Computer programs that calculate manure application rates

Decision support systems (DSSs) operated on personal computers are a convenient means to calculate application rates of livestock manures that meet crop nutrient requirements and avoid excessive nutrient applications. Twelve DSSs that can be used to calculate application rates of dairy manure are described and compared. The major functions of the programs, their input data requirements, and their software and hardware requirements are described. The major functional differences between the programs, their nutrient availability assumptions, and user-friendliness are discussed. The programs examined differ considerably in the number of functions they perform. The simplest programs estimate manure application rates for one field at a time. The more complex programs perform additional functions such as estimating the quantity of manure, calculating application rates for multiple fields, automatically allocating the estimated amount of manure to those fields, and calibrating manure spreaders. All of the programs use the same basic procedure to calculate manure application rates. This is essentially: (i) crop nutrient requirements are estimated, (ii) manure nutrient (N, P, and K) content is entered by the user or estimated by the program, (iii) availability factors are applied to the manure nutrients, (iv) the rate of manure to supply available nutrients to meet crop requirements is calculated, and (v) rates of any supplementary commercial fertilizer are calculated. The programs are typically developed for particular agricultural regions. Four of the programs examined have regional adaptability, achieved by enabling the user to directly enter or to modify factors used in calculating crop nutrient requirements and manure nutrient availability. DSSs have considerable promise in assisting with the many calculations required to determine manure application rates that meet crop nutrient requirements and minimize the risk of environmental pollution.