牧，夏末用于晒制干草，每年施磷（39 kg P2O5 ha(-1)）和钾（68 kg K2O ha(-1)）。此外，我们调查了1993年至2002年与肉牛养殖相关的湖泊（n = 3）水质参数和营养状态指数（TSI）的趋势。总体而言，尽管每年施肥且动物粪便每天都在田间堆放，但土壤磷和其他作物养分没有出现空间或时间上的积累。事实上，作物养分水平的土壤肥力呈下降趋势，尤其是土壤磷（y = 146.57 - 8.14 x年份；r2 = 0.75），尽管这些田地有施磷历史且肉牛被轮流放入豆科植物田地。我们的结果表明，当不过量施用养分时，母牛-小牛系统通过收割干草输出少量的磷、钾、钙和镁。根据佛罗里达水质标准，与肉牛生产相关的湖泊水质“良好”（TSI为30 - 46）。这些发现表明，管理得当的畜牧养殖可能不是地表水养分（尤其是磷）过量负荷的主要来源。
