Once kernels are set, cereal grain yields are proportional to kernel weight. Thus environmental effects on kernel size merit better understanding as a source of yield variability.Plant phenology was observed, environmental conditions were monitored, and kernel weights were determined for wheat during two seasons at 26°N. Lat. These observations provided data sets for relating mean daily temperature during grain filling (from the beginning of flowering to mealy ripeness of the kernels) to kernel weight and to duration of grain filling.The data indicate a 3.1 day shortening of grain filling per degree C increase in mean daily air temperature during grain filling which compares with 2.8 days C‐1 for seven studies reported in the literature. Kernel weight in this study decreased 2.8 mg kernel ‐1 C‐1 compared with 1.5 mg for each degree C increase in temperature for seven studies in the literature.We concluded that temperature is pacing plant senescence and that shortening the duration of grain filling is its common manifestation in commercial winter and spring wheats. Temperature, when in excess of about 15 C, apparently explains the dependence of 1,000 kernel weight on grain filling duration.The findings imply that genetic variability in plant senescence and grain filling rates need to be searched for and exploited to help stabilize the kernel size component of yield.
Ground measurements of leaf area index (LAI) are tedious and costly. If they could be estimated spectrally from earth observation satellite data, evapotranspiration and photosynthesis models that use LAI as inputs could be implemented for large areas. Thus, we related LAI measurements of winter wheat (Triticum aestivum, L.) made in Kansas during the 1974–1975 and 1975–1976 growing seasons to three spectral vegetation indexes in the literature: transformed vegetation index (TVI), green vegetation index (GVI), and perpendicular vegetation index (PVI). The three vegetation indexes were each significantly linearly correlated (r = 0.70** to 0.95**) with measured LAI from the time LA1 was ≃ 0.3 until plant senescence, and their seasonal time courses were similar to those of directly measured LAI. Thus the indexes capture information on crop development and growing conditions manifested by LAI. We conclude that LAI can be calibrated in terms of the vegetation indexes to provide crop model inputs for as many fields as are of interest, or can serve as an independent check on model calculations when not used as a direct input to physical and physiological process models affected by the amount of vegetation present.
The influences of cotton plant relative turgidity (RT), solar radiation (RS), and air temperature at plant height (TA) on leaf temperature (TL,) and leaf minus air temperature (TL — TA) were studied during two crop seasons. The daily data show that (a) a decrease in relative turgidity from 83 to 59% resulted in a 3.6C increase in leaf temperature, and (b) a unit increase in solar radiation (from about 0.5 to 1.5 ly min‐1) resulted in a 9 to 10C increase in leaf temperature. These same changes in relative turgidity and solar radiation resulted in 2.7 to 3.7 and 8 to 10C increases, respectively, in (TL — TA). Seasonal average (TL — TA) was 4C. Leaf temperature and (TL — TA) could be estimated from the seasonal data with an average standard error of 1C by RT, RS, and TA in linear multiple regression analyses. The results of these studies show that variations in plant moisture stress significantly alter leaf temperature and leaf minus air temperature. However, variations in insolation must be carefully monitored under intermittent cloud conditions to account for their influences on plant leaf temperature.
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