Use of radio-active phosphorus in determining the efficiency of fertilizer utilization by cacao plantation

Abstract

Both P32 labelled phosphate solution and superphosphate were used in studying (1) in situ root distribution and activity of 20 year old Amelonado cacao (Theobroma Cacao L.) during wet and dry seasons and (2) the efficiency of fertilizer utilization by the cacao plantation. The P32 content of the leaves was used to determine patterns of root activity. Uptake of P32 was greatest during the wet season and root activity highest within the upper 3 cm soil layer in both wet and dry season. Highest P32 activity was obtained at a distance of 120–160 cm and lowest at 91 cm from the base of the tree. For maximum utilization of phosphate fertilizer by a plantation of 20 year old Amelonado cacao, planted at 240 cm × 240 cm spacing, the fertilizer should be broadcast during the wet season. Under low soil moisture conditions, the placement of P32 labelled superphosphate provides information on relative availability of the fertilizer or soil phosphorus and does not necessarily reflect the activity of the root profile. Active roots of cacao tend to be more extensive and are capable of exploring a much larger area than hitherto expected. re]19740211