Reducing Nitrogen and Phosphorus Excretions from Dairies in Gooding and Jerome Counties, Idaho

Reducing Nitrogen and Phosphorus Excretions from Dairies in Gooding and Jerome Counties, Idaho

Summary

Nine dairies (12,700 cows) from South Central Idaho were involved in this project. Nutrient flow data at farm level and feeds, manure, milk, and soil samples were collected and analyzed for selected nutrients. Work planned for this stage of the project is completed. Whole-farm N and P balance indicated net accumulation of these nutrients on most of the dairies. Dietary P concentration was above current NRC requirements for high-producing dairy cows. Following our recommendations, seven of the participating dairies adopted reduced P feeding, which resulted in reduced fecal P concentrations. Changes in soil P levels will be monitored in 2005.

Objectives/Performance Targets

1. Collect data on the nutritional [nitrogen (N) and phosphorus (P)] status of representative dairies in Gooding and Jerome counties. Samples from feces, urine, manure, milk, and soil will be collected and analyzed for nutrients. These case studies will provide the needed database on the current nutritional practices in relation to nutrient balance in an area having a high density of dairy cows.

2. Recommend dietary modification to cooperator dairies aimed at reducing N and P losses. Implement changes to the lactating cow diets in cooperation with the nutritional consultants. Sample feed, feces, urine, manure, and soil following implementation of recommended dietary modifications.

Additional objectives: Two new objectives were added to the project: (1) In addition to N and P, other minerals (K, Ca, Mg, Na, S, Fe, Zn, Cu, and Mn) were included in the study; and (2) Whole-farm balance of N, P, K, Ca, Mg, Na, S, Fe, Zn, Cu, and Mn was estimated for the participating dairies. These new objectives greatly increased the amount and value of the information that would be provided to producers and public from this project. To our knowledge, such a comprehensive analysis of inflows and outflows of an array of environmentally important minerals from commercial dairies has not been reported in the literature.

Accomplishments/Milestones

CONFIDENTIAL INFORMATION: Whole-farm N and P balance was performed on eight dairies. Dairies 2 and 3 and dairies 7 and 8 are under the same management, and balance data for these dairies were combined. In most cases, feed was the largest source of imported N on the dairies (92 to 96% of all N imported). One dairy was an exception with only 38% of the imported N as feed; this particular dairy was producing a large amount of forage on its own land. The largest import of N on this dairy was through N fixation (42% of the import). Dairies exported from 19 to 70% of the N exported from the dairy as milk N. The lowest value was for Dairy 4, which exported a large proportion of its N export as feed N (77% of the total N exported). On average, 50% of the exported N was with milk. Typical for the large dairies in South Central Idaho, only a small proportion of the N export was with feed (except Dairy 4). Four of the dairies did not export any feed. Dairy 4 used all the manure produced on the farm. All other dairies exported various proportions of manure N. On average, 29% of the N export was as manure N. The efficiency of N use (exported N/imported N) on these dairies was on average 41%. The most efficient dairy was Dairy 4, which had efficiency of 69%. The efficiency of N use varied significantly among dairies (from 25 to 69%). This reflects mostly management practices and land availability, including level of milk production of the cows, own production of forages, manure handling, N losses with ammonia volatilization, etc. Among the participating dairies, the most efficient use of N was on Dairy 4 where almost all forages were produced on the dairy, milk yield was relatively high, and all manure was used on the dairy. The least efficient dairies (Dairies 2 and 3) exported little N with feeds and manure, most likely overdosing nutrients on the available land.

Similar to N, in all dairies the major import of P was with feed; from 88 to 98% of all P imported. Dairy 4 imported the least P due to its own forage production. From 25 to 62% of the P leaving the dairies was as milk P. Except Dairy 4 (68% of the total P export), there was little or no export of P with feeds produced on the dairy. All dairies, except Dairy 4, were exporting a significant amount of P with manure; from 25 to 68% of the total P export. The efficiency of P use on the farm was higher than the efficiency of use of N (due to the fact that there are no volatilization losses of manure P) averaging 67%. Dairy 4 was balanced on P imports/exports (101% efficiency) mostly due to the large import of P with forages produced on the farm. Dairies 2 and 3 and dairies 7 and 8 had the lowest efficiency of P use – 46 to 49%, suggesting accumulation of P on the farm. Indeed, soil P concentrations were in most cases above the maximum recommended P threshold concentration of 40 ppm for surface water concerns and the 20 ppm maximum for ground water concerns in the 0-12 inch sample, exceeding 230 ppm in some samples.

Samples taken from the dairies were also analyzed for nine other minerals (K, Ca, Mg, Na, S, Fe, Zn, Cu, and Mn). When completed, these data will be used to estimate whole-farm balance for these nutrients. Although not considered environmentally important at the present (except maybe K), there is a lack of information on the movement of these minerals in a dairy farm. These elements may be accumulating on the farm, similar to N and P, and may present a concern for the producers and the public in the future.

Based on the results from the diet analyses and the extremely high soil P levels in some fields receiving manure, our priority for the next stage of the project was to convince the participating dairymen and their nutritionists that a reduction in N and P concentration of their lactating cow diets would significantly reduce N and P losses and soil P levels, but will have no effect on milk yield and composition. At this stage, we were not successful in persuading the consulting nutritionists in the benefits of reduced N feeding. Seven of the eight participating dairies, however, accepted our recommendations for reduced dietary P, and the diets from these dairies contained significantly less P in 2004 compared with 2003. Following implementation of the reduced P feeding, all dairies had dietary P concentrations of less than 0.4%, which was within the range recommended by NRC (2001). We consider this a substantial success, which would not be possible without the understanding and cooperation of the dairymen and their consulting nutritionists. As a result of the decreased levels of P in the diets, fecal P was also significantly reduced in all but one dairy. In ruminants, excretion of P is mainly with feces, and reduction of fecal N is expected to significantly reduce P concentration in manure and, consequently, in soil. If the requested no-cost extension of this project is granted (see cover letter), we will take one additional soil sample in 2005 and expect to see reduced soil P levels in the dairies, which adopted reduced P feeding.

Impacts and Contributions/Outcomes

The whole-farm N and P balance indicated net accumulation of these nutrients on most of the participating dairies. This important information has been communicated to the producers at several meetings (Ag and Water Quality Conference, Boise, Idaho, October 18, 2004; Pacific Northwest Animal Nutrition Conference, Seattle, October 5-7, 2004; and United Dairymen of Idaho Annual Meeting, Pocatello, Idaho, November 1-2, 2004) and has already generated a significant interest. In all dairies, dietary P concentration was above current NRC requirements for high-producing dairy cows and soil P levels were above the recommended thresholds for Idaho soils. Following our recommendations, seven of the participating dairies adopted reduced P feeding, which resulted in reduced fecal P concentrations. Manure samples from 2004 are currently being analyzed, but we expect to observe reduced manure P concentration as well. Changes in soil P levels will be monitored in 2005. Overall, the goals of the project have been achieved. We generated critically important information on whole-farm nutrient balance for N and P and will compile data for nine other minerals (K, Ca, Mg, Na, S, Fe, Zn, Cu, and Mn). We were also successful in reducing fecal N losses in seven large dairies, which will serve as an example for other dairies in this intensive livestock area. The expected long-term effect of these measures is reduction in soil P levels.