EFFECT OF SOLAR RADIATION INTENSITY ON THE VEGETATIVE GROWTH AND YIELD OF COFFEE

Abstract

Tn this study, four ecological factors were observed: solar radiation, air temperature, relative humidity and soil moisture. Of the four, solar radiation fluctuates more than any other and undoubtedly the other threefactors are influenced by solar radiation to a great extent. 1—Solar radiation varies widely with season and year. 2—The greatest intensity takes place during the months of June to September and the lowest from November to February. 3—The greatest intensity recorded under full sunlight was 1.91 gr. cal./ min./ cm.² and the lowest was 1.35 gr. cal./ min./ cm.². 4—The yearly average solar radiation under full sunlight was 144,754. 40 gr. cal./ cm.². 5—The cumulative radiation for the 3 years that lasted the experiment was 434,263.20 gr. cal./ cm.², under full sunlight. 6—Shade regulates solar radiation making it more uniform from one year to the other. 7-As solar radiation increases, growth and yield of coffee decrease. 8—Yield, and growth of coffee were definitely higher under 1/2 and 1/3 than under 2/3 and full sunlight. 9—Statistically significant differences in yield, were not found between plots with 1/2 and 1/3 sunlight. Growth was significantly higher under 1/3 exposure. 10—Radiation, produces distinctive formative effects on coffee. Plants under full sunlight were very weak, chlorotie and poorly developed. 11—Four ecological factors were measured: solar radiation, temperature, relative humidity and soil moisture. All are affected by radiation to a great extent, but other factors as vegetation have also some effect. 12—Solar radiation is negatively correlated with yields and growth. 13—Growth and yields are positively correlated. As expected low temperature and yield are associated and soil moisture acts independently in relation to growth. 14—Plants under full sunlight accumulated greater amounts of nitrogen and potash and to a less extent of phosphorous than under any other exposure. 15—An average of 53,143.20 gram calories per square centimeter per year is the optimum cumulative solar radiation for yield and growth of coffee. This amount is obtainable under natural shade of Guaba trees (Inga Inga) planted at not less than 16 x 16 feet.