Influence of Blast on the Nutrition and Yield of Irrigated Rice in Southern Brazil

In recent decades, nitrogen fertilization rates have increased significantly in irrigated rice fields in southern Brazil. However, there is a gap in knowledge concerning the use of these high rates of nitrogen fertilization in cultivars with a high yield potential, and susceptible to rice blast. We therefore conducted a field experiment in the 2014/2015 and 2015/2016 crop year to evaluate blast severity, plant tissue nutrition, and yield and grain quality with increasing nitrogen fertilization levels in a rice blast-susceptible cultivar (Guri Inta CL). The experiment had three factors, with factor 1: N doses (0, 60, 120, and 180 kg ha(-1)), factor 2: sowing dates (early and late), and factor 3: with and without fungicide application. The experimental design was randomized blocks with four replications. The area under the disease progress curve was positively influenced by the increase of N rates in the two crops years. Grain yield had a negative quadratic effect as a function of N rates. Increased N levels reduced the thousand grains weight. Late sowing and non-application of fungicide increased disease severity; there was reduced yield, grain quality, and N use efficiency. It is concluded that the use of N levels greater than 60 kg ha(-1) in rice blast-susceptible cultivars in southern Brazil increases disease severity with lower N use, reduces grain yield and grain quality.