Farm Nutrient Management Assessment Program For
Hog Producers in South Central Minnesota
Denton Bruening
Minnesota Department of Agriculture
In the past 5 years, over 400 farms covering over 300,000 acres, participated in the FArm Nutrient Management Assessment Program
(FANMAP) with staff from the Minnesota Department of Agriculture. Producers volunteered 2-4 hours of their time to share information about their farming operation. Producers were carefully selected to represent a wide diversity of management skills and farm characteristics. The overall purpose of the program was to develop a clear understanding of current farm practices regarding agricultural nutrients and utilize this knowledge to target various forms of assistance.
Pork producers in South Central Minnesota were the focus of the South Central Tills surveys and concentrated on the five counties in Minnesota with the highest densities of hogs.
Information collected focused mainly on nitrogen use on corn acres. Information was collected on a field by field basis for nitrogen inputs of fertilizer, manure and legumes. These inputs were then compared to the University of Minnesota (UM) recommendations for corn based on previous crop, soil type, and yield goal.
The average farm size was 886 acres with 842 acres of tillable cropland and all farms had some type of hog production. Corn accounted for 53% of the cropland acres and soybeans accounted for another 42%. Ninety-seven percent of commercial nitrogen fertilizer used was applied to the corn acres and the average commercial nitrogen fertilizer rate on corn acres was 141 pounds of nitrogen per acre. Seventy-one percent of the nitrogen fertilizer applied to corn was in the form of anhydrous ammonia. In regard to anhydrous ammonia, 49% was fall applied, 36% was spring applied, and 15% was side-dressed during the growing season.
Livestock on farms consisted mainly of hogs, but some farmers also had dairy and beef. The 51 farmers surveyed sold a total of 30,000 feeders, 150,000 finishers and maintained 8,500 sows on the farm. Hog production contributed 93% of the manure, based on nitrogen. Ninety-two percent of the manure was handled as a liquid and 8% as a solid, also based on nitrogen. Eighty percent of the manure was applied on corn, also based on nitrogen. Figure one details the fate of the manure as it travels to the field.
Total pounds of manure nitrogen produced was 1,800,000 for all farms (See figure 1). However, only 450,000 pounds, or 25% of the nitrogen produced, was available for the 1995 crop. Most of the nitrogen was lost though application methods. In fact, more nitrogen was lost, 675,000, than was made available to the 1994 crops! Much of this loss was because of the lack of incorporation of manure (40% of the manure applied had no incorporation). Same day incorporation of manure would double the amount of nitrogen available compared to no incorporation. Also, approximately one-half of the nitrogen "lost" would be available during the second and third years after the application.
Commercial fertilizer, manure, and legumes contributed a total of 4,375,000 pounds of nitrogen available for the 1994 corn crop (See figure 2).
Amounts of nitrogen applied were then compared to the UM recommendations. The corn yield goal averaged 154 bushels per acre across all five counties and 97% of the soils tested were in the medium to high range in regard to organic matter. Most of the corn acres were also in a corn soybean rotation, allowing a contribution of approximately a 40 nitrogen credit for those corn acres. Figure 3 compares the amount of nitrogen contributed to the UM recommendations for corn.
Nitrogen fertilizer rates were also broken down by legume and manure contributions into four scenarios. Figure 4 details the differences in those rates.
Farmers, on average, were reducing nitrogen fertilizer by 5 pounds an acre when comparing corn following corn to corn following soybeans. Soybeans contribute 40 pounds per acre of nitrogen to the following corn crop.
Next, the different scenarios were compared by the rates of excess above the UM recommendations. Figure 5 details those rates.
When farmers were applying fertilizer nitrogen to corn acres with no manure applied or previously in soybeans, they were doing an excellent job. Here reductions of nitrogen would reduce yields and increases of nitrogen would not increase the yields enough to pay for the cost of the nitrogen. Clearly an area where farmers could save money on nitrogen is on those acres with soybean credits. An additional 50 pound per acre reduction could save a farmer $10.00 an acre with the same yield potential. If a fertilizer dealer is applying the nitrogen, it is important to inform the dealer of cornfields previously in soybeans so they can reduce nitrogen rates. Manured corn acres could also be an area where farmers have potential savings on fertilizer. Manured corn acres not previously in soybeans could have reductions of 25 pounds of nitrogen per acre, or a savings of $5.00 per acre, with the same yield potential. And, on manured corn acres previously in soybeans reductions of 80 pounds of nitrogen per acre would be possible, or a savings of $16.00 per acre, with the same yield potential. With nitrogen prices high, farmers should supply information about fields previously in soybeans, or fields applied with manure, to anyone applying nitrogen fertilizer.
Farmers today have an opportunity to save fertilizer costs by replacing nitrogen with manure or legume credits. When discussing nitrogen applications, farmers should make manure and legume crediting known to whoever is applying the nitrogen. Over-applying nitrogen is only a donation to whoever is selling the nitrogen and is a detriment to the environment where the farmer lives.
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