Analysis of spatial and yearly variation in winter survival of winter wheat

Four years of winter survival data for winter wheat (Triticum aestivum L.) were collected on a loam soil located on the Central Experimental Farm at O ttawa, Ontario (45 degrees 23'N, 75 degrees 43'W). The site was low-lying a nd subject to frequent winter flooding and ice sheet formation. It appeared level although there was microtopographic variation with a range in elevat ion of approximately 0.15 m. The objective of the study was to gain insight into factors which might affect winter survival. Two varieties, a soft whi te and a hard red winter wheat, were planted in September. Crop establishme nt was measured in late fall and the percentage survival was measured in Ap ril of the following year. We assumed the large spatial differences in surv ival were not totally random, but rather were affected by spatial variation in environmental factors such as snow and ice depth, soil moisture and tem perature. Hourly measurements of soil temperature at a depth of 0.05 m were recorded throughout the fall, winter and spring. Fall and spring soil mois ture at the same depth were measured on the plot, as well as snow and ice d epth at selected times throughout the winter. Measurements were taken on a grid covering the plot to help explain spatial variation in survival. In ad dition, detailed measurements of elevation were taken on a grid. Meteorolog ical data were available from the nearby weather site. While soil temperatu res were never low enough to kill plants according to the CERES model, the spatial variation in winter survival was associated with differences in ele vation and the resulting surface drainage patterns.