Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2016
Publication Date: N/A
Interpretive Summary: Poultry manure is an important resource for row crop farmers. In cotton, it has proven to increase lint yield beyond that possible with synthetic fertilizers. This increase typically is achieved with rates that may not be economical. We conducted this study to analyze cotton yield response to a range of poultry manure rates, compare optimum rates for yield versus optimum rates for profit, and identify a practical approach for estimating rates for maximum profit. Cotton planted in two private farms during 2005 to 2009 were fertilized with seven target rates of manure ranging from 0 to 6 tons/acre. Manure rates that maximized yield or profit were calculated using economic models based on cotton yield, current cotton and poultry manure prices, and applied manure. The results showed that cotton produced maximum yield of 1275 lbs/acre lint at one farm and 1207 lbs/acre at the other when fertilized with 4.9 and 5.9 tons/acre manure, respectively. These peak yields, however, were not the most profitable. Maximum profit at both farms was achieved with 3.5 tons/acre manure application, which resulted in lint yields of 1218 and 1117 lbs/acre at the two farms, respectively. The profit maximizing manure rate at both farms was similar to the poultry manure rate that produced equal lint yield as cotton fertilized chemical fertilizers practiced by the farms. This finding suggests that applying poultry manure to provide nitrogen fertilization equivalent to the farm standard practice for synthetic nitrogen fertilizers is a practical method for estimating profit maximizing manure rates.
Technical Abstract: Cotton lint yield responds well to increasing rates of poultry litter fertilization, but little is known of how optimum rates for yield compare with optimum rates for profit. The objectives of this study were to analyze cotton lint yield response to poultry litter application rates, determine and compare rates that maximize lint yield (PLy) vs. profit (PLp), and identify a practical approach for estimating PLp. Cotton planted in two separate farms that utilized conventional and no-tillage systems were fertilized with seven target rates of litter from 0 to 13.5 Mg ha-1 or with a farm standard treatment receiving synthetic fertilizers (Std). The PLy and PLp for each year and farm were determined from current cotton and poultry litter prices and response curves fitted into lint yield and actual applied litter rates. The results showed that cotton lint yield peaked at an average across years of 1430 kg ha-1 with 11.1 Mg ha-1 PLy in the conventional tillage system and at 1354 kg ha-1 with 13.2 Mg ha-1 in the no-till system. These peak yields exceeded the respective Std treatment yields, but were not the most profitable. Maximum profit in both tillage systems was achieved with 7.8 Mg ha-1 PLp, which resulted in lint yields of 1367 and 1253 kg ha-1, respectively, in the conventional and no-till systems. The PLp in both systems was similar to the poultry litter rate that resulted in lint yield equal to the Std (PLs), and suggests that applying litter to provide plant available N equal to the farm standard practice for synthetic N fertilizers is a practical method for estimating PLp.