Fertilizing Cotton with Poultry Litter

Poultry litter has long been used to provide nutrients for pastures, hay, and other crops in the south-central Mississippi broiler production region. Volatile fertilizer prices increased interest among cotton producers in using litter as a nutrient source. Fortunately, there is extensive research conducted with poultry litter as a nutrient source for cotton within the state, under Mississippi climatic conditions and on Mississippi soils.

Mississippi ranks among the top five states in both numbers of broiler chickens grown and quantity of meat produced. Broiler production primarily is located in the south central region using production houses with smoothed soil floors usually covered with 4 to 6 inches of wood shavings. Wet material (termed cake) is removed from the house floor after each flock is removed, commonly 5 to 6 times annually. Periodically, all the material is removed in a house ‘cleanout’. This is commonly termed litter and is a mixture of bedding material, manure, feathers, and spilled feed.

There are several considerations about including poultry litter in the cotton nutrient program.

How much is it worth?

The nutrient content of litter varies from integrator to integrator (about 7 currently operate in Mississippi) due to different bird growing management techniques (Table 1).  The value of litter as a fertilizer is determined by the open market factoring in nutrient contents, demand, supply, transportation, storage, competitive products, and other factors.

The Best Management Practice is a current analysis of the litter to be used. Analyses can be done by the Mississippi State Chemical Laboratory or commercial laboratories. More information on this process is available at Soil and Broiler Litter Testing Basics and the Mississippi State Chemical Laboratory price sheet is at http://www.mscl.msstate.edu/pdf/prices.pdf.

What does it take to get litter from the poultry region to a row crop field?

Litter is a relatively light material (31 pounds per cubic foot) compared to inorganic fertilizers (46 to 70 pounds per cubic foot). Therefore transport expense can be high. Some years there is financial assistance available through the Natural Resource Conservation Service under the Environmental Quality Incentive Program for transporting litter from a poultry production county to a non-poultry county in the state.

Can litter be stored until I need it?

Storage of litter is an important issue as the timing of litter cleanout and application to fields is not always well-calibrated. Many poultry growers have covered dry stack sheds to store litter, however farmers acquiring litter from a grower or broker may need to temporarily store it. Litter should be covered while stockpiled outside a storage facility, and there should be no hydrological link between the litter and any nearby water, i.e. a berm must be placed around any outside storage area.

Stacking litter in fields for more than a few days is not recommended. Litter loses mass while sitting in storage which increases P concentrations. Nitrogen is lost from both covered and uncovered piles, but 50% more is lost in uncovered piles. Potash concentrations decrease from leaching out.

What equipment is needed to apply litter to my fields?

Proper spreading equipment is necessary, and should be calibrated and maintained regularly. For more information on poultry litter spreading equipment, see: Calibrating Poultry Litter Spreading Equipment.

When should I apply litter for my cotton?

Litter is most effective when applied close to the time that the crop will utilize the nutrients. Nitrogen in the litter must convert to plant available forms, whether nitrate or ammonium, which will begin one to three weeks after application.

In particular, litter is most efficient when applied a few days prior to planting row crops. Each year, only about 50 to 60% of N applied in spring-applied litter is used by plants. Research in north Mississippi found that with no actively growing cool season crop, fall spread litter provided no N to the next season cotton crop.

Significant amounts of the P in the litter applied in the spring and practically all the K in the litter is plant-available from spring applications. Phosphorus applied in excess of the amount used by plants will be stored in the soil. No carryover credit can be given for litter K to subsequent crops.

How much litter do I use?

In six different studies using litter on cotton in roughly the years 2002-2005 conducted the USDA Agricultural Research Service in cooperation with MAFES; yields were generally higher at five locations for poultry litter-based fertility programs. The only location that did not result in an advantage for broiler litter over standard inorganic nitrogen fertilizer was a Dubbs silt loam soil near Cruger, MS with a very high 3-4 bale yield potential for cotton.

The most effective application rate of litter as cotton fertilizer is two tons per acre applied a few days prior to planting, and then sidedressed with an additional 60 pounds of inorganic fertilizer N. This calculates to 180 pounds N applied per acre using average nutrient contents. However, if about 120 pounds of N is added in the preplant litter application, half of that amount or 60 pounds of N is the plant available quantity in the course of the growing season. Another 60 pounds N should be sidedressed using inorganic fertilizers at layby, thus the net application rate is 120 pounds of N per acre from both sources that will be used during the growing season.

