Efeitos de algumas práticas de cultivo do solo, na nutrição mineral dos citros

Diferentes sistemas de cultivo do solo no pomar cítrico foram comparados no presente trabalho, por meio da análise foliar. Os tratamentos estudados fazem parte de um experimento com plantas da variedade Hamlin sôbre laranjeira caipira (Citrus sinensis Osbeck) instalodo no Estação Experimental de Limeira, do Instituto Agronômico. Amostras de fôlhas do ciclo vegetativo da primavera foram colhidas a intervalos regulares, desde outubro de 1957 a março de 1959 e analisadas para os seguintes elementos: N, P, K, Ca, Mg, Fe e Mn. São apresentados os tendências das curvas de concentração dos elementos nutritivos nas fôlhas e os resultados de produção correspondentes a quatro onos de colheita. Como observação mais importante foi verificado que a cobertura morta de capim e a adubação verde de mucuna aumentaram de modo sensível o teor de fósforo nas fôlhas dos citros. As produções de laranja acompanharam a ordem dos níveis dêsse elemento na folhagem. The influence of several soil management systems on the mineral nutrition and production of citrus trees was studied. This study was mode in an experimental orchard installed in 1949 with Hamlin orange on sweet orange (Citrus sinensis Osbeck). Differential treatments were started in 1953. Since 1956 all plots received uniform fertilizer applications and liming. The cultural treatments employed are as follows: clean cultivation with herbicide; clean cultivation plus a cover crop of velvet bean (Stizolobium aterrimum Pip. & Trac.) planted in the spring and cut down in the fall; clean cultivation plus a cover crop of pigeon pea (Cajanus cajan (L.) Millsp.) planted in the spring and cut down in the fall; molasses grass (Melinis minutiflora Béauv.) mulch; and superficial soil plowing. Leaf samples of the spring cycle were collected from each treatment at regular intervals, from October, 1957 to March, 1959, and analysed for N, P, K, Ca, Mg, Fe, and Mn. The seasonal variations in mineral composition of the leaves were studied in relation to the crop harvest in 1958. Grass-mulched plots showed low level of nitrogen in the leaves in comparison with those which did not receive this treatment. Therefore, extra nitrogen fertilizer may be required to prevent competition for nitrogen due to mulching practices in citrus orchards. Mulched plots produced the highest yields every year, followed by clean cultivation plus cover crop of velvet bean, while clean-cultivated plots produced the lowest. Orange yields and leaf phosphorus levels sh