Shannon L. Osborne

Soil Microbial Community Response to Corn Stover Harvesting Under Rain-Fed, No-Till Conditions at Multiple US Locations

Harvesting of corn stover (plant residues) for cellulosic ethanol production must be balanced with the requirement for returning plant residues to agricultural fields to maintain soil structure, fertility, crop protection, and other ecosystem services. High rates of corn stover removal can be associated with decreased soil organic matter (SOM) quantity and quality and increased highly erodible soil aggregate fractions. Limited data are available on the impact of stover harvesting on soil microbial communities which are critical because of their fundamental relationships with C and N cycles, soil fertility, crop protection, and stresses that might be imposed by climate change. Using fatty acid and DNA analyses, we evaluated relative changes in soil fungal and bacterial densities and fungal-to-bacterial (F:B) ratios in response to corn stover removal under no-till, rain-fed management. These studies were performed at four different US locations with contrasting soil-climatic conditions. At one location, residue removal significantly decreased F:B ratios. At this location, cover cropping significantly increased F:B ratios at the highest level of residue removal and thus may be an important practice to minimize changes in soil microbial communities where corn stover is harvested. We also found that in these no-till systems, the 0- to 5-cm depth interval is most likely to experience changes, and detectable effects of stover removal on soil microbial community structure will depend on the duration of stover removal, sampling time, soil type, and annual weather patterns. No-till practices may have limited the rate of change in soil properties associated with stover removal compared to more extensive changes reported at a limited number of tilled sites. Documenting changes in soil microbial communities with stover removal under differing soil-climatic and management conditions will guide threshold levels of stover removal and identify practices (e.g., no-till, cover cropping) that may mitigate undesirable changes in soil properties.

Insect-damaged corn stalks decompose at rates similar to Bt-protected, non-damaged corn stalks

The relative decomposability of corn (Zea mays L.) residues from insect (Bt)-protected hybrids and conventional hybrids cultivated under insect pressure was investigated in two studies. Above-ground biomass, residue macromolecular composition, and stalk physical strength were also measured. In the first decomposition study, chopped residues (stalks and leaves) were used from a corn rootworm-protected (Cry3Bb1) hybrid and its non-Bt near isoline that were grown in replicated plots infested with corn rootworms (Diabrotica spp.). In the second study, residue (intact stalk sections) was used from three European corn borer (ECB, Ostrinia nubilalis Hübner)-resistant (Cry1Ab) hybrids representing different seed manufacturer/maturity date series, their non-Bt near isolines, two Cry3Bb1-protected isolines, and three additional conventional hybrids, all cultivated in replicated plots under conditions of elevated ECB pressure. In both studies, insect-resistant residues decomposed at rates similar to their non-protected near isolines. No evidence was found that insect-protected hybrids produced more above-ground biomass or had distinct residue composition. While some measures of mechanical stalk strength indicated that ECB-damaged stalks were not as stiff as protected stalks, these physical differences did not translate into differences in residue decomposition. We conclude that while individual hybrids may vary in their production of biomass, residue composition or residue decomposability, these characteristics do not systematically vary with the presence of the Bt gene conferring insect resistance, even under conditions of insect pressure.

Soybean Growth Response to Low Rates of Nitrogen Applied at Planting in the Northern Great Plains

ABSTRACT Cool and wet soils at the time of soybean [Glycine max (L.) Merrill] planting in the northern Great Plains may reduce early crop growth and retard nitrogen (N) fixation. Application of N as starter fertilizer may increase initial growth of soybean, but may also negatively impact N fixation when environmental conditions improve. The objective of this study was to evaluate the impact of low rates of N applied at planting on soybean N fixation and crop growth in the northern Great Plains. A field experiment (2000–2002) was established within a two-year corn [Zea mays (L.)] soybean rotation using a split-plot design with four replications. Whole plots were no-tillage (NT) and conventional tillage (CT) and the split plots were starter fertilizer (two sources × four rates) treatments. Nitrogen sources were either ammonium nitrate (AN) or urea (UR) each applied at 0, 8, 16, and 24 kg N ha−1. Biomass in both 2000 and 2001 growing seasons increased significantly with increasing N rate at both growth stages (R1 and R7) and at the R1 stage in 2002. Ureide concentration and relative ureide decreased with increasing N rate at the R1 stage in all years, indicating a decrease in N fixation up to that point in crop development. This decrease in N fixation was not present at the R7 stage, but the significant increase in plant growth including yield was still present, indicating possibly that starter fertilizer can positively impact soybean production in the cool environmental conditions of the northern Great Plains. However, the positive impact on plant growth and yield is dependent on in-season environmental conditions and time of planting.

