Comparing of the difference and balance methods to calculate percent recovery of fertilizer phosphorus applied to soils: a critical discussion

This article presents a critical discussion comparing the traditional method and a newly proposed balance method to calculate percent recovery of fertilizer P applied to soils. The traditional difference method is defined as P uptake from the soil treated with fertilizer P minus P uptake from a control with no P added divided by the amount of fertilizer P applied. The balance method simply considers the ratio of P uptake from the P fertilized soil to the amount of fertilizer P applied and does not use a control to discount P taken up from soil without fertilizer application. The percentage recovery of fertilizer P calculated by the difference method normally ranges from 10 to 25% for a given crop in a given season and is always lower than that by the balance method which ranges from 50 to 90% and is sometimes over 100%. The balance method is inappropriate to calculate percentage recovery of current fertilizer P applied due to its overestimation and the invalidity of the mathematical equation used. The difference method is superior to the balance method to estimate percentage recovery of fertilizer P applied. The balance method is suitable for determining a percent soil P balance to evaluate if fertilizer P applications are building up, depleting, or maintaining soil P reserves.