Rogério Teixeira de Faria

Photosynthesis of individual leaves in a coffee plant

The great variability in income irradiance over a plant canopy makes difficult the comparison of photosynthesis rates among leaves in a plant and their integration. In this study, photosynthetical rates of ten different leaves of a coffee plant were obtained during a day. The daily variation in photosynthetic rates showed a peak between 7:00 h and 9:00 h with higher values measured for the leaves positioned at the sunrise direction and northern orientation. Lower values were consistently observed for leaves at inner position of the plant. After 9:00 h, despite the increase in photosynthetically active radiation, photosynthetic rates decreased steadily to reach negligible values at sunset. The reductions on photosynthesis rates can also be attributed to increasing stomatal resistance. Since number of leaves is highly variable in coffee plants, those results make evident how difficult is to integrate and estimate whole plant photosynthesis by taking the average of 10 leaves.

Calibração de duas sondas de nêutrons em condições de campo e laboratório

Two different methods were used to calibrate two neutron probes: model CPN 503DR which measures soil water content and CPN 501DR for soil density and water content. The use of drums to hold the soil in the calibration of neutron probe in laboratory condition was appropriate for high clay-content latosol. For low clay-content latosol, a loss of neutrons through the drums was detected. The linear regression equations, determined in both on-field and laboratory conditions for high clay-content latosols, presented slope coefficients similar to the one provided by the manufacturer which, though not determining the real value of soil water content, may be useful to detect the variations of water content in the field. The model CPN 501DR showed lower sensibility to determine the soil water content than the model CPN 503DR.