DOI: 10.5061/dryad.15dv41nzp
title: Soil properties and their interactions on organic farms in Nebraska

description: Sustainable soil productivity is a function of soil chemical, physical,
 and biological main and interaction effects that vary with inherent soil
 properties, topography, crop, location, and management. These effects were
 investigated using soil samples collected at geo-referenced points from
 119 fields on 15 organically certified farms across Nebraska. Observations
 are reported for 46 variables. Most fields had adequate soil conditions
 for high productivity. The irrigated versus rainfed effects differed for
 several soil properties in western compared with eastern Nebraska. On
 average, about 80% of the soil was in water-stable aggregates (WSA) of
 &gt;0.05 mm diameter with more aggregation and arbuscular mycorrhizal
 fungi (AMF) with pasture compared with cropland. Variation in soil
 microbial biomass (SMB) was more affected by variation in soil and climate
 properties than by management. Increased SOM for cropland in eastern
 Nebraska was positively related to SMB but not to AMF or the biomass
 ratios of saprophytic fungi (Fs) to bacteria and of actinomycetes to other
 bacteria. After accounting for the effect of SOM, SMB was most positively
 related to crop growth at the time of sampling, and availability of K and
 S. Mehlich-3 P was positively correlated with SMB but P and Zn
 availability were negatively correlated to AMF. Increased soil pH was
 associated with greater biomass of Fs and eukaryotes but not of bacteria.
 The SMB was generally less for pastures in western Nebraska compared with
 other field types. In conclusion, the soil properties of these organic
 farms were generally suited to high productivity and SMB had a strong,
 positive relationship to SOM.
description: Soil samples for the 0 to 7.5 and 7.5 to 15 cm depths were
 collected in May and June 2013 at geo-referenced points from 119 fields on
 15 certified organic farms across different topographic forms of Nebraska.
 Nine farms were in the rolling hills of eastern Nebraska with loess and
 glacial till soils, five were on the plains with primarily loess soil, and
 one farm was in the Platte River valley. Observations were made on the
 current crop, rotation sequence, irrigation, and use of manure or other
 organic material. Soil samples were collected in three sets
 One set of soil samples was dried, ground, and analyzed for SOM,
 pH, buffer pH, electrical conductivity, Mehlich-3 P,
 SO<sub>4</sub>-S, NO<sub>3</sub>-N, DTPA-extracted
 Zn, and 1-N ammonium acetate exchangeable Ca, Mg, K, Na, and CEC (Ward
 Laboratories, Inc., Kearney NE). Organic C and N were analyzed using a
 Flash 2000 Organic Elemental Analyzer. Another set of
 samples was analyzed for particulate organic matter, particle size
 distribution (Kettler et al., 2001), and water-stable soil aggregation
 (WSA). These were air-dried, sieved to remove and discard aggregates of
 &gt;8 mm diameter, and plant materials were removed. Determination of
 cPOM and fPOM was by weight-loss on ignition
 (450<sup>o</sup>C) according to Cambardella et al. (2001). Dry
 weights (g kg<sup>-1</sup>) of WSA&gt;2, WSA0.25-2, and
 WSA&lt;0.25 were determined (Quincke et al., 2007).
 Soil samples<b> </b>for
 fatty acid methyl ester concentration (FAME)
 analysis were kept in a cooler during transport to the lab and then stored
 frozen at -20 <sup>o</sup>C. Frozen soil was slightly thawed
 in the refrigerator, sieved to 4 mm diameter, and extracted for FAME. The
 FAME biomarkers used to represent taxonomic and/or functional groups
 were:<i> </i>C18:2c9,12 for saprophytic fungi (Fs); C16:1c11
 for arbuscular mycorrhizal fungi (AMF); <i>i</i>C14:0,
 <i>i</i>C15:0, <i>a</i>C15:0, C15:0,
 <i>i</i>C16:0, <i>i</i>C17:0,
 <i>a</i>C17:0, <i>cy</i>C17:0, C17:0,
 <i>cy</i>C19:0(9,10), <i>cy</i>C19:0(11,12),
 10MeC18:0 and 10MeC19:0 for total bacteria. The <i>cy</i>C17:0
 and <i>cy</i>C19:0 represented bacteria that form cyclopropyl
 rings. The 10-methyl fatty acids (B<sub>10Me</sub>) were
 indicative of some actinomycetes. Eukaryotic biomarkers, exclusive of Fs
 and AMF, were represented by C20:4 (5,8,11,14). C20:2, C20:3, and C20:5.
 The total of all FAME biomarkers was used to represent SMB
 concentration.
description: There are a few missing values (marked N/A) due to the values
 being not applicable or unavailable due to missing sample or problems in
 lab analysis but the dataset is sufficient for statistical
 analyses.