Avaliação de uma rocha ígnea como corretivo de acidez e disponibilização de nutrientes para as plantas.

RESUMO: O objetivo deste trabalho foi avaliar o potencial da rocha fresca carbonatito, proveniente da mina de fosfato localizada em Catalao - GO, como um possivel fonte de insumos para a agricultura. O ensaio foi conduzido no campo, com o objetivo de avaliar o potencial de carbonatito como fonte de: (a) P; e, (b) K, para uma pastagem de Brachiaria ruziziensis. Foram realizados tres cortes (abril/2000, fevereiro e maio/2001) das plantas e amostragem de solo e do tecido para analises quimicas. Os resultados obtidos aos 560 dias depois da aplicacao do carbonatito (CBT) demonstram que a maior producao de materia seca (MS) foi atingida com a aplicacao de 200 kg P2O5 / ha ) na forma soluvel. Nao houve efeitos significativos do CBT como fonte de P na producao de MS em comparacao com o tratamento em que nao foi aplicado fosfato ao solo. No entanto, quando uma quantidade de fosfato soluvel (100 kg P2O5/ha) foi aplicada com a dose mais elevada de CBT (200 kg P2O5/ha, o aumento na producao de MS foi significativo. O P acumulado no tecido nos tratamentos com CBT foi significativamente menor que com fosfato soluvel. Depois de tres cortes, verificou-se que o teor de K do solo antes da instalacao do experimento foi suficiente para suprir a demanda da cultura, nao havendo diferencas no teor de K acumulado na parte area. Entretanto, 12 meses depois da aplicacao das fontes de K, o teor de K trocavel no solo decresceu ate valores medios de 0,80 mmolc K/dm3. ABSTRACT: The aim of this work was to evaluate the potential agricultural resource of the fresh rock carbonatite (CBT), originated in Catalao - GO. The trial was carried out with the objective of evaluating the performance of carbonatite rock (CBT), as a source of P and K, for a Brachiaria ruziziensis pasture. Two experiments were established in December/1999. The soil was a clay-loam red yellow Oxisol, with low pH and low nutrients avaliability. The total composition of the rock was 29.8% CaO; 10.3% MgO; 4.8% P2O5 and 1.5% K2O. The Experiment 1 included seven treatments: O; 44 and 88 kg P ha (elevado menos 1) as CBT and the same levels of P as TSP; 88 kg P ha (elevado menos 1) as CBT + 13 kg P ha (elevado menos 1) as TSP and finally 100 kg P ha (elevado menos 1) as TSP. Experiment 2 included four treatments: 0 and 50 K kg ha (elevado menos 1) as CBT and 50 K kg ha (elevado menos 1) as KCI; and na additional treatment: three applications of 16.7 kg K ha (elevado menos 1), as KCI - at planting, and after each cutting. Each treatment, in both experiments, was replicated four times in a randomized blocks design. The seeds of B. ruziziensis were sowed in December/1999. The plants were cut at the flowering stage in: April/2000, in February/2001, and May/2001. The concentration of major and minor nutrients in plant leaves and shoot dry matter were determined. Soil samples were collected and analyzed for chemical compositio. Results obtained 560 days after the application of the treatments demonstrated that higher dry matter (DM) productions were achieved with 88 kg P ha (elevado menos 1) - TSP. There was no significant effect (P < 0.05) of the CBT, as a P source, on DM production, in comparison with the treatment where there was no application of phosphate to the soil. However, when a small amount of soluble phosphate (13 kg P ha (elevado menos 1)) was applied with CBT, there was a significant increase in the DM. The accumulated P in the plant tissue in the treatments with CBT was significantly lower than in the treatments with soluble phosphate. Due to initial K content in the soil, there were no significant differences among the treatments with or without K application , regardless of the K sources.