Fertilizer Management

Chart Fertilizers may be over the volatile price situation of 2008 and 2009. World economic forces, credit issues, demand destruction, transportation costs, labor strikes, commodity price swings, and other influences changed once stabile fertilizer markets for a period.

The recent instability is readily apparent in this graph of prices per pound of fertilizer nutrient derived from the annual Prices Paid report of the National Agricultural Statistics Service for the Midsouth area. This graph ends in April, 2009. It does not reflect the further decline in prices later in the year.

The Fertilization Decison

Each producer manages nutrients through answering a few simple questions:

Are fertilizers necessary to produce the crop?
How much fertilizer is needed if necessary?
What fertilizers are available if needed?
When is the best time to apply fertilizer?
How should the fertilizer be applied?

Fertility management is important. However, variety selection, water management, insects, nematodes, diseases, weed pressure, and climatic conditions also affect crops.

Soil testing is critical

Soil testing is the foundation of nutrient management. Fields should be tested at least every three years and preferably every other year. Many row crop farmers have a crop consultant relationship that helps with this aspect. Information for first time soil testers is available at the local Extension offices or at http://msucares.com/pubs/infosheets/is0346.pdf.

Liming is the most important consideration for managing nutrient budgets. Soil pH controls the plant availability of many nutrients already present in the soil, and is particularly crucial for P. At higher and lower pH values, much of the P in soils is in forms that plants cannot use. In the 6 to 7 pH range, P is more available for plant use. Maintaining pH levels also benefits plant nutrition through better root growth, enhanced microbial activity, and better soil physical properties.

If the soil test indicates lime is needed, fall application allows more time for it to react, and to have the most benefit during the following spring and summer. However, spring applications have benefit, particularly if the recommendation is two tons per acre or more.

Lime can be a significant investment in Mississippi. Calcitic and dolomitic limestones are transported into the state. Soft lime products (marl) are produced in the state, and are good options for soil liming programs. However more material is needed because marl has less chemical neutralizing capacity than calcitic or dolomitic limestones.

Lime is sold in Mississippi based on the RNV of the material. Information on applying this concept is available at http://msucares.com/pubs/infosheets/is1587.pdf.

Soil test based recommendations

Phosphate (P2O5) and potash (K2O) equivalents are usually given as pounds per acre on soil test reports to ease comparisons with fertilizers. Each soil test phosphate and potash result is rated within a category. MSU uses five: very low, low, medium, high, and very high. This relates the amount measured to whether plants will respond if fertilized. Very high levels mean small chance of response; conversely, soils testing very low are more likely to respond.

In the high or very high categories, P and/or K fertilizers are not needed. Medium means there may or may not be a response; the recommendations for P and K in the MSU system in this category are ‘maintenance’ levels. Soils in the very low or low categories should respond to fertilizer, therefore the decision depends on assessing the relative risks of not fertilizing versus fertilizing.

The MSU Extension Service P and K application rate recommendations are based on soil fertility maintenance for the next scheduled crop in the medium and low groups. Recommendations for these nutrients for soils testing very low include a small amount of fertilizer for buildup.

Many farmers work with Extension staff, consultants, or crop advisers for their soil fertility assessment and management program. The farm goals, the appropriateness of the testing laboratory methods and recommendations for Mississippi soils and climates, the philosophy of the recommendations, and budget considerations should be considered by farmers and advisers.

Other considerations in fertilizer rate selection and application

Average nutrient uptake and harvest removal by various crops is easily available. However, crops obtain nutrients from both soil and fertilizer, if used. Relying on this information to determine application rates can lead to inefficiency and unneeded expense.

Equipment maintenance and calibration are fundamental to efficient nutrient applications. Know the correct application width for the equipment and the material being applied. Proper applications also avoid applying too near to surface water bodies.

Precision technologies may allow more efficient fertilizer management through identifying nutrient deficient or acid soil areas, or more responsive zones. However, if not, these tools are not already employed, information management software, equipment acquisition or rental, consulting charges, soil and mapping charges, and training time and costs can be significant investments.

Nitrogen management

Nitrogen fertilizer management in Mississippi is not based on analyzed soil tests. The state is warm and humid, therefore N soil testing techniques have had limited applicability (research is continuing). Nitrogen fertilization strategies are crop specific, and, where applicable, based on common sense attainable yield goals. Nitrogen fertilizer efficiency depends on the particular product and how it is applied.

Urea and urea-ammonium nitrate solutions are popular and easy to use, however N in each may be lost by volatilization to ammonia gas which drifts away from the field. Conditions that contribute to increasing this loss include:

no-till management,
applying when temperatures are above 65°F,
high organic matter/surface residues,
high humidity, and
not incorporating the material.

