Phosphorus Availability Studies on Ten Ethiopian Vertisols

Abstract

Three chemical extraction methods (Olsen, Truog, and Warren and Cooke) were earlier recommended for soil available P determination on Ethiopian soils. In the present study, the applicability of these methods and two others ( Bray II and CAL methods) on ten Ethiopian Vertisols was tested using durum wheat and chickpea, which are traditional Vertisol crops in Africa. Results showed that the magnitude of soil available P extraction was in the order Truog > CAL > Olsen > Bray II > Warren and Cooke. The four methods excluding the CAL were highly significantly (P<0.001) correlated with each other and also with crop P uptake. The CAL method was also correlated with most of the parameters, but the significance was not as high as that with the other extraction methods. The highest correlation was also obtained between wheat P uptake and the four extraction methods. None of the correlations involving dry matter yield were significant. Based on the results it can be generalized that wheat is a better indicator for P availability than chickpea. The results also show that the earlier recommended three methods are applicable to Vertisols and each method may be used in substitution of the other (with the exception of the Warren and Cooke method , the applicability of which on high pH soils may be limited) in case of need. Due to the shortage of chemicals often encountered in soil laboratories in Ethiopia, the need for testing multi-element extraction methods is recommended.