1.    Materials and Methods

2.1 Sites description

The Triplett Van-Doren No-Tillage and Crop Rotation Experiment was established in 1962 in Wooster, Ohio, USA (40° 45′ N, 81° 54′ W) and 1963 in Hoytville, Ohio, USA (41°13'N 83°45'W). These sites include two contrasting soil types; at Wooster a silt loam (well-drained, fine-loamy, mixed, mesic Typic Fragiudalfs) (USDA-SCS, 1973), and at Hoytville, a clay loam (poorly drained, fine, illitic, mesic Mollic Ochraqualfs) (USDA-SCS, 1984). Both sites are located in a humid continental climate. Crop season (April to October) cumulative precipitation, and average, maximum, and minimum atmospheric temperature from 1962 to 2023 are shown in Figure 1a and 1b for Wooster and Hoytville, respectively.

2.2 Experimental design and treatments

The experiment consisted of a two-way full factorial with three levels of tillage intensity and three crop rotations deployed in a randomized complete block design with three replicates. The levels of tillage were: 1) No-Tillage; 2) Chisel; and 3) Moldboard. The No-Tillage treatment consisted of zero soil disturbance with all the residues from previous crop seasons left on the field. The Chisel treatment used a paraplow (1962-1983) and a chisel plow (1984-present) to till the soil while leaving at least 30% of the residues of the previous crop on the soil surface. The Moldboard treatment used a moldboard plow to invert the soil from 0-20 cm depth, with the majority of the crop residues buried in the soil profile. The Chisel and Moldboard treatments were performed in the spring at the Wooster site, and in the fall for the Hoytville site. Crop rotations were: 1) Continuous-Corn; 2) a two-year rotation of Corn-Soybean; and 3) a three-year rotation of Corn-Forage-Forage, with forage crops consisting of oats (Avena sativa L.) as a nurse crop seeded with a grass-legume mix including species such as orchard grass (Dactylis glomerata), tall fescue (Festuca arundinacea), alfalfa (Medicago sativa), red clover (Trifolium pratense), and clover (Trifolium repens L.). Corn, soybean, and oat crop residues remained in the field post-harvest, whereas alfalfa, clover, and red clover were harvested 2-3 times annually for hay after the establishment year. The first years (1962-1963) of the experiment included numerous compromised stands as equipment and field operation were being refined. As such, these years were excluded from the analysis.

The size of the plots was 22.3 x 4.3 m in Wooster and 30.5 x 6.4 m in Hoytville. Field operations not involving tillage or crop rotation were maintained consistently, so that fertility, pest, and weed management were similar across treatments. Historical agronomic management practices are part of The Ohio State University public resource and described in detail by Dick (2013). Crop varieties varied over the long-term experiment as genetic material was improved, but always represented widely available varieties that were typically planted by farmers in the region at the time. A list of the varieties used in the long-term experiment is provided for Wooster (Supplemental Table S1) and for Hoytville, Ohio (Supplemental Table S2). All phases of each crop rotation (corn, soybean, forage year 1, and forage year 2) and tillage treatments were present each year, allowing comparisons of corn yield under all the crop rotations and tillage treatments, and soybean yield under all tillage treatments.

2.3 Field crop yields

Corn and soybean were harvested from the center of each plot at physiological maturity with a small plot grain combine, and final yields were adjusted to moisture content of 15.5% for corn and 13.0% for soybean. The harvested plot area was used to determine annual yield per unit area (Mg ha⁻¹).