Although research and extension programs on nutrient management of perennial forages have been conducted for decades, there is little information about actual on-farm practices. Calculated whole-farm nutrient balances have shown that dairy farms typically import more N, P, and K than are exported in animal and crop products. This can result in excessive soil test P levels, which can pollute surface water, and can cause N losses to the air, surface water, and ground water. Recent surveys by the Minnesota Department of Agriculture indicate that fertilizer N is applied within about 10% of University of Minnesota recommendations on Minnesota farms without livestock, but more fertilizer N than necessary was applied on those farms with livestock, based on manure availability and nutrient content.
Proper manure management is difficult to achieve on many dairy farms because of limited time, labor, equipment, and land (Nowak et al., 1995). Manure application before seeding or on established forages is an attractive option, because it allows farmers to spread manure on more acres and at times when labor is available. Manure nutrients can be utilized particularly well when applied before establishing perennial forages. Schmitt et al. (1993) showed that alfalfa can benefit from preplant manure applications, even when soil test levels of P and K appeared to be adequate. This benefit may be due to N and micronutrients in the manure or to other factors not related to nutrient availability. However, stands can suffer when application equipment causes soil compaction. Topdressing manure on established alfalfa works very well for many farmers, but this practice can reduce stands because of crown damage in wheel tracks, smothering, salt damage, increased competition from grasses, and introduction of weed seeds in the manure. Best results occur when manure is applied within a few days of mowing (Lory, 1993). Although ammonia losses can be substantial, topdressing manure on grass fields during summer provides a desirable option for those producers with limited manure storage (Schmitt et al., 1999).
How are contemporary dairy farmers managing nutrients on perennial forages? To begin answering that question, I surveyed 1007 Minnesota dairy farmers by mail during August and September 1996. Returns of completed mail questionnaires and phone follow-up interviews brought the total response to 433 valid surveys, which were statistically analyzed. The average of a characteristic is overly influenced by a few very high or very low values, so both the average and the median are presented for many results. If the average and median differ considerably, the median provides a better idea of the middle of the sample group, because it is the dividing line between the upper half and lower half of the group.
In order to account for variations in inherent soil characteristics, the state was divided into three generalized soil areas. The prairie soil area (medium shading in the adjacent figure) is mostly neutral to calcareous soils derived from glacial till or lake sediment and developed under prairie species. The cold forest soil area (no shading) is characterized by neutral to acidic glacial till and outwash materials vegetated mainly by brush and by evergreen and deciduous forests. The warm forest soil area (darkest shading) is largely neutral to slightly acidic loess over bedrock or glacial till, which was vegetated by deciduous forest, brush, and prairie.
Dairies in this survey ranged in size from about 16 to 4000 acres of farmed land (median = 300 acres, average = 390 acres). The most prevalent perennial forage was alfalfa hay, reportedly harvested on 95% of the farms from between 5 and 350 acres (median = 65 acres, average = 79 acres), and grass pasture was the second most prevalent, ranging from 3 to 700 acres on 61% of the farms (median = 30 acres, average = 47 acres). Smaller areas of other legume, grass, and mixed grass-legume hay and pastures were reported.
Only small numbers of farmers provided estimates of fertilizer rate, so the following relationships between farm characteristics and nutrient application rate are tentative. About 15% of respondents apply P before seeding perennial forages. Reported rates range from about 5 to 60 lb P/acre (median = 16 lb P/acre, average = 21 lb P/acre). About one-quarter of farmers said they apply K before seeding forages, at rates ranging from 24 to 207 lb K/acre (median = 100 lb K/acre, average = 107 lb K/acre). Greater amounts of K are incorporated before seeding when farmers get information from fertilizer dealers and from the Extension Service, and as the proportion of fertilized forage land increases. The rate is smaller in the prairie soil region, which has higher native soil K availability than the rest of the state.
Aglime is added before seeding perennial forages on about one-quarter of the farms, with rates ranging from about 0.30 to 8 tons/acre (median = 3.0 tons/acre, average = 2.8 tons/acre). Lowest rates were for a highly soluble, finely ground limestone. More aglime is used on larger farms and when fertilizer rate information is obtained from fertilizer dealers and farm magazines, while less is applied, as expected, to farms in the calcareous (high pH) prairie soil area.
About 16% of the farmers reported that they apply N fertilizer on alfalfa, with rates ranging from about 5 to 60 lb N/acre (median = 18 lb N/acre, average = 21 lb N/acre). Application rates are likely to be higher when farmers depend on farming magazines for fertilizer rate information and when greater proportions of forage land are fertilized on a farm. Topdressed N applications on alfalfa are smaller on farms with larger herds. When inoculated with rhizobia, established alfalfa often does not respond to N fertilizer, so it is curious that N is applied. The reason may be that only combination fertilizers are recommended or available, that much of the alfalfa acreage contains grasses or other plants that respond to N, or that the farmers do not realize that no N is needed. It is highly unlikely that this ‘extra’ fertilizer N causes environmental problems, because alfalfa will reduce symbiotic N fixation when fertilizer N is available (Lamb et al., 1995). More Minnesota dairy farmers reported that they apply N to forages other than to alfalfa. These farmers concentrate topdressed N in one or two applications, with most (64%) being applied in late spring (May-June, M-J).
