Closely monitor water use, soil moisture with corn
Much of Colorado's corn is currently in the V8 to V12 growth stages and rapidly growing, crop water use and nitrogen (N) uptake are increasing rapidly as well. Many irrigated growers are starting to closely monitor crop water use and soil moisture conditions in order to anticipate when to begin irrigation.
Fertigation is an efficient method of supplying part of the N needed for the crop through the irrigation system, near the time of maximum nitrogen uptake. While the amounts of uptake will vary slightly with hybrid, the most rapid period of N uptake is between the eighth leaf and tasseling growth stages. During this time, a steady supply of N is critical to insure optimum yield.
Nitrogen fertigation for corn generally should begin with the sixth leaf and be complete by the silking growth stages. Application rates of 20 to 30 lb N/acre per irrigation event are recommended. However, higher rates of up to 50 lb N/acre per irrigation are unlikely to cause crop damage because the fertilizer is diluted in water. Producers should insure that water is applied uniformly, without runoff, to insure even distribution of N. Generally, fertigation is not recommended for furrow irrigation because of the likelihood of uneven water application.
Urea-ammonium nitrate (UAN) solution is the most common N source for fertigation, though ammonium thiosulfate (ATS) also can be used, particularly in sandy soils that may benefit from sulfur (S) fertigation. Anhydrous ammonia is not recommended for fertigation because there is potential for precipitates to form and plug nozzles when ammonia is injected into water with dissolved calcium and magnesium.
While fertigation is efficient because N is applied just when the crop needs it, there are potential disadvantages as well.
--Nitrogen solution fertilizers are generally more expensive per pound of N than anhydrous ammonia or urea.
--The irrigation system must be set up with appropriate check valves, injection pumps, and fertilizer tanks.
--The operator must be certified for chemigation.
--Rainy weather can delay the need for irrigation, thus delaying N application during critical growth stages as well.
While most growers use fertigation to apply a pre-determined amount of N based on recommendations, fertigation does allow N application on an as-needed basis, depending on crop N status. A chlorophyll meter, aerial imagery, or crop canopy sensors can be used to assess crop N status in-season.
Please contact me, Bruce Bosley about this or other cropping systems or natural resource topics at 970-522-3200 extension 285 at Sterling or 970-542-3540 at Fort Morgan.