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 CO2 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 CO2 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 CO2 emission was different for the different management practices (power tiller, bullock and manual tillage) of rice. Furthermore, the soil CO2 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.