About one-half of the dairy farmers fertilize before seeding alfalfa, while over 85% fertilize established alfalfa fields. Some farmers (about 12%) reported that they apply the same rate of fertilizer to all perennial forage crop land. For those that do not, fertilizer decisions for both alfalfa and other perennial forages are based mainly on soil tests. Estimated nutrient removal, visual appearance of the crop, amount of grass present, and land ownership also play important roles. Fertilizer P is topdressed at rates ranging from about 5 to 70 lb P/acre (median = 20 lb P/acre, average = 24 lb P/acre) on 26% of the farms. Phosphorus rates are higher in the prairie soil region, on farms where a large percentage of forage land is fertilized, and when information on fertilizer rates is obtained from the Extension Service.
Nearly one-half of Minnesota dairy farmers topdress K on alfalfa. Reported rates range from about 16 to 350 lb K/acre (median = 110 lb K/acre, average = 124 lb K/acre). Relatively little variation in applied K could be explained by farm characteristics, but rate tends to increase with the relative importance of manure pack in livestock housing and decreases with the relative importance of daily or frequent hauling. Presumably, farmers have adopted the practice of K application to established alfalfa with a wide variety of dairy operations.
Topdressed S reportedly is applied to alfalfa by about 10% of Minnesota dairy farmers, and about 5% apply topdressed B. Sulfur rates range from about 6 to 70 lb S/acre and B rates range from 1 to 5 lb B/acre.
These non-N fertilizers are applied almost entirely during the growing season and are spread all at once or in a simple split. A significant number of Minnesota dairy farmers (about 45% of respondents who gave information on timing) apply non-N fertilizer in September and October.
Almost 80% of the reported soil tests were in excess of 20 mg P/kg, above which no additional P is recommended by the University of Minnesota, and several tests exceeded 120 mg P/kg. Higher soil test P levels were associated with manure storage in a pack and with higher percentages of forage land that are fertilized. Lower soil test P concentrations are characteristic of farms in the prairie soil region and occurred more frequently on farms with daily or frequent haul manure systems. The median soil test P level was 18 ppm for the prairie soil area, but 42 ppm for the warm forest soil area and 50 ppm for the cold forest soil area. About one-half of the reported soil test K values were greater than 160 mg K/kg, the level at which no K fertilizer is recommended. Soil test K concentrations were related positively to pack and lagoon manure storage systems, with increasing proportion of forage land fertilized, and with increasing acreage of permanent grass forages. Pack and lagoon manure handling systems tend to conserve K, which is excreted in urine. There were no differences in reported soil test K among the three soil areas of the state.
It appears from these results that many Minnesota dairy farmers apply commercial fertilizer to alfalfa and other forages. To some extent, the results indicate that native soil characteristics are taken into account when making decisions on liming and nutrient addition, but the large number of high P and K soil tests tend to confirm reports that these nutrients are often in excess on contemporary farms (Lanyon, 1992).
Farmers were asked to describe their manure management systems. The two systems ranked as most typical were daily or frequent hauling (63%) and lagoon (and pit) storage of liquid manure (31%). Dairy farmers apparently rely more on daily or frequent manure hauling in the warm forest soil area of the state, as the percent of forage land that is fertilized increases, and as fertilizer dealers serve as more important sources of information on nutrient needs. This latter point also might be interpreted that farmers who rely on daily or frequent hauling are less likely to employ independent consultants than to rely on personnel at the fertilizer distributor. Daily hauling is less likely on farms with more alfalfa acreage.
Reliance on lagoon storage of liquid manure is more likely as herd size and rolling herd average increase, as one might expect due to environmental regulation of animal feeding operations, and is less likely in the warm forest soil region and when information is obtained from farming magazine articles. Other manure handling systems rarely were listed as most typical, but were employed on many farms. Overall, Minnesota dairy farmers reported that manure storage facilities need to be emptied an average of twice a year, with a range of 1 to 26 times per year.
About one-half of the respondents reported that they apply manure on perennial forages. These dairy farmers are more likely to spread manure before seeding perennial forages when the typical manure source is manure pack in livestock facilities. Manure application either before seeding or as a topdressing on established forage stands is more likely when the farms have larger herds and are in the cold forest soil area of state. Farmers are less likely to apply manure to perennial forages when a larger percentage of their forages received commercial fertilizer. This implies that farmers are distributing manure and fertilizer nutrients to the various crops grown on the farm, and substituting one for the other to some extent. Topdressing manure is less likely the more farmers rely on independent consultants for information on recommended fertilizer rates. Topdressing manure on established grasses is less likely at higher rolling herd averages.
