School of Biological Sciences, Queen's Univ, Belfast.
J Environ Qual. 2010 Nov-Dec;39(6):2138-46. doi: 10.2134/jeq2010.0205.
The increasing use of concentrate feedstuffs within Northern Ireland dairy systems has resulted in significant farm gate phosphorus (P) surpluses, and these have contributed to increased soil P levels and risk of P loss to overland flow. However, the P content of feed concentrates can be lowered without compromising animal performance. This study focuses on P losses from grassland and evaluates how adjusting the P content of manure impacts on the P composition and concentration in overland flow. Dairy cows were offered diets containing 5.3 to 3.0 g P kg(-1) dry matter (DM) and produced manures with a range of P contents. Manure was applied at a rate of 50 m3 ha(-1) to 0.5-m2 grassland plots, and simulated rainfall (40 mm h(-1)) was applied repeatedly 2, 9, 28, and 49 d after during the summer, winter, and spring. Decreasing the P content in the diet, from the highest to the lowest P treatment (43%), produced a proportionately greater reduction in manure TP content (63%), but reductions were not exclusively in the water-soluble fraction. Following surface applications of manure, P concentrations in overland flow increased in all seasons (P < or = 0.001), while the greatest impact of varying the manure P content was most evident during the first simulated overland flow event. When diet P content was reduced from 5.4 to 3.0 g P kg(-1) DM, a statistically significant reduction in runoff P concentration was observed in all seasons. Elevated P concentrations in overland flow were observed for 28 d in spring and 9 d in summer and winter. The large drop in P concentrations between simulated rainfall events on Day 2 and Day 9 suggests that increasing the time interval between manure application and the generation of overland flow has a greater impact on P losses than does varying the dietary P content.
北爱尔兰奶制品生产中浓缩饲料的使用量不断增加，导致大量的农场磷（P）盈余，这增加了土壤 P 水平和 P 经地表径流流失的风险。然而，降低饲料浓缩物中的 P 含量并不会影响动物的生产性能。本研究关注的是草原系统中的 P 流失，并评估调整粪肥 P 含量对地表径流中 P 组成和浓度的影响。奶牛的日粮 P 含量分别为 5.3 至 3.0 g P kg(-1) 干物质（DM），所产粪肥的 P 含量也有所不同。粪肥以 50 m3 ha(-1) 的用量施用到 0.5 m2 的草地小区，在夏季、冬季和春季，分别在施肥后 2、9、28 和 49 d 时，用 40 mm h(-1) 的模拟降雨进行多次重复喷洒。与最低 P 处理（43%）相比，日粮 P 含量从最高降到最低时，粪肥总磷（TP）含量相应减少（63%），但减少并不完全在水溶性部分。粪肥表面施用后，地表径流水 P 浓度在所有季节均增加（P < 或 = 0.001），而改变粪肥 P 含量的影响在第一次模拟地表径流事件中最为明显。当日粮 P 含量从 5.4 降低至 3.0 g P kg(-1) DM 时，所有季节的地表径流 P 浓度均显著降低。春季地表径流水中 P 浓度升高持续 28 d，夏季和冬季升高 9 d。模拟降雨事件后第 2 天和第 9 天之间地表径流水 P 浓度的大幅下降表明，增加粪肥施用和地表径流产生之间的时间间隔对 P 流失的影响大于改变日粮 P 含量。
