Phosphorus fertilization for irrigated rice in soils with different phosphorus adsorption capacities.

Na cultura do arroz irrigado, os solos de v??rzea podem suprir as plantas com diferentes quantidades de f??sforo devido ao material de origem e aos fen??menos que ocorrem nos diferentes ciclos de oxida????o e redu????o desses solos. Um fator importante do solo que regula a disponibilidade do f??sforo para as plantas ?? a capacidade de adsor????o de f??sforo. Nesse sentido, o objetivo deste trabalho foi avaliar a resposta do arroz irrigado adubado com duas fontes de f??sforo em solos de v??rzea com diferentes capacidades de adsor????o de f??sforo e avaliar a capacidade de predi????o dos m??todos Mehlich-1 e Resina Trocadora de ??ons em esfera na disponibilidade de f??sforo para o arroz irrigado. Foram coletadas tr??s amostras da camada superficial (0-20 cm) de solos de v??rzea com diferentes capacidades m??ximas de adsor????o de f??sforo (CMAP): Planossolo H??plico (Pelotas), baixa CMAP; Planossolo H??plico (Bag??), m??dia CMAP e Gleissolo H??plico (Banhado), alta CMAP. As unidades experimentais constitu??ram-se de vasos pl??sticos contendo 6 kg de solo seco, onde foram aplicadas duas fontes de f??sforo (fosfato natural e superfosfato triplo) e seis n??veis de f??sforo: 0, 10, 20, 40, 80, 160 mg kg-1 P, com tr??s repeti????es, totalizando cento e oito unidades experimentais. Os vasos ficaram dispostos na casa de vegeta????o em um delineamento inteiramente casualizado. Cultivou-se o arroz durante quarenta e cinco dias e colheu-se a parte a??rea das plantas para quantificar o peso de mat??ria seca. Foram analisados os teores de f??sforo: no solo pelos extratores Mehlich-1 e Resina em esferas; na solu????o do solo e no tecido vegetal. Os resultados obtidos mostraram que: o Planossolo H??plico (Pelotas) respondeu com aumento de peso de mat??ria seca da parte a??rea do arroz at?? a dose de 10 mg kg-1 de f??sforo aplicado no solo, enquanto que no Gleissolo H??plico (Banhado) a resposta ao f??sforo aplicado foi at?? a dose de 80 mg kg-1. J?? no Planossolo H??plico (Bag??) n??o houve resposta ao f??sforo; o solo com maior capacidade m??xima de adsor????o de f??sforo (CMAP), Gleissolo H??plico (Banhado), necessitou maior quantidade de f??sforo aplicado na forma de superfosfato triplo e fosfato natural para atingir a m??xima produ????o de mat??ria seca da parte a??rea; o superfosfato triplo apresentou maior solubiliza????o do que o fosfato natural Daoui durante o alagamento dos solos de v??rzea utilizados neste experimento; o extrator Mehlich-1 e o m??todo da Resina Trocadora de ??ons em esfera equivaleram-se na capacidade de predi????o da disponibilidade de f??sforo para o arroz irrigado nos solos de v??rzea utilizados neste experimento.In irrigated rice crop, the lowland soils can supply the plants with different phosphorus quantities due to the source material and phenomena that occur in the different oxidation and reduction cycles of these soils. An important soil factor that regulates the phosphorus availability for the plants is the maximum phosphorus adsorption capacity. Therefore, the objectives of this work were to evaluate the response of the irrigated rice fertilized with two sources of phosphorus in lowland soils with different phosphorus adsorption capacity and to evaluate the prediction capacity of the methods Mehlich-1 and Ionic Exchange Resin in Sphere regarding the phosphorus availability for the irrigated rice in these soils. The soil samples were taken from the top 20 cm of three lowland soils with different maximum phosphorus adsorption capacity (MPAC): Typic Albaqualf, low MPAC; Vertic Albaqualf, average MPAC and Typic Endoaqualf, high MPAC. The experimental units were constituted of plastic buckets containing 6 kg of dry soil, where two phosphorus sources (phosphate rock and triple superphosphate) and six levels of phosphorus: 0, 10, 20, 40, 80, 160 mg kg-1 P were applied, with three replications, totaling 128 experimental units. The pots were positioned in the greenhouse in a completely randomized experimental design. The rice was cultivated for 45 days and the dry matter weight was quantified through aerial part of the plants. The phosphorus content was analyzed by extractor Mehlich-1 and Resin methods in the soil, in the soil solution and in the plant. The obtained results showed that: Typic Albaqualf respond with increased dry matter weight of rice plant aerial part up to the level of 10 mg kg-1 of phosphorus applied in the soil, while in the Typic Endoaqualf the response to the applied phosphorus was up to the level of 80 mg kg-1. Vertic Albaqualf did not respond to phosphorus; soil with higher maximum phosphorus adsorption capacity (MPAC), Typic Endoaqualf, required higher phosphorus quantity (phosphate rock and triple superphosphate) to reach maximum dry matter weight of rice plant aerial part up; the triple superphosphate presented greater solubility than phosphate rock Daoui during the flood of the lowland soils in this experiment; the extractor Mehlich-1 and the Ion Exchange Resin method were equivalent in the prediction capacity of the phosphorus availability for the irrigated rice in the lowland soils in this experiment