Livestock manure has been considered an asset to crop production since the beginning of organized agriculture. Because manure contains several essential plant nutrients, it contributes to increased crop yields when properly applied to soils. Thus, manure represents a valuable nutrient resource for crop producers.
Livestock producers must be extremely cognizant of potential environmental risks from manure's nitrogen or phosphorus. An emphasis must be placed on developing and implementing manure management plans as part of an operation's overall nutrient management plan so that agronomic and environmental issues are equally considered.
Manure can benefit an operation's soil nutrient system and overall crop production. Crop yields are increased with manure usage. Soil nutrient levels are boosted, including micronutrients. And manure provides valuable organic matter to soil that improves soil tilth, aids in the retention of water and nutrients, and promotes growth of beneficial micro-organisms.
Previous research from the University of Minnesota Southern Research and Outreach Center (SROC) at Waseca showed that liquid dairy and hog manures injected in April produced yields 5% higher than manures injected in September and October. The study included seven site-years over a 3-year period in southern Minnesota.
Traditionally most producers in the upper Midwest prefer to carry out manure applications in the fall. The potential of a very short window of opportunity for field work during a "typical spring" make the logistics of planting, nutrient application, and tillage very difficult. Fall manure applications should start when soil temperatures at six-inch depth are below 50 degrees F. This ensures that crop nutrient uptake increases and that nutrient losses due to runoff and leaching are reduced.
Manure timing guidelines for this fall
Fall applications of manure, either injected or broadcast (Table 1), allow more time for the organic portions of the manure to break down before the plant needs the nutrients as compared to spring application. In contrast, fall applications also provide more time for potential loss of N. Fall applications of manure should be avoided on coarser-textured soils where leaching can be a threat to the water quality. The University of Minnesota recommends that if fall application is necessary, it should be done in late fall when soil temperatures are below 50 degrees F. Low soil temperatures prevent the nitrogen in the manure to be available for leaching losses. If manure applied to soils when soil temperatures are above 50 degrees F, the inorganic nitrogen converts rapidly to nitrate-nitrogen, which is a very mobile form of nitrogen and increases the risk of nitrogen leaching into the ground waters.