Soil Management for Vegetable Crops
Using Manure and Compost for Vegetable Crops
Manure and compost not only supply many nutrients for crop production, including micronutrients, but they are also valuable sources of organic matter. Increasing soil organic matter improves soil structure or tilth, increases the water-holding capacity of coarse-textured sandy soils, improves drainage in fine-textured clay soils, provides a source of slow release nutrients, reduces wind and water erosion, and promotes growth of earthworms and other beneficial soil organisms. Most vegetable crops return small amounts of crop residue to the soil, so manure, compost, and other organic amendments help maintain soil organic matter levels. Proper use of manure and compost is essential from both a production and environmental standpoint. Applying rates that are too low can lead to nutrient deficiency and low yields. On the other hand, too high a rate can lead to nitrate leaching, phosphorus runoff, accelerated eutrophication of lakes, and excessive vegetative growth of some crops. Thus, understanding how to manage manure and compost is important for vegetable producers who have access to an economical supply of manure, compost, or other organic nutrient sources.
Manure
Raw manure is high in nutrients, especially readily available nitrogen. Fresh, non-composted manure will generally have higher nitrogen content than composted manure while the use of composted manure will contribute more to the organic matter content of the soil. The nitrogen in manure as well as in compost is in two forms: the organic form and the inorganic form (ammonium, NH4⁺ and nitrate, NO3¯). Ammonium is the predominant inorganic form of nitrogen in manure and it is immediately available to the crop following application.
Food Safety Considerations
In addition to using for the plant nutrient value and building soil organic matter, there are food safety considerations when using manure in the production of fruits and vegetables. Fresh manure is known to harbor human pathogens such as E. coli and Salmonella spp. Food safety regulations now implemented by the U.S. Food and Drug Administration through the Food Safety Modernization Act restrict how and when manures can be used in the production of fresh fruits and vegetables.
Compost
The most important benefit of using compost is the increase in soil organic matter in addition to adding nutrients to the soil. Generally, compost contains relatively low concentrations of nitrogen, phosphorus, and potassium compared to manure. Just like manure, the nitrogen content of compost will vary according to the source material and how it is composted. In general, nitrogen in the form of ammonium (NH4⁺) or nitrate (NO3¯) is low in compost compared to manure. The majority of the nitrogen in finished composts (usually over 90%) has been incorporated into organic nitrogen compounds that are resistant to decomposition.
Composted vs. Raw Manure
While raw manure can be used for fruit and vegetable production (provided food safety rules are followed), there are benefits to using compost vs. raw manure:
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