Broiler litter is normally applied to pastures in Arkansas to benefit from its fertilizer value. In an effort to slow down or cease the build-up of phosphorus on soils prone to runoff, reduction or termination of litter application is sometimes recommended. This often causes concern among cattle producers because broiler litter is a low-cost fertilizer that promotes grass growth and therefore maintains high pasture carrying capacity. Replacing litter with higher-cost, commercial nitrogen fertilizer is a financial burden on cattle producers.
We conducted a field study to determine whether producers could shift the timing of litter application from the more normal time of spring clean-out to later in the year when the risk of field losses of phosphorus are lower and still maintain high annual forage yields. Litter applied in March and April consistently promotes heavy growth of tall fescue in April through June because cool, moist growing conditions are favorable for tall fescue. Most pastures also contain bermudagrass, a summer-growing forage. This mix of perennial grasses can provide pasture production in northwest Arkansas for nine to ten months and even longer further south. We wanted to learn whether delaying litter application to July or September, when runoff risk is less, would reduce annual forage production or simply shift the bulk of production to a different season.
Broiler litter was applied at three different times, April 1, July 1 and September 1 in 2004, 2005 and 2006. Treatments consisted of 0, 1.5 or 3.0 ton/ acre. Plots were harvested monthly from May to December, plus the following May to measure the carryover effect. The forage yields we present are averaged over the three years.
Results and Implications
Applying litter on April 1 produced the expected boost in grass growth during April through June. The July 1 application boosted forage growth during July and August, but only in 2004, which had adequate rainfall to support grass growth. The September application did not exhibit a significant increase in grass growth until the following spring. The April and July applications also showed a carryover stimulation of grass yield, but not as dramatic as the September application.
The overall result averaged over three years and including the carryover effect in the following spring showed that the April application yielded the most forage, 8,550 lbs/acre. The July and September applications reduced forage yield to 7,800 lbs/acre, which is an 8.8 percent decline in total forage yield (or 750 lbs/acre) when shifting the date of litter application from the spring period to the summer or fall period. Around 25-30 lbs/acre of nitrogen from urea fertilizer would be required to recoup the lost forage yield, at cost of $15/acre. This compares favorably with having to replace all the litter with commercial nitrogen, which would be approximately 100 lbs/acre, or $50/acre.
Applying no litter to the forage produced 6,640 lbs/acre over 12 months. Adding 1.5 tons/acre of litter increased dry forage yield by 1,400 lbs/acre to 8,040 lbs/acre. Applying 3 tons/acre produced an additional 1,000 lbs/acre over the 1.5 ton/acre rate, which showed diminished gain in forage production for the high litter application rate.
The alternative application dates would allow the use of litter as a fertilizer at times of the year when runoff losses from heavy rainfalls are less likely; however, with diminished efficiency. In general, spring application consistently results in large boosts in forage production in May and June because soil moisture is reliably available to support forage growth; however, summer growing conditions are erratic between years. Applying litter during the hot conditions of July can result in losses of nitrogen as some of the ammonia in the litter escapes to the atmosphere, thereby reducing the fertilizer value of the litter.
Litter applied in early September would be on a soil whose moisture is typically depleted from the hot, dry summer months. Warm, wet conditions with a delayed killing frost would be needed to favor grass growth response to the litter. Progressively shorter days and slow fall recovery of tall fescue when competing with bermudagrass would limit the growth response to September litter application, as it did in our study. Nevertheless, September application resulted in total forage growth that nearly equaled that of the April application. Arkansas pastures typically produce very large quantities of forage in the spring, sometimes exceeding the ability of the cattle to utilize it efficiently. Therefore, shifting litter application to summer or fall could reduce excess spring production while providing acres that can receive litter at time of low risk of phosphorus losses with storm events.
Summary
Delaying litter application to a more favorable period in terms of lower P-runoff risk, such as in July or September, shifts the yield boost later, with a modest (8-9 percent) loss of total annual yield. April application still gives the highest total increase in forage yield, but a viable option exists for lateseason litter application without substantial loss in total forage yield because of carryover fertilizer response to the following spring.
Chuck West and Tommy Daniel are with the Department of Crop, Soil & Environmental Sciences at the University of Arkansas. This article first appeared in the University of Arkansas “Avian Advice” journal, and was reprinted with permission.
