Temporal Crop Coefficients and Water Productivity of Lettuce (Lactuca sativa L.) Hydroponics In Planthouse

Abstract

Almost all countries in the world have used lettuce hydroponic cultivation in planthouses because it is appropriate for plant growth and production. The microclimate inside planthouse is an environmental factor that affects plant growth and development. Vegetables planted in the planthouse have a great deal of water requirement. Selecting a method with a more accurate estimation of crop evapotranspiration is a critical factor for efficient water management. In this research, the climates that are affecting the lettuce evapotranspiration with modification of floating hydroponic technique inside the planthouse were investigated. The objectives of this research are to figure out the microclimate, the appropriate model of the potential evapotranspiration, and the temporal crop coefficients and water productivity of lettuce grown using a floating hydroponic technique in a planthouse. Experimental planthouse uses 90% transparency of polycarbonate roofs and net walls, with the dimension is 9 x 3 x 4 m. Primary data collected in the form of water level, and climate data for both inside and outside the planthouse. ETp value was estimated using seven models of potential evapotranspiration and among those models, the most appropriate model is determined. The climate inside the planthouse was significantly different than that in the outside. In which during 40 days of lettuce cultivation, solar radiation and relative humidity in the inside were lower than in the outside, but the temperature inside was higher than the outside. Potential evapotranspiration inside the planthouse can be estimated precisely by Hargreaves model. Crop coefficient (Kc) changed with time forming a parabolic equation started at 0.7 then decreased to reach 0.4 then increase to 1.4. Lettuce productivity was 1114.6 g/m² having water productivity 29.58 g/l which was linearly related to the consumptive use of water by the plant.