Marcus M. Eichhorn Jr.

Beef and dairy producers in north Louisiana plant more than 30,000 acres of hill land to annual ryegrass each fall for grazing cattle during the winter and spring. Nitrogen is the most limiting plant nutrient required for annual ryegrass production on these sandy Coastal Plain soils. Fertilizer nitrogen requirements for annual ryegrass pasture, baleage and silage production are the highest among the essential plant nutrients, and nitrogen is the most expensive nutrient in the fertilizer budget. Moreover, the source of fertilizer nitrogen can have a considerable effect on cost.

Because of a lack of information on the cost effectiveness of nitrogen fertilizer sources for annual ryegrass production on pastures in the north Louisiana Coastal Plain, two nitrogen fertility studies were conducted at the LSU AgCenter Hill Farm Research Station at Homer. The objectives were to determine forage yields and cost effectiveness of readily available commercial fertilizer nitrogen sources and to determine forage yields and cost effectiveness of soil-incorporated poultry litter rates. Both studies were managed to simulate annual ryegrass production on pastures from fall plantings made into prepared seedbeds with forage yields determined at monthly intervals, mid-December through mid-May.

Commercial Fertilizer Nitrogen Sources
Five different nitrogen fertilizer sources were applied to Marshall annual ryegrass on a Mahan fine sandy loam soil for two years. The total annual actual nitrogen fertilizer rate applied was 250 pounds per acre. This annual rate was applied at 50 pounds per acre on November 1 and 100 pounds after the mid-January and mid-March harvests. The cost of nitrogen fertilizer applied by a forage producer using a commercial fertilizer buggy ranged from $160 per ton for urea to $189 per ton for ammonium nitrate. The cost per pound of actual nitrogen ranged from 17.4 cents for urea to 41 cents for ammonium sulfate. The per acre annual nitrogen fertilizer cost ranged from $43.50 for urea to $102.50 for ammonium sulfate for 250 pounds of actual nitrogen applied per acre. Marshall annual rye-grass yields on the Mahan soil were not significantly different among nitrogen fertilizer sources. Thus, with yield performances being nearly equal among nitrogen sources, maximum economic yield response occurred where urea was applied as the nitrogen source at a cost of .6 cents per pound of forage produced per acre. When available soil sulfur is at very low levels, using blended urea-ammonium sulfate as a source of nitrogen and sulfur would be more cost effective than a blend of ammonium nitrate-ammonium sulfate.

Poultry Broiler Litter As Fertilizer
Poultry production is Louisiana’s largest animal industry. More than 150,000 tons of broiler litter manure waste are produced annually. The broiler litter contains all of the plant nutrients required for crop production. Incorporation of broiler litter or commercial fertilizer into soil before planting a crop is the most “environmental friendly” fertilization practice to follow. Yield responses of Marshall annual ryegrass to soil-incorporated broiler litter rates of 1, 2, 3, 4, 6 and 8 tons per acre were determined for three years on Bowie fine sandy loam soil.

Concurrently, yield responses of Marshall annual ryegrass to soil-incorporated commercial fertilizer at rates of nitrogen, phosphate, potash and sulfur equivalent to those applied at each broiler litter rate were evaluated. Ammonium nitrate was the nitrogen source. Cost effectiveness of soil-incorporated nitrogen rates, as broiler litter or ammonium nitrate, for the production of Marshall annual ryegrass is reported. Results indicate that as soil-incorporated actual nitrogen rates of either broiler litter or ammonium nitrate increased from 62 to 496 pounds per acre, Marshall ryegrass yields increased, and the nitrogen cost per acre for each pound of forage produced increased also. Soil-incorporated nitrogen rates as ammonium nitrate outyielded soil-incorporated broiler litter. Within an excellent seasonal annual ryegrass yield range of 7,000 to 8,500 pounds dry forage per acre, however, use of broiler litter was more cost effective than ammonium nitrate at current prices. Results also showed that a 248 pound per acre soil-incorporated rate of actual nitrogen, from either 4 tons per acre of broiler litter or 728 pounds per acre of ammonium nitrate, was sufficient for Marshall annual ryegrass production.

Selection of Nitrogen Sources for Annual Ryegrass Production
Results revealed that where ammonium nitrate, ammonium sulfate, urea and blends of ammonium nitrate-ammonium sulfate or urea-ammonium sulfate were broadcast on the surface of the crop during the growing season, yield performances were not significantly different among nitrogen sources. Urea was the most cost-effective nitrogen source on the basis of currently quoted vendor prices in north Louisiana. For ammonium nitrate to become more cost effective than urea, based on the ryegrass yield performance in this study, the cost per ton would need to be less than $119. Results also revealed that soil-incorporated broiler litter was more cost effective than ammonium nitrate in the presence of actual nitrogen rates required for acceptable crop production levels. At the price of ammonium nitrate, broiler litter applied at 4 tons per acre had a nitrogen fertilizer equivalency value of $16 per ton for ryegrass forage production.

Overall, these results showed that the source of nitrogen designated for annual ryegrass production will affect the cost of forage production. Livestock producers should consider the cost of actual nitrogen among nitrogen sources when preparing fertilizer budgets for intended fall plantings.

 Marcus M. Eichhorn Jr., Professor, Hill Farm Research Station, Homer, La.

(This article was published in the winter 2001 issue of Louisiana Agriculture.)