LAND APPLICATION OF POULTRY MANURE
Jim Camberato
Land application of poultry manure to forage crop land is an effective way of recycling the nutrients back to the land. There are four key steps to utilizing manure in an environmentally and economically sound manner:
know the available nutrient content of the manure
know the nutrient needs of the crop, and apply the manure at the correct rate and time to provide the nutrients
use application and conservation practices that minimize movement of the nutrients from the field
adjust the use of supplemental fertilizer to compensate for the nutrients applied in the manure
Applications of manure as a pasture crop nutrient source may provide a portion, or all of the plant nutrient requirement, dependent on the rate of application and the relative content of the nutrients. Application rate decisions are usually based on either the nitrogen or the phosphorus content of the manure and environmental concerns are typically based on the amount of nitrogen, phosphorus, zinc, copper, or arsenic added to the soil. Knowing the nutrient content of poultry manure is critical to using it as a crop nutrient source. Not knowing the nutrient content of the manure to be applied can result in large errors in application rate -- either too much or too little.
NUTRIENT CONTENT
Table of broiler and turkey manure nutrient content Table of layer manure characteristics and quantity as removed from the house Estimates of litter production from poultry production houses
Poultry manure additions are often based on the nitrogen requirement of the crop and the available nitrogen content of the poultry manure. Crops that require and remove a lot of nitrogen are favored for receiving poultry manure because more manure can be applied to less land. This approach reduces the hauling costs of implementing a manure management plan. Soil analysis should be used to ensure that soil pH and nutrient conditions are at optimum levels even when manure is applied based on nitrogen.
NITROGEN-BASED APPLICATION RATES Nitrogen fertilizer recommendations for commonly grown crops are listed in Table 1. These rates are suggested as the most profitable rate over a period of years with good management. Ranges in nitrogen rate recommendations reflect differences in yield and management potential. For example, regarding bermudagrass, 240 lb N/acre should be sufficient to produce 4 to 5 tons hay/acre and 400 lb N/acre should produce 6 to 7 tons hay/acre with normal rainfall
Table 1. Nitrogen fertilizer recommendations for pasture crops. Crop Fertilizer N, pound/acre Bermuda grass hay 240 - 400 Bermuda grass pasture about 150 Fescue pasture about 100 Annual rye for grazing about 120
The release of nitrogen from manure should coincide with crop nitrogen accumulation. If the crop is not actively accumulating nitrogen then nitrate-nitrogen in the soil will be subject to loss via leaching. Pasture and hay crops have more moderate nitrogen requirements over longer periods of time than row crops and are not very sensitive to short-term deficits in nitrogen availability. Periods of nitrogen accumulation and nitrogen application windows for crops commonly grown in the Southeast are presented in Table 2. Most poultry manure is typically applied as a solid. Nitrogen availability from poultry litter is greatest and most predictable when incorporated into the soil due to less volatile loss of nitrogen and better moisture for organic N mineralization. Manure applications can be made to pasture and hay fields as long as that particular grass is actively accumulating nutrients. Delayed nitrogen availability and over- or under-estimation of nitrogen availability is not as great a concern with grass fields as with annual crops.
Nitrogen Application Timing
Although manure application rates are usually based on nitrogen availability, applying poultry manure based on its P2O5 or K2O content may also be important. The availability of P2O5 and K2O in manures is similar to that of fertilizer sources, so basing application rates on the manure's content of P2O5 and K2O should be adequate. Recommended rates of P2O5 or K2O are based on soil analysis, soil type, and crop to be grown and are provided with a routine soil test. On soils testing high in P2O5 and K2O, when these nutrients are not recommended by soil test, consider using the manure on other fields requiring P2O5 and K2O. Manure nutrients are much more valuable when applied to low fertility fields.
PHOSPHORUS AND POTASSIUM BASED MANURE APPLICATIONS
Phosphorus movement from the land into surface waters, such as lakes and streams, is considered pollution. Phosphorus movement occurs by erosion and runoff. Erosion is the movement of soil from the field. Runoff is water movement over the surface of a field containing little sediment. In the Southeast, erosion and runoff occur primarily from heavy rainfall or excessive irrigation. Phosphorus in erosion and runoff can be bound to the soil, contained in soil organic matter and manure particles, or dissolved in the water.
