Influence of Subsurface Drainage on Soil Temperature in a Cold Climate

Soil temperature during springtime is an important factor for crop establishment and growth in poorly drained soils of northwest Minnesota. In this region, shallow water tables causing spring planting delays and excess water conditions during the growing season, may have contributed to significant unplanted cropland and yield reductions in recent years. Temperature is a regulating factor for many biological and chemical processes in the soil. One of the most commonly cited benefits of subsurface drainage on poorly drained soils is faster soil warm-up in the spring. Previous studies of this phenomenon do not provide definitive conclusions concerning the influence of soil drainage on soil temperature. The results of three site years of field observations of soil temperatures from drainage research plots at two locations in northwest Minnesota are presented herein. Replicated soil temperature and water table depths were measured continuously at five depths for two drain spacings and an undrained treatment. Subsurface drainage was found to significantly increase soil temperatures in both a coarser textured Vallers loam soil and a finer textured Hegne silty clay loam soil. Up to $4°\mathrm{C}$ temperature increases occurred primarily between May and July with the greatest increases at $30–60\mathrm{cm}$ depths. Treatments with narrow drainage spacing showed a greater spring temperature increase than treatments with wider drainage spacings.