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Effect of Varying the Phosphorus Content of Dairy Cow Diets on Losses of Phosphorus in Overland Flow Following Surface Applications of Manure
Author(s) -
O'Rourke S. M.,
Foy R. H.,
Watson C. J.,
Ferris C. P.,
Gordon A.
Publication year - 2010
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2010.0205
Subject(s) - manure , surface runoff , phosphorus , zoology , manure management , agronomy , dry matter , grassland , chemistry , nutrient , environmental science , biology , ecology , organic chemistry
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 m 3 ha −1 to 0.5‐m 2 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 ≤ 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.