A very important question of sustainability can only be addressed by evaluating agronomic yield data in relation to economic feasibility and soil properties. Furthermore, agronomic experiments conducted on small plots do not provide adequate information on economic feasibility of a highly labor-intensive system. Many agronomic experiments are conducted without the supporting data on soil analysis. The following discussion is based on comparative evaluation of results of the present study with those already published in the literature.
(a) Agronomic yield
The present experiments indicated that the grain yield declined with cultivation duration at the rate of 340kg/ha/yr for maize and 96kg/ha/yr for cowpea. The yield decline with time, however, was more consistent in cowpea than maize. For the six year period as a whole, maize grain yield from alley cropping systems was about 10% lower than that of control. The yield decline in cowpea was at 17% per year.
Comparing the results of present studies with those of others from elsewhere provide a useful evaluation of the alley cropping system. The data by showed that applications of 80kg/ha of N caused more drastic increase in maize yield than addition of Leucaena prunings. Furthermore, prunings had no effect on maize yield in the fourth consecutive year. The data on cassava yield from an experiment by also showed that increase in cassava yield was more drastic with fertilizer than with prunings of Acio barterii. Furthermore, prunings applied with fertilizer had no effect whatsoever.
Somewhat encouraging example of the effects of alley cropping with Leucaena on yield of maize is available from the Philippines [O' Sullivan, [1985]. The data indicated a yield increase by Leucaena of 0.7 t/ha without fertilizer and 0.3 t/ha with fertilizer application. Also in Philippines, Watson and Laquihon [1985] observed that Leucaena hedgerows increased maize