Photosynthetically Active Radiation to Total Solar Radiation Top Canopy Ratio in Tea (Camellia sinensis [L.] O. Kuntze) Genotypes in the Kenyan Highlands

Abstract

Kenya’s leading cash crop is tea. It engages over 4 million Kenyans (about 10%) in gainful employment. Tea is the single largest export commodity, accounting for 26% of the country's total export. It earned the country US$ 1.23 billion in foreign exchange in 2017. Tea production is, however, affected by photosynthesis. The positive gains made by the tea sector can only be achieved through increased yield facilitated by photosynthetic process. Determination of photosynthetically active radiation (PAR) to total solar radiation (RS) ratio is essential in evaluating the ability of tea genotypes to efficiently convert solar to chemical energy for enhanced yield output. PAR:RS has been measured at low altitude and temperate regions only, but none has been reported in the tea growing highlands of Kenya. The current study investigated PAR:RS ratio on top of tea (Camellia sinensis) canopy over Kenyan highlands using the equation Qp=ɛRs. A split-plot layout study was conducted at three sites differing in altitude and climatic conditions in Kenya: Kangaita (0O30’S and 37O16’E, 2100 m.a.s.l.), Kipkebe (0O17’S and 35O3’E, 1740 m.a.s.l.), and Timbilil reference site (0O22'S, 35O21'E, 2200 m.a.s.l.). Four tea genotypes of commercial and scientific interest in Kenya: AHP SC 31/37, EPK TN14-3, TRFK 301/5 and TRFK 31/8, were studied. Statistical analysis was done using two-way ANOVA (P=0.05) for split plot design. The study calculated top canopy constant of PAR:RS ratio to be 0.45, SED±0.0243, and recommended this constant to be used in tea-growing highland regions of Africa to evaluate genotypes for radiation use efficiency.Kenya’s leading cash crop is tea. It engages over 4 million Kenyans (about 10%) in gainful employment. Tea is the single largest export commodity, accounting for 26% of the country's total export. It earned the country US$ 1.23 billion in foreign exchange in 2017. Tea production is, however, affected by photosynthesis. The positive gains made by the tea sector can only be achieved through increased yield facilitated by photosynthetic process. Determination of photosynthetically active radiation (PAR) to total solar radiation (RS) ratio is essential in evaluating the ability of tea genotypes to efficiently convert solar to chemical energy for enhanced yield output. PAR:RS has been measured at low altitude and temperate regions only, but none has been reported in the tea growing highlands of Kenya. The current study investigated PAR:RS ratio on top of tea (Camellia sinensis) canopy over Kenyan highlands using the equation Qp=ɛRs. A split-plot layout study was conducted at three sites differing in altitude and climatic conditions in Kenya: Kangaita (0O30’S and 37O16’E, 2100 m.a.s.l.), Kipkebe (0O17’S and 35O3’E, 1740 m.a.s.l.), and Timbilil reference site (0O22'S, 35O21'E, 2200 m.a.s.l.). Four tea genotypes of commercial and scientific interest in Kenya: AHP SC 31/37, EPK TN14-3, TRFK 301/5 and TRFK 31/8, were studied. Statistical analysis was done using two-way ANOVA (P=0.05) for split plot design. The study calculated top canopy constant of PAR:RS ratio to be 0.45, SED±0.0243, and recommended this constant to be used in tea-growing highland regions of Africa to evaluate genotypes for radiation use efficiency.