Core Ideas Farms with known management histories contribute to soil health research. Rotation‐based systems may increase soil organic carbon when combined with appropriate tillage. Inherent soil properties must be considered in soil health assessments. Rotation effects were more noticeable than manure effects on soil health groupings. Data from on‐farm sites with known management histories are needed to quantify soil biological, chemical, and physical properties influencing carbon stocks and soil health. Surface (0–15 cm) and deep core (0–122 cm) soil samples were collected from fields under two rotations in Boone County, IA. The first was a 5‐yr corn [Zea mays (L.)], soybean [Glycine max (L.) Merr.], corn, oat [Avena sativa (L.)], and alfalfa [Medicago sativa (L.)] rotation to which 0, 18, or 36 Mg ha−1 of a manure/biosolids mixture was applied prior to planting corn. The second was an 8‐yr rotation with 6 yr of mixed grass and legume pasture followed by corn and an oat crop within which the pasture mixture was reestablished. Soil samples were collected evenly across the predominant soil map units (SMUs). Bulk density (BD), soil organic C (SOC), water‐stable aggregates (WSA), microbial biomass carbon (MBC), pH, Mehlich‐3 and diethylenetriaminepentaacetic acid (DTPA) extractable nutrients, electrical conductivity (EC), and nitrogen (total‐, NH4–, and NO3–N) were measured. Surface SOC data were consistent with Soil Survey values for the various SMUs. Crop rotation effects were more noticeable than manure/biosolid application rate effects. Data from this study were combined with previously published SOC data in Iowa. Results suggest extended rotation systems or those with cover crops may increase SOC 8 ± 4 g kg−1 compared to corn–soybean rotations (33 vs. 25 g kg−1). This study provides on‐farm reference values for soil health assessment tools and draws attention to the importance of inherent soil properties for these assessments.

The information presented in this article comes from an on‐farm soil health assessment study in central Iowa. Researchers utilized available farm management records to design a sampling strategy that represented the predominant soil map units and provided soil that was analyzed for biological, chemical, and physical indicators of soil health. Earn 1 CEU in Soil & Water Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/627.

Core Ideas No‐till with 35% stover removal met corn grain yield, income, and soil protection goals. Profitability for no‐till and chisel plow systems were equal due to lower machinery costs. Cost‐efficient stover harvest is essential for bio‐economy development. Developing a bio‐economy by harvesting crop residues from highly productive corn (Zea mays L.) cropping systems requires science‐based management decisions to maintain or enhance grain yield and soil, water, and air resources. Which tillage and stover harvest practices are best for accomplishing these goals? Continuous corn grain yield response to either no‐till or chisel plowing with two stover harvest rates (3.4 or 5.1 Mg ha−1 yr−1) was evaluated for 10 yr in central Iowa. Each tillage and stover removal combination was replicated four times. Year‐to‐year variation affected grain yield more than tillage practice (0.2 Mg ha−1) or stover removal (0.1 Mg ha−1). Grain yields were not statistically different (p = 0.33) between tillage systems. Including machinery costs made return on investment for chisel plow and no‐till equivalent even though no‐till yields were numerically lower. Net stover income per megagram was US$2 to $4 greater at the 3.4 versus 5.1 Mg ha−1 harvest rate because of more efficient harvesting. Among the four practices, no‐till with 3.4 Mg ha−1 stover harvest met multiple goals, including providing acceptable corn grain yields, positive net income per megagram stover, and sufficient residues to protect the soil.

