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Comments by: James I. Sprague, Livestock Nutritionist Cattle Requirements vs. Manure Problem A young cattle feeder asked his teacher, "Professor my father and I have been supplementing our cattle for years with extra phosphorus, and now you tell us we do not need to use as much phosphorus for our cattle? We are confused." The professor's answer may have been like this, "We formerly never worried about excess phosphorus supplementation. We knew that if farmers took good care of their manure the phosphorus was not wasted, because it would be returned to the soil." The story is true. I asked this question and received this answer from a famous ruminant scientist, Dr. "Shorty" Huffman at a nutrition seminar in 1957 at Michigan State University. Now, cattle feeders and their nutritionists know better. We recognize we must not over use manure and flood the capacity of the soil and the subsequent crops to use the amount of fertilizer from the manure. We also must avoid leaching and prevent run off of the nitrogen and phosphorus to streams and lakes. Cost of Over-Formulation of Phosphorus Phosphorus is an expensive nutrient. If supplemental phosphorus is not required in a ration, considerable cost savings can be achieved. For example the cost of a one percent addition of elemental phosphorus to a feedlot supplement from dicalcium phosphate (108 lb per ton) is approximately $14.25 per ton, according to Lance Huck manager of Scott Pro's feed plant at Scott City, Kansas. The savings per year for a 10,000 head feedlot would be approximately $32,000 if the supplement was fed at one and one quarter (1.25) pounds per day. Value of Feedlot Manure's Phos is High When we calculate the value of feedlot manure, we can estimate the value of the nitrogen and phosphorus. Each of these nutrients are valuable in the fertilizer program. The added value of the organic matter is also valuable for the "health of the soil." Manure analysis is highly variable according to tests at SERVI-TECH Laboratory at Dodge City Kansas. Steve Harrold of the lab stresses that the variation depends on the moisture, the grain type, and the fortification of phosphorus. The average phosphorus of feedlot manure on a wet basis is 0.42%P (0.96% P2O5). Therefore, the amount of phosphorus per ton from manure would be on the average 8.4 lb of P (19.2 lb of P2O5) per ton of manure. If 10 ton were applied per acre this equates to 192 lb per acre of P2O5 per acre. Using the value of phosphorus from the feed industry, the value of the average feedlot manure=s phosphorus content is 57 cents per ton. If 10 ton per acre of this average manure was applied the theoretical value is $5.70 per acre Your agronomist and fertilizer suppliers can help evaluate the economics of manure application. Analysis of the manure is needed. Over Application of Manure The problem comes when we over apply our valuable manure. Your nutritionists can help feedlots reduce the phosphorus in the rations and subsequently in the manure. The feedlot will need to work with their farming operation and the agronomists to coordinate the fertility program and any effects on the environment. Reasons for Excess in Rations Some of the reasons why we did not worrying about the excess phosphorus in the rations were: Bone supplement is often used at a feedlot for all cattle. Most of the time only one supplement is available at a feedlot. Bin space is always a problem, so the supplement was formulated to supply the critical phosphorus to the starting and growing rations and over-fortified the finisher ration. *Correcting a deficiency. We justified the inclusion of "a liberal amount" of supplemental phosphorus to correct any possible deficiency of the new cattle. *Experience. We knew cattle would eat free choice mineral when confined on growing and finishing rations particularly when they first came on feed. We assumed they were trying to correct a deficiency. We noted that successful feeding programs contained adequate phosphorus from commercial supplements and included offering the cattle free choice minerals. *Successful farmers supplied phosphorus fertilizers to their soils in addition to manure. Since the clay particles in soil hang onto the phosphorus that is applied to the soil, we assumed that the phosphorus from the manure would eventually be used by the crops. *Meat meal formerly was used as an economical source of high quality phosphorus (meat meal now cannot be used for ruminant animals). When meat was replaced with dicalcium phosphate and other commercial phosphorus sources the cost of phosphorus supplementation increased. *Phosphorus was needed in liquid supplements. Adding phosphorus helps the suspension properties of some liquid supplements. |
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