Root distribution and water use in coffee shaded with Tabebuia rosea Bertol. and Simarouba glauca DC. compared to full sun coffee in sub-optimal environmental conditions.

Root niche differentiation for optimal exploitation of resources was found in an arabica coffee agroforestry system in Nicaragua. Rooting behavior was compared in both unshaded (FS) and shaded (AFS) coffee combined with two previously untested tropical timber species (deciduous Tabebuia rosea Bertol. and evergreen Simarouba glauca DC.). The predominant andisol possesses a compacted soil layer (talpetate). The study was conducted in sub-optimal environmental conditions for coffee cultivation (455 m.a.s.l., annual mean 27 °C, 1300 mm rainfall/year, 6 months dry season) in Nicaragua. Twelve and five trenches 200 cm deep were dug in AFS and FS respectively. Roots per unit area were counted on two perpendicular soil faces. Volumetric water was measured continuously over 2 years by using 45 reflectometers in different soil layers. The talpetate varied greatly in depth, thickness and physical structure. Coffee fine roots were more abundant than tree roots and were concentrated in the shallower strata (0?80 cm) whilst tree roots proliferated more below 100 cm. The S. glauca root system was denser below 100 cm than T. rosea root system. There was no meaningful difference in coffee root counts in FS and under T. rosea, but coffee root counts were higher near S. glauca trees. 2012 and 2014 had mild dry seasons and whole profile soil water content was similar in FS and AFS, but in the 2013 severe dry period volumetric water and water uptake were lower in AFS than in FS. This indicates that the normal advantage of greater soil exploration in AFS was cancelled presumably due to continued water uptake by deep rooting trees whereas the FS still had available water.