Browsing by Author "Sheets, Fact."

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Comparison of quality attributes of mango fruits produced from two contrasting agro-ecological zones of Kenya
(Ruforum, 2014) Ouma, L.; Ambuko, J.; Shibairo, Solomon I.; Owino, WO.; Hutchinson, M.; Njuguna, J.; Books, Ruforum.; Sheets, Fact.; Oer, Ruforum.; Scarda, Ruforum.
Mango (Mangifera indica) is a tropical fruit adapted to a wide range of agro-ecological conditions. In Kenya, mango fruits are produced across various agro-ecological zones (AEZs); from sub-humid to semi-arid. The diverse production conditions found in these AEZs variably affects fruit growth and subsequently the postharvest qualities. This study was conducted to compare the quality attributes of two mango varieties (‘Apple’ and ‘Ngowe’) produced under two different AEZs. Embu County (a high potential AEZ) and Makueni County (a low potential AEZ) are major mango-producing counties in Kenya. The study was conducted over two seasons between 2013 and 2014. ‘Apple’ and ‘Ngowe’ mango fruits were harvested from the two AEZs at four successive maturity stages; from the earliest physiological maturity (stage 1) to the tree-ripened stage (stage 4). In stage 1 fruits, the flesh was mostly cream and had just started turning yellow around the seed. The subsequent maturity stages were determined at 10-day intervals from stage 1 as stages 2, 3 and 4. For all the maturity stages, initial quality attributes were determined immediately after harvest and the again at a predetermined end stage following ripening at ambient room conditions (Temperature: 25 ± 1 oC and RH: 60 ± 5%). The quality attributes determined include sugars (fructose, glucose, and sucrose), °Brix, %TTA, vitamin C, beta carotene and mineral nutrients (Potassium, Magnesium, Calcium). For sensory evaluation, diced fruits were scored for various attributes including acidity, sweetness, mouth feel, flavor, aroma, color and general acceptability by a panel of 33 untrained panelists. For all the parameters evaluated, there was significant interaction (Pd”0.05) between maturity stage, variety and AEZ. Levels of TTA decreased gradually with the stage of maturity irrespective of variety and AEZ. Overall, Embu fruits had higher initial TTA levels for all maturity stages. Although Apple fruits (all stages) had higher initial TTA, at the end of ripening TTA levels were relatively lower compared to Ngowe. Initial beta carotene levels increased while vitamin C levels decreased with maturity stage. Significantly higher beta carotene and vitamin C levels (initial and end stage) were observed in Makueni fruits. Initial and end stage Ca, Mg and K levels decreased with maturity stage, irrespective of variety or AEZ. Stage 1 and 2 fruits retained the highest Ca and Mg levels at the end stage. The highest sugar levels and end stage 0brix levels were observed in stage 4 fruits (regardless of AEZ and variety). Overall, Makueni fruits had relatively higher end stage 0brix levels compared to Embu fruits. In ‘apple’, Makueni fruits scored higher than Embu fruits for all the sensory attributes. On the contrary in ‘Ngowe’,
Modeling potential impact of climate change on sorghum and cowpea performance under different tillage and cropping systems in semi-arid areas of Kenya
(Ruforum, 2014) Onwonga, RN.; Kitinya, Kirina T.; Books, Ruforum.; Sheets, Fact.; Oer, Ruforum.; Scarda, Ruforum.
Field trials were carried out at Kambi ya Mawe location in Eastern Kenya during the long rains (LRS) of 2010 and short rains (SRS) of 2010/2011, to evaluate effect of tillage and cropping system on performance of sorghum (Sorghum bicolor L. Moench) and cowpea (Vigna unguiculata (L.) Walp). The experimental layout was a randomised complete block design with a split arrangement. The main plots were three tillage practices (Tie-ridge-TR, Sub soilingSR and Ox plough-OP) and split plots were four cropping systems (sole sorghum, sole cowpea, sorghum-cowpea intercrop and sorghum rotation). Surface roughness, soil moisture and yields were measured. The Agricultural Production System Simulator model (APSIM) was used to assess the potential impact of climate change on sorghum and cowpea yields. Effect of the following climatic scenarios on crop performances was considered, base temperature (To), elevated temperatures by 1oC (T1), 2oC (T2) and 3oC (T3), base rainfall (Ro) and 10% reduction in rainfall (R1 ) and their combined effect. For Cowpea, Carbon dioxide (CO2 ) fertilisation at 450ppm and 700ppm and their combination with T2 and T3 and R1 were also examined. Soil surface roughness as a result of different tillage practices had a significant effect (p< 0.05) on soil moisture. Soil surface roughness was 72, 29 and 25% for TR, SR and OP, respectively. Cropping season and tillage-cropping system interaction also resulted in significant difference in soil moisture (p< 0.05). Maximum (1.96 t ha-1) and minimum (0.36 t ha-1) grain yield were achieved under TR during the SRS and OP during the LRS, respectively. Intercropping led to a significant (p<0.05) reduction in yield by more than 50% in cowpea (OP and SR) and sorghum (OP) grain yields during the SRS. However, intercropping evaluation using Land Equivalent Ratio method showed that it was still superior to mono-cropping as both biomass and grain yields were greater than one. The APSIM model output and the observed yields for sorghum biomass showed no significant difference (p= 0.54), indicative of a good model performance. However, simulated yields during LRS exceeded the observed yields despite having high correlation coefficient (R2=0.74). The model performance on predicting cowpea grain yield was poor (R2=0.02). There was only a 6% difference in sorghum grain yield during SRS. Temperature and rainfall changes resulted in an average percentage reduction in biomass and grain yields (t ha-1) of 5.5 and 5.6 for sorghum and 17 and 23 for cowpea. Elevated CO2 concentration of 450 ppm had a positive effect on cowpea biomass production, showing an increase of 7 and 0.8% in biomass following temperature increase of 2oC and 3oC, respectively. Higher temperatures accelerated crop growth, leading to early maturity.