Core Ideas Surface and subsurface soil K concentrations are both important. Soil‐test K levels in many central Iowa soils are below recommended levels. A cellulosic‐based bioeconomy will require higher soil‐test K concentrations. Plant‐available K below 15 cm averaged 100 to 110 mg kg‐1 in central Iowa. A reevaluation of plant‐available K within central Iowa soils is needed, especially if crop residues are harvested for animal feed or cellulosic feedstock. This study evaluated plant‐available K concentrations to depths of 120 cm (n = 2433) within soil profiles at 10 experimental sites. Data from 0‐ to 5‐, 5‐ to 15‐, 0‐ to 15‐, 15‐ to 30‐, 30‐ to 60‐, 60‐ to 90‐, and 90‐ to 120‐cm depths were compiled and evaluated. Based on over 400 samples collected from each depth increment below 15 cm, a reference value of 100 mg kg–1 appears common for central Iowa subsoils. Sixty‐four percent of all samples had soil‐test K levels below the 120 mg kg–1 threshold for very low nutrient status for crop production in Iowa. Only 28% of surface soil samples (<15‐cm depth) were considered to have at least optimum nutrient status with concentrations greater than 160 mg kg–1. As K is not an environmentally sensitive nutrient, its management in central Iowa soils has generally been neglected in recent years, particularly when compared with N and P management initiatives. Building awareness of soil K profile concentrations, rather than focusing only on surface concentrations, will be necessary to meet nutrient requirements for 21st century agricultural production.

Core Ideas In no‐till continuous corn, cover crops increased potentially mineralizable N. Particulate organic matter C responded to tillage and residue removal at 0 to 5 cm. Stover removal for 5 yr negatively affected 2 of 12 measured soil properties. Monitoring soil health indicators (SHI) will help ensure that corn ( Zea mays L.) stover harvest is sustainable. This study examines SHI changes after 5 yr of growing continuous corn with either chisel plow or no‐tillage practices and harvesting 0, ∼35, or ∼60% of the stover. Two no‐tillage treatments with a cereal rye ( Secale cereale L.) cover crop and stover harvest rates of ∼35 or ∼60% were evaluated. All eight treatments were replicated four times in a randomized complete block design at an 11‐ha site in Boone County, IA. Soil samples were collected following grain and stover harvest from 0‐ to 5‐ and 5‐ to 15‐cm depth increments. Particulate organic matter C (POM‐C) decreased when stover was removed or the soil was chisel plowed. No‐till with 0% stover removal had 10 mg g –1 POM‐C in the 0‐ to 5‐cm soil layer, which was 1.9‐fold higher than in other treatments. Potentially mineralizable N (PMN) was greater under cover crop treatments. Average PMN values were 56.9 and 45.5 µg g –1 PMN for no‐till with cereal rye at 0‐ to 5‐ and 5‐ to 15‐cm depths, respectively, compared with 17.5 and ‐3.7 µg g –1 PMN for the same no‐till treatments without cereal rye. Other soil properties did not respond to increasing levels of stover removal. At this location and at the studied removal rates, 5 yr of harvesting corn stover did not decrease soil health, but POM‐C data suggest that changes may be occurring. Long‐term monitoring should continue to assess corn stover harvest sustainability.

Crop residue management, provision of animal feed or bedding, and increased income are potential reasons for harvesting corn (Zea mays L.) stover. Reasons for not doing so include the need for crop residue to restore or increase soil organic matter, protect against wind and water erosion, and cycle plant nutrients. Bioenergy market development may increase the number of producers harvesting corn stover. Can farming practice data predict the likelihood for harvesting corn stover at a national scale? Farm operation, technology, and management variables from the 2010 Agricultural Resource Management Survey (ARMS) of U.S. corn growers were compared between operations that removed corn stover and those that did not. Nationwide, stover was removed from approximately 6.3% of all corn operations, indicating stover harvest was not a common practice in 2010. Factors increasing the likelihood for stover harvest included producing feed corn, managing crop residues for pest control, and farmland ownership. Technology and conservation practice adoption rates were similar in both groups. Excessive stover removal can increase soil degradation. Both groups had erosion control adoption rates of ≤10%, which may provide an additional disincentive to harvest stover. Overall, the evaluated variables were similar between producers that did and did not harvest stover. This assessment provides a 2010 national baseline that can be used for future evaluations as bioenergy and bioproduct markets develop.