Wheat fields are firming up across Ohio, and topdressing with nitrogen fertilizer will soon start. Given the current fertilizer prices, more livestock producers may be considering applying liquid swine manure as a topdress for wheat.
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 it generally will not be available when wheat takes up the majority of its nitrogen before mid-June.
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 waterers and surface water occasionally entering the pit can result in nitrogen amounts toward the lower end of this range. The contents of the ration fed to the pigs can also affect manure nitrogen numbers.
In past years, some farmers have used sow manure to topdress wheat. Just know that the nitrogen amount in sow manure will be much lower than swine finishing manure.
In university research, both manure tankers and drag hoses have been used when topdressing wheat. The concern with manure tankers is soil compaction, especially on heavy soils. The drag hose seemed to work well wherever it was used.
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 3 and 4 pounds of P2O5. So, a 100-bushel wheat crop with 1 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 finishing manure would contain, but review your manure test to make this determination.
When applying livestock manure to wheat, it’s recommended to follow the Natural Resources Conservation Service No. 590 Waste Utilization Standard to minimize potential environmental impacts. This standard includes 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% chance of a half-inch of rain in the 24 hours following manure application when surface-applying. Print this forecast so you have proof in the event of a surprise rain downpour.
Arnold is with the Ohio State University Extension Agronomy Team and a certified crop adviser.