If surface application is necessary in these conditions, time it to approaching rain or irrigation. Some products that slow the conversion to ammonia have shown promise in Mississippi tests.

Ammonium nitrate is an excellent fertilizer, and does not volatilize. It has long been the fertilizer of choice for many hay and pasture growers in the state. It also is an explosive, therefore many retail outlets do not stock it due to insurance, liability, and security issues. Many dealers do have an alternative available with the same fertilizer content listed, 34-0-0, that is usually a 50-50 blend of urea and ammonium sulfate. While containing the same amount of N, the alternative also retains the management considerations of urea N loss via volatilization, and the higher soil acidifying capacity of ammonium sulfate.

Legume derived nitrogen

The increase in N fertilizer costs has stimulated interest in legumes as part of a forage crop mixture. Detailed information on this subject is available in Strategies for Better Management of Pasture Fertilization, including appropriate species, establishment procedures, and expected benefits.

Poultry litter as fertilizer

Poultry or broiler litter is an excellent source of plant nutrients. We have about five decades of experience using it in forage and pasture management in Mississippi. In addition to nutrients, litter improves less easily quantified soil properties such as tilth, water holding capacity, and nutrient holding capacity. There is a tendency to credit it as a liming material, and while it seems to positively affect pH over very long time spans, it is not predictable.

Nutrient contents vary due to different bird and litter management programs. The best option is analysis of the actual litter that will be used by the Mississippi State Chemical Laboratory or commercial laboratories. Information on sampling litter for nutrient analysis is available at http://msucares.com/pubs/infosheets/is1614.pdf.

Variable nutrient content leads to several management considerations. It is a slow release organic fertilizer with about 50 percent of the N applied used by plants in the year of application. A significant percentage of the P is available, and practically all litter K is plant available the year of application. Litter is relatively light (31 pounds per cubic foot), so using the proper equipment, calibrating it, and maintaining proper spreading widths are important for uniform application.

The best efficiency is when litter is applied to actively growing plants because the N becomes available over the first one to three weeks after application. With no actively growing cool season crop, fall applications are inefficient, particularly for N use.

Litter storage is important when litter cleanout time and field application is not well-calibrated. Many poultry growers have dry stack sheds to store litter and prevent nutrient runoff. However, other farmers acquiring litter from a grower or broker may need to temporarily store it. Recent research by Auburn University found that litter should be covered with plastic or other materials to protect the investment in the nutrient content of the litter.

Growers interested in using broiler litter and are not in a poultry area may contact potential suppliers through the Mississippi Farm Bureau Litter Clearing House. Based on the discussion above, it is best to have nutrient analysis of the actual litter in question. How much is it worth? The actual value is determined on the open market factoring in demand, supply, transportation, storage, competitive products, and other factors.

Fertilizer Best Management Practices

Best Management Practices are cost-efficient operation methods that ensure that fertilizers are used effectively with minimal impact on the environment including the good business practices mentioned above.

Use realistic yield goals
Use average crop yields from the past three to five years, then add 10 percent for a realistic projection of the production potential on your soils, using your production management, in your climate area.
Use the most suitable nitrogen fertilizer source, depending upon the crop, application method, and climatic conditions
Some fertilizers work better in certain situations due to climate and soil conditions. For example, anhydrous ammonia is lost due to incomplete soil sealing when soils are wet.
Price fertilizers on the cost per pound of nutrient
This is the best way to compare cost of nitrogen among equivalent sources.
Use proper application techniques
Use the correct technique for the particular situation. Refer to the specific commodity pages for more particular information.
Maintain and calibrate application equipment
Improperly maintained and poorly set equipment 'steal' crop input dollars. Make sure owned equipment is properly working and calibrated. Confirm with custom applicators that they have calibrated the equipment.
Avoid application to surface waters.
Care must be taken to avoid direct application to any surface streams.
Time application properly for the crop
Nitrogen use efficiency is best when applied close to the time of crop uptake. We hear reports every year of N application to fields for cotton several weeks prior to planting. These increases the probability of N loss from the field, and may necessitate supplemental N fertilizer later in the growing season.
Control soil erosion
Nutrients move when soil particles move. Using soil conservation keeps soil and nutrients where they can be utilized by growing crops.
Properly control water flow
Nitrogen movement in the landscape is closely linked to water movement. Slow water down when appropriate by conservation practices, or speed water movement when appropriate.
Use cover crops, and maintain crop residue on the soil surface
Cover crops reduce the likelihood of N movement in the landscape by 'scavenging' N left in the soil profile after the previous crop. Using the residual N increases cover crop dry matter production, thus enhancing soil quality attributes such as soil organic matter levels and tilth.