|Green and Growing|
|Written by D. Bruce Bosley, CSU Extension Agent/Cropping Systems|
Higher than normal crop commodity prices combined with good yields from 2010 are benefiting Colorado agricultural producers. Outlooks for next year’s prices are also positive compared to long-term averages, and these prices may entice producers to edge yield goals upward when determining fertilizer application rates.
However, this spring’s fertilizer and other input costs are also trending much higher than previous years. Thus, maximizing the efficiency of applied fertilizer is especially important to achieve desired yield goals and ensure that fertilizer inputs are cost-effective.
Fortunately, crop producers today have many tools available to improve fertilizer use efficiency that were unavailable in the past. These techniques have been defined in various terms, but have traditionally been called best management practices (BMPs).
Recently, nutrient BMPs have been redefined as 4R nutrient stewardship by the International Plant Nutrient Institute (IPNI). The four R’s in their terminology refers to applying fertilizer nutrients in the Right amount for the crop yield goal, at the Right time in the growing season, in the Right place and using the Right nutrient source.
Together, these management practices give producers the best possible economic yield response for their fertilizer dollar. Information on this stewardship program can be found at www.ipni.net/4r.
Advances in precision agriculture, such as crop sensors and variable rate technology, are offering new tools for determining the right place and time for fertilizer application. However, the first approach for determining the right amount of fertilizer to apply is an annual soil analysis and an appropriate yield goal for each field.
Soil testing is particularly critical when determining nitrogen (N) fertilizer application rates since N is a dynamic soil nutrient and is required by crops in the greatest amount. In the western U.S., most public and private laboratories assess soil N status by measuring nitrate-nitrogen (NO3-N), which will be available for crop uptake.
If the depth of the soil sample is known, the amount of nitrate-nitrogen in the soil can be converted to pounds per acre by multiplying the concentration by a conversion factor (typically 3.6 for a one-foot soil sample). Yield goals are used to determine the total amount of N required for the desired production, and the recommendation is adjusted for the soil test level, organic matter (O.M.) content and other potential N credits.
Nitrogen credits that should be considered to adjust a recommendation include irrigation water nitrate, previous legume crop, manure or biosolids applications within the past three years and last year’s sugar beet tops.
Make sure the laboratory, consultant and/or fertilizer dealer has all of the field history regarding crop rotation, past amendments and irrigation water quality so they can provide the most accurate fertilizer suggestion.
Holyoke Enterprise June 9, 2011