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° 08' S, 60° 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 (r2 = 0.52, n = 32) as well as with grain yield (r2 = 0.55, n = 32). Ear dry weight at silking was associated with grain yield particularly for prolific hybrids (r2 = 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.

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Sunflower (Helianthus annuus L.) seed weight and oil concentration are commonly related to post‐flowering source of assimilates (e.g., leaf area index duration, LAD). A predictive variable including both the source of assimilates and the sinks (i.e., seed number) would better account for seed weight and seed oil concentration variability of crops with contrasting seed number and canopy size. We established quantitative relationships between oil weight per seed components and post‐flowering source–sink ratio. Field experiments were conducted in Argentina from 1998 to 2001. Four hybrids were cultivated under contrasting plant populations and nutrient supplies. A wide range of LAD (913–3130 m2°Cd m−2), seed number (4270–8880 seeds m−2), and seed weight (41–62 mg) was recorded. In contrast, seed oil concentration was not modified (about 530 mg g−1). Post‐flowering source–sink ratio (LAD per seed) better accounted (r2 = 0.69) for seed‐weight prediction than LAD (r2 = 0.42). Maximum seed weight (60 mg) was attained with source–sink ratios ≥0.33 m2°Cd seed−1 Results from our data set pooled together with others of different agro‐ecological regions reveal that sunflower crops are normally growing under limiting post‐flowering source–sink ratios and a 47% reduction of seed weight occurs when post‐flowering source–sink ratio is dramatically (100%) reduced. Seed weight is only 23% increased at saturated source–sink ratios. In contrast, for the wide range of post‐flowering source–sink ratios analyzed, seed oil concentration did not vary.

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