As the liginin is not easily decomposiable, high linin content leaves takes realtively more time to decompose & release nutrients. Hence there may be chance for nutrients depletion over a period of time. In general AF system, fast growing, leguminous and easily decomposiable foliage trees preferred.

Mr Durai, thanks for the contribution. What i think is that due to the combined cropping of cocoa and kola. This delayed release of nutrient from lignified leaves of cocoa may be compensated for by the non/ less lignified leaves of kola which readily decompose and mineralize..

Interplanting cocoa and cola trees definitely enhances soil fertility status. Please refere the research work carried by ) O. Ekanade and N.E. Egbe (1990) in Agriculture, Ecosystems and Environment, 30 (1990) pp 337-346

2) Soil fertility status under different tree cropping system in a southwestern zone of Nigeria Clement O. Ogunkunle, Olusegun O. Awotoye Not. Sci. Biol 01/2011; 3:123-128

I agree with both comments, and would emphasize some that it depends on the timeframe that you are thinking of. I haven't worked with Cocoa and Cola, but have worked with several other tropical trees in various agroforestry systems. Because you trees to take a lot of fertility to grow they can deplete soils in the short term, but ultimately they add to the total storage and cycling of nutrients of a system and do increase fertility potential in the long term. It particularly depends what your baseline and starting point is when you ask if fertility is going to be increased.

Hi. I don't know much about these particular trees, but I do know that if you want your soil fertility to improve, then one must not use Glyphosate herbicides. See my essay: http://poisoningandlegalaction.com.au/human-health-and-pesticides.htm. Regards, Murray Thompson.