Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/20/2000
Publication Date: 3/20/2001
Citation: ROTZ, C.A., ROTH, G.W., SODER, K.J., SCHNABEL, R.R. SOYBEAN PRODUCTION AND USE ON PENNSYLVANIA DAIRY FARMS. AGRONOMY JOURNAL. 2001. Interpretive Summary: Economic and environmental concerns are stimulating change in dairy production. Inflation-adjusted milk prices have remained stable or declined for many years, but the costs of most production inputs have continued to increase. Dairy farms have grown more dependent on the use of commercial fertilizer and the import of supplemental feeds to improve production and profit. This heavy import of nutrients, though, has create greater opportunity for buildup of nutrients in the soil and the loss of excess nutrients to ground and surface waters. As sustainable dairy farms are developed for the future, changes must be made to improve their productivity, profitability, and environmental impact. Production and feeding of soybeans on dairy farms reduces the need for nitrogen fertilizer, and the soybeans provide an excellent high protein feed for cattle. A systematic whole farm analysis was done to determine how this practice impacts farm productivity, profitability, and nutrient losses to the environment. In general, production and feeding of soybeans in either a raw or roasted form was determined to be economical only when farmland was readily available. There was no environmental benefit because nitrogen imported through fixation by this legume crop had a similar effect as the importing of nitrogen in fertilizer and feed supplements. Although this practice has become popular in recent years, it does not appear to offer a long-term improvement for the dairy industry.
Technical Abstract: Representative dairy farms were simulated with the Dairy Forage System Model (DAFOSYM) to determine the long-term environmental and economic benefits of growing and feeding soybeans. Component models used to simulate corn (Zea mays L.) and soybean (Glycine max L.) production predicted historical yields that correlated well to county yield statistical data. With typical dairy production strategies for the Mid- Atlantic region, production of soybeans as a cash crop increased farm net return by $266/ha of soybean land when ample cropland was available to produce most of the feed requirement of the herd. With a more restricted land base, there was less economic benefit to shifting land from corn or alfalfa (Medicago sativa L.) production to soybeans. Feeding the soybeans to the dairy herd returned about $90/cow per year compared to a feeding strategy where purchased soybean meal was the sole protein supplement. Compared to more optimal feeding using a low rumen degradable protein mix, the economic benefit for growing and feeding soybeans was small. As cropland per animal unit decreased, the economic benefit of soybean production and feeding decreased. There was little environmental benefit (reduced N loss or P accumulation) for growing soybeans as a cash crop or feed on dairy farms. The annual economic benefit of producing and feeding roasted soybeans improved by $25 to $35/cow when the increased milk production obtained by feeding roasted soybeans was improved 1% or when corn silage provided all the forage on the farm. The economic benefit was moderately sensitive ($10 to 15/cow per year) to the amount of forage fed in animal rations, the predominant soil type on the farm, and the market price of corn.