Previous crop and rotation history effects on maize seedling health and associated rhizosphere microbiome

To evaluate crop rotation effects on maize seedling performance and its associated microbiome, maize plants were grown in the greenhouse in soils preceded by either maize, pea, soybean or sunflower. Soils originated from a replicated field experiment evaluating different four-year rotation combinations. In the greenhouse, a stressor was introduced by soil infestation with western corn rootworm (WCR) or Fusarium graminearum. Under non-infested conditions, maize seedlings grown in soils preceded by sunflower or pea had greater vigor. Stress with WCR or F. graminearum resulted in significant root damage. WCR root damage was equivalent for seedlings regardless of soil provenance; whereas F. graminearum root damage was significantly lower in maize grown in soils preceded by sunflower. Infestation with WCR affected specific microbial taxa (Acinetobacter, Smaragdicoccus, Aeromicrobium, Actinomucor). Similarly, F. graminearum affected fungal endophytes including Trichoderma and Endogone. In contrast to the biological stressors, rotation sequence had a greater effect on rhizosphere microbiome composition, with larger effects observed for fungi compared to bacteria. In particular, relative abundance of Glomeromycota was significantly higher in soils preceded by sunflower or maize. Defining the microbial players involved in crop rotational effects in maize will promote selection and adoption of favorable crop rotation sequences.

Enhancing Corn Production Through the Use of Starter Fertilizer in the Northern Great Plains

Abstract The northern portion of the Great Plains has environmental conditions that require unique management practices to ensure optimum corn (Zea mays L.) yield and quality. The objective was to investigate the effect of starter fertilizer on corn yield and quality under different soil management. A field experiment was established within a 2‐year corn/soybean [Glycine max (L.) Merrill] rotation. Whole‐plot treatments were tillage with split‐plot treatments of starter fertilizer. Starter fertilizer treatments consisted of two nitrogen (N) sources, each at four rates, all contained phosphorus (P) and potassium (K). An additional treatment of no starter fertilizer was also incorporated into the experiment. There was a significant increase in yield with application of starter‐N for all years except 2002. The most dramatic yield increase was obtained with the comparison between the no starter (no N, P, or K) treatment and the P and K treatment (no N+P and K). Starter fertilizer with only P and K also increased yield, oil production, and N removal in all years compared with no starter fertilizer treatment. Application of starter fertilizer can have a significant positive impact on yield and quality of corn grown in the northern Great Plains. Mention of trade name or commercial products in this publication is solely for the purpose for providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

Soil nitrogen dynamics in switchgrass seeded to a marginal cropland in South Dakota

The potential ecological impacts of switchgrass (Panicum virgatum L.), as a biofuel feedstock, have been assessed under different environmental conditions. However, limited information is available in understanding the integrated analysis of nitrogen (N) dynamics including soil nitrate ( NO3− ), nitrous oxide (N2O) emissions, and NO3− leaching under switchgrass land management. The specific objective was to explore N dynamics for 2009 through 2015 in switchgrass seeded to a marginally yielding cropland based on treatments of N fertilization rate (N rate; low, 0; medium, 56; high, 112 kg N ha−1) and landscape position (shoulder, backslope, and footslope). Our findings indicated that N rate impacted soil NO3− (0–5 cm depth) and surface N2O fluxes but did not impact NO3− leaching during the observed years. Medium N (56 kg N ha−1) was the optimal rate for increasing biomass yield with reduced environmental problems. Landscape position impacted the N dynamics. At the footslope position, soil NO3− , soil NO3− leaching, and N2O fluxes were higher than the other landscape positions. Soil N2O fluxes and NO3− leaching had downward trends over the observed years. Growing switchgrass on marginally yielding croplands can store soil N, reduce N losses via leaching, and mitigate N2O emissions from soils to the atmosphere over the years. Switchgrass seeded on marginally yielding croplands can be beneficial in reducing N losses and can be grown as a sustainable bioenergy crop on these marginal lands.

