Any thing that is grown in this country and is harvested takes nutrients out of the soil. If those nutrients are not replaced by nature or by adding fertilizer, the production of hay will go down. Hay can add some nutrients back into the soil like nitrogen and sulfur but they are a high user of phosphate and potash. Some micro-nutrients like boron and copper have shown up as deficient in hay fields. If phosphate, potash and some of the micro-nutrients are not added back into the soil, the soils will become deficient. All plants require nitrogen to grow. For each ton of alfalfa that is harvested, there is 56 pounds of nitrogen removed. With legumes such as alfalfa and clover, no added nitrogen is required to maintain yield. The plants can produce their own nitrogen if they are inoculated with the proper rhizobia. This is a bacteria that attaches to the root of the alfalfa plant and provides the alfalfa with nitrogen manufactured from the air. Each year, a certain percentage of the roots die in an alfalfa field. These dying roots supply between 50 and 100 pounds of nitrogen to the grass plants. This is the reason that any fertilizer program for a mixed stand must focus on the alfalfa. For a grass stand with no alfalfa, nitrogen must be added to get reasonable yields. A brome grass crop uses 36 pounds of nitrogen per ton of hay produced, so significant amounts of nitrogen need to be added to grow a big grass crop. Sulfur is a nutrient that is required at a 4 to 1 ratio for plants of N to S. Some sulfur can come from the soil (dying roots) or from the air in the form sulfur in the rain. In our area, we are generally short of sulfur in our alfalfa hay crops. To maintain reasonable yields with a hay crop, somewhere between 10 to 20 pounds of sulfur needs to be added. With hay fields, the biggest nutrient requirement is for phosphate and potash. In every ton of alfalfa or brome grass harvested, there is 15 pounds of phosphate and 60 pounds of removed. Over a period of years, the levels of these nutrients will be reduced to a point where the fields will not produce hay. The longevity of alfalfa will be reduced. Finally, if the levels are low enough the alfalfa will not live for more than a year or two. We have fields with this problem in the Meadow Lake area. Micronutrients have not been a major issue for hay production although nutrient deficiencies have been identified. If hay production is a problem on a field, a soil test or a tissue test will go a long ways to determining which nutrient is deficient. Hay needs nutrients to grow. When the nutrients run out yield will go down unless fertilizer is added. If the yield on your hay fields is going down, a soil test will help define the problem. Defining the problem will make certain the right nutrients are added.
By Dave Cubbon, P Ag