, Volume 19, Issue 1, pp 65-80

Some significance of soil organic phosphorus mineralization in the phosphorus nutrition of cocoa in Ghana

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Summary

1. Soil samples from a 22 NP:KMg factorial experiment, in which yield response of cocoa to NP was highly correlated to organic phosphorus content of the 0–2″ layer, were studied.

2. It was found that the organic phosphorus content ranged from 46.0 to 69.5 per cent of the total phosphorus and was correlated to the percentage total nitrogen, total phosphorus, organic carbon and pH.

3. Incubation of the soils at 50 per cent of their water holding capacity and a temperature of 27°C for periods of 14, 28, 42, 56, and 70 days resulted in the average mineralization of organic phosphorus equivalent to 4,0. 13.6, 38.2, 50.0, and 54.0 pounds P per acre respectively.

4. More organic phosphorus was mineralized at 50°C than at 27° or 40°C.

5. The percentage of organic phosphorus mineralized was generally higher in the plots where NP had been applied.

6. Laboratory application of nitrogen or phosphorus to the soils before incubation resulted in greater mineralization. The effect of nitrogen and phosphorus together was greater than in the presence of nitrogen alone but only in a few cases was it greater than in the presence of phosphorus alone. The effect of nitrogen and phosphorus was not additive.

7. It is concluded that although the organic phosphorus increased in the NP-treated plots, increased mineralization occurred concurrently; and the effect of nitrogen and phosphorus application in increasing the mineralization of the soil organic phosphorus during laboratory incubation explained the high correlation found between cocoa yield response and organic phosphorus content of the top soil.