Amelioration of sandy soils in drought stricken areas through use of Ca-bentonite

Abstract

Soil moisture shortage is a major limiting factor to agricultural production in eastern Africa, in
view of increased drought incidences and seasonal rainfall variability. This study evaluated the
potential for Ca-bentonite (a 2:1 clay mineral) as a possible amendment for increased moisture
retention by sandy soils in drought stricken/prone areas in Uganda. The study was conducted both
in the greenhouse at NARL-Kawanda and in the field, Nakasongola district. In the greenhouse
(27-30oC), Ca-bentonite was mixed with a sandy soil in proportions of 0, 5, 10, 15 and 20% by
weight, replicated three times. The mixtures were watered to field capacity (30% water) then
maize (Longe V) planted and left to grow for 5 weeks without any additional water application.
Under field conditions, Ca-bentonite was applied on sandy soils in the drought-prone Lwabiyata
sub county, Nakasongola district in central Uganda. Treatments included: Ca-bentonite applied
at 0, 1.25 and 2.5 t ha-1; DAP at 0, 62.5 and 125 kg ha-1; urea at 0 and 60 kg ha-1; and farmyard
manure (FYM) at 0, 1.25 and 2.5 t ha-1, arranged in a randomised block design with three replicates.
Under greenhouse conditions, Ca-bentonite application significantly (P<0.05) increased the soil
moisture retention, pH, N, P, Ca and Mg content, and subsequently, maize dry matter yield.
Averaged over 2 seasons, field application of 2.5 t Ca-bentonite ha-1 increased maize grain yield by
37.6%. Yields were significantly (P<0.05) higher (79.8 to 82.0% above the control) where bentonite
(2.5 t ha-1) was combined with DAP (62.5 kgha-1 or FYM (2.5 tha-1). The results suggest that Cabentonite has potential as a soil amendment for moisture conservation, neutralising acidity, and
improving N, P, Ca and Mg content in sandy soils, and consequently support crop growth and
yield. Thus calcium bentonite presents a possible amelioration for sandy soils of low fertility in
drought stressed environments. It is thus a promising technology for climate change adaptation
in drought prone areas.