Tropical soils typically have low cation exchange capacity and nutrient contents. Both are enhanced by soil organic matter (SOM), which is thus particularly important for the fertility of these soils. In this study, we assessed the influence of urbanization on SOM, carbonate contents and pH of arable soils of Kumasi (Ghana, West Africa), since rapid urban sprawl is widespread in West Africa, whereby in many West African cities urban farming is pivotal to the food security of their population. Based on satellite imagery for the year 1986, we defined long-term and short-term urban arable soils, whereby long-term urban soils were urban already in 1986 (thus ≥30 years, as soil sampling took place in 2016), and short-term urban soils became urban afterwards (<30 years). We took 618 undisturbed topsoil samples (0-10 cm) from 206 urban arable fields. The factors land-use (maize fields) and soil (Ferric Acrisols) were kept largely constant. The fine-earth was analyzed for pH (water), carbonate contents, loss on ignition (LOI), total C (TC) and N (TN). SOM contents were obtained from LOI (SOM LOI). All element contents were transformed to bulk soil element stocks per m 2. Differences between short-term and long-term urban soils were identified by a set of linear mixed models. Coarse fragments were more abundant in the long-term (16%) compared to the short-term (10%) urban soils, because of solid municipal waste that accumulates over time in urban soils. TC and SOM LOI concentrations of the fine earth, pH and C/N ratios were all significantly higher in the long-term urban soils. SOC concentrations in the fine earth, as well as bulk soil stocks of TC, SOC, and SOM LOI were also higher in the long-term urban soils, but at a lower degree of confidence, due to variable bulk densities and contents of coarse fragments. We conclude that dumping of organic and inorganic waste (including ash, bones, egg shells, concrete and mortar) increases SOM stocks and soil pH, but also leads to accumulation of non-degradable solid materials (including plastic, metals etc.). These findings point to the need of an improved urban waste management system, separating degradable and non-degradable waste.

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Climatic parameters such as temperature, rainfall, wind speed, relative humidity and sunshine hours were used to assess reference evapotranspiration and potential crop evapotranspiration of selected crops. The Penmann Monteith method for calculation of Reference Evapotranspiration, which has been incorporated in CROPWAT software, was used. Test crops included rice, tomato and pepper, which were part of the major crops cultivated in the Botanga irrigation scheme. Research findings indicated that temperature (r = 0.653) played a crucial role in assessing reference evapotranspiration and potential evapotranspiration. Temperature was lowest during the months from July to September due to lower solar radiation and higher rainfall. The potential crop evapotranspiration of rice, tomato and pepper were 697, 533 and 427 mm/season respectively. Rice growers will require more water for irrigation to ensure higher production due to its high evapotranspiration rate.

Canola (Brassica napus), with its prominent yellow flowers, has unique spectral characteristics and necessitates special spectral indices to quantify the flowers. This study investigated four spectral indices for high-resolution RGB images for segmenting yellow flower pixels. The study compared vegetation indices to digitally quantify canola flower area to develop a seed yield prediction model. A small plot (2.75 m × 6 m) experiment was conducted at Kernen Research Farm, Saskatoon, where canola was grown under six row spacings and eight seeding rates with four replicates (192 plots). The flower canopy reflectance was imaged using a high-resolution (0.15 cm ground sampling distance) 100 MP iXU 1000 RGB sensor mounted on an unpiloted aerial vehicle (UAV). The spectral indices were evaluated for their efficiency in identifying canola flower pixels using linear discriminant analysis (LDA). Digitized flower pixel area was used as a predictor of seed yield to develop four models. Seventy percent of the data were used for model training and 30% for testing. Models were compared using performance metrics: coefficient of determination (R2) and root mean squared error (RMSE). The High-resolution Flowering Index (HrFI), a new flower index proposed in this study, was identified as the most accurate in detecting flower pixels, especially in high-resolution imagery containing within-canopy shadow pixels. There were strong, positive associations between digitized flower area and canola seed yield with the peak flowering timing having a greater R2 (0.82) compared to early flowering (0.72). Cumulative flower pixel area predicted 75% of yield. Our results indicate that the HrFI and Modified Yellowness Index (MYI) were better predictors of canola yield compared to the NDYI and RBNI (Red Blue Normalizing Index) as they were able to discriminate between canola petals and within-canopy shadows. We suggest further studies to evaluate the performance of the HrFI and MYI vegetation indices using medium-resolution UAV and satellite imagery.

Deforestation for conventional farming has affected soil quality (SQ) worldwide. The goal of our study was to evaluate the impact of land use change, from forest to subsistence farming, on SQ in Benin. Composite soils from forest, horticultural, agricultural, fallow, and degraded lands were collected to analyze for chemical and physical properties. Using inductive additive approach and principal component analysis (PCA), generalized (SQIg) and minimum dataset SQ (SQIMDS) indices were calculated. Results showed that upon conversion of forest, total organic carbon (TOC) decreased by more than 2 folds in fallow and degraded soils. A similar impact was observed on total nitrogen (TN). Soil cation exchange capacity (CEC) and base saturation (BS) were significantly higher under horticulture than in degraded lands. In contrast, carbon protection capacity (CPC) was significantly higher by 12-41% in forest soils compared to the lowest in degraded soils. Among the land uses, aggregate stability index (ASI) was, by far, the lowest (3.2%) in degraded soils and highest (7.5%) in horticulture soils. Soils under fallow and degraded lands had SQIg decreased by 5 to 16%, when compared with forest, indicating a significant SQ degradation. In contrast, SQIg under horticulture increased by 5%, suggesting a similar or even an improvement in SQ comparable to the forest. The PCA-based SQIMDS significantly and positively accounted for 70% of the variability in SQIg with a non-significant biasness (6 ± 3.8% at p<0.12). The TOC and CPC contributed most (20.9% and 21.1%) followed by clay (14.1%) and Ca +2 : (Mg +2 + K +1 + Na + ) (13.7%), TOC (11%), and ASI (10.5%) compared to lowest by K + (9.7%) to account for SQIMDS variability. Our results concluded that there was no significant difference between SQIg and SQIMDS, which justified our results to use SQIMDS detecting management-induced changes in SQ.

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O prof. Kwabena Nketia, após seus estudos fundamentais em Gana, transferiu-se, em 1944, para Londres, onde estudou Lingüística e Música Ocidental (isto é, teoria, musicologia e piano). Em 1949 retomou para sua terra natal onde assumiu uma posição de pesquisador de Música Africana, na Universidade de Gana, durante dez anos. Em 1958 recebeu uma bolsa da Rockfeller Foundation e foi estudar na Julliard School of Music, tendo entre outros professores, o compositor Henry Cowell. Em 1968, Nketia assumiu uma posição na UCLA. Em 1982, transfere-se de Los Angeles para a University of Pittsburgh onde trabalha até hoje. A atividade acadêmica do pesquisador, nos Estados Unidos, alternou-se com as atividades no lnstitute of African Studies da University of Ghana.