Hugh J. Earl

Hugh Earl
Associate Professor
Department Chair



519-824-4120 x58568


B.Sc. University of Guelph;
M.Sc. University of Guelph;
PhD. University of Guelph


Crop Science Building


314 CRSC

In our research program we study the physiological basis of yield determination in several of Canada’s major agronomic crops – soybean, corn and canola.  Modern approaches to plant breeding allow for the efficient and targeted selection of specific physiological traits. This approach offers great potential for rapid progress, but only if we know in advance which traits are desirable!

One goal of our research is to identify those morphological / physiological characteristics that can impart enhanced tolerance of abiotic stresses, such as drought, chilling and excessive heat. A related activity is the screening of available germplasm for useful variability in these traits. Our main focus is always at the level of the whole crop canopy since this is the most relevant level of organization for yield determination.  Surprisingly, many traits that can seem important at the single plant scale turn out to be of little relevance at the crop scale.  Even so, we carry out many experiments at lower levels of organization to try to gain a more thorough mechanistic understanding of processes that emerge at the plant community scale.

In addition to the potential contribution to genetic improvement, better understanding the physiological basis of yield formation in these crops often leads to improved recommendations for agronomic practices.

Research questions currently being addressed in our program:

  • How do maize inbreds compare to their F1 hybrid for respiratory carbon losses over an entire growing season? (Visiting PhD student Javier DiMatteo)
  • What is the physiological basis of yield enhancement resulting from foliar boron application to spring canola? (MSc Research of Laxhman Ramsahoi)
  • Does manure application to spring canola result in benefits that can not be replicated by applying the equivalent inorganic nutrient compliment as starter fertilizer? (MSc Research of Meagan Griffiths)
  • Does the increased branching that occurs in canola at lower seeding rates enhance the crop’s resilience to transient episodes of drought stress during pod set? (MSc Research of Meagan Griffiths)
  • Does the increased branching that occurs in canola at lower seeding rates increase the crop’s susceptibility to Swede midge infestation? (Research conducted by field technicians Godfrey Chu and Laxhman Ramsahoi)
  • Does variation in water use efficiency among commercial soybean varieties grown in Ontario result in differences in their susceptibility to naturally-occurring soil water deficits? (MSc Research of Bridget Visser)
  • What physiological traits underlie genotypic differences in early-season chilling tolerance of maize inbreds and their hybrids?  (PhD research of Wisam Obeidat)
  • What patterns of gene expression are associated with differences in early-season chilling tolerance in maize? (PhD research of Luis Avila Bolivar)
  • How can we use canopy reflectance spectroscopy to identify nutrient  deficiencies in canola?


PBIO*3110 Crop Physiology

Relevant Links:

Selected Publications:

Di Matteo, J.A., K.E. Goldenhar and H.J. Earl. (2018). Minimum daily respiration of maize: effects of growth stage and temperature, and relationship to total daily respiratory carbon loss. Crop Science. 58: 370-379.

Farid, M., H. Earl, K.P. Pauls and A. Navabi. (2017). Response to selection for improved nitrogen fixation in common bean (Phaseolus vulgaris L.). Euphytica. 213: 99.

Ma, B.L., H. Zhao, Z. Zheng, C. Caldwell, A. Mills, A. Vanasse, H. Earl, P. Scott and D.L. Smith. (2016). Optimizing Seeding Dates and Rates for Canola Production in the Humid Eastern Canadian Agroecosystems. Agronomy Journal. 108: 1-11.

Farid, M., H. Earl and A. Navabi. (2015). Yield stability of dry bean genotypes across nitrogen-fixation-dependent and fertilizer-dependent management systems. Crop Science. 56: 1-10

Ma, B., D.K. Biswas, A.W. Herath, J.K. Whaken and H.J. Earl. (2015). Growth, yield, and yield components of canola as affected by nitrogen, sulfur, and boron application. Journal of Plant Nutrition and Soil Science. 178 (4): 658-670.

Davis, R.F., H. Earl and P. Timper. (2014). Effect of simultaneous water deficit stress and Meloidogyne incognita infection on cotton yield and fiber quality. Journal of Nematology. 46 (2): 108-118.

