Agricultural Productivity


 Little is known about the behavior of tropical stone-line soils or

the influence they exert on agricultural systems which they support.

The paucity of internationally available literature on soils of the

tropics, in general, is well known. The habit of national governments

to establish research stations on a region's best soils frequently

limits the generation of knowledge concerning hillside and

agriculturally marginal soils (Zandstra et al.,1981).

 Lal, formerly of the International Institute of Tropical

Agriculture in Ibadin, Nigeria, has conducted several studies

investigating plant-root development and water availability on natural

and synthetic gravelly soils. Babaloa and Lal (1977a) evaluated the

effects of varying gravel concentrations on shoot growth and rooting

depth using soil/gravel mixtures in greenhouse pot studies. The weight

of corn shoots harvested after 21 d decreased by up to 50% as gravel

concentration increased from 10 to 75%. Rooting depth decreased only

slightly as gravel increased from 0 to 10%, but then decreased to 40% of

the non-gravel rooting depth as gravel increased to 25%. The rooting

depth decreased to 5% of the non-gravel rooting depth as the gravel

increased to 75%. Total root length was affected similarly. Shoot

weights increased by 20% as the depth to a 60%-gravel horizon increased

from 5 to 10 cm. Shoot tissue had a nonsignificant increase in

concentrations of N, P, and K as depth to the gravel horizon increased.

The researchers concluded that the gravel retarded rooting depth and

thereby decreased root exploitation of soil nutrients, resulting in

reduced nutrient uptake and consequent reduced overall growth.