-INTRODUÇÃOO estudo da transpiração das plantas interessa à agronomia sob diversos aspectos. O conhecimento, pelo menos aproximado, da quantidade de água retirada do solo, pela transpiração da planta, é uma necessidade básica na elaboração de projetos de irrigação. No caso do cafeeiro (Coíjea arábica L.), este Instituto já iniciou estudos agronômicos sobre a irrigação desta cultura. Pelos resultados preliminares e pela situação atual da lavoura, tudo indica que a irrigação dos cafezais se desenvolverá grandemente em futuro próximo. Há, pois, interesse em estudos visando a determinação da quantidade de água transpirada pelo cafeeiro, em condições de cultura. Além disto, para o prosseguimento dos trabalhos sobre o sombreamento dos cafezais em andamento na Secção de Fisiologia é de grande valor o conhecimento aproximado da quantidade de água retirada do solo pelo cafeeiro e pela árvore de sombra.Convém lembrar que nenhum dos métodos existentes para a medida da transpiração das plantas satisfaz plenamente, quando se trata de medir a transpiração in loco, nas condições de cultura. Todos são mais ou menos falhos e sujeitos à crítica. Devido a isso e também ao fato de serem tantos e tão variáveis os fatores que influem sobre a quantidade de água retirada do solo por uma cultura, os resultados obtidos de estudos desta natureza não devem ser tomados como exatos, mas, apenas, como indicadores da ordem de grandeza do fenômeno.Neste trabalho tratamos da medida da quantidade de água transpirada pelo cafeeiro cultivado ao sol, em todos os meses do ano. -MÉTODOS 2.1-PESAGEM RÁPIDA DAS FOLHASInicialmente, tentamos empregar o método de pesagem rápida das folhas, idealizado por Pfaff (3) e melhorado por Hüber (5) e que Rawitscher (4) iá empregou em folhas de cafeeiro. Este método baseia-se no fato consta-
Two of the more popular solutions for experimental culture of plants show a striking yariation in the amounts of phosphorus used. Shive's socalled best solution, R5-C2 (4) contains 2.45 gm. per liter or 0.018 mols of KH2PO4, partly as a source of phosphorus, but more perhaps as an acid buffer tending to maintain the solution at pH 4.5-5.0. Hoagland's 1940 solution (2) on the other hand contains only 0.068 gm. per liter or 0.0005 mols of the same salt. The Shive solution thus contains 36 times as much phosphorus as the equally successful Hoagland solution. As a portion of a general study of ion balance in nutrient solutions we have compared the growth, color and phosphorus absorption of several plants in these mixtures and in two experimental solutions; the first ("X") somewhat resembling the Hoagland solution, but carrying more than half of its nitrogen as NH4NO3, and the second ("P") being a modification of Zinzadze's buffered solution (6) carrying a moderately high concentration of phosphorus as a colloidal precipitate of the tricalcium salt and with the nitrogen again added as NH4NO3. Methods Plants were grown in quart mason jars with cork stoppers (3). Four seedlings in each jar were thinned to two to obtain maximum uniformity. Five replicates were used for each treatment and some of the experiments were repeated as many as five times. Corn (Zea mays), broccoli (Brassica oleracea var. italica), soybeans (Glycine max), tomatoes (Lycopersicon esculentum), sunflowers (Helianthus annuus), cotton (Gossypium hirsutum), and rice (Oryza sativa) were used in a main test of growth rates in April and May of 1945; corn, soybeans, and rice were used in June and July of the same year for studies of phosphorus absorption. Some of the plants were grown to fruiting, but, because of the small size of the culture jars, most of the work, including the phosphorus analyses, was done with plants 4 to 6 weeks old. Concentrations of the salts used in grams per liter and of the various ions in millimols are shown in table I. Iron was furnished by 10 ml. of a 0.1% solution of ferric tartrate at each change of solutions and by 1.0 ml. additions of the same solution one to three times a week as required. All solutions received 1.0 p.p.m. of boric acid and 0.5 p.p.m. of ZnSO4 at each change. After the seedling period of 2-3 weeks, solutions were changed at
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