About 6% of all respondents said they routinely apply manure to old forage stands before rotating to the next crop. Farmers should recognize that, although these fields are handy places to apply manure, this practice may be environmentally damaging if N fertilizer rates to the following crop are not reduced based on reasonable N credits for the manure and the previous forage crop.
Only 45% of those who apply manure to forages (at any time) answered the question about whether they reduced subsequent N, P, or K fertilizer additions, and 85% of these replied “yes.” About two-thirds of these asserted that they reduced application of all three nutrients, while the remainder reduced application of one or two of these nutrients.
Nearly one-third of the respondents who gave information on manure timing indicated that they topdressed at least a portion of their manure on forages during winter. Spreading manure on frozen soil can lead to serious surface water contamination during snow melt or early spring rains. Farmers should be aware of this potential problem, and select fields for winter spreading to reduce the chance of runoff (Madison et al., 1995).
Perennial forages offer a good area to spread manure during the growing season (Schmitt et al., 1999). About one-sixth of respondents spread manure on forages in all months of the year, because they rely on frequent or daily hauling. In contrast, over one-third reported that they spread nearly all the manure used on forages at one time and almost 60% of respondents said they apply manure to forages in two applications.
The most frequently given reasons in support of topdressing manure on established perennial forages included the opportunity to spread manure in summer and to make good use of nutrients (see table on next page). In contrast, at least 20% of the farmers said that lack of time, lack of uniformity in spreading, and increased weed problems were reasons for not topdressing manure on all perennial forage fields. Nearly 20% of farmers also replied that they used livestock manure mainly on other crops.
About 10% of the farmers indicated that they have concerns about forage nutrition. Of these, nearly one-half were concerned about excess K in dry cow feed because of milk fever, foot and leg problems, and calving problems. Several said that their consultants had made them aware of the problem. Other concerns spanned the range between soil nutrient levels being too low to potential for nitrate poisoning.
When asked what their regular sources of information on recommended fertilizer rates were, over 60% of the farmers reported that they use soil test results as one form of information. More than one-half of the farmers reported that they depend on personnel from fertilizer dealerships for nutrient recommendations. These Minnesota dairy farmers rely more on fertilizer dealers when they have more grass pasture, typically use a daily or frequent haul system for manure, and fertilize a higher proportion of their forage land. However, those who said pasturing their livestock is a typical way of managing manure are less likely to depend on employees of a fertilizer dealership for fertilizer recommendations. Similarly, farmers are more likely to use information from independent crop consultants when they fertilize a larger proportion of their forage land, but also when they have larger herds. Those dairy farmers who spread manure on established forage stands are less likely to use an independent crop consultant for fertilizer recommendations.
Over three-quarters of the farmers rend to rely on information from personnel at fertilizer dealerships to interpred soil test results, and fewer farmers relying on private consultants (27%), Extension (20%), or farming magazine articles (20%) for help in interpreting these tests. Of those farmers who get nutrient management recommendations from fertilizer dealers, 16% also use independent consultants, 13% use Extension, and 20% use farming magazines as other, and sometimes primary, sources of information. Only a small proportion of those who get nutrient management information from independent consultants also use Extension (4%) or farming magazines (5%). Farmers who rely primarily on fertilizer dealers for this information had fewer total cows (median = 49 cows, average = 65 cows) and fewer acres of alfalfa (median = 60 acres, average = 73 acres) than farmers who rely primarily on independent consultants (median = 85 cows, average = 100 cows; median = 120 acres of alfalfa, average = 119 acres of alfalfa). Although Extension does not appear to be a primary source of nutrient management information for many Minnesota dairy farmers, it is part of the mix of information sources for about 14% of them. Many farmers who rely on Extension (38%) also get information from farming magazine articles.
At the same time, improved awareness of nutrient needs and in subsequent nutrient management should increase the yield, persistence, and quality of perennial forages and improve the viability of livestock farming. Fertilizer dealers are the most important source of nutrient recommendations to dairy producers in Minnesota and independent consultants are the most important advisors to larger operations. Providing these two groups with the latest information on nutrient management likely will result in the most rapid transfer of this information to farmers.
Madison, F., K. Kelling, L. Massie, and L.W. Good. 1995. Guidelines for applying manure to cropland and pasture in Wisconsin. Univ. of Wisconsin-Extension Publ. A3392. Madison, WI.
Nowak, P., R. Shepard and F. Madison. 1995. Farmers and manure management: A critical analysis. 31 pp.
Rehm, G., M. Schmitt and R. Munter. 1994. Fertilizer recommendations for agronomic crops in Minnesota. Minnesota Extension Serv. bull. BU-6240-E, University of Minnesota, St. Paul.
Schmitt, M.A., C.C. Sheaffer and G.W. Randall. 1993. Preplant manure and commercial P and K fertilizer effects on alfalfa production. J. Prod. Agric. 6:385-390.
Schmitt, M.A., M.P. Russelle, G.W. Randall, C.C. Sheaffer, L.J. Greub, and P.D. Clayton. 1999. Reed canarygrass yield response to liquid dairy manure. J. Prod. Agric. (in press).