Manure Nutrient Content
Average amounts of N, P2O5, and K2O in manure for various animal types are shown in Table 1.2-13. Although these values are good average figures, they are inadequate if you wish to accurately account for manure nutrients on your farm. Analyzing a sample of well-mixed manure is essential for good manure nutrient management. Figure 1.2-9 is a copy of a Penn State manure analysis report, which is typical of manure analysis reports from labs analyzing manure in Pennsylvania. The minimum recommended analyses are percent moisture or percent solids, total N, ammonium-N, total P, and total K. Most labs will also offer a more detailed analysis for secondary and micronutrients, pH, calcium carbonate equivalent, C:N ratio, water-extractable P, and so on. These tests can be requested to provide information for specific needs. Pay close attention to the units on manure analysis reports. On the Penn State manure analysis report, the results are given in two different units: lbs nutrient/ton of manure and lbs nutrient/1,000 gallons of manure as sampled. This is the same analysis reported in different units to make it convenient for a farmer to do rate calculations in either tons/A or gallons/A. Not all labs use these same units. For example, some labs report liquid manure analysis as lbs nutrient/100 gallons of manure. Also, while most labs report the analysis on an “as sampled” basis, some labs will report the results on a dry matter basis.
For best results when submitting a manure sample for analysis, sample the manure that is in the tank or spreader box being delivered to the field for application. Such samples will be most representative, because the liquid manure pit is likely to have been agitated in order to load the tank, and semi-solid manure scraped from the barn is moderately mixed while being loaded into a box spreader.
Collect several samples of semi-solid manure from the box spreader, mix well, and fill a laboratory container three-quarters full. With daily haul manure-handling systems, periodically repeat this sampling procedure throughout the year. If liquid manure has been agitated well, one sample is sufficient to adequately determine the nutrient status of the manure in the pit. Take a sample from the tank and fill the laboratory container three-quarters full. Caution: do not completely fill the container; leave space for gas expansion.
In many manure storage systems, there is considerable variation in the manure nutrient content, even within the storage unit. For example, in a liquid manure storage, the phosphorus content may be higher in the bottom of the storage than in the top. Also, because the ammonium nitrogen can vary with depth in the storage, the manure nitrogen availability to the crop will change as the storage is emptied, unless there is adequate agitation. In these situations, no manure in the storage actually matches the average results from the analysis of a single composite sample. To overcome this problem, it is recommended that a detailed analysis of the manure be performed at least once after the manure storage is constructed to determine the amount and nature of the variation. The process involves sampling the manure periodically as the storage is emptied for field application. Samples may be taken every so many loads or whenever a significant change in manure consistency occurs. After this intensive sampling and analysis, the farmer will have a basis for making manure rate changes or supplemental fertilizer changes to compensate for the variation. If the management of the storage is constant, or if thorough agitation is accomplished, this intensive sampling may not be necessary every year. Previous results can be used to make adjustments in following years.
Sample mailers and information forms are available through the Agricultural Analytical Services Laboratory (814-863-0841 email@example.com) or from county offices of Penn State Extension. For more details on sampling manure, see Agronomy Facts 69: Manure Sampling for Nutrient Management Planning.
On farms with a deficiency of nutrients, using manure can greatly reduce your fertilizer needs and thus their expense. On farms with an excess of manure, however, these nutrients can represent an environmental threat if they are not used properly.
Reference: The Agronomy Guide - Section 2: Soil Fertility Management