Page 149 - Nutrient Management Planning Guide

143

Chapter 4.2

Sampling Strategies and Manure Variability

Proper manure sampling will ensure the most accurate manure analysis. Manure samples must represent the average nutrient composition of the manure being applied. Two factors influence this:

Changes in manure composition through time (i.e., •

temporal variation) as a result of volatilization, precipitation, drying and other natural processes. Variation within a pile or storage facility (i.e., spatial •

variation).

Changes in manure composition through time can be addressed by sampling as close to the time of application as possible (i.e., prior to or during application). This is particularly true for uncovered lagoons and pits, which are subject to seasonal variations in temperature and precipitation. In contrast, manure from under-barn concrete pits or covered aboveground tanks receive limited exposure to environmental influences and vary little between applications.

The nutrient content of solid manure can vary from one part of the pile to another. This variation depends on the distribution of bedding materials and the depth of the dried surface layer. The nutrient content of liquid manure can be variable due to solids settling with time, referred to as nutrient stratification (Figure 4.2.1). If variability is not addressed, manure analyses will not be representative of the nutrient content of the manure being applied. This could result in management decisions that lead to over or under nutrient application for crops, and potential loss of revenue.

Changes in nutrient content of stored manure occur slowly. A delay of 30 to 60 days between sampling and application will result in minor changes in nutrient content of the manure; therefore, there may be no need to resample.

Sampling during application can account for changes in manure

composition due to nutrient conversions, evaporation, and dilution.

s i d e b a r

s i d e b a r

Generally, total N and P concentration increases with depth, whereas K concentration decreases.

s i d e b a r

Adapted from Zhang et al. (not dated)

Figure 4.2.1 Stratification of Nutrients in a Liquid Manure Storage Facility

Differences in nutrient content throughout a manure pile can be addressed by using proper sampling procedures. To select an appropriate sampling strategy, it is important to consider the advantages and disadvantages of sampling before and during manure application (Table 4.2.3).