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Maize (Zea mays L.) pollen production has been found not to limit kernel set, but there is scarce information on pollen production of modem hybrids and the effect that breeding for reduced tassel size has had on this trait. Our objectives were to study genotypic differences in pollen production and flowering dynamics, and to estimate pollen availability per exposed silk. Four F1 hybrids were grown at different plant densities (between 2.5 and 12.5 plants m[sup -2]) in two distinct environments (cool Midwest USA and temperate Argentine Pampa). Pollen availability was also modified by delayed plantings and detasseling treatments. We measured the dates of anthesis and silking of individual plants, the anthesis-silking interval (ASI), the number of exposed silks per apical ear, the number of pollen grains per square meter (PGM), and kernel number per ear. The number of pollen grains produced per tassel (PGT) and per exposed silk were estimated. Increased plant density promoted an increase in ASI, matched by an enhanced interplant variability in this parameter, and a reduction in PGT. The latter was reduced from 10.3 × 10[sup 6] or 11 × 10[sup 6] at 2.5 plants m[sup -2] to about 3 × 10[sup 6] at 12.5 plants m[sup -2] (USA), and from 9.7 × 10[sup 6] or 11.3 × 10[sup 6] at 3 plants m[sup -2] to 4 × 10[sup 6] or 3.6 × 10[sup 6] at 9 plants m[sup -2] (Argentina). We estimated two thresholds beyond which kernel set could be affected: (i) 227 pollen grains cm[sup -2] d[sup -1] at the end of pollen shedding and (ii) two pollen grains per exposed silk. Some cropping conditions were closer to the second threshold than others. [ABSTRACT FROM AUTHOR]

Accurate prediction of leaf area is critical for precise forecasting of crop growth and yield by most crop simulation models. Most maize (Zea mays L.) models simulate canopy growth using generic functions. In this paper, we present a new leaf area model that can simulate cultivar-specific growth of individual leaves of maize. The new model was linked to CERES-Maize and validated for several cultivars and environments. The model describes three processes of the life cycle of leaves articulated in a dynamic thermal time framework: expansion, longevity and senescence. Calculations are performed on a per leaf basis since current environmental conditions and stresses affect specific processes on individual leaves. Three cultivar-specific inputs are used to distinguish genotypes. These are: area of largest leaf (cm2), longevity of most longevous leaf (growing degree days, base temperature 8 °C), and final leaf number. We tested the model by linking it to CERES-Maize and making the expansion and senescence processes responsive to the canopy-based carbon balance and stress indices of CERES. Model predictions were compared with field measured leaf area for different genotypes and with data available in DSSAT (version 3.5). The new model improved the accuracy of leaf area prediction compared to the original CERES-Maize. Our evaluation also showed that the carbon balance in CERES does not simulate correctly the effect of reduced assimilate supply for leaf growth caused by inter-plant competition. A sensitivity analysis revealed that this new leaf area model is very sensitive to the number of leaves predicted. The new model provides a flexible system to simulate area of leaves in maize. It also facilitates the evaluation and calibration of carbon, water, and nitrogen balances at the leaf level. [Copyright &y& Elsevier]