CONTROLLING PHOSPHORUS MOVEMENT FROM THE FIELD Many factors affect the amount of phosphorus that moves from the field to the water. These factors include:
slope of the land
Manure application on sloped land is subject to greater loss via runoff and erosion than applications made on flat land. The greater the distance between the application area and the surface water the lower the chance of phosphorus movement into the water. Hence, the rationale for application setbacks from ditches, streams, ponds, and lakes. On tilled soils, incorporated manure results in less phosphorus runoff and erosion then when the manure is left on the soil surface. High soil phosphorus is another factor that increases the potential for phosphorus pollution of surface waters. The higher the level of phosphorus at the soil surface the greater the concentration of phosphorus in the runoff water and erosion sediments. When soil test phosphorus is high at the soil surface, application of manure to other fields should be considered. Installation of conservation practices that reduce runoff and erosion are beneficial to reducing phosphorus pollution of surface waters.
soil type
distance to the water
rainfall and irrigation intensity and duration
method of manure application
soil phosphorus level
presence of conservation practices-filter
strips, contour planting, riparian zones
In most soils with moderate phosphorus application rates, phosphorus remains in the soil where it is placed with little downward movement. Phosphorus added to the soil is bound by clay particles so that only a portion remains available to the crop. This process reduces the amount of dissolved phosphorus in runoff water, but does not affect the loss of phosphorus in erosion sediments. Soils have finite capacities to absorb phosphorus. When the capacity is exceeded, added phosphorus remains dissolved in the soil water and can be leached downward. Leaching of phosphorus can occur on coarse sandy soils with high application rates of phosphorus and on high organic matter soils commonly occurring in Carolina Bays. In these soils, phosphorus leaching into the water table and lateral movement of ground water can move phosphorus to the stream or lake. In soils with clay subsoils, however, the leaching of phosphorus through the soil profile is slow since these soil layers have a substantially greater capacity to absorb phosphorus than surface soils.
Poultry manure applications may be based on crop removal of phosphorus when soil phosphorus levels are high to prevent further increases in soil phosphorus. Phosphorus removal for crops commonly grown in the Southeast are listed in Table 3. Row crops remove about 30 lb P2O5/acre at typical yield levels and hay crops remove more than 50 lb P2O5/acre.
CROP NUTRIENT ACCUMULATION Crop accumulation of nutrients from the soil and removal from the field determines the efficiency of crop nutrient utilization (Table 3). Nutrient utilization is routinely less than 100% due to inefficiencies in nutrient uptake by the crop, soil reactions that render the nutrient unavailable, and loss of the nutrient from the soil by leaching, erosion or volatilization. Only a portion of the nutrients in the crop will come from that year's application of animal manure or fertilizer. The remainder of nutrient accumulation will have come from nutrients already present in the soil. Nutrients in the crop parts that remain in the field, such as corn or wheat stover, will be recycled to the soil and available to the next crop. Nitrogen has been the plant nutrient most studied. Accumulation efficiency from fertilizer is typically around 60% of the nitrogen added and removal efficiency is about 50%. These efficiencies are determined by accounting for the amount of nitrogen that came from the soil without added fertilizer. Nitrogen efficiency from manures is usually less than that from fertilizer.
The law in South Carolina regulates animal waste applications by the concentration of Zn, Cu, and As in the manure or by the amount of Zn, Cu, and As that can be applied on a cumulative basis. Good record-keeping of the amounts of manure applied to a field and the concentration of Zn, Cu, and As in the manure is necessary to meet the conditions of the law.
ZINC AND COPPER REGULATIONS AFFECTING LAND APPLICATION Zinc (Zn) and copper (Cu) are present in poultry manure in varying amounts and are essential crop nutrients. However, long-term use of poultry manure based on providing the total N requirement of the crop provides more Zn and Cu than the crop requires, and these nutrients can accumulate to high levels in the soil. Crop toxicities may occur in certain situations. Crop removal of Zn and Cu from the field is quite small, around 0.03 pounds of Cu per acre per year and about 0.11 pounds of Zn per acre per year (see Table 3) and no leaching of these nutrients occurs. Therefore, once applied to the soil they remain there. The toxicity of high soil Zn and Cu is reduced by increasing soil pH, however, increased soil pH will not completely eliminate Zn and Cu toxicity in some instances. If soil pH is increased too much, deficiencies of other micronutrients may be induced by the high pH.
Arsenic is not an essential plant nutrient. Crop production problems are unlikely to occur from As applications typically applied in poultry manure, about 2 pounds of As per acre per year. The main concern with As in poultry litter is the potential movement of As from the field to surface and ground water.
Soil Zn levels potentially injurious to crops occur in the Southeast. The sources of excessive Zn in soils include poultry manure, Zn containing fungicides, burned tires, and some industrial byproducts. Zinc levels in a number of soils receiving poultry manure have been found to exceed 20 pounds of Zn per acre with some as high as 90 pounds per acre. Reduced growth and yield of peanuts, soybeans, and cotton due to Zn toxicity have occurred in Southeastern fields.
CROP PRODUCTION PROBLEM FROM HIGH SOIL ZINC
Delivering the proper amount of animal waste to the field in uniform fashion is the next step in effectively utilizing animal waste. Spreaders must be calibrated to apply the proper rate and be adjusted for uniform application.
