Browsing by Author "Dowuona, G.N."
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Item Farming system-induced variability of some soil properties in a sub-humid zone of Ghana(Plant and Soil, 2001-09) Atsivor, L.; Dowuona, G.N.; Adiku, S.G.K.This study assessed the effects of different farming systems, namely woodlot (WL), alley farming (AL), conventional tillage (CT) and natural fallow (NF) on the variability of organic carbon (OC) content and mean weight diameter (MWD) of a degraded Ferric Acrisol in the sub-humid zone of Ghana. The soils under woodlot accumulated the highest amount of organic carbon (18.6 g kg-1) with the least spatial variability apparently due to the greater additions of litter and minimum tillage. The conventionally tilled soil had the least OC content (13.1 g kg-1). Similar to the OC content, the woodlot soils also had the highest aggregate stability (MWD = 1.78 mm) and the least spatial variability. The stability of soil aggregates under the farming systems was greatly influenced by OC content; there was a good correlation between OC and MWD (r > 0.62**). Correlograms showed that OC and MWD are space dependent. The correlation length for OC under the different farming systems followed the order WL > NF > AL > CT, indicating that WL ensured a greater uniform distribution soil organic matter. The spatial distribution in MWD followed the same trend observed for OC. The MWD in the other farming systems was poorly related from point to point with shorter k-values, suggesting lack of uniformity due to low accumulation of OC. Generally, the woodlot system appeared to be a better, low-input restorer of soil productivity.Item Short-term effects of crop rotation, residue management, and soil water on carbon mineralization in a tropical cropping system(Plant and Soil, 2008-10) Adiku, S.G.K.; Narh, S.; Jones, J.W.; Laryea, K.B.; Dowuona, G.N.The purpose of this study was to investigate the short-term effects of maize (Zea mays)-fallow rotation, residue management, and soil water on carbon mineralization in a tropical cropping system in Ghana. After 15 months of the trial, maize-legume rotation treatments had significantly (P < 0.001) higher levels of potentially mineralizable carbon, C 0 (μg CO 2-C g-1) than maize-elephant grass (Pennisetum purpureum) rotations. The C 0 for maize-grass rotation treatments was significantly related to the biomass input (r = 0.95; P = 0.05), but that for the maize-legume rotation was not. The soil carbon mineralization rate constant, k (per day), was also significantly related to the rotation treatments (P < 0.001). The k values for maize-grass and maize-legume rotation treatments were 0.025 and 0.036 day-1 respectively. The initial carbon mineralization rate, m 0 (μg CO2-C g-1 day -1), was significantly (P < 0.001) related to the soil water content, θ. The m 0 ranged from 3.88 to 18.67 and from 2.30 to 15.35 μg CO2-C g-1 day-1 for maize-legume and maize-grass rotation treatments, respectively, when the soil water varied from 28% to 95% field capacity (FC). A simple soil water content (θ)-based factor, f w, formulated as: fw = [θ-θd/ θFC-θd], where θ d and θ FC were the air-dry and field capacity soil water content, respectively, adequately described the variation of the m 0 with respect to soil water (R 2 = 0.91; RMSE = 1.6). Such a simple relationship could be useful for SOC modeling under variable soil water conditions. © 2008 Springer Science+Business Media B.V.Item Simple formulation of the soil water effect on residue decomposition(Communications in Soil Science and Plant Analysis, 2010-02) Adiku, S.G.K.; Amon, N.K.; Jones, J.W.; Adjadeh, T.A.; Kumaga, F.K.; Dowuona, G.N.; Nartey, E.K.Soil water content, θ, is a major factor affecting residue decomposition, but simple formulation of this factor is often lacking. We observed that θ significantly (P < 0.001) affected the residue decomposition constant, kd· When θ varied from 0.09gg-1 to 0.23gg-1, kd ranged from 0.009 to 0.013d-1 and from 0.009 to 0.022d-1 for residues with carbon to nitrogen ratio (C/N) > 30 and C/N < 25, respectively. A θ factor was formulated in terms of the field capacity θFC and the air-dry θ d in the form fw = (θ - θd) / (θFC - θd), and this was used to modify the potential kd as θ varied. Coupling fw with a first-order residue decomposition equation resulted in the prediction of the decomposition of four residue types in the greenhouse (R2 = 0.94; relative root mean square error, RRMSE, = 0.06) and in the field (R2 = 0.93; RRMSE = 0.11). © Taylor & Francis Group, LLC.Item Simplifying the analysis of soil particle sizes. I. Test of the Sur and Kukal's modified hydrometer method(Communications in Soil Science and Plant Analysis, 2005-01) Adiku, S.G.K.; Osei, G.; Adjadeh, T.A.; Dowuona, G.N.This study tests the validity of the Sur and Kukal modified hydrometer method for particle size analysis on eight Ghanaian soils of varying texture. The method assumes that hydrometer readings at any time could be predicted from an exponential equation provided that two important parameters are known: the 4.5-min hydrometer reading (R4.5) and the exponent (B). In a series of sedimentation experiments conducted on each soil in this study, 11 hydrometer readings were taken between 40 s and 8 h. Some of these data were used to determine the value of the parameters R4.5 and the exponent B. The B values for the light textured soils were within the range of 4.2 × 10 -3 to 9.7 × 10-3 and were comparatively lower than those for the heavy textured soils (1.0 × 10-2 to 1.5 × 10-2). In addition, the R4.5 values were much lower for the light textured soils than for the heavy textured soils. Using these parameter values in the Sur and Kukal's equation enabled the prediction of the hydrometer readings at different times during the sedimentation process. The predicted 8-h hydrometer reading also was used to calculate the percent clay. A comparison between the observed and predicted hydrometer readings was satisfactory. The predicted percent clay also agreed very well with that observed for all soils (R2 = 0.96). It is concluded that the Sur and Kukal method indeed simplifies the determination procedure and yields acceptable results for a wide range of Ghanaian soils.