Effect of simulated rain on head rice yields of varieties under delayed harvest

Rain can cause harvest delays and losses in rice milling quality. Cycles of high and low moisture can increase the proportion of broken grains during milling. To test the effect of continuous evening rain on the milling yield of rice, 20 varieties were stagger-planted to obtain simultaneous maturity in Palmira, Colombia. Each variety was transplanted in plots of nine rows, 10 m long and 30 cm apart. At maturity (20-25% moisture content), each plot was divided in half with a plastic curtain extending from ground level to 30 cm above the top panicle. Simulated rain was applied to one-half of the plots with an atomizer operated at a water pressure of 2 atmospheres, delivering 60 liters/ha and covering a diameter of 1.5 m. Grain moisture measurements at harvest indicated that misting resulted in mean values 2.5% higher (20.9 vs 18.4%) after the first week and 1.1% higher (13.0 vs 11.9%) after the second week. Misting had no significant effect on grain moisture content at harvest with a delay of three weeks. Rough rice samples of 125 g were dried and milled using standard McGill laboratory equipment. Head rice yield slopes for each treatment within each variety were calculated. Seven varieties showed similar slopes under simulated rain and control conditions, whereas the rest showed faster head rice reduction when simulated rain was applied. Within the first group, varieties INTI from Peru and Sinaloa A 80 from Mexico seem to have acceptable initial milling yields and a slow rate of quality loss, which suggests a certain degree of tolerance for delayed harvest. Within the group of varieties with faster rate of loss with simulated rain, BR IRGA 409 could also be classified as tolerant; such varieties could be useful in areas where delayed harvest is common and milling quality is demanded. Varieties Oryzica 2 and INIAPA 415 represent genotypes with acceptable milling yields when harvested on time, but would be discarded if milling evaluation included samples harvested 10-15 days after maturity