Dairy Diet Phosphorus Effects on Phosphorus Losses in Runoff from Land-Applied Manure

Abstract

Phosphorus (P) losses from land-applied manure can contribute to nonpoint source pollution of surface waters. Dietary P levels influence P concentrations in animal manures and may affect P losses from land-applied manure. The objective of this study was to determine the effects of dairy diet P concentration on P losses in runoff from landapplied manure. Manures with P concentrations of 0.48 and 1.28 % P from two dietary P levels were applied to a silt loam soil 25 wet ton/a (36 and 96 lb P/a, respectively). The high P manure was also applied at 9.4 wet ton/a (36 lb P/a) to provide an equivalent P rate as the low P manure. Plots were subjected to simulated rainfall (2.83 in/hr) in June and again in October. Runoff was analyzed for dissolved reactive P (DRP), bioavailable P, total P, and sediment concentration. Natural runoff from the same plots was collected from November through May and analyzed for P as described above. At equivalent manure rates, DRP in June runoff from the high P manure was about 10 times higher (0.30 vs. 2.84 ppm) than the low P manure, and 4 times higher (0.30 vs. 1.18 ppm) when applied at equivalent P rates. Phosphorus concentrations in October runoff and November -May natural runoff were lower (0.02 -1.69 ppm), but treatment effects were the same as for June runoff. These results show that excess P in dairy diets increases the potential for P loss in runoff from land-applied manure. Furthermore, diet P effects on potential losses in runoff from land-applied manure should be considered in P-indexing and nutrient management planning.

Evidence for a delayed response of riverine phosphorus exports from increasing agricultural catchment pressures in the Lough Neagh catchment

“…Additionally, the mobility of P in cattle manures may have increased because of an increase in the P content of winter feed of cattle caused by a switch from hay to silage and the inclusion of high P concentrate feeds. Enhanced dietary P increases the proportion of TP in manure that is soluble or colloidal, and these P fractions have a greater vulnerability to runoff loss in comparison with PP (Ebeling et al 2002). Quantitative information on these changes is limited, leaving the mobility of manure P and vulnerability to loss an unresolved issue to be addressed in interpreting eutrophication history and the identifying control and remedial measures.…”

Effect of offering dairy cows diets differing in phosphorus concentration over four successive lactations: 2. Health, fertility, bone phosphorus reserves and nutrient utilisation

“…Thus, reducing the P content of dairy cow rations to the extent adopted within the current experiment has the potential to have a significant impact on farm P balances, and thus the likelihood of P loss to the environment. In addition, Dou et al (2002) observed an increased proportion of water soluble P in the faeces of cows offered high P diets, while Ebeling et al (2002) showed that P runoff from slurry produced from cows offered a high P diet was considerably greater than for slurry produced by cows offered a low P diet.…”

Methods for assessing phosphorus overfeeding on organic and conventional dairy farms

“…Many studies have shown that dairy cows are often fed more P than they require according to current recommendations (Wu et al, 2001;Valk et al, 2002;Knowlton et al, 2004;Nennich and Harrison, 2008). Manure from dairy cows fed high levels of P has been shown to increase the potential for P runoff losses (Ebeling et al, 2002). Dealing with P losses from livestock production is becoming increasingly important as farms grow larger in number of animals and the P load thereby is becoming concentrated to these spots.…”