Growth, Fruit Production and Phosphorus Critical Level In the Soil for Okra In Relation to Phosphate Fertilization.

The okra crop is considered as an alternative source of income for family farms in Brazil conditions, however, studies that relate growth and yield of this culture with the phosphorus (P) dynamics in the soil are sporadic. Thus, the objective of this study was to evaluate plant growth, productivity and the P critical level in the soil to the Clemson Spinless okra cv. American 80, in relation to the phosphorus fertilization. The research was conducted under field conditions, in the Zona da Mata of Pernambuco, Brazil. The experimental design was randomized blocks with six replicates. Treatments consisted of dose 0, 8, 16, 32, 65, 130 and 260 kg P₂O­₅ ha^-1 defined according to the soil Maximum Phosphorus Adsorption Capacity (MPAC). The growth was determined in the period from 15 to 57 days after germination (DAG). The production and number of fruits per plant was determined from the results accumulated during 70 days of harvest at intervals of three days between each assessment. The P critical level in the soil of was performed at 30 days after phosphate fertilization and determined from 90 % of the maximum production. The okra development was adjusted to the sigmoidal model featuring three stages of growth, in which found the period of maximum growth, on average, between 11 and 61 DAG. The dose of 130 kg P₂O₅ ha^-1 gave the highest growth rate, with values ​​of 2.9 cm day^-1 occurred at 32 DAG, increased production and quantity of fruit produced. The maximum economic production (MEP) has occurred with the addition of 83 kg P₂O₅ ha^-1. The 54 mg dm^-3 P critical level in the soil was related to the production of 7.4 t ha^-1 the okra fruits.