Response of Soil Surface Greenhouse Gas Fluxes to Crop Residue Removal and Cover Crops under a Corn–Soybean Rotation

Excessive crop residue returned to the soil hinders farm operations, but residue removal can affect soil quality. In contrast, cover cropping can return additional residue to the soil and improve soils and environmental quality compared with no cover cropping. Residue and cover crop impacts on soil surface greenhouses gas (GHG) emissions are undetermined and site specific. Thus, the present study was conducted to investigate the impacts of corn ( L.) residue management and cover cropping on GHG fluxes. The fluxes were measured from 2013 to 2015 using static chamber under corn and soybean [ (L.) Merr.] rotation initiated in 2000 at Brookings, SD. Treatments included two residue management levels (residue returned [RR] and residue not returned [RNR]) and two cover cropping (cover crops [CC] and no cover crops [NCC]). Results showed that RR under corn and soybean phases significantly reduced cumulative CO fluxes (2681.3 kg ha in corn and 2419.8 kg ha in soybeans) compared with RNR (3331.0 kg ha in corn and 2755.0 kg ha in soybeans) in 2013. The RR emitted significantly less cumulative NO fluxes than RNR from both the phases in 2013 and 2014, but not in 2015. The CC treatment had significantly lower cumulative NO fluxes than the NCC for corn and soybean phases in 2013 and 2014. We conclude that crop residue retention and cover cropping can mitigate the GHG emissions compared with residue removal and no cover cropping.

Corn Residue Removal Effects on Hydraulically Effective Macropores

ABSTRACT Enhanced understanding of biomass removal effects on soil quality could be achieved with greater knowledge of how corn residue removal and cover crops interact to affect surface pore structure. This study was conducted to evaluate the effects of corn (Zea mays L.) residue removal on soil macropore characteristics and to assess the effectiveness of cover crops in mitigating the potential negative impacts of corn biomass removal on surface pore structure. Three different corn residue removal rates and the presence or absence of cover crops were evaluated in a no-till corn/soybean (Glycine max L.) rotation near Brookings, SD. Following eight years of residue removal high (HRR) and medium (MRR) rates of residue removal reduced water inflow into the soil surface compared to the low (LRR) residue removal treatment. The representative mean pore radius (λΔψ) for both rotation phases of LRR approached the same value (≈ 235 µm). However, nine months after corn residue removal the λΔψ for HRR in the soybean phase of the rotation was significantly lower than LRR at 161 µm. There was no significant difference in λΔψ between HRR (214 µm) and LRR (236 µm) 21 months after residue removal during the corn phase of the rotation. The initial reduction in λΔψ following corn residue removal in HRR followed by soil surface recovery the following year suggests that inclusion of decaying corn residue is critical in the maintenance of hydraulically functional macropores in this fine textured soil. Cover crops were not observed to mitigate these impacts of crop residue removal on surface soil structure within the time period of the study.

Intensified Agroecosystems and Changes in Soil Carbon Dynamics

Abstract Land use change, intensive farming systems, and poor land management practices are related to reduced soil organic carbon (SOC) and soil health. One way to address these concerns is by implementing ecological principles to manage agroecosystems for environmental and economic benefits. This chapter examines diverse crop rotations, cover crops, and integrated crop-livestock (ICL) systems as examples of sustainable intensification. Long-term diverse crop rotations, cover crops, no-tillage systems, and ICL systems alter SOC dynamics, microbial activity, and impact ecological services such as nutrient cycling and water quality. Research has shown that effects of sustainable intensification on increasing soil carbon content and improving ecological services such as reduced greenhouse gas emissions, and improved nutrient cycling often require long-term sustained management. Short-term effects have been observed but less frequently. The observed impacts of sustainable intensification are location-dependent, being sensitive to the local climate, soil, and details of management practice implementation.

Row and forage crop rotation effects on maize mineral nutrition and yield

Abstract: Diverse crop rotations are an integral component of sustainable agriculture. The objectives were to investigate row and forage crop rotation effects on stover biomass, grain yield, and mineral nutrient concentrations of maize (Zea mays L.) grown under a maize–soybean [Glycine max (L.) Merr.] 2-yr rotation (C–S); maize–soybean–spring wheat (Triticum aestivum L.) 3-yr rotation (C–S–W); maize–soybean–oat/pea (Avena sativa L./Pisum sativum L.) hay 3-yr rotation (C–S–H); and maize–soybean–oat/pea hay underseeded with alfalfa (Medicago sativa L.) – alfalfa – alfalfa 5-yr rotation (C–S–H/A–A–A). Rotations were established in 1997 and maize plots were sampled in 2008–2011. Across the 4 yr of the study, grain yield was 10% greater (1.0 Mg ha-1) in C–S–H/A–A–A and C–S–W rotations compared with C–S with C–S–H intermediate. Under C–S–H/A–A–A, kernel N concentration was 7% greater, kernel P was 17% less, and kernel K was 7% less compared with C–S–W. Kernel Zn concentration was 16% lower in C–S–H than in C–S and C–S–H/A–A–A. Thus, diversification of the C–S rotation with wheat (C–S–W) increased yield while conserving kernel P and K concentration, whereas diversification with oat/pea hay + alfalfa (C–S–H/A–A–A) increased grain yield and kernel N concentration but decreased both kernel P and kernel K concentration.