Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu and Amy Shober, Extension Nutrient Management and Environmental Quality Specialist; ashober@udel.edu
There are many benefits of long term no-till. However, using surface applications of poultry litter in no-till has several drawbacks. The following are some thoughts on how to manage poultry manure to reduce nutrient losses while maintaining some of the benefits associated with no-till.
No-till has been shown to reduce erosion losses from fields and, therefore, reduce the transport of nutrients attached to soil particles that would subject to erosion. Phosphorus losses are reduced considerably upon initial adoption of no-till. Nitrogen losses from surface flow are also reduced, but a significant portion of nitrogen in runoff exists in a soluble form rather than a particulate form. Over time, surface additions of poultry litter in continuous no-till leads to a buildup of soil P at the surface, which can increase soluble P losses in surface runoff. In addition, surface applications of poultry litter do not conserve the ammonium fraction. If litter is not incorporated shortly after application, much if not all of the ammonium can be volatilized and lost to the atmosphere as ammonia gas; only the organic fraction remains, thus reducing the fertilizer (and economic) value of the manure. Long term no-till provides significant soil quality and productivity benefits by increasing organic matter in soils. Tillage will greatly reduce organic matter accumulation by increasing oxidation rates. Balancing the benefits of long term no-till with the disadvantages of P surface buildup and ammonia losses when poultry manure is surface applied is difficult.
However, there are some management options that provide many of the benefits of no-till (such as reduced erosion and organic matter accumulation) while conserving ammonium N in applied poultry litter and reducing stratification of P. A number of farmers in Delaware have adopted the use of special minimum tillage tools, including aerators, vertical tillage devices (Turbotill), and “no-till harrows”. These devices allow for partial incorporation of poultry litter, which helps to conserve some of the ammonium N and reduce P stratification. The action of these devices is such that much of the benefits of no-till remain. Surface cover is reduced minimally, ensuring that erosion rates will not increase significantly; in some cases infiltration rates are improved further reducing erosion potential. Organic matter oxidation is increased under minimum tillage, but organic matter accumulations will be higher than what is expected when using standard tillage practices.
Another innovation that is on the horizon is a poultry litter injector. A narrow furrow is opened; the dry poultry litter falls into the slot and then the slot is closed again with closing wheels. The process of litter injection is expected to better maintain no-till benefits, conserve most of the ammonium N, and reduce surface P stratification than minimal tillage options.
Our current recommendation is to apply poultry litter and use an aerator, vertical tillage device, or no-till harrow to do a partial incorporation, while leaving as much crop residue as possible. Once poultry litter injectors become available, farmers may want to adopt that technology, if economically viable (cost of purchase and operation is less than the benefits received).