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Mid-Continent Fall Temperatures at the 10-cm Soil Depth

USDA-ARS, North Central Soil Conservation Research Lab., 803 Iowa Ave., Morris, MN 56267

View larger version (18K): [in this window] [in a new window]   Fig. 1. Average daily soil temperatures at 10-cm depth from Grand Forks, ND, during autumn in 1999 and 2003. In 1999, once soil temperature dropped below 10°C, it stayed low for the remainder of the cold season, which is the desired scenario for fall-applied nitrogen fertilizer. In contrast, in 2003, after first dropping below 10°C, soil temperature rose above this level three times, which possibly enhanced nitrogen losses.

View larger version (38K): [in this window] [in a new window]   Fig. 2. Locations of sites from which soil temperature data were recorded and analyzed.

View larger version (20K): [in this window] [in a new window]   Fig. 3. Average dates (±SD) of the first day in autumn that soil temperature at 10-cm depth dropped below 10°C and the last day in autumn that soil temperature exceeded 10°C. Data are for 26 sites with weather stations along a north-south transect between 36° and 49° N latitude, approximating the mid-continent of the USA.

View larger version (20K): [in this window] [in a new window]   Fig. 4. (A) Average ranges of days between the first day in autumn that soil temperature at 10-cm depth dropped below 10°C (First10) and the last day in autumn that soil temperature exceeded 10°C (Last10) among 26 weather stations along a latitudinal transect. (B) Coefficients of variation associated with averages in Fig. 4A.

View larger version (30K): [in this window] [in a new window]   Fig. 5. (A) Cumulative number of days between the first day in autumn that soil temperature at 10-cm depth dropped below 10°C (First10) and the last day in autumn that soil temperature exceeded 10°C (Last10) during which average daily soil temperature at 10-cm depth exceeded 10°C along a latitudinal transect of weather stations. (B) Cumulative degree-days (base 10°C) associated with Fig. 4A.