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Carbon and Nitrogen Storage are Greater under Biennial Tillage in a Minnesota Corn–Soybean Rotation

^a USDA-ARS, Soil & Water Management Unit, 439 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108
^b Dep. of Soil, Water, and Climate, 1991 Upper Buford Circle, Univ. of Minnesota, St. Paul, MN 55108; current address: USDA-ARS, North Central Soil Conservation Research Lab., 803 Iowa Ave., Morris, MN 56267

View larger version (56K): [in a new window]   Fig. 1. (a) Soil carbon (C) and (b) soil nitrogen (N) summed over varying depth intervals, as determined in 2000 and 2005 in plots maintained under conventional (CT), biennial tillage (BT), and no-till (NT) (mean ± standard error). Within each depth interval and across years, bars with the same letter designation are not significantly different (p < 0.05).

View larger version (23K): [in a new window]   Fig. 2. Relative storage rates of (a) carbon (C) and (b) nitrogen (N) as function of summarized depth interval during 1990–2000 and 1990–2005. Left-hand plates represent storage rates under biennial tillage (BT) and no-till (NT) relative to conventional tillage (CT), and right-hand plates represent storage rates under BT relative to NT. Each point is calculated as the difference in means between treatments from corresponding data in Fig. 1. Symbols () indicate that differences in corresponding means are not statistically significant at p < 0.05.

View larger version (24K): [in a new window]   Fig. 3. Soil CO2 fluxes (FCO2) and ancillary variables in 2003 (mean ± standard error). (a) FCO2, (b) cumulative 10-d precipitation and soil water-filled pore space, and (c) air and soil (50-mm depth) temperatures, under conventional (CT), biennial tillage (BT), and no-till (NT). LSD = least significant difference (p < 0.05). Significant differences are indicated by the symbols: a: NT > CT; b: NT > BT; c: BT > CT; d: CT > NT; e: BT > NT; f: CT > BT.

View larger version (27K): [in a new window]   Fig. 4. Soil CO2 fluxes (FCO2) and ancillary variables in 2004 (mean ± standard error). (a) FCO2, (b) cumulative 10-d precipitation and soil water-filled pore space, and (c) air and soil (50-mm depth) temperatures, under conventional (CT), biennial tillage (BT), and no-till (NT). LSD = least significant difference (p < 0.05). Significant differences are indicated by the symbols: a: NT > CT; b: NT > BT; c: BT > CT; d: CT > NT; e: BT > NT; f: CT > BT.

View larger version (20K): [in a new window]   Fig. 5. Relationships between water-filled pore space (WFPS) and (a) Q10 factors, (b) Ratkowsky parameters, and (c) temperature responses. Data shown in (a) and (b) represent annual mean values (± standard error). Data shown in (c) are from individual chamber measurements made 13 July– 29 July 2004.