Manure application considerations for this Spring
April 28, 2012
The method and timing of manure applications can make a significant difference in nutrient availability to the crop.
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 planting during a typical spring make the logistics of planting, nutrient application and tillage very difficult. This year, however, a mild winter and relatively dry spring in Minnesota is giving the opportunity to livestock producers to apply manure before planting.
Typically, farmers like to apply the nutrients as close to planting as possible. Manure applications in the spring ensure that crop nutrient uptake increases and nutrient losses due to runoff and leaching are reduced.
Manure timing guidelines
Fall applications of manure, either injected or broadcast, 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 nitrogen. 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.
Manure applied in the spring has the least amount of time for loss to occur. However, with high organic matter manures, the rapid breakdown of organic material in the spring is more likely to temporarily tie up some of the otherwise available nitrogen in the soil, creating some short-term nitrogen imbalances for manure with high levels of organic nitrogen (dairy and beef, or manure with bedding).
While winter application of manure to cropland is inevitable for a number of livestock producers, the practice is generally discouraged. First, in the winter, incorporation of the manure into the soil is not possible; therefore, most of the available, inorganic nitrogen will be lost. Second, the manure is lying on the soil surface, susceptible to movement by runoff into waterways, ditches, streams, etc. If manure must be spread in the winter, select level land and apply only conservative rates of manure to minimize nutrient concentrations susceptible for movement. In addition, avoid applying manure where tillage was performed going up and down the slope and avoid applying during times of snowmelt. With good management, winter-applied manure will provide the same P and K and about a third of the available N amounts as fall- or spring-applied manure.
Spring manure applications can increase yields
Research from the University of Minnesota Southern Research and Outreach Center (SROC) in Waseca in 1999, showed that liquid dairy and hog manures injected in April produced yields 5% higher than manures injected in September and October, the study included 7 locations in Southern Minnesota.
A 2009 study at the SROC with swine manure showed that April applications were comparable with October applications. In addition, both of those application times yielded 10 to 12 bushels per acre of corn higher than the September and August application times. The study also showed that by June, when the corn roots require more nitrogen, most of the leachable form of nitrogen (nitrate) was still in the root zone for the April timing application while the other treatments showed lower nitrate values, suggesting that nitrogen was leached during early Spring.
Of course, all of these nitrogen processes are controlled by soil type and rainfall patterns. In general, application of manure after fall harvest potentially increases the risk for overwinter nitrogen leaching losses since there is no crop present for nitrogen uptake. Simply changing the timing to a spring application seems to reduce the risk for leaching losses.
A tool to assess the nitrogen status of the fields
Use of the soil nitrate test has been fine-tuned by research and has now evolved as an accepted best management practice to improve the accuracy of making nitrogen fertilizer recommendations in Minnesota. This measure of residual or carryover nitrogen present in the soil in the form of nitrate-nitrogen can be used effectively to fine-tune the nitrogen fertilizer recommendations for a variety of crops in the state.
This test can be a great management tool for farmers applying manures. By taking a soil sample in the late fall or early spring, producers can determine how much carryover nitrate is in the soil and determine supplemental nitrogen needs for the following crop.