In a two-year study of 22 grazing and confinement dairy farms in northeast Ohio, we investigated carbon (C) and nitrogen (N) balance in soil, plants and animals. Most conventional dairy farmers applied too much soluble N to the soil, whereas most grazers fed too much soluble N to their cows. Conventional dairy farmers worked to solve soil C and N imbalance by reducing fertilizer rates based on their soil test results. Grazing dairy farmers brought rumen C and N into balance by supplementing pasture with grain for energy and hay for rumen health, using milk data to fine-tune their cows’ diets.
The goal of this project is to build upon farmers’ observations that healthy soil grows healthy plants, which in turn grow healthy animals. For years, dairy farmers have known that, “in the soil and rumen, microbes eat first.” Biologically-minded farmers maintain the health of their crops and cows by “feeding the soil and rumen bugs” (microbes) using good organic matter management. Dairy farms rely on microbes to recycle nutrients through the food chain. In both the soil and rumen, nutrients are released from plant material by microbial action. Since microbes require carbon (C) for energy and nitrogen (N) to build protein, the balance of organic matter C and N is very important. Thus, organic matter can be managed for nutrient content to promote microbial efficiency. Health and productivity of the soil, plant and ruminant animal increase when carbon (C) and nitrogen (N) are in balance because metabolism and production are closely linked.
1) Identify key linkages between the soil and plants in terms of nutrient and energy balance.
2) Measure the quantity and form of substrate available to microbes in the soil and rumen, in the context of nutrient and energy balance.
3) Collect whole-farm data on nutrient inputs and outputs to describe the link between nutrient balance, efficiency, and health on dairy farms.
In 2001, soil and forage were sampled on 22 dairy farms in late April / early May, late June / early July, and late August / early September. Animal feed, milk, and manure were sampled in late April / early May, late June / early July, late August / early September, and mid-late November. Animal rations, milk production numbers, and body condition score (body fat) were also recorded at these times. Soils were analyzed for total carbon, total nitrogen, NH4, NO3, pH, LTI, P1, K, Ca, Mg; P, K, Ca, Mg, Al, B, Cu, Fe, Mn, Zn, S, particulate organic matter, and microbial biomass nitrogen. Plant and mixed feed samples were analyzed for total carbon, total nitrogen, NO3, pH, ADF, NDF, P, K, Ca, Mg, Al, B, Cu, Fe, Mn, Mo, Zn, and S. Manure samples were analyzed for total carbon, total nitrogen, pH, NH4, NO3, P, K, Ca, Mg, Al, B, Cu, Fe, Mn, Mo, Na, Zn, and particulate organic matter. Milk was analyzed for milk urea nitrogen, protein, fat, lactose, somatic cell count, and percent solids. In 2002, hay and pasture samples were collected in May and June, along with feed, milk and manure samples. In September, 40 cornfields were sampled for soil nutrients, as well as plant biomass, nutrients and insect damage. In January 2003, a dairy nutrient management survey was conducted.
In a 2-year study of 22 grazing and confinement dairy farms in northeast Ohio, we investigated carbon (C) and nitrogen (N) balance in soil, plants and animals. Soil microbial N increased with soil organic matter content, indicating a positive microbial response to the augmented food source. In 2001 and 2002, soil NO3 was higher in cornfields receiving inorganic-N, relative to those receiving no synthetic fertilizer, but subsequent grain yields were not higher. Hay and pasture quality was variable in crude protein (11–31%) and acid detergent fiber (14–53%). Among grazing herds, those fed little supplemental energy (< 9 lb grain/day and no hay) tended to have elevated levels of milk urea nitrogen (> 16 mg/dl) during peak pasture growth, indicating inefficient use of N by ruminal bacteria. These results suggest that N inputs are used more efficiently when balanced with C.
Most conventional dairy farmers applied too much soluble N to the soil, whereas most grazers fed too much soluble N to their cows. Some conventionally managed cornfields had high soil nitrate readings of 30–70 ppm NO3-N (whereas 15–25 ppm would have been sufficient), and some grazing herds had high milk urea N (MUN) tests of 16–24 mg/dl MUN (whereas 10–14 mg/dl is optimal, and 26 mg/dl is deadly). The microbes and organic matter in each system could not assimilate and buffer this much N, and excess N was detected in the soluble N fractions (NO3-N and urea-N). This evidence of wasted N convinced these farmers that they needed to balance their N budgets.
Conventional dairy farmers worked to solve soil C and N imbalance by reducing fertilizer rates based on their soil test results. Grazing dairy farmers brought rumen C and N into balance by supplementing pasture with grain for energy and hay for rumen health, using milk data (MUN, fat, protein and production numbers) to fine-tune their cows’ diets. In both cases, timing was very important. Based on the results of the pre-sidedress nitrate test (PSNT), some of the conventional dairy farmers are cutting back on N at planting and applying a fraction of that cutback as sidedress N. Grazers found that they needed to use caution regarding spring N applications to pasture, as this practice could result in an extremely high crude protein content of pasture (> 23%).
At the beginning of the study, some grazers fed little or no stored feed during the grazing season, and had elevated levels of MUN and suboptimal production. To balance the soluble protein in pasture, these managers fed their cows energy and fiber before turning them out to graze. They fed grain mix (small grain/ corn/ minerals) at 5–8 lb at morning and evening milkings, for a total of 10–16 lb/ grain mix/ day. They also fed free-choice hay or straw (with molasses in some cases) to buffer the rumen. Forage tests on hay were worthwhile, and neutral detergent fiber (NDF) was an important number to watch. We don’t recommend feeding straw or extremely mature hay (> 50% NDF), as this material is digested so slowly that it causes prolonged rumen fill and decreases production as a result (think of Jerry Brunetti’s example of a BAD diet: fence posts and urea). By balancing the soluble protein in their pastures with energy (grain mix) and fiber (hay), grazers lowered herd MUNs to healthy levels (10–15 mg/dl) and increased production and conception rates.
Areas needing additional study
Clearly, there is a need for further research on grazing dairies in areas such as: nutrition for animals on pasture, herd health risks posed by feeding only grass for high CLA content in milk, soil fertility balance, economics of alternative management systems, breeds of cows and pasture species mixes best suited to grazing in Northeast Ohio, increasing opportunities and support for direct marketing, addressing regulatory concerns prohibiting the sale of raw milk, etc.