Eficiência do fosfato natural para o arroz irrigado em solo do sul do Brasil

Phosphate rock efficiency to lowland rice was evaluated in a study that we tested: a) phosphorus sources (P): 1- triple superphosphate (TSP); 2-Phosphate rock (PR); and b) phosphorus rates: 0, 10, 20, 40 and 80 mg kg-1. Rice variety EMBRAPA 7 "TAIM", was grown in a pot for thirty days. Soil solution pH values were similar between rates for the same source; however, the PR was superior to TSP in both soil solution sampling. The P concentrations in solution increased according to P rates. P amounts in the second soil solution sampling were similar between rates of the same source, but the differences were observed at P (TST) rate of 80 mg kg-1. Shoot dry matter increased with P rate and the 80 mg kg-1 P rate was superior in both sources. However, the TSP was superior to PR and this tendency was similar with the P in plant tissue and P uptake by plants. P in soil solution, P plant content, P uptake by plants and rice growth increased according to P applied in soil; PR showed high agronomic efficiency at rates over 40 mg kg-1 de P.Com o objetivo de avaliar a eficiência do fosfato natural na cultura do arroz irrigado, foi desenvolvido um experimento onde testou-se: a) fontes de fósforo(P) : 1- Superfosfato triplo (SFT); 2- Fosfato natural (FN); e b) Doses de P: 0, 10, 20, 40 e 80 mg kg-1. Arroz da cultivar EMBRAPA 7 "TAIM", foram cultivadas em vasos durante trinta dias. O pH na solução do solo não diferiu entre as doses na mesma fonte. O P na solução aumentou com o acréscimo das doses de P, porém na primeira coleta não diferiu entre as fontes. Na segunda coleta os teores de P foram similares nas diferentes doses para a mesma fonte, diferindo apenas no SFT na dose de 80 mg kg-1. A produção de matéria seca aumentou conforme a dose de P sendo que a dose de 80 mg kg-1 foi superior nas duas fontes. Os teores de P na solução do solo e na planta, a quantidade acumulada de P e a produção de matéria seca do arroz, aumentaram com o acréscimo das doses de P aplicadas ao solo; o fosfato natural apresentou alta eficiência agronômica a partir de doses equivalentes à 40 mg kg-1 de P