Temperature Effect on Yield and Yield Components in Field -Grown Maize in Different Planting Densities

In order to evaluate the temperature effect on yield and yield components of maize in different planting densities in the field condition, two field experiments were conducted with a Randomized Complete Block Design on 19(th) April (as a main crop) and 18(th) June (as a second crop) 2008 in Agricultural Research Center of Golestan - Iran (36 53 N, 54 21 E) Each experiment included seven planting densities (0 16, 2 5, 4 5, 6 5, 8 5, 10 5 and 12 5 plants m (2)) with four replications Both experiments were conducted without any water and nutrient limitations All phenological events including planting date, emergence date, tasseling, silking, physiological maturity and harvesting time were recorded during the growing season To evaluate temperature effect, from weather data, daily maximum and minimum temperature, cumulative mean temperature, days with temperature > 34 degrees C, and cumulative growth degree-day (GDD) were computed for different plant growth stages in each season The result showed, in the second season, because of higher mean daily temperature (28 2 vs 24 4 degrees C) and more days with maximum temperature > 34 degrees C (38 vs 17) the values of total dry matter (TDM), grain yield, ear per plant, W1000, harvest index, LAI, seed number per rows, and (cob+ husk) weight, were significantly less than the values of them in the first season (269, 43 1, 33, 9 7, 21 4, 14 7, 13 2 and 52 7 % respectively) ANOVA showed a significant interaction between season and density for 7 of 9 properties Maximum grain yield observed in middle planting densities in the first season while, in the second season the grain yield was same in planting densities between 2 5 and 12 5 plant m (2) This study found that corn should be planted in the first season for higher growth and yield with 6 5 plant m (2) and in the heat stress condition (in the second season) planting density should be reduced to 2 5 - 4 5 plants m (2)