Doses e épocas de aplicação de nitrogênio na suscetibilidade do arroz a temperatura baixa na fase reprodutiva

Abstract

The release of new cultivars and improvement in management practices is necessary to examine the time and nitrogen (N) rates to be applied to obtain high yields. Also there is little information about the effect of the N rate and stage (vegetative or reproductive) on the sensitivity of plants of rice to cold in the reproductive stage. For these reasons four experiments were installed two in field and two in a greenhouse with the objective of determining the effect of N rates and application timing on yield and on the susceptibility of rice plants to low temperature in the reproductive stage. The experiments were conducted in the 2006/2007 and 2007/2008 growing season at INIA Treinta y tres, Uruguay. The experimental design in greenhouse was completely randomized in a factorial experimental design (factor A: stages or rates of N application and B factor: treatment of temperature), with four replications. To study the effect of the time of application of N, The treatments were application of N (30 kg ha-1) in the stages V4, V5, V6, V7, V8, R0, R1 and control without N in topdress. To study the effect of rates were applied to the factor A 0, 23, 46 and 69 kg ha-1,in V4 stage and the same rates in R0 stage. For the factor B of the two experiments were carried out two treatments: with and without cold (cold with the plants were treated with 12.5°C for 7 hours in 4 nights when the collar of the flag leaf was at the same height as the collar of the leaf below). Treatments from the field experiments were the same for the factor A of the experiments in greenhouse later explained, in a randomized block design with four replications. In a greenhouse the spikelets sterility was not affected by the application of N in different stages or the rates applied when the plants were subjected to cold. The cold treatment caused a temporary effect on the SPAD index retarding panicle emergency and reducing the size of the panicle, but did not affect yield. In the rice grown in the area after three years of livestock the plants respond to low rates and times of application of N in yield and its components