Not All Manure is the Same – Liquid Swine Manure

The nutrient characteristics of a manure is dependent the species of animal, the diet of the animals, and how the manure is handled. In recent years crop managers have been advancing the use of liquid swine manure from waste product to nutrient source. To efficiently utilize the nutritional benefit of liquid swine manure takes a bit of management.

The nutrient content of liquid swine manure is less concentrated than other manures which adds additional handling challenges handling large application volumes per acre. Effective manure management of liquid swine manure starts well before the day of application. The greatest variable in liquid swine manure is moisture content. The moisture content of liquid swine manure is mostly dependent on external water sources. Excess drinking water loss to barn manure pits, wash water from the barn, along with rainwater additions to open exterior pits increases water content of the manure resulting in a dilution of nutrient content. Reduction of external water making its way into storage pits and lagoons can help reduce dilution. In pits and lagoons, the solids settle to the bottom of the pit or lagoon creating a stratification of manure moisture content with depth.  As much agitation as can be safely achieved at application time can help reduce variability in the nutrient content of the applied manure.

Most of the nitrogen in liquid swine manure is in an ammonium form rather in organic forms. The amount of organic N is directly related to the solids content in the manure, which is usually low. The solid fraction separated from whole manure or cleaned from the bottom of a lagoon/pit after settling, can have more organic nitrogen than ammonium.  Any organic forms of nitrogen in manures need to be mineralized into inorganic ammonium before becoming plant available, this additional step in making organic nutrient forms plant available further slows the release to plant and help reduce potential losses. Especially in cold soils which are not conducive to microbial activity needed to break down the complex organic molecules. The ammonium form of nitrogen is held by the soil cation exchange capacity (CEC) and is directly available to plants for use and to soil microbes for conversion to nitrate. Ammonium is subject conversion to nitrate and possible loss in warm (over 50⁰F) and moist soils. For fall and early spring liquid swine manure applications, ammonium nitrogen stabilizers can be added to reduce/delay the conversion of ammonium to nitrate.

If liquid swine manure is applied in the fall before the soil temperature falls below 50⁰F, or if a period of warm temperatures occurs in the spring prior to planting allowing soils to warm up above 50⁰F for period of several days, non-stabilized ammonium nitrogen can rapidly convert to nitrate and become subject to loss. If these conditions occur when the manure was applied as a planned nitrogen source for corn, it is highly recommended to perform a presidedress soil nitrate test (PSNT) to evaluate soil nitrogen levels and the need for supplemental nitrogen. Given that most of the nitrogen in liquid swine manure is plant available at time of application makes liquid swine manure a good nutrient fit for side-dressing corn, and top-dressing winter wheat.

Most of the phosphorus in liquid swine manure is in an organic form so the concentration of phosphorus is directly related to the solid content of the manure. Liquid swine manure phosphorus content increases with increasing solids content. Potassium is water soluble in the liquid fraction and the concentration remains relatively constant regardless of manure solids content.

Ammonium nitrogen, soluble phosphates, and potassium contained in liquid swine manure are highly water soluble and contained within the liquid fraction of the manure. Off-site movement of liquid swine manure nutrients could occur rapidly if surface applied to the soil without incorporation, applied to areas of the field prone to concentrated surface flow, close to open drains/ditches, shortly before heavy rains, and to frozen or snow-covered fields. Incorporation of liquid swine manure greatly increases the retention of nutrients and reduces odor.

Nutrients targeted in feed rations can become elevated in the manure. High concentrations of zinc used in nursery feeding often leads to elevated zinc levels in manure. Repeated application of high zinc manures on the same field can lead to elevated zinc soil test levels. Some zinc is beneficial to crop growth, especially corn, however elevated zinc levels can lead to reduced plant growth.

Sources:

Chastain, J.P., J. J. Cambarato, J. E. Albrecht, and J. Adams. (1997). “Swine Manure Production and Nutrient Content. Swine Training Manual.” (pp 3-1:3-15). South Carolina Cooperative Extension.

Lorimor, J., W. Powers, A. Sutton. (2004). “Manure Management System Series. MWPS-18, Section 1 - Manure Characteristics.” 2^nd ed. Midwest Plan Service, Iowa State University.