Improving Nutrient Management on a 100-Cow Free-Stall Dairy Farm
1. Conduct a detailed evaluation of the nutrient balance on the 100-cow Miner Institute dairy farm, comparing it to the average New York dairy farm.
2. Improve existing models to predict the flow of N, P, and K through the cow, to manure, and to the field.
3. Evaluate the effects on the farm nutrient balance of P by substituting manure for commercial fertilizer for established alfalfa.
4. Evaluate the effects on the farm nutrient balance of N by the use of pre-sidedress nitrogen tests.
Nutrient balances were completed for 1992 through 1995. Nutrient efficiency in 1992 and 1993, prior to the initiation of this project, was considerably less than for the typical NY dairy farm. Beginning in 1994, dairy feed and mineral programs were adjusted to reduce unnecessary nutrient inputs. Purchased nutrient inputs in 1994 were greater because of increased animal numbers, but outputs (sales) increased by a greater relative amount, and the nutrient balance improved considerably. Nutrient efficiency declined slightly in 1995 vs. 1994, but total tons of N and K remaining on the farm declined for the second consecutive year. P efficiency did not change significantly from 1992 to 1995. Though we decreased fertilizer P purchases considerably, this was over-come by decreased crop and livestock sales.
Three models were investigated for their ability to predict nutrient flow on dairy farms. DAFOSYM and the Penn State Farm Balance model were found inadequate for this purpose, but the Net Carbohydrate Protein System model was found to have the potential to predict nutrient output for dairy animals.
High soil clay content prevents spring application of manure to corn fields at The Miner Institute and many other farms in the Champlain Valley. Beginning in 1994, we increased the use of topdressed dairy manure on alfalfa fields. For the seven years prior to 1994, an average of 18 percent of Miner Institute dairy manure was applied to alfalfa. In 1994, over 40 percent of dairy manure was topdressed on alfalfa, permitting a reduction in commercial fertilizer purchases. In 1995, 65 percent of the manure was applied to alfalfa, either as a top-dress or just prior to seeding, permitting further reductions in fertilizer purchases. For the first 7 months of 1996, 75 percent of manure applied was to established alfalfa or land to be seeded to alfalfa. The 1996 total is expected to be within the 1994-1995 range.
Presidedress nitrate tests (PSNT) were done for the first time at The Miner Institute in 1994 and have been done each year since then. Soil nitrate levels have been low enough that the application of supplemental N was required, so no reduction in nitrogen fertilizer use was achieved through this practice. However, we have publicized the value of this test in our monthly Farm Report with readership of 11,000, and PSNT use in the region is increasing. On farms with heavy manure use, PSNT has the potential to greatly reduce nitrogen fertilizer inputs.
The direct impact of substituting dairy manure for fertilizer on alfalfa has been a savings of $24 per acre per year. This practice represented a savings of $1800 in 1994, $1400 in 1995, and an estimated $1400 in 1996. We have also changed our crop rotation to permit the application of manure prior to seeding alfalfa in late July. By using relatively high rates of composted manure we can supply the nutrients required for the alfalfa seeding as well as for the first production year. Since we begin to topdress manure in the second production year, it is possible that we will be able to completely replace fertilizer with manure in our alfalfa production system. We seed an average of 40 acres of alfalfa per year. At our normal fertilization rate, the change would represent an annual savings of about $1,000.
The impact on our total fertilizer purchases has been dramatic. In 1988 through 1993 we purchased an average of 54,698 pounds of fertilizer nutrients each year. From 1994 though 1996, we purchased an average of 33,652 pounds of fertilizer nutrients, or 38.5 percent less. Soil fertility levels continue to be maintained at medium to high levels, indicating that reduction of fertilizer purchases should not adversely affect crop yields. The initial nutrient balance caused us to take a close look at the mineral program for the dairy operation, and we eliminated unnecessary K (and therefore unnecessary expense) from the mineral mix.
A detailed analysis of the nutrient balance on the Miner Institute farm has been useful in discussions with farmers and agricultural professionals. At the beginning of this project the institute’s nutrient balance was worse than for a typical NY dairy farm and caused us to take a critical look at the various nutrient inputs. We were surprised at the amount of nutrients entering the farm as straw for bedding and made changes in cropping practices to reduce this purchased input. Since then, we have counseled many farmers about the economic and environmental impact of large nutrient imbalances.
Our nutrient cycling results also show the impact that feed minerals can have on the nutrient balance. Often one or more nutrients can be reduced with no effect on animal performance. Most dairy ration balancing programs predict production based on feed inputs, or vice versa. There is little accounting for excess nutrients, and it is common practice to overfeed some nutrients or to feed them in forms which are not efficiently utilized by the animal. The value of the Net Carbohydrate Protein System (NCPS) as a nutrient management tool is its ability to predict not only production but also nutrient output. Managers can then assess changes in quantity and form of nutrient outputs as different feed ingredients are used to balance the ration. The NCPS will allow farmers to assess the impact that a particular feeding regime will have, not only on the cow but on the environment.
Changes in practice
The amount of manure topdressed on alfalfa fields in the US continues to increase. This is supported by recent recommendations that little or no manure be applied to grass fields which will be used for dry cow forage. The proportion of dairy manure stored as a liquid or slurry continues to increase, and farmers with these systems are better able to topdress manure on alfalfa. Most farmers are pleased with the results: Topdressing manure decreases fertilizer purchases, maintains yields, and supplies nutrients to a growing crop when there is less chance of leaching and runoff.
After many years of nutrient balances on the Miner Institute farm, we know that while almost all dairy farms have large nutrient imbalances, there are practical steps which can be taken to reduce inputs and save money while maintaining high levels of production. Farmers can substantially reduce fertilizer purchases by applying manure to growing alfalfa and just prior to forage seeding. In some cases fertilizer purchases for alfalfa can be eliminated entirely, but fertilizer may need to be purchased for land which is next to non-farm neighbors who may object to the strong odors of liquid manure.
In two of the three years in which PSNTs were done at Miner Institute, soil nitrate levels were unusually low throughout the Northeastern US. This may contribute to why the tests at the institute indicated a need for supplemental N. Nonetheless, PSNT should continue to be stressed as an important analytical tool for dairy farmers.
Areas Needing Additional Study
A nutrient balance provides a snapshot view of what is occurring on a particular farm. It does not improve our understanding of the effects of the farm ecosystem. We need to understand the effects of changes in manure handling systems on nutrient loading and pollution potential, and the influence of dairy farm type (pasture-based vs. confinement, for instance) on nutrient efficiency.
We need to better understand the relationship between the nutrient balance on a particular dairy farm and changes in soil fertility. In spite of annual surpluses of 200 percent or more of P and K on the Miner Institute dairy farm, soil fertility levels as measured by Cornell University soil analyses have changed very little in the past ten years.
How much phosphorus is too much? We need to know at what soil test level this nutrient will be susceptible to leaching losses. This is important since topdressing manure at a rate which will meet the K needs of alfalfa will result in a considerable surplus of P.