Swine & U: Manure application in warm weather

By Diane DeWitte, UMN Extension swine educator
Originally printed in The LAND as April 29/May 6, 2022 Swine & U column.

Spring’s here and for some swine producers, moving manure is an important step as the crop gets planted. UMN Extension Nutrient Management Specialist Melissa Wilson provides good information for farmers who need to make both nutrient management decisions and who may need to get manure out of the way.

When is the best time to apply manure?

That depends on the logistics of each farm, weather, and soil conditions. It is also influenced by what risks you are willing to take. Those risks include:

• losing nutrients if the manure is applied too early
• running out of storage for the manure
• reducing time for nutrients to release if the manure is applied too late
• having a wet and/or cold spring which could delay manure application and then planting.

As producers consider planting season activities, they’re encouraged to take a look at potential Spring or Summer application and evaluate the pros and cons of each.

• Springtime manure application pros include the fact that manure is available closer to when a growing crop will begin using the nutrients and the chance of nutrient losses is lower.
• The cons of spring application are that manure with high organic matter may have less time to break down and nitrogen release may be slower than expected. In addition, if soil conditions are poor, delaying manure application may further delay planting. Wilson’s recommendations are to wait until snowmelt has occurred and the soil is completely thawed. Avoid applying on wet soil to reduce compaction.

Wilson and her team have completed several years’ research on growing season application of manure directly into young crops. Here are the pros and cons of Summer manure application. The pros are that a producer can apply manure directly to a growing crop and reduce nutrient losses. Growing season application also gives farmers another window of opportunity for applying manure. Some of the disadvantages of summer application are that a producer would need specialized equipment and growing season application may not be ideal for timing of livestock operations or solid manures. Dr. Wilson recommends that producers interested in summer manure application Inject or incorporate manure between rows of growing crops as soon as possible to maximize nutrient value.

Manure Sampling and Nutrient Analysis

UMN Extension Educator Chryseis Modderman provides these thoughts regarding manure sampling and why producers should do it.

Manure is a valuable source of nutrients for crops. Testing manure for nutrient content helps meet crop nutrient needs efficiently. This leads to increased profit and decreased risk of pollution. Nutrient estimation tables give a general idea of nutrient content, but they tend to differ from actual values due to factors like storage type and animal diet. Therefore, we don’t recommend producers rely on those tables. The most accurate way to manage manure for nutrients is to analyze for nutrient content.

Manure uniformity

Nutrient content in manure varies from one area to another. Solids tend to settle to the bottom of liquid storage systems. Solid storage systems vary based on bedding content and time of stacking. It is important to make the manure as uniform as possible so that the applied rate is accurate.

Use a pit agitator to mix liquid manure to make it more uniform. The solid portion of the manure will begin to settle to the bottom right after agitation. Solid manure is more difficult to make uniform. When piling the manure, alternate between areas with large amounts of bedding and areas of small amounts of bedding.

How to sample manure for nutrient analysis

Manure sampling timing can change the accuracy of a manure test. We recommend taking the sample at manure application. The main drawback of this method is that you cannot use the test results to adjust application rates for the current year. However, the results will help with future fertilizer rate calculations. Keeping detailed records of manure test results will allow for accurate rates in the following years.

Sampling in storage and before manure application allows time to receive results and adjust rates in the current season. However, nutrients are lost with further storage and handling, so it may not give an accurate picture of the nutrients applied. This is particularly true for farms with large numbers of livestock and amounts of manure since collecting a representative sample of the manure may not be easy to do.

Manure should be tested each year for the first three years of operation; then every three or four years. Also test whenever management practices change that could alter nutrient content, like the storage system or feed. The Minnesota Pollution Control Agency (MPCA) requires farms with over 100 animal units to test manure at least once every four years. Visit the MPCA website for more information.

Manure Sampling Helps Producers Know

Just like regular soil tests help farmers know the nutrient condition of their soils, manure tests assist in making application decisions. Dr. Wilson offers these tips for collecting a through manure sample for laboratory analysis.

Always use caution and proper safety measures while sampling manure.

Liquid and semi-solid manure

• The best and safest time to sample liquid manure is after the pit or lagoon has been agitated and is being pumped out.
• Collect 15 to 25 samples as the pit is pumped out from beginning to end. Dump into a 5-gallon bucket.
• Mix the manure thoroughly.
• Take a subsample, usually about a quart, and place in a plastic container.
• Freeze the sample prior to sending to the lab.
• This method will not allow you to get the analysis results back prior to application for the current year. But the analysis can be used to determine whether appropriate amounts of manure were applied to meet crop needs and for estimating the Year 2 and 3 nutrient credits.

Solid manure

• Manure can be sampled from the stockpile or during hauling.
• Stockpile: Using a pitchfork or shovel, collect 15 to 25 samples from many different depths in the pile but avoid the crust.
• During hauling: Collect several subsamples from each load.
• Place samples into a 5-gallon bucket and mix very well.
• Take a subsample and place in a sealable plastic bag, then double up the bag.
• With the stockpile method, you may be able to have your manure analyzed prior to application.
• If sampling during hauling, you will not get the analysis results back prior to application for the current year.

Nutrient availability

Nutrients are not entirely available for crop use the first year after application. This is because nutrients can change forms, and only some of these forms are available for plants to use.

When nutrients are bound to carbon they are in an organic form. If not bound to carbon, they are in an inorganic form. Typically, plants can only use the inorganic form of nutrients, but manure supplies both organic and inorganic forms. Microbes can break down organic forms of nutrients and mineralize them into inorganic forms. However, this can take several years and depends on soil moisture and temperature conditions.

The UMN Extension nutrient management team of Wilson and Modderman are currently conducting additional research to provide best practice recommendations for warm season manure application. They can be reached via email to answer specific questions, Chryseis Modderman: cmodderm@umn.edu, and Melissa Wilson: wilso984@umn.edu, and their latest findings are available through the UMN Extension Crops website at https://extension.umn.edu/crop-production.