Increasing Warm-Season Native Grass Biomass Using Fire, Herbicide, and Nitrogen Applications

The North American Great Plains tallgrass prairie was once a system of native cool and warm season grasses, which have been degraded by non-native invasive plants. Native grass restoration is highly desirable to improve ecosystem functions and productivity. In this two-year study, the impact of fire, herbicide, and nitrogen on productivity and the presence of invasive species [primarily the cool season grass, smooth brome (Bromus inermis Leyss.)] and native warm season native grass species [big bluestem (Andropogon gerardii Vitman), sideoats and blue grama (Bouteloua curtipendula (Michx.) Torr.), and B. gracilis (Willd. Ex Kunth) Lag. ex Griffiths] were investigated. Spring fire or a glyphosate application increased warm season grass biomass and decreased cool season grass biomass at peak warm season growth (August) during the treatment year. A second consecutive year of fire or herbicide further increased warm season grass biomass. If left untreated in the second year, cool season grasses tended to increase when sampled in August. Long-term management implementation is needed to suppress the tenacious cool season species and encourage the reestablishment of warm season grass populations

Transport of Agrichemicals by Wind Eroded Sediments to Nontarget Areas

Water and wind erosion are the primary mechanisms by which surface soil is removed from agricultural fields. Wind erosion accounts for as much or more soil loss (tons/acre/year) than does water erosion. Sediments moved by wind may carry agrichemicals from agricultural fields to nontarget areas. Nontarget areas may include road ditches, shelterbelts, and waterways. The objective of this study was to determine if agrichemical movement via wind blown sediment is a potential pollutant of surface and/or groundwater. Samples of sediment that had been deposited in ditches on top of snow were collected during winters of 1994 and 1995 near or around Brookings, SD. Soil samples from adjacent fields (top 1 inch) were also collected. Soil and sediment samples were extracted and alachlor, atrazine, and atrazine metabolites, desethylatrazine and desisopropylatrazine were quantified. Alachlor was detected in about 30% of soil and sediment samples in both years with an average concentration of 2.2 ppb in soil and 5.44 ppb in sediment in 1995. In 1994, atrazine, desethylatrazine, and desisopropylatrazine were detected in 70%, 100%, and 50% of the sediment samples and 70%, 90%, and 60% of the soil samples, respectively. In 1995, atrazine, desethylatrazine, and desisopropylatrazine were detected in 73%, 27%, and 9% of the sediment samples at average concentrations of 8.9, 0.89, and 56.4 ppb, respectively. Atrazine, desethylatrazine, and desisopropylatrazine were detected in 70%, 40%, and 10% of the soil samples in 1995 at average concentrations of 11.9, 2.0, and 0.9 ppb, respectively. Herbicides were detected in most of the sediment samples. This suggests that wind erosion may be a transport mechanism by which herbicides are deposited into nontarget areas

Imapct of Biochar Application on Soil Properties and Herbacide Sorption

Biochars are the byproduct of anaerobic combustion (pyrolysis) of organic materials. Three biochars (switchgrass, cornstover, and Ponderosa pine woodchip) were created by burning the materials under anaerobic conditions for four hours at maximum temperatures of 850 o C (fast pyrolysis). Biochar samples were sorted by size (\u3c 2 mm, 2-4 mm, and \u3e 4 mm) and electrical conductivity (EC) and pH characteristics were determined in 1:5 (w/v) water and 0.01M CaCl2 . Each biochar type and size was added at 1 and 10% (w/w), to two South Dakota soils, Barnes (loamy) or Maddock (loamy fine sand). Atrazine sorption and changes in soil pH and EC were measured in slurry experiments (1:2 w/v). Biochar pH values were higher than soil pH values; however, the addition of biochar had minimal influence on soil pH. Biochar size affected soil EC values; the smallest sized chars at the 10% addition increased the soil EC. Atrazine sorption from solution increased from about 35% in soil only to almost 99% with each biochar treatment. Targeted biochar addition to soil may be warranted. If atrazine carryover is suspected, addition of biochar may reduce unwanted affects; however, higher sorption may require higher application rates to provide weed control similar to that of nonamended soil

Understanding N Mass Balance in a Long-Term Production Fields Using Various Tools

Monitoring long-term impacts of fertilizer N and the fate of N sources in production fields are needed. The objective of this study was to determine total soil N temporal and spatial changes over an 8 year period in a ¼ section. The site was located in east-central South Dakota in a 65-ha field. Crop rotation was corn and soybean. During the study corn was grown for 5 years (1995, 1997, 1999, 2001, and 2002) and soybeans were grown for 3 years (1996, 1998, and 2000). Two tillage methods were used; no-till between 1995 and 1999 and strip-till between 2000 and 2002. More than 600 soil samples from the 0- to 15-cm soil depth were collected from a 30- by 30-m offset grid in May, 1995 and between May and June, 2003 and were aggregated to a common 40- by 40-m grid cell. Soil samples were air dried (35 ºC), ground, sieved, and analyzed for total N, total C, 13C discrimination (∆), and δ15N on a ratio mass spectrometer. Findings from this study can be used to an improved understanding of N cycling in production fields