APPLY THE CORRECT AMOUNT OF POULTRY MANURE UNIFORMLY
When poultry manure is used as the primary N source for crops, supplemental phosphorus, potassium, and micronutrient applications are usually not needed. Eliminating unnecessary fertilizer applications is a benefit both economically and environmentally. For nutrients other than N, traditional manure, soil testing, and plant tissue analysis methods are adequate for determining if further additions of these nutrients are required.
REDUCE FERTILIZER APPLICATIONS ACCORDINGLY
Table 3. Nutrient accumulation and removal by pasture crops commonly grown
in the Southeast.Crop Yield level Plant part N P2O5 K2O Cu Zn ----- pounds of nutrient per acre ----- Bermuda grass 6 tons/acre hay 300 84 252 ---- 0.12 Fescue 3 tons/acre hay 116 56 159 ---- ---- Annual ryegrass 3 tons/acre hay 129 51 144 ---- ---- Corn 10 tons/acre hay 71 24 72 ---- ---- Sorghum 5 tons/acre silage 74 28 141 ---- ----
DETERMINING THE VALUE OF MANURE NUTRIENTS The value of manure nutrients is dependent on soil fertility level, crop nutrient needs, manure nutrient content, and the cost of purchased nutrients and manure application.
Major Nutrients Manure has the greatest nutrient value when applied to low-fertility fields and the least value when used on the same field year after year. When soil fertility status is low, high nutrient application rates of phosphorus and potassium are recommended in addition to the standard nitrogen application. In this situation the crop will benefit from the addition of phosphorus and potassium and the application of these nutrients in the manure is valuable. However, most manures when applied based on the crop's nitrogen requirement provide more phosphorus and potassium than is required and these nutrients accumulate in the soil. When soil fertility status becomes high, supplemental nutrients are not required, and the application of phosphorus and potassium is not recommended. In this situation the phosphorus and potassium in the manure does not have any value. If manure is continually applied to the same field, then the main benefit derived is the nitrogen content of the manure. No benefit is derived from the continual application of excess phosphorus and potassium and the potential for phosphorus runoff polluting lakes, rivers, and streams is greatly increased. Applying manure to low-fertility fields first and having enough land to use manure every second or third growing season are good ways to maximize the nutrient value of the manure and minimize the potential for polluting.
This point is illustrated in Table 4. A producer applies 3 tons of poultry manure per acre to three fields varying in soil fertility level to provide 120 lb N/acre in anticipation of growing a 100 bu/acre corn crop. The manure also applies 180 lb P2O5/acre, 120 lb K2O/acre, and 30 lb S/acre. One field has a low phosphorus and potassium level and 80 lb/acre P2O5 and K2O are recommended, therefore, a significant amount of the potassium and phosphorus in the manure has value. In this low soil fertility situation, the nutrient content of the 3 tons manure per acre is worth $64.80 or $21.60 per ton. An extra 100 lb P2O5/acre was applied. However, when soil test phosphorus and potassium is medium, less P2O5 and K2O is recommended and the poultry manure is worth less, $52.20 per acre or $17.40 per ton. At medium soil fertility levels an extra 130 lb P2O5/acre was applied. At high soil test phosphorus and potassium , no P2O5 or K2O is recommended, and the nutrients in the lagoon water are worth only $31.20 per acre or $10.40 per ton. One-hundred eighty lb P2O5/acre, valued at $43.20, was wastefully applied to the high fertility soil.
Excess crop nutrients are not necessarily lost from the soil and without value for the next growing season. In most soils some of the excess phosphorus added in one year will be available to future crops over several years. If phosphorus applications in future years are reduced or eliminated by the initial manure application, then some of the excess phosphorus provided in the initial year has value. Excess potassium will also be available to some extent in future years in clayey Piedmont soils and Coastal Plain soils with clayey subsoils within 15 inches of the soil surface. In coarse sandy soils with deep subsoils, however, much of the potassium may be lost between the first and second cropping season and that value will be lost. Even though some of the value of manure nutrients is captured after the first year, fertilizing one year for several years is generally not recommended because some of the phosphorus and potassium will be wasted.
The key to getting the most value from manure nutrients after the initial growing season is not to apply any more phosphorus and potassium when soil test in subsequent years indicates those nutrients are adequate.
