Do cover crop mixtures improve soil physical health more than monocultures?

Rationale and Purpose — Adding multispecies cover crop (CC) mixtures could diversify the current simplified crop rotations and enhance soil health more than monoculture CCs. Further, CC mixtures with diverse plant species could adapt better to changing climatic and environmental conditions than monoculture CCs. However, our current understanding of the soil benefits of CC mixtures is still limited. This review discussed whether CC mixtures are better than monoculture CCs to improve soil physical health. Methods — All studies published up to May 25, 2023, comparing soil physical properties between CC mixtures and their constituents grown as monocultures were searched in the available databases. To avoid potential sampling bias, only studies that compared mixtures against all its constituents grown alone were discussed. Results — Cover crop mixture studies on soil physical properties were relatively few. Mixtures did not reduce soil bulk density in 83% of cases, penetration resistance in 75%, wet aggregate stability in 67%, and dry aggregate stability and saturated hydraulic conductivity in 100% compared with monoculture CCs. Mixtures had inconsistent effects on water infiltration and plant available water. The number of CC species in the mixture and management duration do not differently affect mixture impacts. The limited or no differences in soil physical properties between mixtures and monocultures could be due to the similarities in CC biomass production and soil C between these two systems. Conclusion — Cover crop mixtures do not enhance soil physical properties relative to monoculture CCs in most cases. However, the few cases where mixtures outperformed monocultures suggest soil benefits of mixtures should be evaluated on a site-specific basis. More long-term (\u3e 10 yr) data are needed for more definitive conclusions. Highlight — Cover crop mixtures do not generally improve soil physical health more than monoculture CCs

Predicting soil wind erosion potential under different corn residue management scenarios in the central Great Plains

Various models and simplified equations are available to predict wind erosion potential. However, their performance can be often site-specific, depending on soil characteristics and agronomic practices, warranting sitespecific model validations. Thus, in this study, we 1) validated the wind erodible fraction (WEF) predictive equations by Fryrear et al. (1994) and López et al. (2007) and 2) estimated the total soil loss with the Singleevent Wind Erosion Evaluation Program (SWEEP) using 3-yr measured data from six experiments located across a precipitation gradient in the central Great Plains. Each site had three corn (Zea mays L.) residue removal treatments: control (no removal), grazed, and baled. The measured and predicted WEF were significantly correlated. While the Fryrear et al. (1994) equation performed better than the López et al. (2007) equation, it underestimated WEF with 59% uncertainty across site-years. To reduce this underestimation and uncertainty, we developed a new statistical equation (WEF%=84.3+2.64×% silt-0.30×% clay-7.43×% organic matter- 0.15×% residue cover; r2=0.56). The predictive ability of the new equation was, however, no better than that of the existing predictive equations, suggesting the need for further refinement of WEF equations for the region. Simulated total soil loss by wind using the SWEEP model indicated that corn residue baling may increase soil loss if residue cover drops below 20% in the study region. Overall, the existing WEF equations could under- or overestimate WEF based on site-specific residue management, warranting further model refinement and site-specific validation, whereas the SWEEP estimated soil loss corroborates the critical importance of maintaining sufficient residue cover (\u3e 20%) to reduce wind erosion

Soil aggregation as affected by application of diverse organic materials

Application of organic materials can amend soil for improved water infiltration and reduced erodibility with effects varying with soil properties and the organic amendment type and rate. The effects of four livestock manures, three municipal biosolids, and one industrial by-product on dry and wet soil aggregate stability were evaluated at six sites in Nebraska. The amendments had similar C/N ratios but the biosolids had relatively high concentrations of lignin and cellulose. Soil organic matter (SOM) ranged from 21 to 65 g kg−1 and soils were silty clay loam, silt loam, or loamy sand. Soil was sampled for the 0- to 0.05-m depth at physiolog- ical maturity of the second corn (Zea mays L.) crop following amendment appli- cation. Aggregation was high with no amendment applied as \u3e95% of the soil was in water stable aggregates (WSA) \u3e 0.053 mm and was not affected by amend- ments with a few exceptions such as an increase in dry aggregate size and WSA 0.25–2.0 mm at one location. Dry aggregate size was much less for the loamy sand than with other soils. With SOM \u3e60 g kg−1 compared with less SOM, there was 42% more WSA \u3e2 mm and 38% less WSA \u3c2 mm diam. It cannot be concluded that organic amendment application will improve aggregation if SOM \u3e20 g kg−1 but larger effects may have occurred with: sampling sooner after amendment application; a 0- to 0.025-m sampling depth; or sampling at several months after harvest for reduced effect of the rhizosphere on aggregation