Waden-Coleman A.E., I. Rajcan and H.J. Earl. (2013). Dark-adapted leaf conductance, but not minimum leaf conductance, predicts water use efficiency of soybean (Glycine max L. Merr.). Canadian Journal of Plant Science.

Earl, H.J., C. Bernacchi and H. Medrano. (2012). Crop Photosynthesis. Chapter 32 in J. Flexas, F. Loreto and H. Medrano (eds.), Terrestrial Photosynthesis in a Changing Environment. Cambridge University Press. ISBN:9780521899413. (Published).

Earl, H.J., W. Liu, S.R. Bowley and M. Tollenaar. (2012). Effects of abiotic stress on respiratory carbon loss of two maize (Zea mays L.) inbred lines and their hybrid during silking and grain-filling. Crop Science. 52: 1795-1802.

Khanal, R.R., H. Earl, E.A. Lee and L. Lukens. (2011). The genetic architecture of flowering time and related traits in two early flowering maize lines. Crop Science. 51: 146-156.

Davis, R.F., H.J. Earl and P. Timper. (2009). Effect of simultaneous drought stress and root-knot nematode infection on cotton yield and fiber quality. Journal of Nematology. 41: 323.

Fish, D.A. and H.J. Earl. (2009). Water use efficiency is negatively correlated with leaf epidermal conductance in cotton (Gossypium spp.). Crop Science. 49: 1409-1415.

Queen, A., H.J. Earl and W. Deen. (2009). Light and moisture competition effects on biomass of red clover underseeded to winter wheat. Agronomy Journal. 101: 1511-1521.

Hufstetler, E.V., H.R. Boerma, T.E. Carter Jr. and H.J Earl. (2007). Genotypic variation for three physiological traits affecting drought tolerance in soybean. Crop Science. 47: 25-35.

Ennahli, S. and H.J. Earl. (2005). Physiological limitations to photosynthetic carbon assimilation in cotton under water stress. Crop Science. 45: 2374-2382.

Earl, H.J. and S. Ennahli. (2004). Estimating photosynthetic electron transport without photosystem II light saturation. Photosynthesis Research. 82: 177-186.

Earl, H.J., J.A. Ferrell, W.K. Vencill, M.W. Van Iersel and M.A. Czarnota. (2004). Effects of three herbicides on whole plant carbon fixation and water use by yellow nutsedge (Cyperus esculentus). Weed Science. 52: 213-216.

Ferrell, J.A., H.J. Earl and W.K. Vencill. (2004). Duration of yellow nutsedge (Cyperus esculentus) competitiveness after treatment with various herbicides. Weed Science. 52: 24-27.

Earl, H.J. (2003). A precise gravimetric method for simulating drought stress in pot experiments. Crop Science. 43: 1868-1873.

Earl, H.J. and R.F. Davis. (2003). Effect of drought stress on leaf and whole canopy radiation use efficiency and yield of maize. Agronomy Journal. 95: 688-696.

Ferrell, J.A., H.J. Earl and W.K. Vencill. (2003). The effect of selected herbicides on CO2 assimilation, chlorophyll fluorescence, and stomatal conductance in johnsongrass (Sorghum halepense L.). Weed Science. 51: 28-31.

Earl, H.J. (2002). Stomatal and non-stomatal restrictions to carbon assimilation in soybean (Glycine max) lines differing in water use efficiency. Environmental and Experimental Botany. 48: 237-246.

Earl, H.J. and M. Tollenaar. (1999). Using chlorophyll fluorometry to compare photosynthetic performance of commercial maize (Zea mays L.) hybrids in the field. Field Crops Research. 61: 201-210.

Earl, H.J. and M. Tollenaar. (1998). Differences among commercial maize (Zea mays L.) hybrids in respiration rates of mature leaves. Field Crops Research. 59: 9-19.

Earl, H.J. and M. Tollenaar. (1998). Relationship between thylakoid electron transport and photosynthetic CO2 uptake in leaves of three maize (Zea mays L.) hybrids. Photosynthesis Research. 58: 245-257.

Earl, H.J. and M. Tollenaar. (1997). Maize leaf absorption of photosynthetically active radiation and its estimation using a chlorophyll meter. Crop Science. 37 (2): 436-440.