By Glen Arnold
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. With the limited fall and winter opportunities to apply manure to fields, many livestock farms have more manure than usual for this time of year.
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.
Some manure tests also list a “first year available” nitrogen amount. This number is basically the ammonia nitrogen portion of the manure plus about half the organic nitrogen portion. Again, for the purpose of fertilizing wheat, the organic portion of the nitrogen should not be considered available in time to impact yields.
Most deep-pit swine finishing manure will contain between 30 and 42 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.
To capture the most nutrients from manure farmers should consider incorporation. Incorporation can result in less nitrogen loss and can especially reduce the loss of dissolved phosphorus. Unfortunately, there are very few toolbars designed to incorporate manure into wheat.
Three years of on-farm wheat top-dress results are summarized in Table 1. Each field trial was replicated four times. In each plot, the manure ammonia nitrogen application rate was similar to the nitrogen amount in the urea fertilizer; typically about 105 pounds per acre. The manure was applied using a 4,800 gallon tanker with a Peecon toolbar 13.5 feet in width. This toolbar cut the soil surface with a straight coulter and a boot applied the manure over the soil opening. Urea was applied using a standard fertilizer buggy.
Table 1. On-farm Swine Fishing Manure Topdressing of Wheat Results (bu/ac)
Swine manure (surface applied)*
Swine manure (incorporated)
Date of nutrient application
*Incorporation was performed with a modified Peecan toolbar attached to a 4,800 gallon tanker
In addition to the Peecon toolbar, OSU Extension as also conducted manure research on wheat using the both the Veenhuizen (Grassland applicator) toolbar and Aerway toolbar. All toolbars cutting through the soil surface cause some damage to the growing wheat, but side-by-side yield comparisons with conventional surface applied fertilizer have rarely shown any difference in yields.
Some Ohio commercial dragline operators are routinely applying livestock manure to wheat each spring. This practice is gaining acceptance as it’s faster and more efficient than manure application with a tanker. The risk of soil compaction is also reduced.
Dairy manure has been utilized with on-farm research plots when topdressing wheat. Dairy manure contains far less ammonia nitrogen per 1,000 gallons than swine finishing manure and does not consistently produce wheat yields similar to commercial fertilizer. Research on dairy manure as a top-dress to wheat by adding 28%UAN to the dairy manure to increase its fertilizer value has produced wheat yields similar to commercial nitrogen.
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. Print this forecast out so you have proof in the event of a surprise downpour.