Abstract

Notwithstanding a voluminous body of literature on the subject there is still poor agreement regarding the relative merits of lime requirement indices based on exchangeable Al and those based on pH measurements. The work reported here was conducted in an effort to obtain greater clarity on the subject. Lime × P × Mg factorialized pot experiments were conducted on Mollisols, Ultisols, and Oxisols using corn as an indicator crop. Plant tissue was analyzed for several essential elements plus Al and the soils were tested for exchangeable cations, P, and pH. Yield responses fell into three categories: (i) those in which liming neither promoted nor depressed growth, (ii) those where growth was initially promoted by liming with no depressive effect and (iii) those where liming to neutral pH values depressed yield. The results showed that corn response to lime was essentially similar over a wide range of soils when Al saturation of the soil was used as the index of lime requirement. Corn response was poorly related to pH in water but the relationship improved when salt pH was used. As nearneutral pH values were approached, the uptake of a number of nutrients was reduced, suggesting that the long-held view that such pH values have beneficial effects on nutrient availability warrants re-investigation.