Two Models to Improve Undergraduate Writing Perception and Capabilities in Plant and Soil Sciences

Integration of professional writing with peer and instructor feedback as a graded component can be a strategy for writing improvement in an applied science undergraduate curriculum The objective of this study was to assess the benefit of professional writing in first and second-year undergraduate courses in Agronomy and Horticulture with two different models for the writing experience In the first-year course students communicated the results of two plant growth experiments in the format of a standard research article In the second-year course students wrote a group report as a review of published research or a research-based proposal to address a soil management issue Students were surveyed to determine their major and learning style evaluated with an 18-question assessment Students also chose their level of agreement with seven statements about the process and importance of professional scientific writing at the beginning and then at the end of the semester Survey results showed that confidence in using and creating professional writing increased among students for both courses Students in the first-year course showed a greater understanding of the value of peer reviewed researc

Cover Crops and Corn Residue Removal: Impacts on Soil Hydraulic Properties and Their Relationships with Carbon

Large-scale crop residue removal may negatively affect soil water dynamics. Integrating cover crop (CC) with crop residue management can be a strategy to offset potential adverse effects of residue removal. We studied: (i) the impact of corn (Zea mays L.) residue removal (56%) with and without the use of winter rye (Secale cereale L.) CC on soil hydraulic properties, (ii) whether CC would ameliorate residue removal effects on hydraulic properties, and (iii) relationships of hydraulic properties with soil organic C (SOC) and other properties under irrigated no-till continuous corn on a silt loam in south central Nebraska after 5 and 6 yr of management. Cover crops did not affect soil hydraulic properties. However, residue removal reduced cumulative water infiltration by about 45% in one year. Across years, residue removal reduced plant available water (PAW) by 32% and mean weight diameter of water-stable aggregates (MWD) by 23% for the upper 5-cm soil depth. Under no CC, residue removal reduced SOC concentration by 25% in the 0- to 5-cm and by 11% in the 5- to 10-cm depths. Under residue removal, CC increased SOC concentration by 18% in the 0- to 5-cm and by 8% in the 5 to 10-cm depths. Cover crop did not completely offset the residue removal-induced decrease in SOC concentration in the upper 5-cm depth. Plant available water decreased as SOC concentration and MWD decreased. After 6 yr, corn residue removal adversely affected soil hydraulic properties and SOC concentration, but CC was unable to fully offset such adverse impacts

Role of runoff and interflow in chemical transport for claypan soils

Students supported: 2 Student AssistantsNo-tillage systems have been found to increase water runoff for some soils. This is a major concern because this increased runoff has the potential for increasing the runoff of dissolved herbicides in the spring since these chemicals are not incorporated into the soil with no-tillage systems. This study was conducted to evaluate the effects of seven longterm crop and tillage systems on runoff and saturated hydraulic conductivity. The study was conducted near Kingdom City, Missouri on a Mexico silt loam (fine, montmorillonitic, mesic Udollic Ochraqualf). Runoff records from 1983 through 1993 were collected. The seven treatments consisted of no-tillage (NT), moldboard plow (MP), and chisel plow (CP) continuous corn (Zea mays L.) and continuous soybean (Glycine max L.) and fallow (F). Saturated hydraulic conductivity (Ksat), bulk density, organic matter, and water content were determined on soil cores removed from two interrow positions (trafficked and non-trafficked) and two soil depths (0 - 125 mm, 125 - 150 mm). Tillage had a small but significant effect on runoff, Ksat, bulk density, water content at sampling, and organic matter. The Fallow treatment produced the lowest values of Ksat (0.2 mm/h), bulk density (1.3 g cm^-3), and organic matter content (0.9 percent) for the surface 125 mm, as compared to the NT, MB and CP treatments. No differences in Ksat were found (p=0.587) among NT, MP and CP tillage treatments. Complex interaction effects of tillage vs. wheel traffic (p=0.039) and tillage vs. depth (p=0.003) suggested that tillage effects on Ksat vary with interrow position and soil depth. The NT (0.301 mm mm^-3) had significantly higher field volumetric water content than MP (0.285 mm mm^-3) and CP (0.282 mm mm^-3), when averaged across crops. Plots planted to corn had greater water content (0.297 mm mm^-3) compared to soybean plots (0.281 mm mm^-3). Runoff under F was the highest in each year from 1983 to 1993. The greatest amount of runoff occurred during Period 4 (harvest to planting). Runoff was lowest during Period 1 and 2. No-tillage had significantly higher runoff than MP and CP treatments during Period 4, spring (p=0.006); Period 4, fall (p=0.011 ); Fallow period (p=0.005); and Period 1 and 2 (p=0.021). Cumulative runoff with NT was significantly (p=0.001) higher compared to MP and CP, except from 1991 to 1993 in which differences were not significant (p=0.374). Corn produced lower runoff rates than soybean at the 0.05 level in Period 4, fall. Increased runoff in NT was attributed to higher water content and subsequently lower infiltration for this soil which had a nearly impermeable subsurface argillic horizon.Project # G-2029-02 Agreement # 14-08-0001-G-2029-0

