DOI: 10.5061/dryad.g79cnp5qt
title: Positive associations of soil organic matter and crop yields across a regional network of working farms

description: The amount of soil organic matter (SOM) is considered a key indicator of
 soil properties associated with higher fertility. Despite the ubiquity of
 assumptions surrounding SOM’s contributions to soil functioning, we lack
 quantitative relationships between SOM and yield outcomes on working
 farms. We quantified the relationship between SOM and yields of corn (Zea
 mays L.) and silage for a dataset of 170 fields arrayed across 49 farms in
 a network of growers based in Wisconsin and Minnesota, USA. As SOM
 concentrations increase, so do yields, though gains start to level off
 around 4% SOM. When examining the relationship between yield and soil
 health indicators representative of biologically active carbon pools, we
 found that mineralizable carbon (min-C) has a stronger relationship with
 yield than permanganate oxidizable C (POXC). Mineral fertilizer, manure,
 and SOM had relationships of similar magnitude with yield, highlighting
 that SOM in combination with exogenous inputs likely plays an important
 role in driving agricultural productivity in this region. An SOM by crop
 rotation interaction indicated that the impact of SOM on crop yields
 varied depending on rotation (continuous corn versus corn in rotation).
 That is, continuous corn had lower yields than corn in rotation despite
 higher SOM concentrations. Our findings provide insight into the
 relationship between indicators of soil health, farm management, and crop
 yields for a set of working farms and lend support to the goals of soil
 health initiatives that rest on building SOM in agricultural soils to
 improve agricultural outcomes.
description: Soil samples were collected across farm fields across Wisconsin
 and Minnesota across the years 2015, 2016, and 2017. Agronomic data were
 collected through interviews with participating farmers and were collected
 for each field. Field sampling of soils and yield was carried out within
 an 80-m<sup>2</sup> area on each farm. Yield data was
 determined as grain yield (n = 99) or silage yield (n = 71) based on how
 the field was to be harvested. For both silage and grain, yield data was
 collected by hand from three separate row lengths and harvested from a
 length of 3 m per row. Silage was cut 22.86 cm (9 inches) above the
 ground. The three areas for hand harvest were located by selecting three
 3-m replicates that were from different rows within the sampling area and
 were staggered lengthwise. Replicates were selected to be representative
 of the sampling area. The three yield samples were aggregated to produce
 one yield estimate per field. Yield data contained both yields of grain
 (at 15.5% moisture) and silage (at 65% moisture), so conversion factors
 specific to Wisconsin were used to convert grain yield to silage yield
 (Lauer 2006). We then converted silage yields (tons per acre) to metric
 units (megagrams per hectare) by multiplying silage yields by
 2.242.  Soil series, texture class, drainage class and
 slope class information was collected for each sampling area during the
 year of data collection using GPS coordinates and the NRCS SSURGO database
 via the SoilWeb soil survey browser developed by the California Soil
 Resources Lab at the University of California-Davis. 
 All fields were planted into corn the season soil samples were
 collected. Soil samples were also collected from within the same
 80-m<sup>2 </sup>area as yield data collection. In each area,
 three composite soil samples that each consisted of five soil cores were
 taken from a depth of 0 to 15 cm using a probe with an internal diameter
 of 2.5 cm. The soil samples collected from Minnesota fields were extracted
 to the same depth of 15 cm with a 3-inch diameter bulb planter and each
 composite soil sample consisted of five to 15 cores depending on the field
 size.  Lab analysis for POXC and min-C followed
 established laboratory methods (see accompanying paper for
 specifics). Additional soil analyses (pH and SOM) were performed according
 to methods prescribed by Wisconsin’s agricultural department and
 standardized across Certified Soil Testing Laboratories across the
 state.
description: This dataset is comprised of two tabs in a single excel file. See
 the "metadata" tab for information pertaining to the variables
 measured and analyzed. The "data" tab includes measured field
 and lab data as well as extracted data from SSURGO.