Managing Manure in Potato and Vegetable Systems (E2893)

Managing Manure in Potato and Vegetable Systems (E2893)

Both short-term yield benefits and long-term soil building can occur through the addition of organic matter.

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Role of manure

Maintaining and improving soil quality in vegetable and potato systems is a difficult task. Heavy equipment can cause compaction, crop residues tend to be minimal in these rotations, and sandy soils generally have low organic matter levels. Degraded soils can be revitalized by adding manure or compost. To minimize costs while enhancing organic inputs, a combination of manure and cover crops is recommended to rebuild soils.

Both short-term yield benefits and long-term soil building can occur through the addition of organic matter. Recent studies in Michigan suggest that application of poultry manure with a reduced fertilizer rate can enhance potato tuber yields by 30 to 60 cwt/acre at some sites (Figures 2 and 3). The mechanism is under study but may be related to any of the following: enhancement of soil microbial activity, the active organic matter fraction or enhanced nutrient supply.

Other benefits take time to accrue and are generally associated with manures that contain large amounts of organic materials, such as dairy manure or manure from straw-bedded livestock. Soil quality benefits include increased water-holding capacity, improved soil structure and nutrient buffering ability (Grandy et al., 2002). An increase in soil organic matter of 0.5 percent will increase water-and nutrient-holding capacity by about 10 percent.

Benefits and potential negatives associated with using manure depend on the type of manure, how it is stored and the timing of application. It is highly advisable to obtain a laboratory analysis to judge the quality of the manure. Your county MSU Extension office has a list of manure testing laboratories. The list can also be accessed at <http://www.maeap.org/cnmp.htm>.

Manure analysis: Nitrogen and phosphorus content, pH and the amount of organic matter added are all useful measurements that provide insight into the quality of the manure. Total N and inorganic N (ammonia and nitrate) are particularly useful for estimating N availability. Phosphorus builds in the soil, and the amount added with manure should be accounted for and subtracted from fertilizer applied.

A sample is only as good as the sampling technique used, and it is important to obtain a representative sample from the manure storage facility. Your county MSU Extension office can provide guidance, or check with the testing laboratory to determine a recommended sampling procedure. One useful method is to obtain a sample from at least three different depths of the storage facility, preferably just after the slurry or pile has been well mixed.

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