Corn production on irrigated sandy soils is an important enterprise throughout Minnesota. The large majority of acres devoted to this enterprise is found in central Minnesota. Yet, other small, localized areas of sandy soils are scattered throughout the state. Management of nitrogen is an important factor for corn grown under irrigation. Management of this input is the focus of this blog.
The determination of the RATE of nitrogen fertilizer to apply is one of the most important management decisions. Beginning in 2006, the concept used for making suggestions for rate of fertilizer nitrogen changed. Yield goals were discarded being replaced by: 1) price of a pound of fertilizer N ,2) value of a bushel of corn ($/bu.) and the grower’s attitude toward risk.
Some suggested rates of fertilizer nitrogen (N) for production of irrigated corn on sandy soils are listed in Table 1. These suggestions are derived from research conducted in fields of cooperating farmers since 2007. The first step is to calculate the N price/crop value ratio. to do this, divide the price of a pound of fertilizer N by the value of a bushel of corn (usually obtained from the Chicago Board of Trade). For N at $.50 per pound and corn valued at $5.00 per bushel, this ratio is 0.10. Suggested N rates for several ratios are listed in the center column of Table 1. An appropriate range for each ratio is listed in the right hand column. Use the lower rate in the range if the corn producer is conservative For more aggressive producers, use the higher rate in the range.
These N rate suggestions are appropriate for production situations where corn follows corn, small grains, potatoes, or other non-legume crops. Some N CREDITS for common legume crops are: soybean (30 lb. N /acre), harvested alfalfa (100 lb. N/acre), and edible beans (20 lb. N/acre).
Nitrogen in IRRIGATIO WATER is also a credit. If the concentration of nitrate-nitrogen is higher than 10 ppm, this N should be accounted for and will vary with planned or intended amounts of irrigation water to be used. Don’t make any adjustments if the concentration of nitrate-nitrogen is less than 10 ppm. Don’t ignore or neglect the amount of N applied in a started fertilizer as well as the N supplied in the 18-46-0 or 11-52-0 when calculation the total amount of N applied.
The impact of TIMING of fertilizer N for irrigated corn production has been the focus of considerable research. This research leads to the conclusion that split applications are superior to single applications for corn production on sandy soils. There can be a considerable amount of flexibility in these split applications. My preference for ranking the split application is as follows.
1. N in a starter, 2/3 of total chosen as a siredress application; remainder with the irrigation water
2. N in a starter, weed and feed, split sidedress applications (no preplant
3. preplant N, N in a starter, sidedress N N added to the irrigation water
4. N in a starter, sidedress application
5. preplant N, N in a starter, two sidedress N applications
These N management programs are ranked in order of preference. Both economic and environmental were consequences in formulating the priority listing. Selection #1 probably has the lowest potential for negative environmental consequences. The highest potential for leaching of nitrate-nitrogen is associated with choice #5.
There are, of course, various ADDITIVES that can be added to N fertilizers for the purpose of reducing the probability of N loss. Some work; some don’t. At this time, a brief review is probably in order. The products, N-Serve, and Instinct are formulated for the purpose of delaying the conversion of ammonium-N (NH4-N) to nitrate – nitrogen (NO3-N. They work, and when these products are used, the conversion is delayed 7 to 10 days. The most obvious plan is to use when 82-0-0 is applied before planting. Use of these products is not suggested if anhydrous ammonia is used for a sidedress application.
The product, Agrotain, is designed for production situations when urea is used in some part of the fertilizer program. This product delays the conversion of urea-N to ammonium-N. The delay lasts for 7 to 10 days and, then, conversions of N in soils proceeds s usual. Use of this product is a good choice if 46-0-0 or 28-0-0 is applied without incorporation before planting. This product is not suggested if these two N sources are to be incorporated. Rainfall and/or irrigation water will incorporate any fertilizer containing urea. The amount needed to produce incorporation is about 0.25 inches.
The product, ESN, does not affect conversion of N in soils. Instead, it is a slow release N fertilizer that is probably best suited for preplant N applications. It is more expensive than other N sources. Therefore, the best fit is probably a mixture of this product with urea, broadcast and incorporated.
There are several other products that are marketed with claims that they affect conversion of N in soils. Research has shown that these products do not work as advertised. I’ve recently noticed that a new product, Take-Off, is being marketed as an additive for fertilizer N. The advertising suggests that it will accelerate nutrient acquisition and assimilation. This appears to me to be a new concept and, of course, there was no supporting data. Sounds like more foo-foo juice to me.
To some, planning a fertilizer program for irrigated sandy soils might be confusing and even overwhelming. That’s not really the case. The plan can be flexible and still provide for optimum profit without having an negative impact on the environment.