Abstract:
The research was conducted at the crop plantations of Akenten Appiah Minkah
University of Skill training and Entreprenuarial Development (AMUSTED –
Mampong in the forest-savannah transition agro-ecological zone of Ghana. The
objective of the research was to assess the seasonal variations in litter fall, soil carbon
accumulation and hydro-physical properties of soils under different agricultural land
use. The experiment was a 5 × 6 factorial, laid in a randomized complete block
design, with 5 different land uses and 6 distinct seasons. The land uses were forest
stand, cocoa plantation, coffee plantation, cashew plantation and mango plantation
while the seasons were dry season 2016, major rainy 2016, minor rainy 2016, dry
season 2017, major rainy 2017 and minor rainy 2017. A field test was conducted to
measure soil bulk density, volumetric moisture content, total porosity, air-filled
porosity, degree of saturation and aggregate stability of soils under the different land
uses. Cumulative infiltration, infiltration rate, sorptivity, steady state infiltrability and
saturated hydraulic conductivity were also evaluated. For carbon accumulation,
quantity of litter fall, soc, soil carbon stocks and soil carbon sequestration were
measured. A laboratory analysis was carried out to measure total nitrogen,
phosphorus, pH, exchangeable bases like calcium, magnesium, potassium. Microbial
biomass (Cmic, Nmic and Pmic), microbial quotient (qCmic, qNmic and qPmic) and
microbial biomass ratios (Cmic/Nmic, Cmic/Pmic and Nmic/Pmic) were all measured. The
bulk densities of soils under the different land uses were significantly different
(p<0.05) from each other, in the order mango > cashew > coffee > cocoa > forest.
Both the soil gravimetric and volumetric moisture content differed significantly
among land uses, with cashew and coffee recording the highest and lowest values in
both instances, respectively. Significant (p<0.05) seasonal variations in soil moisture
were observed in the order MNRS2017 > MNRS2016 > MRS2017 > MRS2016 >
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DS2017 > DS2016. The study showed, significant difference in total porosity, airfilled
porosity and degree of saturation of the different land uses and seasonal
variations, with aeration decreasing with increased rainfall amount. Aggregate
stability was significantly different among the different land uses and season.
Aggregate stability gradually improved over seasons by 1.5 % to 11.1 % from season
DS2016 to MNRS2017. Hydrological and hydraulic properties of soils under the
different land uses were significantly different from each other. Seasonal cumulative
infiltration amount and hydraulic conductivity of soils ranged from and 90.2 to 154.1
mm and 0.036 to 0.077 mm s-1, respectively. Litter fall significantly differed among
the different land uses, forest stand (3.28 t/ha) and mango plantation (2.27 t/ha)
recorded the highest and lowest. Significant seasonal variations of litter fall were
recorded, with DS2017 (4.06 t/ha) and MRS2016 (1.80 t/ha) recording the highest and
lowest, respectively. Soil carbon stocks and soil carbon sequestration was highest
(48.04 Mg C/ha and 179.2 CO2 Mg/ha) and lowest (45.7 Mg C/ha and 167.7 CO2
Mg/ha) in mango plantation and forest stand, respectively. Total nitrogen, available
phosphorus, potassium, magnesium, calcium and pH were significantly different
among the different land uses. Soil microbial biomass (Cmic, Nmic and Pmic) which
ranged from 151.3 to 323.8 mg/kg, 22.28 to 47.32 mg/kg and 7.89 to 25.5 mg/kg,
respectively differed significantly among the different land uses and seasons.
Microbial quotients (qCmic, qNmc and qPmic) decreased in the dry seasons (DS2016
and DS2017), while it was highest in the minor rainy reasons (MNRS2016 and
MNRS2017). It is recommended that, mango, cashew, cocoa and coffee could be used
to store and sequester as much carbon as the forest when they are properly managed.
Coffee > cocoa > cashew > mango improved soil hydrological and hydraulic
properties in this order of efficiency.
Description:
A thesis in the Department of Crop and Soil Sciences Education, Faculty of Agriculture Education, submitted to the School of Graduate Studies in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy (Soil Science) in the University of Education, Winneba
JUNE, 2022