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Aggregation and Organic Matter Protection Following Tillage of a Previously Uncultivated Soil

W.K. Kellogg Biological Station and Dep. of Crop and Soil Sciences, Michigan State Univ., Hickory Corners, MI 49060. A.S. Grandy currently at: University of Colorado–Boulder, Dep. of Geological Sciences, Boulder, CO 80309-0399

View larger version (36K): [in a new window]   Fig. 1. Mean weight diameter (MWD) of soil aggregates at 0- to 7- and 7- to 20-cm soil depth. The June 2002 sampling was performed before cultivation. The May 2003 samples were taken before the second cultivation. Treatment means are shown ± standard error (n = 4). * Indicates statistically significant (P < 0.05) differences between control and tilled treatments within a single sampling date; indicates significant differences between depths within a treatment and sampling date.

View larger version (37K): [in a new window]   Fig. 2. Tillage effects on the distribution of soil in four aggregate size classes at 0- to 7- and 7- to 20-cm soil depth. Numbers along the x axis correspond with aggregate size: 2000 = 2000–8000 µm; 250 = 250–2000 µm; 53 = 53–250 µm; and <53 = <53 µm. The May 2003 samples were taken before the second cultivation. Treatment means are shown ± standard error (n = 4). * Indicates statistically significant (P < 0.05) differences between control and tilled treatments within a single sampling date; indicates significant differences between depths within a treatment and sampling date. Size classes within a sampling date and treatment with different letters are significantly different.

View larger version (26K): [in a new window]   Fig. 3. Tillage effects on total sand-free aggregate C in 2002, 2003, and 2004. Initial cultivation was in June 2002. Treatment means are shown ± standard error (n = 4). * Indicates statistically significant (P < 0.05) differences between control and tilled treatments within a single sampling date; indicates significant differences between depths within a treatment and sampling date. Size classes within a sampling date and treatment with different letters are significantly different.

View larger version (25K): [in a new window]   Fig. 4. Tillage effects on the distribution of sand-free inter-aggregate light fraction organic matter in 2002, 2003, and 2004. Initial cultivation was in June 2002. Treatment means are shown ± standard error (n = 4). * Indicates statistically significant (P < 0.05) differences between control and tilled treatments within a single sampling date; indicates significant differences between depths within a treatment and sampling date. Size classes within a sampling date and treatment with different letters are significantly different.

View larger version (28K): [in a new window]   Fig. 5. Tillage effects on the distribution of sand-free intra-aggregate light fraction organic matter in 2002, 2003, and 2004. Initial cultivation was in June 2002. Treatment means are shown ± standard error (n = 4). * Indicates statistically significant (P < 0.05) differences between control and tilled treatments within a single sampling date; indicates significant differences between depths within a treatment and sampling date. Size classes within a sampling date and treatment with different letters are significantly different.