Soil carbon change and CO2 fluxes under different agricultural land use in the Vea catchment, Upper East Region of Ghana
Abstract
Soil organic carbon is an index for soil fertility and sustainable land management.
Monitoring soil respiration and carbon provide quantitative information on soil carbon
stocks at a given location. This study assessed soil carbon change across predominant
land-uses and soil types in the Vea catchment of Upper East Region, Ghana. The goal
was to assess soil carbon change and CO
2
emissions from selected (rice, maize, millet
and sorghum) cropping systems in the Vea catchment. To achieve this, farmers were
interviewed for information on cropping history; establish the proportion between
land use and soil type; determine crop yield components, yield and biomass for
selected crops under different tillage (i.e. power tiller, bullock and manual) and
amendment; estimate soil carbon stock; and determine the fractions and future trend
of soil carbon stock and measure soil CO2
flux using respiration chamber under
different land uses. The majority of the land is occupied by cropland about 41 % with
63 % of Leptosols, 52 % of Fluvisols and 46 % of Lixisols (i.e. the three main soil
type) being cultivated. The highest grain yield obtained was 5675 kg/ha, 1375 kg/ha
and 970 kg/ha for rice, maize and sorghum, respectively. The mean soil organic
carbon stock for the major land-uses obtained in the study area were 10.24 ± 1.2 t/ha
for cereals (maize and sorghum), 14.96 ± 2.4 t/ha for paddy irrigated rice 15.88 ± 2.1
t/ha for semi natural area, 16.53 ± 2.3 t/ha for grazing area, 18.5 ± 4.9 t/ha for
eucalyptus forest and 23.5 ± 7.1 t/ ha for paddy rain fed rice. Eucalyptus forest had
high carbon stock, but this carbon is mainly composed of the light fraction, which is a
non-stable fraction. The Introductory Carbon Balance Model (ICBM) simulation
revealed a future trend of soil carbon depletion of 8 - 15 % was obtained continuous
cereal (i.e. maize and sorghum) production with or without fertilisation with the
current management system. However, fertilised maize production in rotation with
groundnut will prevent the depletion of soil carbon stock. Soil CO
2
emission had
similar trends under the maize - kenaf and sorghum - kenaf cropping systems.
However, the cumulative soil CO2 emission for sorghum - kenaf cropping system was
higher (22 %) than that of maize - kenaf cropping system. The study also showed that
the trend of soil CO
2
emission was different for the different management practices
(power tiller, bullock and manual tillage) of rice. Furthermore, the soil CO
2
emission
was sensitive to soil moisture stress but not soil temperature for maize and sorghum
cropping systems. For high yield but low CO2
emission, rice cropping system with
bullock tillage and urea in deep placement (UDP) as amendment as well as power
tillage with NPK + urea application are the best options for climate change mitigation
for rainy and the dry season under irrigation, respectively. Therefore cereal-legume
rotation is one of the best ways to sustain SOC in the study area.
Description
A thesis submitted to the Department of Civil Engineering, College of Engineering in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Climate Change and Land Use,