SOWING DATE EFFECTS ON GRAIN-YIELD COMPONENTS FOR DIFFERENT MAIZE GENOTYPES

Shoot dry weight of maize (Zea mays L.) depends on the amount of photosynthetically active radiation intercepted by the crop (IPAR). The present work was conducted to analyze the variation in shoot dry weight production and its partitioning to reproductive sinks when seasonal changes of temperature and solar radiation occur during the growing cycle of the crop. Four commercial hybrids were grown at 8 plants m(-2) on four sowing dates (20 Aug., 20 Sept., 20 Oct., and 20 Nov.) at Rojas (34 degrees 08' S, 60 degrees 59' W), Argentina, on a silty clay loam soil (Typic Argiudoll) during 1990-1991 and 1991-1992, with no water or nutrient restrictions. Shoot dry weight at physiological maturity was associated with the amount of IPAR, with radiation use efficiency before silking (4.14 g MJ(-1)) higher than after silking (2.45 g MJ(-1)). Grain yield was correlated with shoot dry weight at physiological maturity, resulting in a stable (0.46 +/- 0.02) harvest index. Shoot dry weight at silking showed a significant relationship with final grain number (r(2) = 0.52, n = 32) as well as with grain yield (r(2) = 0.55, n = 32). Ear dry weight at silking was associated with grain yield particularly for prolific hybrids (r(2) = 0.64, n = 16). Provided postsilking conditions do not limit assimilate supply to the grains, shoot dry weight at silking could be considered a good grain yield predictor. In temperate regions, maize potential productivity seems to be more limited by the amount of solar radiation available around silking (determinant of grain set) than during grain filling (determinant of grain weight). Early and intermediate sowings tend to best utilize solar radiation for grain production.