With the current economic challenges faced by Michigan farmers, taking full advantage of the plant nutrients found in livestock manure is a sort of no-brainer. But if you aren’t testing manure for nutrient content, you have to depend on published “book values” to estimate nutrients applied from manure application. This can result in significant miscalculation of nutrients actually applied.
There are several factors to consider when attempting to fine-tune your nutrient credit from manure application, including manure nutrient content at the time of application, manure application rate and nutrient losses during and after application. The first item of concern is the manure nutrient content at the time of application. Without a good estimate of the nitrogen, phosphorus and potassium content of the applied manure, application rate and percent of nutrient loss will also be less meaningful.
Let’s be clear, using book values for manure nutrient content is a better practice than failing to consider manure nutrients. Every farmer keeping animals should be familiar with the Michigan Department of Agriculture and Rural Development’s Manure Management GAAMP (Generally Accepted Agricultural Management Practices). This document provides good guidelines for estimating manure nutrient content, losses during scraping, handling and spreading, as well as nutrient needs of most common Michigan crops. Also included are instructions for completing a manure management system plan. This plan will be specific to your farm and especially important if a manure-related complaint is filed against your farm.
Another place to find very useful book values is the Midwest Plan Service’s “Manure Characteristics” publication. It includes tables for liquid pit manure generated by several livestock species with pounds of nutrient per 1,000 gallons listed. Solid manure information is also included in terms of pounds per ton.
However, the best way to make efficient use of manure nutrients is to have manure from your farm tested for nutrient content. Several certified laboratories are available, with a typical cost of around $30 per sample for a basic analysis. It is important to use proper collection technique when the sample is collected. The lab you select will have instructions on their website.
An on-farm demonstration was conducted involving five Michigan’s Upper Peninsula dairy farms to highlight the difference between book values and nutrient values determined by sampling and testing. Water content of the stored manure is a big factor. Rations fed to cattle or other livestock will also affect manure nutrient content. The following results show that some manures will closely resemble the book value, while others will be very different.
If manure is a significant source of crop nutrients on your farm, Michigan State University Extension recommends you have it tested annually following recommended sampling procedures. With the current low commodity prices, the cost of manure sampling in time and cash, along with good manure storage, handling, application and incorporation practices, can be a very good investment.