A long-term experiment on a clayey, kaolinitic, thermic Rhodic Hapludox where dolomitic lime was applied to the surface (either at 4.5 t ⁄ ha or at 1.5 t ⁄ ha per yr for 3 yr), or incorporated into the topsoil (4.5 t ⁄ ha), and gypsum applied to the surface (3, 6, and 9 t ⁄ ha), was carried out to evaluate their effects on soil profile chemical properties and yields of corn (Zea mays L.) and soybean (Glycine max L. Merrill). Lime applied to the soil surface at either full or split rates, or incorporated and surfaceapplied gypsum had long-lasting effects on soil acidity or calcium and sulphur availability respectively, as measured 8 yr after application. Grain yields of corn and soybean were not influenced by liming. Gypsum at 9 t ⁄ ha significantly increased corn grain yields by 7 and 8% respectively 7-10 yr after application, but did not affect soybean grain yields. The differences in response of the corn and soybean crops to gypsum might be related to the Ca 2+ uptake by plants because of cation exchange properties of roots, being smaller for corn than for soybean. The use of gypsum in no-till systems becomes more viable when corn is grown with a greater frequency in crop rotation.

The conditions in which a favorable response to a gypsum application can be expected on crop yields are not clear. A 3-year field trial was carried out to evaluate the effects of gypsum application on soil chemical attributes and nutrition and yield of corn (Zea mays L.) and soybean (Glycine max L. Merrill) on a clayey Typic Hapludox of high fertility and low acidity under no-till in Guarapuava, Parana State, Brazil. Treatments were arranged in a randomized complete block design with four replications, and consisted of gypsum application on the soil surface at 4, 8, and 12 Mg ha -1. Gypsum application increased the P content in the soil most superficial layer (0.0 -0.1 m) and also the exchangeable Ca and S-SO4 2-contents and the Ca/Mg ratio in the soil profile (0.0 -0.6 m). Gypsum also caused leaching of Mg and K exchangeable in the soil. An increase in Ca concentrations in the corn leaves, and in P and S concentrations in the corn and soybean leaves occurred following the gypsum application. A yield response of corn to initial application of gypsum was found, but subsequent soybean crops did not respond. Gypsum application proved to be an effective practice to maximize no-till corn grain yield. Key words: Zea mays, Glycine max, Brazil, phosphogypsum, calcium, sulfur Aplicação superficial de gesso num Latossolo de baixa acidez sob sistema plantio direto RESUMO: Não estão claras as condições em que se podem esperar efeitos favoráveis da aplicação de gesso na produção das culturas. Em um experimento de campo avaliaram-se, durante três anos, os efeitos da aplicação de gesso nos atributos químicos de um Latossolo Vermelho argiloso de alta fertilidade e baixa acidez sob plantio direto e na nutrição e produção de milho (Zea mays L.) e soja (Glycine max L. Merrill), em Guarapuava (PR). Os tratamentos, dispostos em blocos completos ao acaso com quatro repetições, constaram da aplicação superficial de gesso nas doses 4, 8 e 12 Mg ha -1. A aplicação de gesso aumentou a concentração de P na camada mais superficial (0.0 -0,1 m), bem como os teores de Ca trocável e de S-SO 4 2-e a relação Ca/Mg no perfil do solo (0.0 -0,6 m). A adição de gesso também ocasionou movimentação de Mg e K trocáveis no solo. A concentração de Ca nas folhas de milho e as concentrações de P e S nas folhas de milho e soja foram aumentadas com a aplicação de gesso. Houve aumento na produção de milho após aplicação de gesso, mas as culturas de soja subseqüentes não responderam ao gesso. A aplicação de gesso foi eficiente para maximizar a produção de grãos de milho no sistema plantio direto.

Gypsum has been used in tropical and subtropical agriculture when subsoil acidity is an important yield-limiting factor. However, the conditions that promote increased crop yield as a result of gypsum addition in no-till (NT) systems still remain unclear. A fi eld trial examined the eff ects of newly and previously surface-applied gypsum in a long-term NT system on the soil chemical properties and nutrition and yield of corn (Zea mays L.), wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.] on a clayey Rhodic Hapludox in Parana State, Brazil. Gypsum was surface-applied at 0 and 6 Mg ha -1 in 2004 on plots that had received gypsum previously at 0, 3, 6, and 9 Mg ha -1 in 1998. Surface-applied gypsum newly and previously improved exchangeable Ca and SO 4 -S availability throughout the soil profi le, and increased the cumulative grain yield of the crops. Exchangeable K losses through leaching caused by gypsum application were low, and a larger mobility of exchangeable Mg as compared with exchangeable K in soil was found as a result of gypsum addition.

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