Water requirements and crop coefficients of tropical forest seedlings in different shading conditions

Necessidades hídricas e coeficientes de cultivo de mudas florestais tropicais em diferentes condições de sombreamento

ABSTRACT

The objective was to determine the crop evapotranspiration (ETc) and crop coefficients (Kc) of tropical forest seedlings over a 135-day cycle, in the climatic conditions of the Cerrado-Amazon transitional region (11º 51’ 08 “S; 55º 30’ 56” W; altitude of 371 m). Five native species (Tabebuia impetiginosa, Tabebuia roseoalba, Handroanthus chrysotrichus, Parkia pendula and Parkia platycephala) and one exotic species (Adenanthera pavonina) were evaluated in seven shading conditions: 35, 50 and 80% black nets (Polyolefin); green Frontinet^®, red ChromatiNet^® and blue ChromatiNet^® of 50% shading; and full sun. Reference evapotranspiration (ETo) was obtained by the Penman-Monteith FAO-56 method and the crop evapotranspiration of the seedlings (ETc) was given by daily weighing. The Kc values were obtained by dividing ETo by ETc. At 135 DAT, destructive analysis was performed to determine the leaf area. In full sun conditions, ETc varied from 3.9 (P. pendula) to 5.0 mm d^-1 (T. roseoalba). The increase in the shading percentage promotes reduction in leaf area, ETc and Kc. Colored nets with 50% shading generate similar water demands.

Key words:
evapotranspiration; irrigation management; leaf area; solar radiation