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Fluid Journal : Fluid Journal 2005-2007
Spring 2005 Fluid Journal 2 encourage growers to use row crop application equipment in harmony with tramlines. This procedure is being used on many acres across the U.S. and around the world, and has helped the Opti-Crop team increase yields by offering a higher standard of application accuracy than was previously used. If row crop equipment is available, then UAN forms of N can be dribbled on using stream bars. Stream bars virtually eliminate leaf scorch that is generally associated with N sprayed onto wheat through flat fan nozzles. One of the main obstacles centers on being able to reliably predict how much N will be available to the plant from the soil over the course of the growing season. One sensible approach is to measure total soil nitrate N (preferably measuring ammonium nitrogen also) on deep soils down to 3 feet. This deep sampling technique offers a good snapshot in time, but it is highly rainfall, temperature, and soil type specific, so it should be backed up with sound agronomic experience. Winter wheat Fall N applications. Depending on planting date, we strongly discourage growers from applying more than 20 to 30 lbs/A of actual N at that time. Higher rates of fallapplied N may lead to too much early fall growth. That can trigger excessive moisture use, which can be a major yield limiting factor in low rainfall areas. An application of 30 lbs/A of N would be appropriate for later planted fields or fields no-tilled into high residue crops such as wheat after wheat or wheat after corn. The 20-lb/A rate would be more suitable for wheat crops following soybeans that yielded 30 bu/A or more, or legumes such as alfalfa. In fact, most growers seeding wheat after good yielding soybeans or alfalfa could probably get by without using any fallapplied N. Spring N applications. Total amount of N applied in the spring to a winter wheat crop must be primarily dictated by its yield potential. Historic yield records and local varietal performance can be used together with moisture status close to N application timing to help streamline more accurate recommendations. Secondly, the 3-foot deep soil N test should provide insight regarding soil N reserves. Another important piece of information to consider is the ability of the soil to either release or tie up N during the season. A good wheat crop with 14 percent protein will require on the order of 2 lbs/bu of actual N. That means a 100-bu/A crop would require around 200 lbs/A of N. However, this does not mean 200 lbs/A needs to be applied in the form of fertilizer, as soil reserves and N mineralization from organic matter may make up for 40 to 60 percent of this total amount. Spring N timing. Application timing is critical for high yields, both from the standpoint of canopy manipulation (adjusting tiller numbers up or down to achieve the desired head population per square yard) and with respect to crop moisture use. Applying N too early can result in a crop canopy that gets too big too soon, which usually offers no yield advantage (many times in a dry environment it may result in a negative yield impact). On the other hand, putting spring N down too late may lower the number of tillers and primordial grain sites at harvest time. Therefore, an experienced agronomist will need to weigh all these factors carefully--- in conjunction with rainfall forecasts---to make sound decisions about application timing. Design of the plot in Figure 1 was randomly replicated four times. We have found that yields can be increased on the listed varieties of spring wheat by post-applying the majority of the N, compared to the standard practice of applying it all at or prior to planting. We encourage growers to add 20 to 30 lbs/ AofNand30to40lbs/AofP2O5to help with earlyseason establishment, then apply the balance as a topdress application around Feekes growth stage 4 to 6, depending on plant health. The reason for increased yield on these varieties (Figure 1) is that tiller density is controlled when the majority of N is post-applied, rather than encouraging excessive tiller when N is applied preplant. More information on spring and winter wheat management can be found on the Opti-Crop website at www.opticrop.com Needham is Opti-Crop manager from Owensboro, Kentucky. Figure 1. Comparison trial on intensive spring wheat N management, applying UAN on field in Fargo, North Dakota, 2004.
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