『Abstract
The availability of native phosphorus (P) in Zambian Alfisols,
Utisols and Oxisols, the dominant agricultural soils in the country,
is relatively low. Given that crop production in the country is
dominated by low external input practices, native P remains important
to plant P nutrition in many locations. There is a dearth of knowledge
about soil P distribution, transformations and fertility in Zambia.
The distribution of total P, organic P, inorganic P [aluminum
plus iron P (Al+Fe-P) and calcium P (Ca-P)] and occluded P was
determined in twenty soils of Zambia belonging to several soil
orders and originating from different agro-ecological zones. Total
P in the soils were observed to be similar to those found in more
productive regions, ranging from 126 mg kg-1 in the
Bulozi Inceptisol to 742 mg kg-1 in the Malashi Alfisol.
There was overlap in total P contents determined among soil orders.
This is attributed to interruptions in the pedogenesis process
whereby new material was deposited on more weathered old basement
complex. Soil organic P content was relatively low (3-175 mg kg-1)
and constituted an average of 15% total P. The ratio of organic
carbon to organic P was generally less than 200, suggesting the
potential for significant mineralization of organic P. The Al+Fe-P
was the dominant inorganic P pool because of high Al and Fe oxides
contents of these soils. The range of Al+Fe-P was 1-246 mg kg-1
while Ca-P was 1-78 mg kg-1. A disproportionately high
fraction of total P (18088%) was tied up in the occluded P pool.
It was observed that clay content, and Fe plus Al oxides contents
of the soils explained 62 and 51%, respectively of the variation
in occluded P. Therefore the presence of high amounts of oxides
and the rate of soil weathering due to high temperatures and moisture
in part explain the low availability of P in Zambian soils.
Keywords: Fractionation; Phosphorus; Soil order; Zambia』
1. Introduction
2. Materials and methods
2.1. Site description
2.2. Soil analysis
2.3. Phosphorus fraction analysis
2.3.1. Total and organic P
2.3.2. Inorganic-P and occluded-P
2.4. Statistical analysis
3. Results and discussion
3.1. Soil properties
3.2. Soil phosphorus fractions
3.2.1. Total P
3.2.2. Organic P
3.2.3. Inorganic P
3.2.4. Occluded P
3.3. Relationships between soil properties and soil phosphorus
pools
4. Conclusions
Acknowledgements
References