Aquatic Pollution and Coastal Zone Managememnt (2+1)

Unit 3 : Agricultural wastes and eutrophication

3.3.Nutrients in Manure and Commercial Fertilizers
Plant nutrients in commercial fertilizers are mostly water soluble and readily available for plant uptake. Not all the nutrients in manure are available to crops during the year of application because some are in their organic form, while others can be lost during application. Therefore, an availability factor (percent of nutrients available) is used for rate calculations based on the quantities of nutrients available during the first year. The availability of nitrogen can vary from 30 to 80 percent depending on the type of manure and application method.

Most of the nitrogen in lagoon effluent is in the ammonium form and is more subject to volatilization loss during storage and land application. The greatest response from animal manure application can be obtained by promptly incorporating the waste into the soil either by injection or cultivation. The practice of injecting, chiseling, or knifing liquid animal waste beneath the soil surface minimizes loss of nitrogen to air or runoff. Therefore, use a lower availability factor if manure is surface applied and not incorporated within two days. Otherwise, a higher factor can be used. The time of manure application also affects the quantity of nutrient available to a crop. Higher availability is expected when manure application matches the crop nutrient uptake.

The availability of phosphorus and potassium in manure is considered similar to that in commercial fertilizer since the majority of phosphorus and potassium in manure is in the inorganic form. For all manure types, 90% of phosphorus and potassium is considered to be available during the first year of application and 10% for future years.