Field evaluation of traffic-induced compaction and its potential impact on soil physical characteristics and crop yield

Demonstration sites: We selected 4 unique locations to set up our field demonstrations during the harvest season of 2019. Three study sites (Freeman, Hutchinson County; Plankinton, Aurora County and Red Rock Township, Minnehaha County) were located in South Dakota and one located at Gales Township, Redwood County, Minnesota. However, no. of sub-fields and no. of blocks/replications in each location varies. Freeman site did not contain any subfield but had seven blocks of two treatments: ‘control’ vs ‘traffic’ of the combine with 180 bushels of soybeans load in addition to the weight of the combine. At Plankinton, four blocks were made of two treatments: ‘control’ vs ‘traffic’. Soil cores and other measurements were performed twice within each block during one sampling time. At Gales Township, we made two sub-fields: a single pass and a double pass experiment of a combined load of tractor and grain cart full of soybeans. In both subfields, 5 blocks were made of ‘control’ vs ‘traffic’ and each block was sampled twice to contain within block variability. At Red Rock township, we selected two side-by-side fields, representing the long-term no-till and conventional-till practices of two different producers. Due to the large variability within sites, we made two blocks in each field representing 'upslope' and 'downslope' and replicated them five times within each slope area. 

The first task in each demonstration site was to do compaction measurements with the availability of producer types of equipment. In some experiments, grain carts and tractors (e.g., Plankinton, Gales and Red Rocks Township's) were used and in the Freeman site, only combine weight was applied. So, the load in each experiment is different. There were sufficient replications (blocks) were made to draw a representative sample to conduct the experiments. For physical measurements, soil penetration resistance and bulk density were conducted. Other information, such as weight of machinery, wheel load, width of tires,  soil management and field operations information were collected from the producer during the field visits. In the next year, spring-2020, we were not able to collect the samples from Gales Township because of COVID restrictions due to out of state travel. However, the other three sites followed the normal sampling procedure just like the fall-2019. In this study, we were not able to collect agronomic measurements because of crop failures. 

Data Collection: After trafficking, measurements were taken within each wheel rut and from the non-trafficked area. Measurements within the wheel rut were taken at the deepest point of the cross-sectional area, corresponding to the area displaced by the tyre lug. We used the standard procedures described in the Methods of Soil Analysis, Part 4 – Physical Methods (Dane and Topp, 2002) to perform measurements of soil bulk density and penetration resistance. These measurements guide us about soil compaction and soil strength. Soil moisture content was measured simultaneously at each of the locations using disturbed samples that were analyzed using the gravimetric method.