Effect of cordia africana lam shade on physiology, yield and quality of arabica coffee
Coffee (Coffea arabica L.) is native to the shaded forests of Southern Ethiopia where it evolved as an understory crop. It was originally thought to be shade obligatory, but it has been shown to perform well in full sun. The question of whether shade is beneficial or not, has been debated and studied over the years mainly in Central and South America and to some extent in Southeast Asia. In Kenya, however, information on the effects of natural shade on coffee is scarce. Therefore a study was conducted at the Kenya Agricultural and Livestock Research Organization-Coffee Research Institute‟s (KALRO-CRI) demonstration farm in Namwela and two neighbouring small-holder farms from 2010 to 2012, with the following objectives: 1. to determine the effect of Cordia africana shade on physiological parameters of coffee plants namely transpiration, stomatal conductance and photosynthetic rate; 2. to determine the effect of Cordia africana shade on soil nutrient levels and nutrient uptake in coffee plants; 3. to assess the impact of Cordia africana shade and agronomic management on yield and quality of coffee; 4. to determine the effect of Cordia africana shade and agronomic management on the biochemical components of coffee beans. Coffea arabica L. variety, K7 and cordia (Cordia africana Lam.) shade tree were used in the study. In objective 1, photosynthetically active radiation (PAR), leaf temperature, transpiration, stomatal conductance and photosynthetic rate were assessed in coffee plants that were at regular distances from the shade tree trunk namely, 0 – 1.5 m, 1.5 – 3.0 m, 3.0 – 4.5 m, 4.5 – 6.0 m and > 6.0 m (full sun). In the first objective, the experiment was laid out as a randomized complete block design with seven replicates. Measurements of the physiological parameters were taken in the early morning, at midday and late afternoon on intact plants in the field during two consecutive coffee growing seasons in the dry and rainy periods. In objective 2, Soil and plant nutrient analyses were carried out using standard procedures. xviii In objective 3, the effect of Cordia africana shade on coffee growth, yield and raw bean quality under different agronomic management levels was studied in the three farms; Coffee Research Institute‟s demonstration farm under high management, and two small holder farms under medium and low management respectively. The shade level was represented by distances from the shade tree trunk, 0 – 1.5 m, 1.5 – 3.0 m, 3.0 – 4.5 m, 4.5 – 6.0 m and > 6.0 m (full sun). The experimental design was a split plot, with management level as main plot treatment and shading levels represented as the sub-plot. To determine biochemical components and beverage quality (objective 4) fully ripe cherries were harvested wet processed and the wet parchment dried to final moisture content of 10.5 to 11%. Caffeine, trigonelline and total chlorogenic acids (CGA), oil and sucrose were determined using standard methodologies. Fragrance/aroma, flavour, aftertaste, acidity, body, balance and overall beverage quality were evaluated by a panel of seven judges. Photosynthetically active radiation (PAR) was highest in full sun in both the dry and rainy periods. It was also higher at midday in the dry period, however, no apparent trend was observed during the rainy period. Leaf temperature was highest at midday during the dry and rainy periods. The effect of shade on leaf temperature was only significant in the dry period. Generally, the rate of transpiration was significantly higher in shaded coffee in the morning, during both dry and rainy periods. Shade significantly increased stomatal conductance during the rainy period. Photosynthetic rates were generally higher, in the morning hours, in shaded coffee during the dry period. Shaded coffee recorded longer primary branch length extension, but had lower number of nodes than coffee in full sun. Shading significantly increased the content of the major soil nutrients namely N, P, K and Mg. There was, however, a reduction of soil Ca content under shade. Leaf nutrient accumulation was positively correlated with most major plant nutrients, except Ca. Coffee yields were significantly higher under high xix agronomic management than under medium and low agronomic management. Shaded coffee had significantly higher bean yields than un-shaded coffee under medium and low management levels. The % grade „A‟ beans among shading levels in high and low management levels were not different. Coffee at higher shading levels, 0 – 1.5 m and 1.5 – 3.0 m away from the shade tree trunk (equivalent to 80 and 70% shade) had significantly higher % grade „A‟ coffee beans than un-shaded trees. Caffeine, oil, and trigonelline contents were higher in shaded coffee than in unshaded coffee. Sucrose was higher in coffee under medium and low management level. Shading significantly reduced sucrose content. Most of the biochemical components were positively correlated with shade and management levels. This showed the possibility of manipulating the two parameters to enhance the quality of coffee. The beverage quality attributes, except for acidity and balance, on the other hand were mostly unaffected by shade levels and management , nevertheless, trends showed that most of the parameters had higher scores in shade than in full sun. Shade was positively correlated with all sensory variables. The findings of this study indicate that shade can be used to increase coffee yields with no adverse effect on raw bean and beverage quality, particularly under smallholder low input conditions. The use of shade trees could also be beneficial in terms of diversifying farmers‟ incomes through provision of timber and other products. Overall, use of shade trees even under conditions of high agronomic management would enhance biodiversity and promote environmental sustainability.