Converting soil phosphorus readings based on mechlich 3 extraction methods into mechlich 1 in two florida flatwoods citrus groves

Esa Ontermaa


In the Southern U.S., the adoption of the Mechlich-3 (M3) soil extraction method by farmers far surpasses that of governmental entities. To benefit from the superior versatility of the M3 over Mechlich 1 (M1), particularly in regards to phosphorus (P), a grower either can accept the recommendations devised by commercial soil testing laboratories or must convert the M3 readings into M1 values to use University recommendations. The relationships between M1P and M3P appear to be unique to each region of the U.S. where studies have been made. This suggestion of local dependency was confirmed by this study. In a citrus grove with sandy soils, the relationship between M3P to M1P had an r2 of 0.68 and a slope of 0.47. In a grove with loamy soils less than 32 km (20 miles) away, these values were 0.73 and 0.56, respectively. Where soil pH ? 6.3, M3P > M1P and when pH > 6.3 then M1P > M3P. Only where M1P > M3P was there a dependency on pH suggesting that soil pH was a more significant factor influencing an increase of M1P over M3P than soil P concentration. When soil pH > 6.5, the use of a conversion equation to convert M3P to M1P appeared to be a more reliable method to assess available P in the soil than the analysis with M1.


soil test; citrus fertilization

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283