| dc.description.abstract | The relationship between soi I factors (soil moisture, soil temperature and
soil nutrients), plant factors (stomatal conductance, leaf temperature, leaf area
index (LAI ) and photosynthetic rate) and environmental factors (diffuse and
global irradiance) was studied in a sunflower field. The sunflower was planted at
four density plots with plot 1 having a higher than normal and plots 3 and 4
having ~l lower than normal plant densities. Plot 2 had normal plant density and
acted ~lS control. Measurements of global and diffuse irradiance, photosynthetic
rate. photosynthetically active radiation (PAR), stomatal conductance and leaf
temperature were made in the upper and lower strata of sunflower canopy. Soil
moisture was measured weekly at 30cm, 40cm, 60cm and 1OOcm while soil
temperature was measured once a week at 5cm, 10cm and 20cm depths.
Measurements were done at three stages of crop growth. These were the
vegetative. reproductive and maturity stages.
The experimental site was located at the University of Nairobi, Kabete
Field Station, The field station is about 1800 metres A.S.L. and about 10 km north
of Nairobi. It is located at at 1(l lS'N, 3611 44'E. The station experiences two rainy
seasons. with the main rainy season being March-May (long rains) and October-
November (short rains).
The land was prepared for planting and subdivided into four equal plots of
9m by om The plots were 1m apart up the slope and 2m apart across the slope (cf.
fig . .:;).The land was planted with sunflower seeds (Hybrid 8998) on 1-4-97. No
fertiliser was applied to the plots. Weeding was done twice during the
experimental season; on 24-4-97 and on 26-5-97.
l.eaitemperature, stomatal conductance, PAR and photosynthetic rate
measurements were done using an Infrared Gas Analyser (lRGA). These were
done 1'01' three Jays during each of the three phenological stages of sunflower
growt Daily duration period of measurements was from 800-1700 hours local
time. The global and diffuse irradiance were measured at the same time as the
physiological parameters using Kipp solarimeters.
Results showed that leaf temperature increased from morning hours to
afternoon hours before decreasing slowly as sunset approached. Photosynthetic
rate and PAR were highest in late morn ing and early afternoon hours. Stomatal
conductance was highest in early morning and late afternoon hours. The average
soil temperature was higher at 5cm depth than at lOcm and 20cm depths.
However. in early morning hours. soil temperature at 5cm was lower than at the
other t\\0 depths. Global and diffuse irradiance in the upper strata of canopy were
independent of plant density. In the lower strata of canopy, the global and diffuse
irradiances decreased with increasing plant density. The irradiances were also
greater during the vegetative stage than during the reproductive and maturity
stages.
Results of yield assessment (above ground dry matter) and economic yield
sho« eel that plot 1 gave the highest yield for total above ground dry matter per
plot followed by the control (plot :2). Plots 3 and 4 recorded the lowest values both
on the above ground dry matter and economic yield per plot.
The plant physiological parameters did not reveal much about the effects of
planting density, as evidenced by the results of the analysis of variance. However,
the annual patterns presented for the various parameters shed some light on the
differences as manifested by the plant density. These differences were mostly
pronounced on irradiance (global and diffuse) below the sunflower canopy. The
irradiance decreased with increasing plant density. Soil temperature at all depths
also decreased with increasing plant density. | en |
