Phosphorus Status, Inorganic Phosphorus Forms, and Other Physicochemical Properties of Acid Soils of Farta District, Northwestern Highlands of Ethiopia

Asmare Melese,Birru Yitaferu,Heluf Gebrekidan,Markku Yli-Halla

doi:10.1155/2015/748390

Abstract

Soil acidity and low availability of P limit crop production in the highlands of Ethiopia. The objective of this study was to determine the P status, distribution and forms of inorganic P and relate them to selected chemical properties of eight representative acidic surface soil samples from Farta District. Soil pH (H2O) varied between 4.74 and 5.50. The moderate to high CEC suggests that besides kaolinite, the soils also contain expandable 2 : 1 clay minerals. Though the total P content was high, the available Olsen P content was very low or low in all soils except one. In most soils, the abundance of inorganic P fractions was as follows: P bound by oxalate extractable iron (Feox-P)>reductant soluble Fe-P>occluded Al-Fe-P>P bound by oxalate extractable aluminum (Alox-P)>calcium bound P (Ca-P). Olsen P had a very strong positive correlation (P≤0.01) withAlox-P (r=0.98),Feox-P (r=0.96), and oxalate extractable P (r=0.94). Though Fe bound P reserves were quite abundant and the degree of P saturation ofAlox+Feox(median 3.3%) was moderate, the extremely low P saturation ofAlox(median 0.5%) explains the P deficiency of the soils.

Highlights

Ethiopia has a long history of intensive agriculture and human settlement in the highlands [1]
The abundance of inorganic P fractions was as follows: P bound by oxalate extractable iron (Feox-P) > reductant soluble Fe-P > occluded Al-Fe-P > P bound by oxalate extractable aluminum (Alox-P) > calcium bound P (Ca-P)
According to the Regional Office of Planning for Northwestern Ethiopia [17], geologically, the study area is covered with thick trap series volcanic rocks which were erupted from fissures during the early and middle Tertiary and from Choke Shield volcanic mountain center during the Miocene and the Pliocene

Summary

Introduction

Ethiopia has a long history of intensive agriculture and human settlement in the highlands [1]. Misuse of soils, arising from a desperate attempt by farmers to increase production for the growing population, has resulted in soil quality degradation It is associated with soil nutrient depletion by repeated cultivation with low external inputs of nutrients and soil erosion caused by long-term deterioration of natural vegetation and intensive cultivation [2,3,4]. Phosphorus (P) deficiency is widespread in rain-fed upland farming systems throughout the tropics and remains a major plant nutrient constraint In this respect, the Ethiopian soils are similar to the other agricultural soils of the tropics being generally low in P [5,6,7,8] and P is one of the limiting elements in crop production in the highlands of Ethiopia. P supply is apparently essential in the management and sustainability of upland land use systems in the tropical environment [9,10,11,12]

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Conclusion