Alterações edáficas decorrentes de diferentes manejo de solo e rotação de culturas em latossolo sob condições subtropicais

Apos vinte e tres anos da instalacao de um experimento (1985 a 2008), o nivel de fertilidade e de MOS foram avaliados, num Latossolo Vermelho Distrofico tipico, em Passo Fundo, RS, em quatro sistemas de manejo de solo (SMS) - 1) sistema plantio direto (SPD), 2) cultivo minimo (CM), 3) preparo convencional de solo com arado de discos (PCD) e 4) preparo convencional de solo com arado de aivecas (PCA) - e por tres sistemas de rotacao de culturas (SRC): I - trigo(T)/soja(S); II - T/S e ervilhaca (E)/sorgo (So); e III - T/S, aveia branca/soja e E/So). Amostras de solo tambem foram coletadas em um fragmento de floresta subtropical adjacente ao experimento, como testemunha da condicao original do solo. O delineamento experimental foi em blocos completos ao acaso, com parcelas subdivididas, e tres repeticoes. A parcela foi constituida pelos SMS, e as sub-parcelas, pelos SRC. Houve acumulo de MOS, Ca e P, no SPD, na camada 0-5 cm. O teor de C acumulado foi mais elevado sob SPD em relacao aos demais SMS, na camada 0-20 cm. Os SMS e de SRC mostraram menor teor de MOS do que a floresta, na camada de 0-5 cm. Os teores de P e de K, nos SMSs, foram maiores na camada de 0-5 cm, diminuindo com a profundidade. A floresta mostrou menor valor de pH e teores P e K, e maior teor de Al, em relacao aos SMS e de SRC. Palavras-chave: sistemas de producao, plantio direto, materia orgânica, fosforo, potassio EDAPHIC CHANGES CAUSED BY DIFFERENT SOIL TILLAGE MANAGEMENTS CROP ROTATION SYSTEMS IN OXISOL UNDER SUBTROPICAL CONDITIONS ABSTRACT Soil fertility and organic matter were assessed after twenty years of implementation (1985 to 2005) on  a typical Dystrophic Red Latosol soil located in Passo Fundo, State of Rio Grande do Sul, Brazil. Four soil tillage managements – 1) no-tillage system, 2) minimum tillage, 3) conventional tillage using a disk plow, and 4) conventional tillage using a moldboard plow - and three crop rotation systems: I (wheat/soybean), II (wheat/soybean and common vetch/sorghum), and (wheat/soybean, common vetch/sorghum and white oats/soybean) were evaluated. As a control, soil samples were collected in a subtropical forest fragment adjacent to the experiment. A randomized complete block design, with split-plots and three replicates, was used. The main plots were formed by the soil tillage systems, while split-plots were composed the crop rotation systems. Higher levels of SOM, Ca and P were observed in the 0-5 cm layer for the SPD. The values of soil organic C, in the 0-20 cm layer was higher in NT as compared soil management tillage. Values of SOM observed in all soil management tillage and crop rotation systems were lower than in the forest. The values of P, and K were higher in the 0-5 cm layer, when compared to the ones observed in the 15-20 cm layer in soil management tillage. Values of pH, P, and K observed in the forest were lower and Al was higher than all soil management tillage and crop rotation systems. Keywords: crop production, no-tillage, organic matter, phosphorus, potassium DOI: http://dx.doi.org/10.14583/2318-7670.v03n04a02