AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Spring 2000, No. 6
For years, experienced agronomists have advocated that farmers look beyond a one-year approach to soil fertility management, especially on land that is not leased or rented. Perhaps it is time to consider a fertility management program that is not “just enough to get by.”
Soil test summaries indicate that phosphorus and potassium soil tests are trending lower in some key states, and fertilization beyond maintenance is needed. Most soil testing labs are observing increased numbers of soil samples from this past fall and this winter, which may indicate a higher priority on improved plant nutrition. Many public and private labs offer soil test recommendations to build soil test levels over four to eight years, from low to medium levels up to high levels. Once high soil test levels are achieved, some may mistakenly think it is time to quit fertilizing. Instead, soil test levels should be maintained with fertilizer rates that will keep pace with nutrient removals in harvested crops. Such rates and recommendations are considered maintenance programs.
With all the uncertainty in agriculture, farmers have the opportunity to be relatively sure that soil phosphorus and potassium levels do not limit yields. Limiting phosphorus and potassium can result in limited response to nitrogen, lowered nitrogen-use efficiency, and potentially increased residual soil nitrate that may impact ground or surface waters. Higher soil fertility levels afford growers more flexibility in managing other inputs while lowering risks of lost yields and lost profitability.
National trends for most field crops reflect increased yields over the last decade. Higher yields and profitability cannot be sustained without increased attention to fertility needs. Once soil test levels drop to the medium and lower test ranges, it may take several years to build them back to optimum. For example, it may take six to 14 pounds of P2O5 per acre to raise the soil test phosphorus level one pound and four to eight pounds of K2O per acre to raise soil test potassium one pound, after considering crop removal. Whole-field fertility management can be refined to site-specific fertility management, especially where yield monitors indicate considerable variation in yields...and consequently, variations in nutrient removal. Identification of responsive areas can help prioritize proper phosphorus and potassium fertilization, in balance with other nutrients, for increased net returns and reduced costs per bushel or pound of commodity produced.
Anticipating the potential for higher crop yields with improved crop hybrids and varieties, many farmers are in the position to provide present crop nutrient needs and some for the future. For those who have been in the “draw-down” mode for the last few years, it may be time to change strategies. As many wise, successful farmers can attest, paying attention to the details usually increases profit. Now is the time for many farmers to prevent soil fertility problems in 2000 and beyond!