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Crop evapotranspiration (ETc) was measured as evaporative heat flux from a drip-irrigated coffee (Coffea arabica) plantation with 5-year-old trees using the Bowen ratio-energy balance technique. Crop transpiration (T) was determined with the stem heat balance method. Irrigation requirements were determined by comparing the ETc and T with reference evapotranspiration (ETo) derived from the Penman-Monteith equation and expressed as the ETc/ETo (Kc) and T/ETo (Kcb) ratios. Also, relationships were established between ETc and T and class A pan evaporation (ECA). The influence of inter-row vegetation on ETc was analysed, since the measurements were taken in a period of transition between dry-wet seasons. The average Kc value obtained was 1.00. The strong coupling of coffee plants to atmospheric conditions and high sensitivity of coffee plants to large vapour pressure deficits and air/leaf temperatures caused variations in Kcb in relation to ETo. Kcb ranged from 0.67, when ETo exceeded 4 mm d−1, to 1.27 when ETo was less than 2 mm d−1. When vegetation did not occupy the inter-row ground spaces, T represented about 0.87ETc, but 0.68ETc when ground vegetation filled the inter-row spaces.

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Daily rainfall variability at a local scale (1,000 ha) was studied at Piracicaba, SP, Brazil, for the period of one year (1993)(1994), in order to better understand the process of soil water recharge. Coefficients of variation of daily data for ten observation points varied from 2.2 to 169.3% and the variability was independent of rain type, i.e. whether convective, frontal or of other origin. Data were not related to separation distances between observation points and it is concluded that one observation point does not represent areas as far as 1,000 to 2,500 m apart, for daily, monthly or even quarterly averages. Yearly totals for the ten observation points presented a coefficient of variation as low as 3.06%, indicating that all points can replace each other in annual terms.

Leaf vapor diffusive conductance (gl) and transpiration (T) measurements in an irrigated orchard of the acid lime "Tahiti" were carried out in a subtropical climatic condition in the State of São Paulo, Brazil. Measurements were made using steady-state null-balance porometers and were taken throughout the day, on several occasions from February to November, 1998. During September and October, measurements were performed on exposed and shaded young and fully expanded leaves, as well as on old leaves inside the tree canopy. The old leaves showed lower values of gl and T when compared to the other groups. In the other months, measurements were taken only with exposed and shaded fully expanded leaves. The highest values of gl and T were obtained from February to April. For exposed leaves gl was higher from early morning to midday, decreasing thereafter with some oscillation in the afternoon. Shaded leaves produced a pattern of increasing gl and T from 8:00-9:00 a.m. to midday, followed by a decrease when values matched those of the exposed leaves in the afternoon. In April, the first measurement in midmorning showed low gl and T values, increasing sharply in the exposed leaves until midday and then decreasing until the end of the afternoon. Between May and November, gl and T decreased sharply compared to the previous months. Boundary line and regression analysis were used to find the mathematical relationships between mean values of gl for the tree and photosynthetic photons flux density, temperature, and vapor pressure deficit of the air measured in the orchard. Based on this analysis, the reasons for the gl and T diurnal and annual variation patterns are discussed, with emphasis on the effects of atmospheric variables upon stomatal regulation.