Sampling and Application of Dairy Lagoon Effluent

Field Application

      Dairy farms import tremendous quantities of nutrients when feed and fertilizers are purchased. Significant portions (50 to 80 percent) of the nitrogen (N), phosphorus (P), and potassium (K) in the diet end up in the manure and are disposed of in the lagoon or manure pile. Application of the manure (or effluent) to hay and silage fields helps to recycle these nutrients, which reduces commercial fertilizer needs, since they are already bought in the grain and other ration items!

      Long-term application of dairy lagoon effluent to the same fields (typically, those closest to the lagoon within range of the traveling gun pipe system) raises concerns about excessive quantities of nutrients building up in the soil, particularly at the soil surface.

      Runoff of agricultural nutrients into streams and other bodies of water can cause excessive algae growth and reduce oxygen levels that result in fish kills--and it's not just agricultural nutrients. Home lawns and urban street runoff and a certain amount of natural or background nutrient runoff also contribute to environmental problems. All of these factors contribute, but none of the factors are precisely defined or well quantified. It is obvious that excessive nutrient applications are not in anyone's best interest because the nutrients are wasted in forage or other crop production and contribute to environmental concerns.

      The amount of nutrients in a lagoon system depends on the quantity in the diet passing to manure and stored in the liquid waste system and the length of time between pumping of the lagoon. The amount of nutrients (N, P, and K) applied in a lagoon pumping is based on the concentration (percent or PPM) and the number of inches of effluent applied per acre. You can use traveling gun irrigation systems to pump effluent from the lagoon to nearby hayfields. Typically, the pumps apply about an inch of effluent with each application, but you can apply rates ranging from 3/4 of an inch to 1 1/4 inches by making adjustments to the nozzle size and hose retrieval speed.

      The fertilizer value of the nutrients in the effluent can only be determined by conducting a chemical analysis through a laboratory familiar with effluent analysis. Interpretation of the chemical lab data needs to be by individuals trained in converting PPM or mg/l values into equivalent fertilizer values such as 13-13-13.

      Typical fertilizer values for dairy effluent vary widely throughout an April to October growing season. Fertilizer equivalent values typically range from 30 to 45 pounds of N, 10 to 40 pounds of P₂O₅, and 30 to 70 pounds of K₂O per acre-inch of effluent application. Table 1 and Table 2 illustrate the variation in fertilizer nutrients applied from the lagoon at the Dairy Research Center in Sessums, Mississippi, in 1996 and 1997.

Hayfield Response

      A total of 298 pounds N, 131 pounds P₂O₅, and 168 pounds of K₂O per acre was applied in 1996, and a total of 208 pounds N, 123 pounds. P₂O₅, and 302 pounds of K₂O per acre was applied to the soil in 1997 over five irrigation events (Table 1 and Table 2). Nutrient concentration was higher early in the spring of 1996 and somewhat higher in the spring of 1997 following accumulation over the winter. The quantity of fertilizer nutrients available from the lagoon generally declined through the summer. Late-summer irrigations, however, may also provide significant moisture benefits during the dry months of September and October when forage production is generally limited.

      Yield response of mixed bermudagrass-dallisgrass hayfields to dairy effluent application depends on initial soil test levels and other limiting factors such as micronutrients. For optimum growth, plants require 13 minerals in addition to N, P, and K. Dairy effluent likely contains many of these plant nutrients since they are included in the dairy ration. Most analytical labs do not test for other micronutrients, and limited research data are available regarding relative levels of these "minor" nutrients. (Minor in the sense they are required in small amounts but not small in importance to adequate plant growth.) It appears that dairy effluent will provide many of these micronutrients as well as the commonly required fertilizer nutrients (N-P-K).

      Table 3 and Table 4 illustrate the yield response of a bermudagrass-dallisgrass hayfield to three rates of dairy effluent in 1996 and 1997 at the Dairy Research Center. Initial soil test levels of P and K are low to very low and are expected to respond to balanced fertilizer additions.

      During the first year of dairy effluent application, there was an increase in forage production of 42 percent (1,755 pounds per acre) or nearly 1 ton per acre. There was a 54- percent increase in forage production the second year, with almost 1.5 tons per acre more produced. Over the 2-year period, soil test levels of P and K increased to medium levels, and pH increased from 6.0 to 6.3. Dairy lagoon effluent application to an underfertilized hayfield obviously has a positive short-term impact on soil fertility and hay production on this particular field.

      Land used as hayfields provides ideal sites for dairy effluent application because of the tremendous nutrient-removal capability. Nutrient removal, due to forage uptake, ranged over 2 years from 126 to 188 pounds of N, 32 to 52 pounds P₂O₅, and 107 to 220 pounds of K₂O per acre. Compared with the amount of nutrients removed by the forage, there was an excess of 30 to 172 pounds N, 70 to 100 pounds P₂O₅ , and 60 to 82 pounds K₂O applied in the effluent at 5 inches per year. Although this did not remove all the nutrients applied in the effluent, the extra P and K were justified over the short term because of the initial low soil tests.

