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Rotational and Cover Crop Determinants of Soil Structural Stability and Carbon in a Potato System

Dep. of Crop and Soil Sciences, Michigan State Univ., Kellogg Biological Station, East Lansing, MI 48824-1325

View larger version (34K): [in this window] [in a new window]   Fig. 1. Total monthly precipitation at Montcalm Research Farm near Entrican, MI for 2001–2004, and the 8-yr average. Annual precipitation was 991, 827, 478, and 735 mm for 2001, 2002, 2003, and 2004, respectively.

View larger version (21K): [in this window] [in a new window]   Fig. 2. (A) Annual carbon inputs from seven potato rotations (see Table 2 for system descriptions) and (B) averaged across systems for preplanned contrasts, S1 and S4 for the low input category; S2 and S6 for the medium category; and S3, S5, and S7 for the high carbon input category. Carbon inputs included above- and belowground organic material averaged over 2 yr (i.e., 2003 and 2004) and two entry years. Bottom, middle, and upper letters designate statistical significance for main crop, cover crop, and total carbon input across but not within systems. Columns with similar letters are not significantly different at 5%.

View larger version (22K): [in this window] [in a new window]   Fig. 3. Response over time of mean weight diameter (MWD, mm) as shown by percentage change observed in 2004 compared to 2001 at the Montcalm Research Farm, Entrican, MI. (A) Influence of seven potato rotations (see Table 2 for system descriptions); (B) Influence of the systems when grouped by carbon input based on low (LC, 1.2 Mg ha–1), medium (MC, 2.0 Mg ha–1), and high (HC, 2.8 Mg ha–1) carbon input. Values averaged over rotation entry point. Bars with the same letter designation are not statistically different at 5%.

View larger version (20K): [in this window] [in a new window]   Fig. 4. Response over time of macroaggregates as shown by percentage change observed in 2004 compared to 2001 at the Montcalm Research Farm, Entrican, MI. (A) Influence of seven potato rotations (see Table 2 for system descriptions); (B) Influence of the systems when grouped by C input based on low (LC, 1.2 Mg ha–1), medium (MC, 2.0 Mg ha–1), and high (HC, 2.8 Mg ha–1) C input. Values averaged over rotation entry point. Bars with the same letter designation are not statistically different at 5%.

View larger version (18K): [in this window] [in a new window]   Fig. 5. Relationship of total soil carbon (C, %), carbon input, and water stable macroaggregates (2–0.25 mm diam.) for a potato short rotation system study at the Montcalm Research Farm, Entrican, MI. Letters refer to comparisons in water stable aggregates. Systems with similar letters are not statistically different at 5%. 1 = potato-bare/snapbean-bare, 2 = potato-rye/snapbean-rye, 3 = potato-rye/corn-bare, 4 = potato-wheat/wheat-rye, 5 = potato-wheat/(wheat/clover)-clover, 6 = potato-(rye/vetch)/snapbean-(rye/vetch), 7 = potato-(rye/vetch)/corn-(rye/vetch).

View larger version (31K): [in this window] [in a new window]   Fig. 6. Potato U.S. No. 1 tuber yield expressed relative to yield of system 1, over 4 yr of a field trial study comparing seven short potato rotations at Montcalm Research Farm, Entrican, MI. Systems S1 through S7 are described in Table 2.