Skip to main content

The influence of inherent soil factors and agricultural management on soil organic matter


Ruark, Matt et al. (2023), The influence of inherent soil factors and agricultural management on soil organic matter, Dryad, Dataset,


The accumulation of soil organic matter (SOM) is vital to the agronomic and environmental functioning of agroecosystems, yet the relative influence of inherent soil properties and agricultural management practices on SOM dynamics are not often addressed in individual studies. Using a network of 218 operating farm fields across Wisconsin and southern Minnesota, USA, this research employs single variable analysis (ANOVA and regression) and regression tree analysis to assess the effects of soil properties (texture, drainage class, pH) and management variables related to crop rotation, tillage, cover cropping, and manure application on SOM, as well as total organic carbon (TOC) and total nitrogen (TN) in the upper 15 cm. Single variable analysis revealed that greater SOM, TOC, and TN were associated with poorly drained soil, tile-drained fields, high-clay content soil, and high biomass crop rotations. Soil organic matter (SOM) and TOC were strongly related (R2=0.71), but different regression trees were produced; SOM was most influenced by clay content, while TOC was most influenced by drainage class. Future assessment for the building of SOM or TOC should be conducted with drainage and texture class categories and on a regional basis, given that these factors influence the practices that occur within landscapes. A rapid building of data sets through unstructured sampling, including an abundance of meta-data, should be a research priority in agricultural science to identify practices to build SOM on a regional basis.


Field descriptions and samplingSoil samples were collected from 218 farm fields across Wisconsin (n=212) and Minnesota (n=6) (Fig. 1) between 2015 and 2017. The fields represent a range of cropping systems common in the Upper Midwest. Six distinct regions were sampled and identified by either general region of a state (northeast Wisconsin, southeast Wisconsin, and southern Minnesota) or by watershed (Dry Run, Elk Creek, Jersey Valley) (Fig. 1). Elk Creek and Jersey Valley exist within the Driftless Region, an area characterized by steep slopes and flash flood events. All fields were planted into corn the season soil samples were collected. In each field, three composite soil samples were collected that consisted of five 0- to 15-cm soil cores collected with a probe of 2.5- or 7.5-cm internal diameter. Most soil samples (194) were collected prior to fertilizer application and corn planting (mid-April); 24 samples were in late June (2017 only). Soil sampling was conducted with an area of 36 m2 within the dominant soil map unit as identified by the USDA NRCS Web Soil Survey (Soil Survey Staff, 2019) and from an area identified by the farmer where average crop yields were obtained. The composite samples were stored cold and transferred into a freezer with 1 to 6 hours of sampling to stagnate microbial metabolism and organic matter mineralization. Within 30 days, soil samples were thawed and dried for 1 week at 32˚C in a forced-air drier, ground to pass through a 2-mm sieve, and stored at room temperature until analysis.

Inherent soil properties such as texture class, sand and clay content of the surface horizon, and drainage class were obtained from the USDA NRCS Web Soil Survey (Soil Survey Staff, 2019). Agronomic management information regarding crop rotation, tillage practices, cover crop use, tile drainage, and manure and fertilizer applications were obtained directly from each farmer through an in-person interview. Long-term crop management practices were difficult to obtain for all farms; for example, it was difficult to get accurate information on how long a field had received manure. The dataset constructed uses recent cropping history (past 5 years) as a representation of specific management practices (that often have occurred much longer than just the past 5 years). Based on the collected data, four categories for crop rotation (continuous corn, corn-soybean, corn with small grain, and corn with alfalfa) and five categories for previous crop were created (Supplementary Table 2). Two categorical data were developed for cover crops: if there was a cover crop planted last fall (yes or no) and the number of times a cover crop was planted in the past 5 years. Tillage practices were categorized by practice [no tillage, minimum tillage (including vertical tillage or strip tillage), and conventional tillage (chisel, disk or moldboard)] and by the number of tillage passes that occurred between harvest of the previous year’s crop and the planting of the current year’s crop (0 to 4). Tillage was only considered no-till or minimum tillage if practiced for more than 4 years. Manure was categorized based on the number of manure applications that occurred in the past 5 years (0 to 5), when manure was applied in the past year (none, summer, fall, winter, or spring), and manure type (species and if solid or liquid). Tile drainage presence was also noted (yes or no). The manure N, fertilizer N, and total N input (which includes manure, fertilizer, and legume N inputs) (kg ha-1) to the previous corn crop were also collected. If farmers did not have manure analysis, estimates of available N were used (Laboski & Peters, 2012); N input from alfalfa biomass was assumed to be 101 kg ha-1 (Laboski & Peters, 2012). 

Soil analysis.  Soil pH and SOM were analyzed by the University of Wisconsin Soil and Forage Analysis Laboratory (Marshfield, Wisconsin). Soil pH was calculated using a 1:1 slurry of 10 g soil and 10 mL of deionized water and measured with a glass electrode (Peters et al., 2015). Soil organic matter values were determined through loss on ignition by heating the soil to 360˚C for 2 hours (Combs et al., 2015). Total C (TC) and total N (TN) levels were determined via the dry combustion method using a Flash EA 1112CN Automatic Elemental Analyzer (Thermo Finnigan, Milan, Italy). Between 8 to 10 mg of finely ground soil were packed into a 5 mm by 9 mm tin capsule prior to combustion at temperatures exceeding 1000°C. Soils with pH greater than 7.0 were tested for effervescence using 5% HCl as an indicator if carbonates were present. If carbonates were not observed, TC was assumed to be TOC; if carbonates were observed, they were subject to acid-fumigation prior to dry combustion (Harris et al., 2001). Only 25 samples were analyzed for carbonates and 13 of those had carbonate concentrations above the detection limit. There were 218 samples for SOM, but only 2016 for TOC and TN because two samples were accidently discarded.


USDA NRCS, Award: 69-3A75-14-270

North Central SARE Grad Student Project, Award: GNC17-249

Dairy Farmers of Wisconsin

University of Wisconsin-Madison

Dairy Innovation Hub