      As soil test P levels increase, current forages will not be able to remove enough P to sustain "long-term" application of effluent at 5 acre-inches per year. The long-term nutrient loading of P on a particular site depends on the particular soil's ability to adsorb P and the runoff susceptibility of the particular hayfield into a sensitive watershed. Soils that test high to very high in P need to have dairy effluent applications limited to expected nutrient removal (32 to 52 pounds P₂ or 2 to 3 inches of effluent per acre).

Table 1. Fertilizer nutrients applied in dairy lagoon effluent at the Dairy Research Center, 1996

	Date of application
Fertilizer nutrient	4/1/96	5/6/96	6/10/96	7/29/96	9/5/96	Total
	Pounds per acre-inch
Nitrogen	171	36	44	35	36	298
P2O 5	38	27	12	32	22	131
K2O	35	40	22	33	38	168

Table 2. Fertilizer nutrients applied in dairy lagoon effluent at the dairy research center, 1997

	Date of application
Nutrient	4/8/97	5/6/97	6/24/97	7/23/97	7/31/97	Total
	Pounds per acre-inch
Nitrogen	65	46	40	27	30	208
P2O 5	41	41	18	14	9	123
K2O	76	76	61	52	37	302

Table 3. Influence of dairy lagoon effluent application on forage yield at the dairy research center, 1996

	Date of harvest
Effluent rate¹	6/28/96	8/14/96	10/1/96	Total
	Pounds per acre
High	1,409 A	2,740 A	1,708 A	5,857 A
Low	1,090 AB	2,239 AB	1,706 A	5,035 AB
None	913 B	1,829 B	1,360 A	4,102 B
LSD0.05	377	504	467	976

Forage yield was taken from four 10-foot strips to a height of 2.5 inches.
Means followed by the same letter within each column are not statistically different.
¹ Effluent Rate: High = 1 inch of effluent applied five times; Low = 0.25 inch to 0.40 inch of effluent applied five times.



Table 4. Influence of dairy lagoon effluent application of forage yield at the dairy research center, 1997

	Date of harvest
Effluent rate¹	5/19/97	7/14/97	8/25/97	Total
	Pounds per acre
High	2,287 A	2,552 A	3,227 A	8,066 A
Low	1,305 B	2,519 A	2,492 A	6,316 B
None	673 C	2,301 A	2,658 C	5,231 C
LSD0.05	239	NS	197	976

Total herbage yield was taken from 10-foot strips to a height of 2.5 inches.
Means followed by the same letter within each column are not statistically different.
¹ Effluent Rate: High = 1 inch of effluent applied five times; Low = 0.5 inch to 0.60 inch of effluent applied five times.

Taking a Representative Wastewater Sample

      When using commercial fertilizer, computing the correct quantity of primary nutrients (N-P-K) to apply is relatively simple. Because commercial fertilizer is purchased, producers typically match applied nutrients to specific crop requirements. The same fertilizer-to-crop nutrient matching should also occur when applying lagoon wastewater.

      To determine the nutrient value of lagoon wastewater, take a "representative sample" from the lagoon and have it analyzed by a commercial or state laboratory. The laboratory will return a report showing the concentration of various nutrients in the wastewater, typically expressed in milligrams per liter (mg/l). These units may not be familiar to producers who commonly work with English units. To convert mg/l to pounds per acre-inch (lb/ac-in), multiply by 0.224. For example, if the wastewater report indicates that the ammonia as nitrogen (NH3-N) concentration is 168 mg/l, you can determine the pounds of nitrogen per acre-inch by multiplying 168 mg/l x 0.224 = 37.6 pounds of nitrogen per acre-inch (lb-N/ac-in).

Taking the Sample
      The question is, What constitutes a representative sample? Since a lagoon has many complex biological processes occurring simultaneously (aerobic, facultative, and anaerobic biological processes), you need to get a "composite sample," which is a single sample achieved by mixing many smaller samples together.

      To obtain a representative lagoon sample, take small (16 ounces) samples at multiple points and depths around the entire perimeter of the lagoon. Place these "mini samples" in a clean 5-gallon bucket (or another suitable container). Thoroughly mix these samples in the container and pour the mixed sample into a single clean plastic bottle (some labs provide the sample bottle). If you use mechanical agitation during the lagoon pump-out, take the sample in the same manner described but after the agitation process has thoroughly mixed the lagoon contents.

Preparation for Shipment
      Since biological activity continues in the wastewater sample bottle, do not fill it completely. Leave some air space; press in the sides of the bottle as you tighten the cap. This allows the sample bottle to expand and reduce the likelihood of rupture during transit.

      Keep the sample cool (with ice or refrigerate) before shipment. Always check with the laboratory doing the wastewater analysis for specific recommendations regarding the packaging and shipment of wastewater samples.

This publication is based on work supported by the United States Department of Agriculture Extension Service under Special Project Grant number 94-EHUA-1-10088.

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Publication 2208
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director

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