I expect that this headline may lead some to believe I am about to discuss the monetary value of poultry litter and tell everyone how much they should be paying for this formerly given-away byproduct of the poultry industry.
But I can’t attempt that since that number is one of the most elusive moving targets in agriculture.
Just for the sake of discussion let’s make a couple of basic assumptions. First, this is broiler litter with a fairly standard nutrient content of around 60 pounds of N, 70 pounds of P2O5, and 50 pounds of K2O per ton. The litter is around 40 percent moisture, which right off tells you that for every ton of product you haul to the field and apply 800 pounds of it is water. Bottom line here is to “try” to avoid getting litter that is overly damp since you get more value for your dollar with litter that is even just a little drier than the average.
An application of two tons per acre will likely contribute something like 35 to 40 pounds of N to the crop during the current growing season, or around twenty percent of the total N contained in the litter. Then where cotton follows crops like soybean or corn the soil may release about that same amount of residual N that may be available to the crop during the season.
Given that a cotton crop may need as much as 110 pounds of N per year the grower needs only apply the remaining 30 to 40 pounds of N, and that probably needs to be done as a sidedress sometime around first bloom in order to avoid too much vegetative growth and poor fruit retention.
As for P2O5, if the soil test P level is 100 or above you may be paying for phosphorus you don’t need for the current crop. So, if you are paying about what everybody else is for the litter you may be buying phosphorus that will not contribute to increased yield, and may actually reduce yield if the P level is 500 or higher, even though this is a very elusive issue in itself. It is especially true that when you buy more phosphorus than you need it is not a good deal.
As for K2O, cotton likes a soil test K level around 300 to 400, especially if the soil test P level is where it should be at around 100 pounds per acre.
I get scoffed at sometimes when I mention the issue of phosphorus to potassium ratio (P:K ratio) even though research by Dr. Gordon Tupper at Stoneville has shown this to be a real issue in cotton.
Other work I have been involved with has suggested to me that this ratio interacts with the functioning of mycorrhizal fungi which are very important in cotton and soybean. Several years ago I went through a lot of random soil test data from dryland cotton growers and put together a set of numbers that validate this statement pretty well. I can share it with you if you are interested.
In addition to the “macro” nutrients in broiler litter, you can expect to get an almost complete compliment of secondaries like sulfur and magnesium, along with quantities of the “micro” nutrients sufficient for the current crop. We normally get something like 300 pounds of lime value per ton of litter, so pH levels should not drop as rapidly in soils that receive litter. Please don’t take this to mean that poultry litter is a sufficient liming material, because it is not.
Poultry litter is a valuable nutrient resource for many agricultural uses, but it should be used in conjunction with a good soil testing and fertilization program and that includes other fertilizers and lime products. A total reliance on litter will lead to nutrient imbalances that can be problematic in some crops.