Number of kernels in wheat crops and the influence of solar radiation and temperature

Abstract

SUMMARYThe number of kernels per m2 (K) in well managed and watered wheat crops was studied using results of experiments in Mexico and Australia in which short spring wheat cultivars were subjected to independent variation in radiation, largely via artificial shading, and in temperature. Also crops subjected to differences in weather (year), sowing date and location within Mexico, revealed responses to the natural and simultaneous variation which occurs in radiation and temperature. Responses in K were interpreted in terms of spike dry weight at anthesis (g/m2) and number of kernels per unit of spike weight.K was linearly and most closely related to incident solar radiation in the 30 days or so preceding anthesis, herein termed the spike growth period; for the cultivar Yecora 70 with full ground cover the slope was 19 kernels/MJ. This response seemed largely due to a linear response of crop growth rate to intercepted solar radiation. The proportion of dry weight increase partitioned to the spike increased somewhat with reduced radiation. Also increasing temperature in the range 14–22 °C during this period reduced K (slope approximately 4% per CC at 15 °C). The cause appeared to be lower spike dry weight due to accelerated development. The number of kernels per unit spike weight at anthesis was little affected by radiation or temperature, and averaged 78±2/g for the cultivar Yecora 70.With natural variation in radiation and temperature, K was closely and linearly correlated with the ratio of mean daily incident or intercepted radiation to mean temperature above 4·5 °C in the 30 days preceding anthesis. As this ratio, termed the photothermal quotient, increased from 0·5 to 2·0 MJ/m2/day/degree, K increased from 70 to 196 × 102/m2. These responses of K to weather, sowing date and location were closely associated with variation in spike dry weight.It was concluded that the ratio of solar radiation to temperature could be very useful for estimating K in wheat crop models. Also the analysis of K determination in terms of spike dry weight appeared promising, and suggests that wheat physiologists should place greater emphasis on the growth period immediately before anthesis.

Drivers of spatial and temporal variation in soybean yield and irrigation requirements in the western US Corn Belt

“…As first proposed in the now classic papers authored in the mid-1980s by French and Schultz (1984) and Fischer (1985), and then further supported by Calviño and Sadras (1999), we argue in favor of simple, agronomically meaningful models based on few, key environmental and management factors as an alternative to large statistical models with numerous variables, which have limited biological relevance because of intrinsic empiricism and co-linearity among independent variables. Asterisks denote significance at F-test * P < 0.15, ** P < 0.10, *** P < 0.05.…”

“…Separate analysis using the July 15th-August 31st time interval (which covers roughly the R3-R6 stage period) showed no improvement in the predictive power of the meteorological factors; in fact, it decreased for rainfed crops (data not shown). Following Fischer (1985), a photo-thermal quotient (Q) was calculated as the ratio between incident solar radiation and average temperature during the July 1st-August 31st time interval. Briefly, Q integrates the effects of solar radiation and temperature on crop growth and development during critical stages for yield determination.…”

Effects of Non-Structural Carbohydrates on Spikelet Differentiation in Rice

“…W ada ( 1969) reported that the amount of carbohydrate stored in the plants did not affect the spikelet differentiation. In wheat, kernel number per m 2 was related to the photothermal quotient (Fischer, 1985), which is the ratio of solar radiation to cumulative effective tempera- Means in the same cultivar within a column followed by the same letter are not significantly different at 5% level of LSD.…”

More fertile florets and grains per spike can be achieved at higher temperature in wheat lines with high spike biomass and sugar content at booting

“…Dougherty et al (1975) and Fischer and Stockman (1980) have shown that increased levels of water soluble carbohydrates (WSC) in the spike were concurrent with higher grain number per spikelet and per spike in crops responding to shading, thinning, irrigation and fertilisation. Subsequently, Fischer (1985) captured the response of grain number m -2 to resource availability during the period of rapid spike growth in the photothermal quotient, the ratio between daily photosynthetically active radiation (PAR) and average temperature. Essentially, a higher amount of radiation absorbed during that period was positively related to grain number, whereas higher temperatures had the antagonistic effect of shortening the period, leading to a lower spike biomass and grain number per unit area (Fischer 1985).…”

“…Subsequently, Fischer (1985) captured the response of grain number m -2 to resource availability during the period of rapid spike growth in the photothermal quotient, the ratio between daily photosynthetically active radiation (PAR) and average temperature. Essentially, a higher amount of radiation absorbed during that period was positively related to grain number, whereas higher temperatures had the antagonistic effect of shortening the period, leading to a lower spike biomass and grain number per unit area (Fischer 1985). Temperature effects on floret fertility at the spike level have not yet been explored to the depth that photoperiod effects have, except for the shortening of the spike growth period and its indirect impact on spike biomass.…”