Net Returns from Microbial Phytase When Crop Applications of Swine Manure Are Limited by Phosphorus

Soil P buildup can be stopped by limiting swine manure application to the crop's P requirement. Limiting application rates will increase manure disposal costs on many farms. Microbial phytase can improve the availability of P in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] meal to swine and lower P concentration in manure. Potential net returns from microbial phytase were estimated for two representative swine farms when manure applications are limited to the crop's P requirement. Net returns were estimated as savings in swine lagoon liquid application costs plus savings in supplemental feed P costs minus costs of microbial phytase. The first farm, a low land-hog ratio farm, applied lagoon liquid at higher rates per acre to bermudagrass [Cynodon dactylon (L.) Pers. van. dactylon] hay, while the second, high land-hog ratio farm, applied lagoon liquid at lower rates to corn. Microbial phytase was assumed to lower P in lagoon liquid by 27.75%. With manure applications limited to crop P requirement, microbial phytase reduces the land area required for lagoon liquid disposal from 98 acres to 71 acres on the low land-hog ratio farm and from 191 to 138 acres on the high land-hog ratio farm. Net return to phytase is $7334 ($0.49/hog) on the low land-hog ratio farm, and −$336 (−$0.02/hog) on the high land-hog ratio farm. The net return to phytase is sensitive to the price of hay or corn and the amount of P reduction in swine manure obtained with phytase. Phytase has the potential to reduce farm economic losses resulting from limiting manure applications to crop P requirements. Research QuestionSoil P buildup from heavy swine manure application can result in runoff of soluble and sediment-adsorbed P and potential damage to surface water quality. Phosphorus buildup can be stopped by limiting swine manure applications to the level of crop P removal. Lower manure application rates would increase the land area required for manure disposal and swine manure disposal costs. Adding microbial phytase to swine rations reduces the supplemental P requirement in swine rations, reduces P content in swine manure, and lowers the land area required for manure application when application rates are based on crop P requirements. This study estimates the net returns to swine farmers from microbial phytase when manure applications are limited by crop P requirements. Literature SummaryEarly work showed that preparations of Aspergillus ficuum containing phytase improved the availability of P in corn and soybean meal. More recently a highly active genetically engineered microbial phytase has been developed to improve the availability of P in corn and soybean meal. Research studies have shown that when microbial phytase is added in amounts ranging from 76 to 726 units per pound of feed, phytase reduces swine manure P₂O₅ concentrations from 5.5 to 62.4%. Study DescriptionThe potential net economic benefits from microbial phytase were estimated using budgets for two swine farms, each producing 14 874 feeder-to-finish hogdyear. The farms were not actual farms but were constructed so as to be representative of many farms in Duplin County, North Carolina. Both farms stored swine manure in anaerobic lagoons and applied lagoon liquid through irrigation systems. In the baseline, both farms applied lagoon liquid to crops based on crop N fertilization guidelines (N-based waste management plan [WMP]). Under the P-based WMP, both farms applied lagoon liquid to crops based on crop P₂O₅ removal per acre. The first farm, labeled the low land-hog ratio farm, applied lagoon liquid to bermudagrass hay at higher rates per acre. The second farm, labeled the high land-hog ratio farm, applied lagoon liquid to corn at lower rates per acre. Net returns from microbial phytase equaled savings on swine lagoon liquid application costs plus savings in supplemental P added to swine rations minus costs of supplemental phytase. Savings on swine lagoon liquid application costs were based on increases in net returns from crops where lagoon liquid was applied under the P-based WMP. Phytase was assumed to be added to the ration at 109 units/lb of feed and to reduce swine manure P content by 27.75%. The amount of land required for swine lagoon liquid application was reduced also. Applied QuestionsWhen no phytase is used, how are net returns from land where swine lagoon liquid is applied affected by the requirement limiting manure P applications to crop P requirements? The total land area for lagoon liquid disposal increases from 44 to 98 acres (122%) on the low land-hog ratio farm where lagoon liquid is applied to bermudagrass hay. The land area increases from 106 to 191 acres (80%) on the high land-hog ratio farm applying lagoon liquid to corn. On the low land-hog ratio farm, total gross returns from bermudagrass hay increase by $10 437 (from $8574 to $19 011). Total leasing, irrigation, fertilizer, and other costs increase by $27 799 (from $26 906 to $54 705) causing net returns from bermudagrass hay to decline by $17 362 (from −$18 332 to −$35 694). On the high land-hog ratio farm, net returns from applying lagoon liquid to corn decline by $2630 (from −$4203 to −$6833). How does phytase use affect net returns from land receiving swine lagoon liquid when lagoon liquid is applied based on crop P requirements? The land required to apply lagoon liquid on the low land-hog ratio farm falls from 98 to 71 acres when phytase is used. Gross returns from hay sales fall by $5276 (from $19 011 to $13 735) but costs decline by $14 631 (from $54 705 to $40 074). As a result, the net losses from lagoon liquid application are reduced by $9356 (from −$35 694 to −$26 338) or 26%. The land required to apply lagoon liquid on the high land-hog ratio farm falls from 191 to 138 acres when phytase is used. The net losses on the high land-hog ratio farm decline by $1686 (from −$6833 to −$5147) or 25%. Phytase reduces losses by less on the high land-hog ratio farm, because corn has higher net returns than bermudagrass hay. Is phytase use profitable when manure applications are limited by crop P requirements? Phytase is profitable on the low land-hog ratio farm. Adding phytase to achieve a 27.75% P reduction in swine manure costs $4735/farm ($0.32/hog). Phytase lowers the cost of supplemental P in the feed ration by $2713 ($0.18/hog). The net cost of phytase addition is $2022/farm. Savings on swine lagoon liquid application costs are $9356 and net return to phytase is $7334. Phytase reduces but does not eliminate the farmer's net losses resulting from having to apply swine lagoon liquid based on crop P requirements. On the high land-hog ratio farm, savings on swine lagoon liquid application costs are $1686 and the net return to phytase is −$336 (−$0.02/hog). What factors affect the profitability of phytase when manure applications are limited by crop P requirements? Phytase returns are sensitive to the selling price of the crop on which swine lagoon liquid is applied. If hay prices decrease by 32% to $22.50/ton, the net return to phytase increases by 23% on the low land-hog ratio farm. A 32% increase in hay price causes similar declines in net returns to phytase use. Returns to phytase on the high land-hog ratio farm increase from −$336 to $4505 when corn prices fall by 32% to $1.98/bu. Increasing corn prices by 32% causes phytase net returns to fall to −$5178. Returns are also sensitive to the percentage reduction in P with phytase. Increasing the P reduction in swine manure from 27.75 to 31.75% causes net returns to phytase to increase from $7334 to $8662 (18%) on the low land-hog ratio farm and from −$336 to −$103 (69%) on the high land-hog ratio farm. Lowering the P reduction in swine manure from 27.75 to 23.75% causes net returns to phytase to decline by 18% on the low land-hog ratio farm and by 70% on the high land-hog ratio farm. Returns are also sensitive to P content of swine lagoon liquid without phytase. Increasing the initial P content increases the return to phytase. RecommendationsPhytase use will reduce the cost of supplemental P in swine rations and will reduce swine lagoon liquid application costs, when applications are limited by the crop's P requirement. On many farms having limited land for manure application, microbial phytase will mitigate but not eliminate the adverse impact on net returns of limiting manure applications to crop P requirements.