Stubble Height Effect on Winter Wheat in the Northern Great Plains: I. Soil Temperature, Cold Degree-Hours, and Plant Population
Soil temperatures at the crown-depth of winter wheat (Triticum aestivum L.) that effect winterkill are generally known. In contrast, estimates of the effect that duration of the low temperature has on winter survival have not been published for winterhardy cultivars. Objectives were to relate temperature at the 4-cm soil depth to winter survival and develop capability to estimate survival based on accumulated cold degree-hours. Field trials were conducted during a 4- yr period on Williams loam (fine-loamy, mixed Typic Argiborolls) at Mandan, ND. Soil temperature at the 4-cm depth was measured at 2-hr intervals under three cultivars (Roughrider, Mironovskaya and Centurk) grown on four stubble heights (0, 5, 20, and 36 cm) and with two preplant water levels (0 and 50 mm supplemental water applied 1–2 wk before planting). Based on postwinter pretillering plant populations, complete winterkill was effected at about −20 °C soil temperature for Roughrider and Mironovskaya; Centurk did not survive at −18 °C. Population reductions began to occur when 4- cm depth soil temperatures were about 7 °C warmer than the lethal soil temperature. Duration of the lethal temperature effecting complete winterkill appears to be a matter of hours, based on cold degree- hours lower than a threshold temperature. This information, coupled with that of soil temperatures estimated from models, has utility in predicting degree of potential winterkill and reduction in plant populations.
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