Effect of plant height on microclimate, evapotranspiration and water use efficiency of a banana plantation in a screenhouse
Uri Dicken1, Josef Tanny1, Shabtai Cohen1
1 Inst. Soil, Water & Environmental Sciences, Agricultural Research Organization
P36 in Poster presentations
The area of agricultural cultivation of vegetable crops and orchards in screenhouses and under screens is constantly increasing in Israel and other countries. The porous screens provide protection from unfavorable climatic conditions (e.g. hail, wind and supra-optimal radiation), reduce insect invasion and fruit sunburn, and allow savings of irrigation water. The aim of the present study was to investigate microclimate and crop water use during the initial growth stages of crops cultivated in screenhouses. This information will assist farmers in improving irrigation management of young plantations. Measurements were conducted in a screenhouse in northern Israel which covered a banana plantation. Screenhouse dimensions were 300 m x 190 m and 6 m high. Energy and CO2 flux measurements were made in the middle of the screenhouse using an eddy covariance system consisting of a three-axis ultra-sonic anemometer and an open path infra-red gas analyzer, positioned 4.25 m high. During the measurement period, plant height increased from 2.7 to 3.9 m. Additional instruments were installed to measure net radiation, air temperature and humidity and soil heat flux. Outside climatic conditions were measured by an external meteorological station. Energy balance closure analysis of half hourly covariances resulted in the following relation between available (X) and dissipated (Y) energy: Y = 0.71X - 2.09 (R2 = 0.79), generally supporting the validity of measured energy fluxes. Daily evapotranspiration rose during the measurement period from about 2.2 mm d-1 for the smaller plants, up to about 3.4 mm d-1 for the taller plants. A Penman-Monteith evapotranspiration model, modified for the screenhouse conditions, was in general agreement with the measurements, especially for the taller plants. The increase in net CO2 consumption was 2-fold during the same period, from about 10.7 g m-2 d-1 to about 21.5 g m-2 d-1. Thus water use efficiency, defined as the ratio between net vertical fluxes of CO2 and water vapor, was higher for taller than for smaller plants. Diurnal courses of CO2 concentration above the plants showed significantly lower concentration for the taller plants as compared with the smaller plants. This corresponds well with the increase in CO2 flux with plant height. Diurnal courses of the difference in air absolute humidity between inside and outside showed a significantly larger humidity difference for the taller than the smaller plants. Ventilation rate was estimated using the mass balance approach; it is demonstrated that the taller plants reduce the air exchange rate of the screenhouse as compared with the smaller plants, presumably due to their higher resistance to air flow.
Full presentation file: fp_P36 (07.12.2009 13:57)