Different Indices as Indicators of Phosphorus Availability to Wheat on Vertisols in Central Highlands of Ethiopia

ABSTRACT

Vertisols are important soils in the agricultural activity of Ethiopia. Their wide distribution and erratic crop responses to recommended phosphorus (P) fertilizer application justify the attempt for determining the P status and most suitable P availability estimation on these soils. In the present study, the forms of soil P and their relationship with different indices of available P and P uptake by wheat grown under greenhouse were evaluated. Total P, organic P, seven indices of available soil P, and fractions of soil inorganic P were determined from surface soil samples of ten Ethiopian central highland Vertisols. The amount of active inorganic P fractions i.e. water-soluble and loosely bound P, Al-phosphates (Al-P), Fe-phosphates (Fe-P) and Ca-phosphates (Ca-P) found to contain; < 0.5, 4–33, 4–66, and 15–73 mg P kg⁻¹, respectively. As for the different indices of soil available P, the extraction efficiency of the tested methods was found to decrease in the order: ammonium oxalate > Olsen > Mehlich3 > Bray1 > ammonium acetate > ammonium bicarbonate-diethylene triamine pentaacetic acid (AB-DTPA) > 0.01 M calcium chloride (CaCl₂). Olsen-P (r = 0.83) and AB-DTPA-P (r = 0.83) showed significant (P < .001) correlation with the P uptake by wheat and the active inorganic P fractions (Al-P and Fe-P). Moreover, multiple regression analysis indicated that the variation of P extracted by Olsen and AB-DTPA methods were best predicted by Fe-P (84%) and Al-P (68%), respectively. Consequently, Olsen and AB-DTPA methods were found to be most suitable for determining wheat available P on vertisols of central highlands of Ethiopia.

KEYWORDS:

• Soil phosphorus status
• inorganic phosphorus fractions
• available phosphorus indices
• plant phosphorus uptake
• vertisols
• Ethiopia

Acknowledgments

The support provided by Natural Resources Institute Finland (formerly MTT Agrifood Research Finland) is strongly acknowledged. We also wish to extend our appreciation to Riitta Sarkkinen, Paivi Allen, Helena Merkkiniemi, Merja Eurola and Anna-Liisa Kyläsorri-Tiiri from Natural Resources Institute Finland for their technical assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00103624.2022.2101659