Should I Use my Beef Manure as Fertilizer?

Manure produced from any livestock operation has tremendous fertilizer value. When we consider fertilizing crops, the most expensive nutrient (per unit) that our crops need is Phosphorus (P). For the beef farmer, the good news is that manure from most feeder operations contains P in excess of what crops need. While the excess P presents a nutrient management challenge that producers must acknowledge, some of the reasons P in beef cattle manure oversupplies what is necessary for crops can be easily remedied.

For instance, P is the second most abundant mineral element found in the animal's body and is absolutely essential in almost all metabolic reactions. For this reason, there has been a tendency for nutritionists to formulate rations with P levels above the National Research Council (NRC) recommendations. Thus, cattle rations often contain P in excess of requirements. There are many reasons the nutritionists add these "P insurance policies," including:

1. to add safety margins to account for variations in animal needs throughout the pen, P concentration of feeds, accuracy of feed delivery, and feed bunk management
2. to account for issues with P availability
3. to target improvements in reproduction

These insurance policies address some of the challenges in formulating to meet the P requirements of cattle. For example, there is considerable variation in P concentrations of both concentrates and forages. In general, cereal grains are uniformly greater in P than forages with byproduct ingredients (i.e., wheat midds) and oilseed meals (i.e., soybean meal) being especially high. Forages tend to be more variable than grains in P concentration, and because of this, book values should not be counted on as an accurate source of information. Producers and nutritionists should formulate rations based on analyzed feed results. Testing ingredients and adjusting rations accordingly can help ensure animals are receiving nutrients in the proper amounts.

Another feed challenge for many beef producers is that we may not have enough cattle at the operation to justify ordering a bulk mineral mix. Many bagged beef cattle minerals are generically formulated to meet the needs of all classes. Most of us feed cows and feeder animals quite differently. Because of the inherent differences between P concentrations in grains and forages discussed above, we often end up grossly overfeeding P to those feeder cattle we are attempting to finish efficiently on a grain-based diet by using these general beef cattle minerals. Feeder cattle consuming grain-based diets typically consume P in excess of their requirements anyway and need little, if any, supplemental P.

The consequences of feeding excess P equate to more manure P. Environmental concerns with P have forced a re-evaluation of the necessary levels needed in cattle diets. Adjusting rations for P content can significantly affect excretion in the manure. The most effective way to reduce manure P is to feed less P. Formulating rations to meet the animals' requirement for P and not exceed it should be the primary objective of the producer and nutritionist.

The main goal of implementing good feed management practices is to reduce manure P and thus the amount being applied to the soil. The reason why soil P increases is that in many areas of intensive livestock production, manure is normally applied at rates designed to meet crop nitrogen requirements or to control manure spreading costs. There is a mismatch between manure nutrient content and crop nutrient needs. In addition, when P is applied at rates exceeding crop needs, it stays where it is applied. Once available P levels have built up, they decline slowly after manure applications have stopped. Studies have shown that without additional applications, 10 to 20 years of corn or soybean production are needed to reduce available soil P (Mehlich-3) levels from 150 ppm to agronomic threshold levels of 20 ppm. The best management practice should be to evaluate its status on a field-to-field basis and apply manure only to maintain optimum levels of P.

Pennsylvania is in phase III of its Watershed Implementation Plan, or WIP. Nutrient reduction goals must be met by 2025. So, the bad news is that P presents a nutrient management challenge that we, as responsible stewards of our land, should address. The good news is that there is potential to reduce ration costs by reevaluating the mineral program and feeding P specifically to meet the animal's requirements, instead of in excess. Often, P is the most expensive nutrient in the cattle ration.