Manure Applications Prior to Planting
Spring manure applications may provide environmental and crop production advantages compared to fall manure applications. These benefits include reduced nitrogen leaching, increased crop yields, and higher phosphorus and potassium nutrient soil storage.
Nitrogen Losses vs. Needs
Iowa Nutrient Research Center research summarized by Daniel Andersen, Iowa State University Assistant Engineer, in the ‘National Hog Farmer’ - Nov. 22, 2017 issue, document soil nitrogen leaching losses as 6% less when manure was spring pre-plant applied versus fall applied. This Iowa study also revealed that average corn yields were 4% higher in fields where manure was spring applied versus fall. Nitrate leaching was further reduced 4 to 7% when the spring applied manure program was added into a side-dress application or a split pre-plant / side-dress application.
Regarding nitrogen needs, beef solid manure is usually surface broadcast and not incorporated since the organic nitrogen (N) content is 10 times higher than volatile ammonium N content. Broiler litter has 5 times more organic N compared to ammonium N form, so there may be some incentive to incorporate poultry manure into soil to reduce ammonium N volatile nitrogen losses. Swine manures are typically injected below the soil surface to reduce nitrogen ammonia losses. On average, pig finisher manure has 42 lbs. per 1,000 gallons of volatile ammonium N versus 17 lbs. per 1,000 gallons of the more stable organic N.
Fall applied manure applications may increase nitrate leaching especially when rainfall is higher and/or winter precipitation snowmelt is excessive. Warmer soil temperatures (>50°F) may also contribute to leaching as soil microbes convert ammonium N nitrogen forms into leachable nitrate (N). An option to reduce fall nitrate leaching may be growing cover crops to help take up free soil nitrate and slowly release the nitrogen during the next cropping season as the cover crop plants decompose. More on estimating manure’s nitrogen value can be found at Estimating Nitrogen Credit from Manure.
Spring planting season can be a busy time, and excessive rains may cause delayed planting and reduced crop yield risks. Therefore, although spring manure applications usually lower environmental leaching risk, wet spring field conditions may increase field soil compaction risks.
Manure applications may build soil phosphorus levels and provide yield benefits for both corn and soybean production. Charles Wortmann, Nebraska Extension Soils specialist, recommends applying and maintaining phosphorus above 20 ppm Bray P-1 soil test phosphorus for corn and 15 ppm Bray P-1 for soybean production.
Phosphorus Removal by Crops
When manure applications are made every 2 to 6 years, higher value nutrients such as phosphorous and potassium can be added to lower field fertilizer costs. For example, phosphorus grain removal would be 112 lbs./A for a 300 bu./A corn yield, so 4 years of corn production would require 448 total pounds of phosphorus to replace field grain removed. Since typical beef cattle manure contains 23 lbs. of phosphorus per ton, an application rate of just under 20 tons per acre beef manure every four years would be required to replace the phosphorus grain removal. At current commercial fertilizer prices, the phosphorus manure nutrient value per year would be $224 per acre minus manure transportation and application costs.
Raising Soil Phosphorus Levels
Rick Koelsch, Nebraska Extension Manure Management Specialist, says that 18 pounds of phosphorus (P2O5) field applied will usually raise soil phosphorus (P) content by 1 ppm in the top 6 to 8 inches. This rate equates to about 0.8 tons of beef feedlot manure or 0.4 tons of broiler litter applied per 1 ppm needed. Therefore to raise the soil phosphorus content by 10 ppm, application rates needed would be 8 tons/A for beef manure and 4 tons/A for poultry litter manure.
Swine manure can often be applied every other year in a corn/soybean rotation to meet the phosphorus crop requirements. Most of the crop nitrogen needs will be met as well, since the swine manure has a higher N to P ratio.
Manure’s Impact on Soybean
Patricio Grassini, Nebraska Extension Soybean Specialist, says that manure applications may also benefit soybean fields. When field soil phosphorus levels are low, phosphorus applications have increased soybean yields 2-3 bushels per acre based on long-term Nebraska Extension research.
Although soybeans may use their root nodules to fix nitrogen, it takes about 2-3 weeks after emergence before their roots start fixing nitrogen. Also, since it takes less energy for the soybeans to utilize stored soil available nitrogen versus fixing their own nitrogen; the plants fixes less nitrogen when excess soil nitrogen is already available.
This article was reviewed by Rick Koelsch and Brian Krienke