Spatial interrelationships between wheat phenology, thermal time, and terrain attributes

Authors: McMaster, Gregory; Green, Timothy; Erskine, Robert - Rob; Edmunds, Debora; Ascough Ii, James

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2012
Publication Date: 7/23/2012
Citation: Mcmaster, G.S., Green, T.R., Erskine, R.H., Edmunds, D.A., Ascough II, J.C. 2012. Spatial interrelationships between wheat phenology, thermal time, and terrain attributes. Agronomy Journal. 104(4):1110-1121.

Interpretive Summary: How the phenology, or timing of developmental stages, of winter wheat varies across a field has received little attention. Yet, this spatial and temporal variability is important for assessing overall crop status and making key management decisions. An example would be the fungicide application to control Fusarium head blight is typically only done once at the time of flowering. The greater the variability in plants reaching flowering in a field, the less effective the fungicide application is in controlling the disease. The objectives of this study were to quantify the phenological variation across a landscape and determine if the observed variation could be correlated with air/soil thermal time and landscape position using quantitative terrain attributes. Four years of phenology and temperature data were collected on a 100-ha field of alternating wheat-fallow strips located in northeast Colorado. The developmental stages of jointing (J), flag leaf blade growth completed (FL), heading (H), anthesis (A, i.e. flowering), and physiological maturity (M) were monitored at 10 landscape positions (sites) each cropping season. At each site, 20 individual plants were tagged for phenological observation. Soil temperature at 3 cm below the surface and air temperature above the crop canopy (1 m height) were measured at each site. Variation in the timing of developmental stages across a landscape varied from less than 2 days to nearly 12 days for the same cultivar. The relative rankings from earliest to latest of when a developmental stage was reached at a site for different years were often, but not always consistent, so that normally the relative ranking of when a site reached J was indicative of reaching A and M. Mean phenological development at each site was best explained by soil thermal time. However, relative differences in thermal time among sites provided inconsistent explanations of phenological timing, with up to 72% of the relative difference in timing explained in 2004-05 season. The two years with the highest relationship between soil thermal time to a developmental stage and terrain attributes were 2004-05 and 2006-07. Terrain attributes also explained timing well in two relatively wet years, but not in the dryer years, and the attributes with the highest explanatory power varied among years and even among developmental stages. We conclude that further research is needed to clarify the complex interaction between wheat phenological variation and terrain attributes and how this influences the environmental variables controlling wheat phenology.

Technical Abstract: Variation of winter wheat (Triticum aestivum L.) phenology across complex terrain has received little attention. Spatial and temporal variability of a stand is important for assessing overall crop status and making key management decisions. The objectives of this study were to quantify the phenological variation across a landscape and determine if the observed variation could be correlated with air/soil thermal time and landscape position using quantitative terrain attributes. Four years of phenology and temperature data were collected on a 100-ha field of alternating wheat-fallow strips located in northeast Colorado. The developmental stages of jointing (J), flag leaf blade growth completed (FL), heading (H), anthesis (A), and physiological maturity (M) were monitored at 10 landscape positions (sites) each cropping season. At each site, 20 individual plants were tagged for phenological observation. Soil temperature at 3 cm below the surface and air temperature above the crop canopy (1 m height) were measured at each site. Terrain attributes were computed using 5-m grid elevation data. Variation in the timing of developmental stages across a landscape varied from less than 2 days to nearly 12 days for the same cultivar. The relative rankings from earliest to latest of when a developmental stage was reached at a site for different years were often, but not always consistent, so that normally the relative ranking of when a site reached J was indicative of reaching A and M. Mean phenological development at each site was best explained by soil thermal time. However, relative differences in thermal time among sites provided inconsistent explanations of phenological timing, with up to 72% of the relative difference in timing explained in 2004-05 season. The two years with the highest relationship between soil thermal time to a developmental stage and terrain attributes were 2004-05 and 2006-07. Terrain attributes also explained timing well in two relatively wet years, but not in the dryer years, and the attributes with the highest explanatory power varied among years and even among developmental stages. We conclude that further research is needed to clarify the complex interaction between wheat phenological variation and terrain attributes and how this influences the environmental variables controlling wheat phenology.