last final thesis of umer

The maize seeds were planted three weeks before the planting of cowpea varieties at a spacing of
80 cm and 25 cm between and within rows, respectively for both sole and intercropping maize and
the rows for cowpea varieties were separated 40 cm from each other. The blocks and plots were
separated by 1m and 0.5 m, respectively.
3.5. Soil Sampling and Analysis
Before planting, soil samples were taken in zigzag manner randomly from the experimental site
from ten locations at a depth of 20 cm using an auger based on procedures described by Munson
and Nelson (1993) and the samples were mixed thoroughly to produce one representative
composite sample. About 1.0 kg of composite sample was taken (using polyethylene bag) to
Haramaya University soil laboratory for testing total nitrogen, available phosphorous, cation
exchange capacity (CEC), organic matter, pH and to determine soil textural class.
Soil organic carbon (SOC) was estimated for organic matter determination by wet digestion
method and organic matter was calculated by multiplying the SOC% by factor 1.724 as described
by (source). The soil pH was measured potentiometrically in 1:2.5 soil-water suspensions with
standard glass electrode pH meter.
The cation exchange capacity (CEC) was measured using 1 M ammonium acetate washed with
ethanol and the adsorbed ammonium was replaced by sodium (Na). Then, the CEC was determined
titrimetrically by distillation of ammonia that was displaced by Na. The proportion of the soil
particles was analyzed by Bouyoucos Hydrometer Method and the soil textural class was
determined using the textural triangle of USDA system. Total N in the soil was determined by the
Kjeldahl method (Dewis and Freitas, 1975). Available P was determined by the Olsen's method
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