Oxalate and EDTA extractable soil phosphorus and iron in relation to P availability in Iowland rice soils of West Africa

1999

English

There is a complex relationship between iron (Fe) and phosphorus (P) in Jowland soils grown to rice. There is, therefore, the need for quick and reliable extraction methods to assess their availability. The abiiity of ethylene diamine tetra acetic acid (EDTA) and ammonium oxalate (NH ) C O •H20) to simultaneously extract Fe and P in soils was assessed With 15 soils from five important ricegrowing countries in West Africa. The relationships between Olsen and Bray II P, inorganic P fractions and rice dry matter production and P uptake were also evaluated. The results showed that inorganic P fractions werc in the order: Fe-P>Ca-P>AI-P for 12 of the test soils, whereas Al-P>Fe-P>Ca-P was the order followed for two soils, and Ca-P>Fe-P>AI-P for one soil. The mean Fe-P recorded was 77 mg P kg-1, although residual P recorded a higher mean of 153 mg P kg-1 . Results of correlation analysis showed that correlation between EDTA-Fe and Oxalate-P was positive and highly significant (r= 0.92; P<O.OOI). Similarly, highfy significant relationship was established between EDTAFe and Fe-P, indicating that the two extractants were similar in selectivity of dissolution of inorganic phosphates and extractabie Fe. Results from greenhouse pot experiments showed that there was higher and significant relationship (r 0.75; P = 0.001) between Oxalate-P and P uptake by the rice cultivar Bouake 189 than With EDTAP (r 0.70; P = 0.004). The plant P uptake data also showed the superiority of Olsen's method over that of Bray Il in predicting P nutrition of rice. The results underscored the usefulness of EDTA and ammonium oxalate to simultaneously extract both Fe and P in West African rice soils.

Narteh, L. T.; Sahrawat, K. L.