Further work has shown that because litter provides all nutrients that can be difficult to determine which limiting nutrient has been alleviated by the litter application. However, as the Cruger location demonstrated, if no soil-based nutrients are limiting production, litter and inorganic nitrogen are roughly equivalent. Therefore, a sound soil testing program must be in place to ensure balanced plant nutrition.

Are there environmental considerations?

Other states have suggested restricting litter applications to row crops to the quantity needed to supply sufficient phosphorus for the current growing season. The Mississippi research has shown that soil test phosphate can build up over time with repeated, multiple year application of litter. However, it is not thought at this that litter use should be limited to the phosphate-need based rates. Rather, if elevated soil phosphate is a resource concern in the row crop field, request a Phosphorus Index risk assessment from the local office of the Natural Resource Conservation Service or a certified Technical Service Provider. Interpreting this assessment will determine a field-specific proper litter application rate.

Is litter a lime?

In addition to providing plant nutrients, litter applications to fields can improve soil properties such as tilth, water holding capacity, and nutrient holding capacity. In many instances, including research plots, the pH of the soil has increased following litter applications. Therefore there is a tendency to credit it as a liming material. There is significant calcium in litter from bird feed; however the soil pH response is not sufficiently predictable to offer it as a recommended liming material.

Why is the litter fertilized cotton paler than the other cotton fertilized with UAN?

Remember that the nitrogen in poultry litter is in organic forms that must be converted to plant-available forms in biologically mediated processes. Nitrogen in inorganic fertilizers such as UAN are plant-available about as soon as they dissolve in the soil. Therefore, while the quantity of nitrogen is the same, the amount that the plant roots see in one case is one big gulp versus a straw in the other. The real question is not whether you should be concerned about how green the crop is in July, but much will it yield in October, and research has shown that higher chlorophyll readings did not lead to higher yields in litter/inorganic comparisons.

Litter Calculations

The laboratory analysis will report the nutrient contents as percent N, P₂O₅, and K₂O, and a moisture percent determination. From this report it is simple to calculate the macronutrient fertilizer equivalency of the litter on a per ton basis.

• For an analysis of 3.5% N, 2.1% P₂O₅, and 3.8% K₂O with 20% moisture content:

–        2000 * (1-0.2) = 1600 lbs dry matter per ton of ‘as is’ litter.

–        1600 * 0.035 = 56 lbs N per ton of dry litter.

–        1600 * 0.021 = 34 lbs P₂O₅ per ton of dry litter.

–        1600 * 0.038 = 61 lbs K₂O per ton of dry litter.

While it adds error, the fertilizer content can be approximated on an ‘as is’ basis if the moisture content is not readily available:

• “As is” nutrient calculations (no adjustment for moisture) for an analysis of 3.5% N, 2.1% P₂O₅, and 3.8% K₂O:

–        2000 * 0.035 = 70 lbs N per ton of litter “as is”.

–        2000 * 0.021 = 42 lbs P₂O₅ per ton of litter “as is”.

–        2000 * 0.038 = 76 lbs K₂O per ton of litter “as is”.

With the fertilizer content of the litter, and calibrated spreading equipment, application rates using litter can be calculated. Remember only about 50% of the N in the litter will be available to growing plants during the season of application (and 0 if fall-applied for the next year crop).

–         (150 lbs N/ac/application) / (56 lbs N/ton) = 2.7 tons per application.

• Using the ‘as is’ value for N content:

–        (150 lbs N/ac/application) / (70 lbs N/ton) = 2.1 tons per application.

Summary

Six recent studies in Mississippi have shown that broiler litter can provide sufficient nutrients at two tons per acre applied shortly before planting cotton with supplemental sidedressing of 60 pounds nitrogen per acre at lay-by. Litter has distinct properties that must be considered in the economics of transportation and application. It is always best to have a recent nutrient analysis of the litter actually used on a farm. A sound soil-test based soil fertility management program is required to maximize the overall efficiency of litter used as fertilizer.

Acknowledgement

The sharing of data by Dr. Haile Tewolde of the USDA Agricultural Research Service is gratefully acknowledged.

Table 1 (From Chamblee and Todd).