Annual manure production in Iowa now exceeds 14 billion gallons of liquid manure, with most of this predominately produced on swine farms. This manure needs to be applied annually and its management is often cited as one of the critical factors impacting water quality. Some research suggests, this is in part to a mismatch in timing of when crop nutrients are needed and when the manure is applied. Moreover, unlike other fertilizer sources, the management of manure is complicated by the fact specific management activities at the facility does not always align with the most appropriate agronomic decisions. For example, manure application could be driven by a full storage rather than appropriate field conditions, or a turn at the facility that allows manure agitation and removal at a time when the facility is empty, improving withdrawal safety for employees and animals.
Moreover, given the predominately row crop (corn/soybean) agriculture that typifies much of the corn belt, manure application windows are typically limited to either spring after the soil thaws but before planting occurs or fall after harvest but again before the soil freezes. While these windows have typically proven sufficient, changing weather patterns, the expansion of livestock agriculture, and the separation of ownership of the cropping and livestock production portions of the operation have put new and greater stresses on the way the system is managed. Furthermore, the move from independent ownership of manure application equipment at the farm level, to a system where it is owned by an independent contracting business has taken much of the control away from the individual farmer and created a system.
In a system based on single ownership of the crop and livestock facility, the decision when to apply manure was a compromise for both the cropping production system and the livestock production side, with the farm manager typically wanting to balance the decision to maximize overall farm profits. There is great incentive to optimally manage manure as a fertilizer resource with more ideal application timing, but not to the extent it would prohibit the production of livestock. If the storage was full, there is incentive to perform emergency manure application, so animals could continue to be raised in the production facility. Since these farms often owned their manure application this would typically occur only to draw down the storage to an adequate level until more appropriate application timing.
However, in more modern setups where ownership of the crop and livestock is divided among different individuals, there are competing interests in different decisions. For example, the crop farmer still would want optimum timing for crop performance, but the barn owner often focuses his decision process solely on what is best in terms of barn management. When the fields open up, the livestock farmer may find themselves in a situation where they may be giving away or selling the manure at far below the market value of the nutrients it contains. This, in turn, allows the crop producer to view it as a free fertilizer only minimally impacts his other fertility decisions. While from an economic perspective this arrangement is perhaps beneficial to both parties, it also creates a situation where the environmental constraints on the system are not given priority.
This, along with the rising costs of manure application machinery, is putting the equipment out of reach for many farms. Thus, the greater stress to get all manure applied in shorter time windows. While I don’t have the answers on this, it is important as we go about facing these challenges, we look at all the options – new crop rotations, bigger and faster equipment, altering our manure management systems to make within season application possible, and potentially numerous others. It seems like a first step is to understand how different crops may open up new application windows, a first attempt at that, which I’ve shown below. Note: I’m not saying we need to have lots of acres devoted to other crops, the next fun steps are figuring out how much will be enough.
Figure 1. Cropping activity windows for different crops in Iowa.