Inorganic phosphorus fractions and their relationship to residual value of large applications of phosphorus on high phosphorus fixing soils
Shelton, J.E.; Coleman, N.T.
Soil Science Society American Proceedings 32(1): 91-94
Large applications of P to a high P fixing soil were rapidly converted into Al and Fe-P. Over an 8 yr. period a decrease in Al-P with an increase in Fe-P occurred. Reductant soluble Fe-P occurred 3 and 5 years following P applications at 1371 kg/ha (1224 lb./acre) and 685 kg/ha (612 lb./acre). Soil test P was highly correlated with Al-P. Regression analysis indicates that increasing rates of P application, or increasing Al-P level, up to the reported P adsorption maximum, resulted in greater efficiency in increasing the soil test P. At a 1371 kg/ha rate of application, which was above the reported 719 kg/ha (642 lb./acre) adsorption maximum, the efficiency was greater than at 343 kg/ha (306 lb./acre) rate of application but slightly less than at 685 kg/ha application rate. A method of investigating long-term field equilibrium conditions in a relatively short period, by boiling, was investigated and resulted in equilibrium conditions requiring several years under field conditions. It is suggested that this method when coupled with other data may be used as a means of estimating P applications which would result in sufficient available P for maximum yields over an extended period.