Tillage and root heat stress in wheat in central Alberta

Heat stress occurs often in wheat on the Canadian Prairies especially during reproductive growth, which has markedly negative impacts on yield. As previous studies reported that wheat growth was affected more by heat stress in roots than in shoot, we suspected that the cooling effect of no-till (NT) on soil may reduce the risk of root heat stress and benefit the yield compared with conventional tillage (CT). Data were collected between 2000 and 2003 from a tillage study using a continuous wheat cropping system on a Thin Black Chernozemic clay loam in central Alberta. Consistently lower soil temperatures at 5 and 10 cm in NT than CT were observed in the whole growing season every year. At the grain growth stage, NT mitigated heat shock (> 32 degrees C at 5 cm) which occurred in 2001 and 2002 under CT and considerably reduced root heat stress index (HSI), calculated as accumulations of hourly soil temperatures greater than 20 degrees C, every year compared with CT. By reducing root heat stress especially during the grain growth stage and slightly increasing pre-seeding soil moisture, no-till increased above-ground biomass (33-160%) and grain yield (18-147%) every year except 2003 when heat and water stress were relatively mild.