ASSESSMENT OF EXTRACTANTS FOR AVAILABLE FE AND SOIL FACTORS AFFECTING IRON CHLOROSIS IN UPLAND RICE IN SOUTHWESTERN NIGERIA.

Abstract

Available Fe in 23 surface soils from southwestern Nigeria was determined with five ectractants, namely: 1N NH₄OAc, 0.01 M EDTA, pH 7.0; (2)1N NH₄OAc, pH 4.8 (3) 0.01M EDTA; (4) 1N NaOAc, pH 4.8 and (5) 0.005M DTPA and correlated with Fe uptake by rice plants (CV, ART8) grown under upland conditions in pot trials in the glasshouse. 0.005 M DTPA showed the highest correlation (r = 0.54**) and 1N NH₄OAc pH 4.8 showed the least correlation (r = 0.35), with plant Fe uptake. The range of available Fe extracted by 0.005 M DTPA and 1N NH₄OAc + 0.01 EDTA was 1.8 6.7 ppm and 3.3 10.5 ppm respectively.

Regression analysis indicated that soil pH is a strong factor controlling both Fe availability and Fe uptake by upland rice in the moderately acid tropical soils. Organic carbon accounted for 17.4% and 15.0% of available Fe extracted in 1N NH₄OAc + 0.01 M EDTA, pH 7.0 and 0.005 M DTPA respectively. 0.005 M DTPA extractant appeared the best of the five extractants for assessing the availability of Fe in the moderately acid tropical soils. Incorporation of organic manures - poultry and brewers grain wastes. improved Fe uptake by the upland rice plants in a pot trial.