Affiliations: TTMI-Project, Department of Geography, University of
Nairobi, P.O. Box 30197, Nairobi, Kenya | TTMI-Project, Department of Environmental Sciences,
C.T. de Wit Graduate School of Production Ecology and Resource Conservation,
Wageningen University, Duivendaal 2, 6701 AP Wageningen, The Netherlands.
E-mail:Kees. [email protected] METAIR. WAU. NL | TTMI-Project, Department of Botany, University of
Nairobi, P.O. Box 30197, Nairobi, Kenya | TTMI-Project, Department of Meteorology, University of
Nairobi, P.O. Box 30197, Nairobi, Kenya
Note:  Corresponding author
Abstract: Six seasons of experiments in Machakos, Kenya, revealed that above
about 150 mm of rainfall, maize yields per row in alley cropped "replacement"
agroforestry (AF) plots, of Cassia siamea Lam. and maize (Zea mays, cv.
Katumani Composite B), may be expected to exceed those in the control (sole
maize) plots. Such yields were insufficient to compensate for the area "lost"
to the hedgerows. Below about 150 mm the control plots may be expected to
perform better. This result was due to competition for water. Greater
association of the fine roots of Cassia and maize was observed in the middle of
the alleys than near the hedgerows. Photosynthetic consequences of shading were
insignificant relative to other factors. In the alleys, reductions of soil
temperature due to shade in the western and eastern maize rows were higher than
in the middle row. Soil moisture extraction was higher in the AF than in the
control plots. In the AF plots, moisture extraction was greater under the
central maize rows than under those nearest the Cassia. Yield patterns followed
such soil temperature and soil moisture patterns. Maize transpiration and
photosynthetic rates were significantly higher in the control than in the AF
plots during a below-average rainy season but not during above-average rainy
seasons. It is concluded that alley cropping under semi-arid conditions should
be approached differently from the system worked on. It must at least provide
strong physical protection of crops and/or soils and have a strong economic
incentive to be of interest to the farmers.