University of Maryland Extension

Developing Management Units for Nutrient Management Planning

Patricia Hoopes, Harford County Nutrient Management Advisor

Planning management units is one of the most important activities when developing a nutrient management plan. Many operators want to combine several fields into one management unit to reduce expenses and simplify fertilizer applications. This is an acceptable practice in some scenarios but not all. The following are points to consider when planning management units:

1)  Pay attention to the soil type. All the fields in a management unit should have the same soil type. For example, if you had one field with a clay-type soil and the other fields were silt loam, the field with clay-type soil should be treated as a separate management unit.

2) Consider the production potential of the fields.  If one field has less potential for production than the other fields, it should be treated as a separate management unit. There are many factors that can affect production in a field, but good crop yield records can help you determine the production potential of your fields.

3)  All fields in a management unit must have the same crop histories. Crop histories affect both soils and recommendations.  For example, a field that is currently in soybeans cannot be combined into a management unit with a field that is currently in corn grain, even if you are planning the same crop for these two fields next season. The soybean field will have a nitrogen credit that the corn field will not have.

4) All fields in a management unit must have the same history of nutrient application. For example, a field with a past manure application cannot be in the same management unit as a field that did not have a manure application, even if you are planning the same crop for these two fields next season. The manure application affects the soil and recommendations as nutrients from manure are plant-available for three years after application.

5) Other physical characteristics in the landscape demand separate management units. For example, eroded slopes and gentle slopes demand separate management units.

A little thought when developing management units will help generate better recommendations, resulting in better yield results.  Even so, it is understood that there are situations that make it impossible to manage different areas separately, and in these cases they should be treated as one management unit.


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