Soil carbon stock dynamics of hedgerow intercropping and conventional soil management practices on a ferric acrisol in the semi-deciduous forest zone of Ghana

Soil carbon (C) storage on croplands has been described as a developmental strategy because the accumulation of soil C improves cropland productivity for the production of the needed food to feed the ever-increasing population of tropical Africa. The storage of C in the soil also reduces carbon dioxide (CO2) build up in the atmosphere with its attendant global warming reduction and other environmental benefits. In addition the accumulation of C in the soil provides that land users are able to benefit from C trading under the Clean Development Mechanism (CDM) as C stocks become a commodity for trading on the international market. The overall objectives of this study were to monitor soil C dynamics under hedgerow intercropping and other conventional cropland management practices, monitor the corresponding effect of soil C build up on cropland fertility and productivity as well as cropland quality as measured using Carbon Management Index (CMI) over the study period. This study was based on six seasons of field investigation on the carbon sequestration potential of the different soil management practices for the continuous production of maize on a Ferric acrisol within the semi-deciduous forest zone of Ghana. The hedgerow species studied under hedgerow intercropping (also known as alley cropping) was Gliricidia sepium. The types of cropland management systems studied included: continuous cropping with no fertilizer application and plant biomass burnt at the start of every season (CCBB); Continuous cropping with no fertilizer application and plant residue mulch (CCBM); Continuous cropping with full rate inorganic fertilizer application and plant residue mulch (CCMF); Alley cropping with pruning and plant residue mulch & no inorganic fertilizer application (ACPM); Alley cropping with pruning and plant residue mulch & half rate fertilizer application (ACPf); Alley cropping with pruning and plant residue mulch & full rate fertilizer application (ACPF); Alley cropping with pruning removed & full rate fertilizer application (ACPR). Soil C sequestration rate of 4.02 Mg C ha-1 year-1 was attainable under hedgerow intercropping adopted for continuous maize production on a Ferric acrisol, within the semi deciduous forest zone of Ghana. Highest soil C sequestration was recorded under hedgerow intercropping with no inorganic fertilizers application (ACPM). Higher doses of inorganic fertilizer application under hedgerows reduced soil C sequestration potential whilst under non-hedgerow conditions, inorganic fertilizer use improved soil C sequestration potential. Regular biomass burning and the removal of high quality Gliricidia pruning at the beginning of every cropping season depleted soil C stocks. In terms of cropland productivity improvement, six-season mean maize grain yield was highest at 5.30 Mg ha-1 on the fertilized non-hedgerow plot (CCMF) which was comparable to 5.20 Mg ha-1 obtained on the hedgerow plot with full rate inorganic fertilizer application (ACPF). Maize grain yield levels on the CCMF plot had however started to record significant decline by the end of the sixth season as compared to the levels recorded at the start of the study. In addition, the adoption of hedgerow intercropping was also able to reduce the inorganic fertilizer requirement by half for comparable and sustainable higher maize production of 5.00 Mg ha-1 in the semi deciduous zone of Ghana. Hedgerow intercropping improved long term maize yield even under reduced application of inorganic fertilizers thereby conserving energy resources and the environmental impact of agricultural production. The burning of plant residues at the beginning of every cropping season however reduced cropland productivity over the season. Hedgerow intercropping enhanced soil available P but reduced soil pH and exchangeable bases. Cropland quality assessed using CMI was highest under hedgerow intercropping with reduced inorganic fertilization whilst the other forms of hedgerow intercropping led to CMI reduction. The studied non-hedgerow plots however recorded high CMI levels which were expected to decline if the study has continued for a longer period. Cropland quality improvement recorded during the study was closely related to other known soil quality indicators as MBC/SOC ratio and LC. Therefore, the adoption of hedgerow intercropping for continuous and sustainable maize production improved soil C sequestration, ensured sustainable maize production and enhanced cropland quality of a Ferric acrisol within the semi deciduous forest zone of Ghana.

Source: KNUST