Ohio Soil Quality Research
Dr. Manbir Rakkar, assistant professor of nutrient management, took over for Dr. Stephen Culman at Ohio State University. She shared that Hoytville and Wooster have two of the longest-running soil quality research experiments. Started in 1962, over 100 research publications have been published on this research. This research was started by soil quality and no-till pioneers, Dr. Grover Triplett and Dr. David Van Doorhan, both deceased.
These pioneers had three basic research questions they wanted to answer. First, how much tillage, if any, is required to grow a good crop? Second, how do tillage and crop rotation affect crop yields? Third, how does tillage or no-till vary by soil type? All good questions, still being debated!
To answer these questions, they set up long-term plots at Hoytville on a flat (0-2%) heavy clay soil (Hoytville) and at Wooster on a silt loam soil with 6-10% slope. The tillage was continuous no-till, chisel plow, and moldboard plow. They included crop rotations of Corn (C) – Soybeans (S), C-S-W (wheat), C-C, and C-S-W-H (hay). They researched soil quality changes.
The most important soil quality factor is soil aggregation or soil structure. A lack of good structure would be described by farmers as soil compaction. Soil aggregates are the building blocks of good soil, increasing water infiltration, improving drainage, protecting carbon, building soil organic matter (SOM), decreasing soil erosion, and improving soil aeration. Good soil structure looks like black cottage cheese; the soil crumbles, but it also acts like a sponge to soak up nutrients and water and gives soils stability for equipment traffic.
The long-term research looked at what happened to soil structure over time. At Wooster (silt loam), there were significant differences or changes in the amount of good soil aggregates (good soil structure) over time as tillage changed from plowing to chisel plowing to no-till. However, the biggest positive change occurs when both no-till and a good crop rotation were employed. Cover crops were not part of this experiment, however, the C-S-W-H rotation had by far the biggest improvement.
At Hoytville, the change was much slower. The same positive gains were seen; it just took longer. On heavy clay soils, the plow pan is very hard, and it took years for the roots to recover from past tillage operations. All the plots had been tilled for at least 75 years before this experiment was started. The no-till plots (although slightly better) were not significantly different than the chisel plots. It was not until the crop rotation with more roots (C-B-W-Hay) that soil structure and soil quality improved dramatically. Again, live roots and crop diversification build soil aggregates along with no tillage disturbance. Key point: silt loam soils respond faster than clay loams.
At Wooster, the soil started out at 1.4% SOM and decreased over time to 1.0% on the plowed plots while the no-till plots improved to 2.5%. No-till by itself showed a very slow but steady gain in SOM. At Hoytville, the SOM started out at 1.5-2.0%, raised to 2-2.5% under chisel, and 2.0-3.5% under no-till. On the C-S-W-Hay plots, the no-till plus the diversified crop rotation increased SOM to 5%, followed closely by the continuous C-C. Corn is a grass and has lots of carbon. Typically, corn roots raise SOM while soybeans lose SOM. The soybean residue and root mass is so much less, plus it’s high in nitrogen, so it breaks down quickly.
The real question was how crop yields varied over time. The highest corn yields came with no-till plus the most diversified crop rotation (C-B-W-Hay). More roots, higher aggregates, better drainage, and less disease played a major factor in higher crop yields. An important note: at Wooster, the plowed plots were so badly eroded about 12 years ago that they took a bulldozer and redistributed the eroded sediment evenly across those plots. Yields went back up to about where the no-till plots were on the least diversified crop rotation (C-B). In my opinion, that ruined the plots, but it is what it is.
At Hoytville, no-till soybeans took 15 years to recover back to the chisel and plowed plots. Why? Soybeans have fewer roots and cannot break up the plow pan, especially on drilled soybeans. Soybeans are thin-stemmed, not many roots, and are hurt by compaction. Also, extreme weather (heavy rains, poor drainage) and less diversified crop rotations (C-B) make it take a long time for the soil to heal itself. Overall, no-till plus a diversified crop rotation (C-B-W-Hay) had a 26-bushel corn advantage over the plowed plots due to improved soil aggregates and soil quality.