Best Management Practices for Corn Production in South Dakota: Soil Fertility

Corn requires sufficient amounts of at least 14 nutrients for optimal production (fig. 7.1). Soil fertility strategies should consider soil residual plant nutrients, cost of fertilizer relative to the value of corn, and management techniques that increase efficiency

Microarray and Growth Analyses Identify Differences and Similarities of Early Corn Response to Weeds, Shade, and Nitrogen Stress

Weed interference with crop growth is often attributed to water, nutrient, or light competition; however, specific physiological responses to these stresses are not well described. This study\u27s objective was to compare growth, yield, and gene expression responses of corn to nitrogen (N), low light (40% shade), and weed stresses. Corn vegetative parameters from V2 to V12 stages, yield parameters, and gene expression using transcriptome (2008) and quantitative polymerase chain reaction (qPCR) (2008/09) analyses at V8 were compared among the stresses and with nonstressed corn. N stress did not affect vegetative parameters, although grain yield was reduced by 40% compared with nonstressed plants. Shade, present until V2, reduced biomass and leaf area \u3e 50% at V2, and recovering plants remained smaller than nonstressed plants at V12. However, grain yields of shade-stressed and nonstressed plants were similar, unless shade remained until V8. Weed stress reduced corn growth and yield in 2008 when weeds remained until V6. In 2009, weed stress until V2 reduced corn vegetative growth, but yield reductions occurred only if weed stress remained until V6 or later. Principle component analysis of differentially expressed genes indicated that shade and weed stress had more similar gene expression patterns to each other than they did to nonstressed or N-stressed tissues. However, corn grown in N-stressed conditions shared 252 differentially expressed genes with weed-stressed plants. Ontologies associated with light/photosynthesis, energy conversion, and signaling were down-regulated in response to all three stresses. Shade and weed stress clustered most tightly together, based on gene expression, but shared only three ontologies, O-METHYLTRANSFERASE activity (lignification processes), POLY(U)-BINDING activity (posttranscriptional gene regulation), and stomatal movement. Based on morphologic and genomic observations, weed stress to corn was not explained by individual effects of N or light stress. Therefore, we hypothesize that these stresses share limited signaling mechanisms

Mob vs. Rotational Grazing: Impact on Forage Use and Artemisia absinthium

Short duration (≤24 h), high stocking density grazing systems (e.g., mob grazing) mimics historic prairie grazing patterns of American bison (Bison bison), and should minimize selective grazing. We compared mob [125 cow-calf pairs on either 0.65 ha for 12 h; or 1.3 ha for 24 h] vs. rotational [25 cow-calf pairs on 8.1 ha for 20 days starting in mid-May with or without 2,4-D application prior to grazing; and 15 days starting mid-April (no herbicide)] grazing systems based on forage utilization and impact to Artemisia absinthium (absinth wormwood) in a tall grass pasture of Eastern South Dakota. Grass height and density, and Artemisia absinthium patch volume were quantified pre- and post-grazing at sampling points along multiple transects. Mob grazing had >75% forage utilization, whereas rotational grazing averaged 50% (all consumption). Within a grazing season, three grazing systems suppressed Artemisia absinthium patches with rotation/spray (100% decrease) > mob (65 ± 10% decrease) > mid-May rotation (41 ± 16% decrease), whereas Artemisia absinthium patches in the mid-April rotation followed by summer rest dramatically increased in size. Artemisia absinthium patches <19,000 cm3 were browsed, whereas larger patches were trampled in mob-grazed areas, but avoided in rotational grazing. All Artemisia absinthium patches had regrowth the year following any grazing event

Do Synergistic Relationships between Nitrogen and Water Influence the Ability of Corn to Use Nitrogen Derived from Fertilizer and Soil?

To improve site-specific N recommendations a more complete understanding of the mechanisms responsible for synergistic relationships between N and water is needed. Th e objective of this research was to determine the influence of soil water regime on the ability of corn (Zea mays L.) to use N derived from fertilizer and soil. A randomized split-block experiment was conducted in 2002, 2003, and 2004. Soil at the site was a Brandt silty clay loam (fine-silty, mixed, superactive frigid Calcic Hapludoll). Blocks were split into moderate (natural rainfall) and high (natural + supplemental irrigation) water regimes. Nitrogen rates were 0, 56, 112, and 168 kg urea-N ha–1 that was surface applied. Water, soil N, and N fertilizer use efficiencies were determined. Plant utilization of soil N was determined by mass balance in the unfertilized control plots and by using the δ15N approach in fertilized plots. Findings showed that: (i) plants responded to N and water simultaneously; (ii) N fertilizer increased water use efficiency (170 kg vs. 223 kg grain cm–1 in 0 and 112 kg N ha–1 treatments, respectively); and (iii) water increased the ability of corn to use N derived from soil (67.7 and 61.6% efficient in high and moderate water regimes, respectively, P = 0.002) and fertilizer (48 and 44% efficient in high and moderate water regimes, respectively, P = 0.10). Higher N use efficiency in the high water regime was attributed to two interrelated factors. First, total growth and evapotranspiration (ET) were higher in the high than the moderate water regime. Second, N transport to the root increased with water transpired. For precision farming, results indicate that: (i) the amount of N fertilizer needed to produce a kg of grain is related to the yield loss due to water stress; and (ii) the rate constant used in yield goal equations can be replaced with a variable