Root biomass and soil carbon response to growing perennial grasses for bioenergy

Background: Dedicated bioenergy crops such as switchgrass (Panicum virgatum L.), miscanthus [Miscanthus x giganteus (Mxg)], indiangrass [Sorghastrum nutans (L.) Nash], and big bluestem (Andropogon gerardii Vitman) can provide cellulosic feedstock for biofuel production while maintaining or improving soil and environmental quality. To better understand bioenergy crop effects on soils, we studied changes in soil properties of a Tomek silt loam under inorganic fertilization of switchgrass after 4 years and warm-season grass monocultures and mixtures after 6 years in eastern Nebraska. Methods: The first experiment had two study factors: two switchgrass harvest dates (August and November) and nitrogen (N), phosphorus (P), and potassium (K) fertilization rates. Nitrogen fertilizer levels (0, 60, and 120 kg N ha−1) were the main plots, while P levels (0, 22, and 44 kg P ha−1) were the split plots and K levels (0, 11, and 22 kg K ha−1) were the split-split plots. The second experiment included six bioenergy feedstocks comprised of four monocultures [switchgrass (cv. Shawnee and an experimental strain tracked as Kanlow N1), indiangrass (Chief), and miscanthus (Mxg)] and two mixtures [big bluestem (Goldmine) + indiangrass (Warrior) + switchgrass (Shawnee) and big bluestem (Bonanza) + indiangrass (Scout) + switchgrass (Shawnee)]. Soil samples were analyzed for root biomass, soil organic C (SOC), total N, bulk density, aggregate stability, and pH. Results: In the first experiment, inorganic fertilization and harvest dates had no effect on switchgrass root biomass, SOC pools, soil aggregate stability, and other properties. In the second experiment, cumulative root biomass under Chief indiangrass monoculture was lower than that under other grass monocultures and mixtures except miscanthus. These results suggest that inorganic fertilization and harvest dates do not affect soil properties in the short term, but Chief indiangrass monoculture may have lower root biomass than other grasses. Conclusions: Overall, fertilization management did not induce changes in root biomass and soil properties, but Chief indiangrass monoculture had lower cumulative root biomass compared with mixtures and switchgrass monocultures, suggesting that cultivar selection will affect root biomass accumulation. Further monitoring is needed to determine long-term changes in root biomass and soil properties under these bioenergy crop systems

Identifying and Addressing Soil Property Issues Affecting Roadside Vegetation Establishment

Attaining adequate vegetation cover along highways is important for NDOR to comply with EPA’s stormwater regulations. However, low plant cover is a common problem on shoulders (first 16 feet off the pavement) of many highways in Nebraska. The ultimate goal of this study is to identify cost-effective engineering solutions that assure adequate seed beds (i.e., soil conditions) for establishment of selected seeding mixtures. The objectives of this study are to (1) characterize the soil properties along roadsides where vegetation stands have not developed well, and (2) verify the effects of select soil property parameters on plant germination and establishment. Sampling occurred at multiple locations along the highways near Beaver Crossing and Sargent, NE. At each location, soil samples were collected from a transect of multiple landscape positions, perpendicular to the highway. The soil physical properties measured included cone index, sorptivity, and aggregate stability, while the soil chemical properties measured included EC, pH, organic matters, Na, and Ca. Results show that the soils near the edge of the highway pavement were highly compacted. Also, the soils had higher pH, lower organic matter, and higher salt levels than optimal conditions. In the subsequent greenhouse studies, a factorial design was used to test three factors: soil compaction (i.e., 1.5, 1.7, and 1.9 g cm-3 soil compaction levels as well as sand as control), timing of salt stress (2 pulses of salt treatment applied pre-germination and post-germination as well as no-salt control), and plant species (buffalo grass, tall fescue, and western wheat grass). Results from the greenhouse studies showed that the three plant species exhibited different germination and early survival responses to the soil compaction and salt treatments. Tall fescue is better suited for site re-vegetation especially if salt is present in the soil prior to germination. Statistical analysis show that salt treatment had the most impact on species performance. Finally the project recommends a few engineering remediation strategies for plant establishment. Creating microsites on compacted soil surfaces could potentially alleviate the soil compaction issue by creating local environmental conditions favorable to plant establishment at microsites. To remediate the high salt levels in soil, it is recommended to consider alternative de-icing agents and amend zeolites and organics in soil

