Abstract:
The effect of irrigation, nitrogen fertiliser and planting density on green leaf area index
under field conditions was determined. Field experiments were carried out at Sonning
(UK)in summer 1992,and two experiments at Kabete, Kenya from November 1992to
February 1993(K1)and from February to May 1993(K2)using beans (Phaseolus vulgaris
var. Mwezi Moja). The treatments included two irrigation levels (not irrigated and
irrigated), two fertiliser levels (no fertiliser and 100 kg N ha-1) and two planting
densities (22and 44 m-2) arranged in a split-split plot design. Irrigation was done using
a drip system at Sonning and watering cans at K1 and K2. Changes in individual leaf
length of the first four middle trifoliate leaflets, the number of leaves per plant and the
number of branches per plant were monitored. Leaf area index was largest at Sonning
and least at K2.Although irrigation did not have a significant effect on LAI in the three
experiments, it was important in maintaining leaf area late in the season at Sonning.
Nitrogen increased LA! at Sonning and at K1 when water was not limiting. Nitrogen
effect on LA! depended on the growth stage of the crop and total seasonal rainfall.
Nitrogen effect on LAI was through increased leaf emergence and extension rate. High
planting density increased LAI if water and N supply were not limiting. Leaves at
Sonning were thin and wide (photoperiod effect) but small and thickest at Kabete in
the dry season (water stress effect). Effective irrigation (above atmospheric evaporation
demand), N application and judicious planting density increased LAL
