Las fosfatasas actúan en la mineralización del fósforo (P) orgánico del suelo, sin embargo, la actividad enzimática puede afectarse por las fuentes inorgánicas de P o el encalado del suelo. Este estudio evaluó el efecto de las fuentes del P y del encalado en las actividades de las fosfatasas ácidas (AFÁ) y alealinas (AFa) y en la producción de braquiária, Braquiaria ruziziensis, y de guandu, Cajanus cajan. Se usó un modelo experimental de bloques al azar en factorial 3 x 3 x 2 (plantas x fertilización x encalado) con dos repeticiones. Los contenidos de P total, orgánico y disponible del suelo también fueron determinados. La AFÁ del suelo fue 3,3 veces mayor que la AFa y aumentó en el suelo cultivado con braquiária en relación con el suelo cultivado con guandu o no cultivado. La AFa también aumentó en el suelo cultivado con braquiaria respecto a los otros tratamientos, pero no significativamente. La AFa fue reducida por el superfosfato, pero no así la AFÁ. En ausencia de encalado, la actividad de ambas enzimas disminuyó en el suelo no fertilizado o fertilizado con superfosfato en relación con la roca fosfórica (RF). La aplicación de superfosfato aumentó la disponibilidad de fosfato del suelo, la producción y el contenido de P foliar de braquiária y de guandu. El contenido de P total fue el mayor en todos los tratamientos que recibieron RF o superfósfato.

Summary Phosphates act in the mineralization of soil organic P, however enzyme activity can be affected by plants, P inorganic sources or soil liming. This study evaluates the effect of the phosphorus sources and liming on activities of acid and alkaline phosphatases and on production of Braquiaria ruziziensis and Cajanus cajan. Statistical design used was a randomized block in a 3x3x2 (plants x fertilizers x liming) with two replications. Contents of total, organic and available phosphate of the soil were also determined. The acid phosphatase activity of the soil was 3,3 times more than the alkaline phosphatase activity and increased in the soil cultivated with B. ruziziensis in relation to the C. cajan or to the non cultivated soil. The alkaline phosphatase activity also increased in the soil cultivated with B. ruziziensis in relation to other treatments, but not significantiy. The alkaline phosphatase activity was repressed by the superphosphate, but not the acid phosphatase activity. In non lirned plots, the activity of both enzymes was repressed in the not fertilized soil or in the fertilized with superphosphate in relation to the rock phosphate. Superphosphate increased phosphate avaliability of the soil, production and P uptake of B. ruziziensis and C. cajan. Contents of total phosphate were largest in all the treatments that reccived rock phosphate or superphosphate.

O objetivo deste trabalho foi avaliar o efeito de diferentes espécies de plantas, fontes de fósforo e calagem sobre a população microbiana total e solubilizadora de fosfato. Foram isolados fungos e bactérias capazes de solubilizar hidroxiapatita, proporcionando P solúvel. O experimento utilizado foi em blocos ao acaso com fatorial 3x3x2. E os fatores avaliados foram espécies de plantas (controle, braquiária e guandu), fertilizantes (controle, superfosfato simples e fosfato de rocha, ambos na dose de 400 kg ha-1 de P(2)0(5) ) e calagem (com e sem calcário). A população bacteriana cresceu pelo efeito da calagem, e a de fungos aumentou, independentemente da calagem, nas parcelas cultivadas com braquiária e fertilizadas com superfosfato. Foi constatado incremento de biomassa-P microbiana sobre o controle por influência da braquiária (23,9%), do superfosfato (30,9%) e da calagem (46,9%). O número de bactérias solubilizadoras foi favorecido pela calagem ou pelo plantio de guandu adubado com fosfato natural ou com braquiária sem adubação. Os fungos solubilizadores aumentaram na ausência de planta ou de adubação e na presença de guandu com fosfato natural. Finalmente, a calagem favoreceumais o crescimento dos fungos solubilizadores, em comparação com o controle, nos tratamentos fosfato natural, braquiária ou guandu.

The objective of the present study was to evaluate the effect of different plant species, phosphorus sources, and liming on the total microbial and phosphate-solubilizing population. In order to achieve that, bacteria and fungi capable of solubilizing hydroxyapatite providing available P were isolated. An experiment was carried out in a randomized factorial block design 3x3x2. The factors evaluated were plant species (control, Brachiaria ruziziensis and Cajanus cajan), fertilizers (control, simple superphosphate and rock phosphate, both at the dose of 400 kg ha-1 of P(2)0(5)) and liming (with and without lime). While the bacterial population increased due to the effect of liming, the fungal population also increased independently of liming in the soil cultivated with B. ruziziensis and fertilized with superphosphate. An increase of the microbial biomass-P compared to the control was observed under the influence of B. ruziziensis (23.9%), superphosphate (30.9%) or liming (46.9%). The number of solubilizing bacteria was favored by liming andby the planting of C. cajan fertilized with rock phosphate or with unfertilized B. ruziziensis. The solubilizing fungi increased in the absence of plants or fertilization and in the presence of C. cajan fertilized with rock phosphate. Finally, liming enhanced more the growth of solubilizing fungi than did the control in the treatments using rock phosphate, B. ruziziensis or C. cajan.