Wheat fields will begin to firm up in Ohio and the topdressing with nitrogen fertilizer will soon start. There is usually a window of time, typically around the last week of March or the first week of April, when wheat fields are firm enough to support manure application equipment. By this date, wheat fields have broken dormancy and are actively pulling moisture and nutrients from the soil.
The key to applying the correct amount of manure to fertilize wheat is to know the manure’s nitrogen content. Most manure tests reveal total nitrogen, ammonia nitrogen and organic nitrogen amounts. The ammonia nitrogen portion is readily available for plant growth. The organic nitrogen portion takes considerably longer to mineralize and generally will not be available when wheat uptakes the majority of its nitrogen in the months of April and May.
Most deep-pit swine finishing manure will contain between 30 and 40 pounds of ammonia nitrogen per 1,000 gallons. Finishing buildings with bowl waters and other water conservation systems can result in nitrogen amounts towards the upper end of this range. Finishing buildings with fixed nipple waters and surface water occasionally entering the pit can result in nitrogen amounts towards the lower end of this range.
The typical application rate for liquid swine finishing manure on wheat is 4,000 gallons per acre. Wheat removes 0.49 pounds of P2O5 per bushel harvested. When also harvesting the wheat straw, a ton of wheat straw contains between three and four pounds of P2O5. So, a 100 bushel wheat crop with one ton of straw also removed would withdraw about 52 pounds of P2O5 per acre. This is likely about the same amount of P2O5 as 4,000 gallons of swine manure would contain but review your manure test to make this determination.
If you are participating in the H2Ohio program, manure must be incorporated if being applied to wheat in the spring. The grassland application toolbar (also known as the Veenhuis toolbar, see header above and picture below) slices furrows in wheat, forage, and pasture fields at a spacing of about 7.5 inches and places manure over the furrows. I believe the Ohio Department of Agriculture will approve this as incorporation but check with your local Soil and Water Conservation District in advance to be sure. OSU Extension has conducted manure research using the grassland applicator in replicated plots and got yields slightly better than top-dressed urea.
A farmer near New Washington, Ohio has a refurbished 22-foot wide grassland applicator with a hitch designed to be pulled behind a manure tanker. He is willing to rent the toolbar on a per acre basis if anyone wants to give the technology a try. Aerway and Gentill toolbars will not currently qualify in the H2Ohio program as manure incorporation toolbars.
When applying livestock manure to wheat it’s recommended to follow the NRCS #590 Waste Utilization Standard to minimize potential environmental impacts. These standards include a 35 foot wide vegetative strip setback from ditches and streams. Applicators in the Western Lake Erie Basin also need to look at the weather forecast to be certain there is not greater than a 50 percent chance of a half-inch of rain in the 24 hours following manure application if surface applying. Print this forecast so you have proof in the event of a surprise rain downpour.