Este trabalho foi conduzido em ambiente protegido (AE) e natural (AN), e teve como objetivo avaliar o desenvolvimento e quantificar a ação dos elementos meteorológicos e graus-dia sobre o crescimento da alface em duas épocas diferentes. O trabalho de pesquisa foi desenvolvido na Empresa Estadual de Pesquisa Agropecuária da Paraíba -EMEPA, nos períodos de 30/05 a 08/08/2007 (Inverno) e 10/09 a 22/11/2007 (Primavera), utilizando-se a alface tipo Americana Irene. As temperaturas médias do ar no AE foram sempre maiores que no AN nos dois experimentos. Os valores de umidade relativa média do ar obtida no AN foram sempre maiores que os do AE. Os maiores valores de graus-dia no AE acarretaram na redução do ciclo e da fitomassa seca total da alface. O ambiente protegido proporciona um micro-clima favorável ao desenvolvimento da cultura, antecipando a colheita em uma semana, nas duas épocas de cultivo, e no inverno oferece as melhores condições energéticas para o crescimento e desenvolvimento desta cultivar.Palavras-chave: Lactuca sativa, ambiente protegido e natural, estações do ano.Cabbage lettuce development based on the environment, season and degree-days
ABSTRACT. Results of a climatological study of soil moisture under corn crop at Campina Grande (NE Brazil) are presented in this paper. Daily values of available moisture content during the crop growing period are evaluated for a period of 25 years. A six zone versatile soil moisture budget model is used for this purpose and approximately 5. 7.5, 12.5, 25, 25 and 25% of the available water capacity (AWC) are attributed to zones one to six respectively. Different root activity coefficients are assumed for the six zones in different growth stages and the dependence of these coefficients on moisture content is taken into consideration. The same moisture releasing characteristics are assumed for all soil zones. On rainy days moisture loss due to evapotranspiration is assumed to take place before precipitation. Four AWC values and three corn growing periods between March and September are considered in this study. A first order Markov chain model is applied to the daily soil moisture data. Soil moisture averages and probabilities are used to identify the optimum growing period for corn at this station. The irrigation requirements of the crop are briefly discussed.
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