Factors Affecting the Relative Benefit of Deep-banding versus Broadcast Application of Phosphorus and Potassium for Corn and Soybean

Scientifically based recommendations concerning the choice of deep banding versus traditional broadcast application of phosphorus (P) and potassium (K) for corn and soybean production in conservation tillage systems have been hampered by insufficient research and inconsistent results. Even when the decision is made (e.g. by strip-tillage corn farmers) to go with deepbanding of P and K, numerous questions remain about fertilizer rates, optimum deep-banding depth and frequency, whether to have a constant or changing band position over time, accompanying starter fertilizer and nitrogen (N) fertilizer delivery programs, and optimum soil sampling methods. Although Dr. Tony Vyn’s oral presentation for this conference will address what recent research has found for the example of deep-banding of K, this paper will review some of the general factors that influence the possible advantage of deep banding versus broadcast application. Potential advantages for deep banding of P and K, as well as optimum management of deep banding itself for a particular field situation, are very dependent on (a) soiltest P and K, (b) extent of P and K stratification, (c) inherent soil properties that affect availableP and exchangeable-K availability, (d) soil temperature and moisture regime during periods of high plant demand for P and K, (e) crop species and cultivar, (f) the associated starter fertilizer (if any) and, (g) fixed or random fertilizer band positions over time. Deep banding of P and K is particularly well suited to strip-till production systems but, even for that tillage system, fieldspecific circumstances will influence the potential advantage to be gained from deep banding.