Table 4. Nutrient value of poultry manure containing 40 pounds available nitrogen, 60 pounds of phosphorus (as P2O5), 40 pounds of potassium (as K2O), and 10 pounds of sulfur per ton. The litter was applied to the field at a rate of 3 tons per acre in anticipation of growing a 100 bushel corn crop. The value of the manure nutrients changes dependent on the soil fertility status of the field. Fertility
StatusNutrient Recommended
ApplicationAmount Applied
With ManureValue Excess
Nutrients
AppliedPounds Per Acre $ Per Application lb/Acre L
O
WN 120 120 120 x $ .24 =
$ 28.800 P2O5 80 180 80 x $ .24
$ 19.20100 K2O 80 120 80 x $ .18=
$ 14.4040 S 10 30 10 x $ .24=
$ 2.4020 M
E
D
I
U
MN 120 120 120 x $ .24=
$ 28.800 P2O5 50 180 50 x $ .24=
$ 12.00130 K2O 50 120 50 x $ .18=
$ 9.0070 S 10 30 10 x $ .24=
$ 2.4020 H
I
G
HN 120 120 120 x $ .24=
$ 28.800 P2O5 0 180 0 x $ .24=
0180 K2O 0 120 0 x $ .18=
0120 S 10 30 10 x $ .24=
$ 2.4020
The example above did not consider the value of micronutrients (zinc, copper, manganese, etc.) because soil testing and plant analysis has shown that micronutrient levels in most fields are adequate most of the time. When soil testing or plant analysis identifies micronutrient deficiencies and recommend micronutrient additions, however, the value of the micronutrient application in the manure should also be considered. Calculate the value of the micronutrient by multiplying the recommended application rate by the fertilizer cost of the nutrient.
Micronutrients
Application of manure may decrease or increase the need for liming dependent on the type of manure and the rate of application. Liming soils in the Southeast is a very important aspect of crop production. Generally, most Southeastern soils will be limed with a ton of dolomitic limestone every two to three years to maintain soil pH in the range of 5.8 to 6.5 (for most crops). The use of acid forming nitrogen fertilizers is the main reason that soil pH decreases and the estimate of one ton of lime per acre every three years is for nitrogen application rates of around 120 pounds of nitrogen per acre per year. Higher application rates will cause the soil pH to drop faster and lime will be required more frequently and in greater amounts.
Liming Value or Cost The type of poultry manure determines its effects on soil pH because poultry feed contains varying amounts of calcium carbonate. Broiler and turkey feed contains relatively low amounts of calcium carbonate, therefore, the litter typically is less than 5% calcium carbonate (100 lb calcium carbonate per ton). This amount of calcium carbonate is not enough to offset the acid generated by the nitrogen in the litter so broiler and turkey litter generally decrease soil pH. The acidity of these litters is about the same as common fertilizer sources such as urea and ammonium nitrate when added at the same rate of available nitrogen.
Laying hens are fed more limestone than broilers and turkeys and consequently have higher amounts of calcium carbonate in their manure. Typically hen manures have calcium carbonate contents of 15 to 18% (300 to 360 lb calcium carbonate per ton). Soil pH may increase substantially with applications of hen manure because the amount of liming material added to the soil exceeds the amount of acidity released by the conversion of nitrogen. Too high a soil pH due to the over application of lime can be just as detrimental to crop production as too low a soil pH. High pH in most Southeastern agricultural soils does not occur naturally, but occurs from the over application of commercial limestone or some other liming material. Layer manure is a source of liming material that can result in too high a soil pH. Soil pH's greater than 7.0 in the upper one foot of soil and nearly 7.0 in the one to two foot sampling depth, were found in a number of Piedmont fields receiving repeated applications of hen manure and no commercial limestone applications. No crop production problems associated with these unusually high soil pH's have been documented in these clay soils; however, pH's this high would likely cause problems in sandy Coastal Plain soils. The liming value of layer manure should be considered when layer manure is used as a crop nutrient source. This value is not trivial as one ton of lime per acre every three years currently costs about $30 per acre or $10 per acre per year.
Uncovered stockpiling results in decreases in the nitrogen and potassium content of the manure. Also, the manure becomes sticky and difficult to spread uniformly. Leaching and run-off of nitrogen and phosphorus from the stockpiled manure may pollute ground and surface water. Covered stockpiles are not a problem. If manure is covered while stockpiled, the nutrient content and spreading characteristics of the original material will be preserved. The cover will eliminate any pollutant runoff from occurring. The proper siting of covered stockpiles on high ground should prevent, movement of the water table into the pile and the potential for groundwater pollution.
Stockpiling Manure Solids Lowers Value
Studies have determined conclusively that there are no weed seeds in poultry manure as it is removed from the rearing house. However, poultry manure does stimulate the germination of some weed seeds already in the soil and the growth of all weeds will be stimulated by the nutrients in poultry manure.
ARE THERE WEED SEEDS IN POULTRY LITTER? Weed seeds, particularly pigweed, may be deposited in stockpiled litter and flourish in that environment. Application of stockpiled litter to crop land may introduce weed seeds into the field.
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