Can Cover Crop Use Allow Increased Levels of Corn Residue Removal for Biofuel in Irrigated and Rainfed Systems?

Corn (Zea mays L.) residue removal at high rates can result in negative impacts to soil ecosystem services. The use of cover crops could be a potential strategy to ameliorate any adverse effects of residue removal while allowing greater removal levels. Hence, the objective of this study was to determine changes in water erosion potential, soil organic C (SOC) and total N concentration, and crop yields under early- and late-terminated cover crop (CC) combined with five levels of corn residue removal after 3 years on rainfed and irrigated no-till continuous corn in Nebraska. Treatments were no CC, early- and late-terminated winter rye (Secale cereale L.) CC, and 0, 25, 50, 75, and 100% corn residue removal rates. Complete residue removal reduced mean weight diameter (MWD) of water-stable aggregates (5 cm depth) by 29% compared to no removal at the rainfed site only, suggesting increased water erosion risk at rainfed sites. Late-terminated CC significantly increased MWD of water-stable aggregates by 27 to 37% at both sites compared to no CC, but early-terminated CC had no effect. The increased MWD with late-terminated CC suggests that CC when terminated late can offset residue removal-induced risks of water erosion. Residue removal and CC did not affect SOC and total soil N concentration. Particulate organic matter increased with late-terminated CC at the irrigated site compared to no CC. Complete residue removal increased irrigated grain yield by 9% in 1 year relative to no removal. Late-terminated CC had no effect on corn yield except in 1 year when yield was 8% lower relative to no CC due to low precipitation at corn establishment. Overall, late-terminated CC ameliorates residue removal-induced increases in water erosion potential and could allow greater levels of removal without reducing corn yields in most years, in the short term, under the conditions of this study

Soil carbon increased by twice the amount of biochar carbon applied after six years: Field evidence of negative priming

Applying biochar to agricultural soils has been proposed as a means of sequestering carbon (C) while simultaneously enhancing soil health and agricultural sustainability. However, our understanding of the long‐term effects of biochar and annual versus perennial cropping systems and their interactions on soil properties under field conditions is limited. We quantified changes in soil C concentration and stocks, and other soil properties 6 years after biochar applications to corn (Zea mays L.) and dedicated bioenergy crops on a Midwestern US soil. Treatments were as follows: no‐till continuous corn, Liberty switchgrass (Panicum virgatum L.), and low‐diversity prairie grasses, 45% big bluestem (Andropogon gerardii), 45% Indiangrass (Sorghastrum nutans), and 10% sideoats grama (Bouteloua curtipendula), as main plots, and wood biochar (9.3 Mg/ha with 63% total C) and no biochar applications as subplots. Biochar‐amended plots accumulated more C (14.07 Mg soil C/ha vs. 2.25 Mg soil C/ha) than non‐biochar‐amended plots in the 0–30 cm soil depth but other soil properties were not significantly affected by the biochar amendments. The total increase in C stocks in the biochar‐amended plots was nearly twice (14.07 Mg soil C/ha) the amount of C added with biochar 6 years earlier (7.25 Mg biochar C/ha), suggesting a negative priming effect of biochar on formation and/or mineralization of native soil organic C. Dedicated bioenergy crops increased soil C concentration by 79% and improved both aggregation and plant available water in the 0–5 cm soil depth. Biochar did not interact with the cropping systems. Overall, biochar has the potential to increase soil C stocks both directly and through negative priming, but, in this study, it had limited effects on other soil properties after 6 years