Comparision of four phosphorus extraction methods on rice soils from Mali

Inorganic forms of phosphorus in soils are largely tied up by aluminium (P-Al), iron (P-Fe) or calcium (P-Ca). Numerous selective extraction methods are available to evaluate the uptake of phosphorus by plants. However, a large variety of soil properties will affect the results making one single method in a selected area difficult to use and interpret. The aim of this study is to identify the methods most useful for the extraction of phosphorus in rice soils in Mali and assess which physical and chemical factors affect the results and determine the strength of the selected methods. Seven soils cultivated from the two main rice cultivation areas of Mali, i.e. Office Niger in the Niger Inland Delta and Longorola in the southernmost part of Mali are used in the study. The results obtained show that there are large differences between both soils and extraction methods in mobilised phosphorus. Bray I gave statistically identical values for the Danga soil. Bray I and DA-4 methods gave higher extraction rates on alluvial Seno type soil. Bray II gave high values on Danga, Seno aeolian and Longorola backwater soils. Bray II seems to be relatively less dependent on the physical and chemical properties (pH, organic matter).