Crops
Summer fertilization programs
By Dr. Paul Tracy
In general terms, producers in our region think of the “fertilizer season” running from November through April. I don’t particularly subscribe to that line of thinking. In fact, many of our progressive growers use late-spring to summer fertilization programs to obtain the best agronomic efficiencies possible.
For corn, there are many post- emergent fertility programs. I am a strong proponent of a planned corn sidedress nitrogen application. You can also evaluate previously fertilized fields now through tasseling to determine if they are in jeopardy of becoming nitrogen deficient. In this situation, the post-emergent application becomes a rescue operation.
Summer provides an excellent time to apply base fertilization programs on fields that are being renovated to perennial forage crops.
Proactive approaches to monitor in-season corn nitrogen applications involve soil testing for available nitrogen, tissue testing for nitrogen already taken up by the plant, aerial imagery and sensor technology. Soil testing, tissue testing and aerial imagery programs can be affective but involve time delays that can be restrictive.
Sensor-based technology offers real-time nitrogen applications based on on-the-go crop measurements combined with real-time fertilizer application. The sensors are attached to a variable-rate fertilizer applicator that applies the needed amount of mid-season nitrogen. A full-scale launch of this technology is scheduled for 2010.
If you have not fertilized soybeans this year, or are planning double-crop soybeans behind wheat, you still have time for preplant applications of phosphorus and potassium. Many producers in our region apply phosphorus and potassium to corn but not soybeans. This practice generally works if enough nutrients are applied before the corn crop to feed both crops. My experience is that two seasons worth of phosphorus and potassium are rarely applied to a corn crop. Also, many soils in our region have the ability to tie-up phosphorus and potassium—a process known as fixation. Fixation is time, temperature, soil type and moisture dependent. Over a 2-year period, the possibility for fixation becomes greater.
By annually fertilizing each crop, we can reduce potential fixation. Economically, annual fertilizations spread out fertilizer expenses more evenly.
Cool-season grasses, especially tall fescue, often experience usable regrowth after the first hay crop is taken. Given adequate moisture conditions, this regrowth responds extremely well to nitrogen fertilizer. Last year, folks who fertilized post-hay fescue saw tremendous economic response.
Alfalfa is a crop that should receive late-spring combined with mid-summer plant food. Our most common alfalfa fertilization timing calls for half of the annual fertilizer applied after the first cutting (May) and the other half applied after the third cutting (July/August). We split applications to avoid luxury consumption (especially potassium), where the crop takes up more nutrient than it needs. Luxury consumption can be wasteful in forage crops when the entire crop biomass is being removed from the field.
Like alfalfa, bermudagrass hay needs to be spoonfed throughout the season. We recommend fertilizing bermudagrass after every cutting. Bermudagrass fertilization rates should be based on soil testing, but generally can be applied in a 4:1:3 nitrogen:phosphorus:potassium ratio based upon using 35 to 40 pounds of nitrogen per expected ton removed.
May is the recommended time to fertilize warm-season annual grass crops like pearl millet, sorghum-sudan or sudangrass. These crops should be planted in May with recommended fertilizer applied near planting. Nutrients applied too far ahead of planting can stimulate the growth of competitive early emerging weed species. Nitrogen fertilizer applied prior to planting can also be lost to the environment before the targeted warm-season grass is ready to utilize it.
Summer provides an excellent time to apply base fertilization programs on fields being renovated to perennial forage. Renovated fields should be soil-sampled, fertilized and limed during the summer before fall crop establishment. Do that, and you ensure the best possible health and survivability for a perennial crop you have spent time and money to establish.
Depending upon your cropping systems and the local environment, you can greatly increase efficiencies employing the benefits of timely nutrient applications, including those necessary over the next few months.
Paul Tracy is Director of Agronomy for MFA Incorporated.
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