Bluegrass Sod Research Articles

Sustainability of athletic field turf comparing organic and synthetic practices under two heights of cut

AbstractLong‐term comparisons over several years between organic and synthetic management are lacking in sports turf research. Our objective was to investigate playing surface qualities and soil properties over an 8‐year period. For this trial, Kentucky bluegrass (KBG, Poa pratensis L.) sod was established and annually inter‐seeded with perennial ryegrass (Lolium perenne L.) and KBG. Factors included height of cut (3.2 and 6.4 cm) and management systems (MSs; synthetic and organic) with three replicates. Synthetic practices included chemical fertilizers and pesticides, while the organic system used hand‐weeding and biological fertilizers (leaf compost and naturally derived organics) with biological controls. In all years, wear was simulated in the fall using a slip‐wear machine and evaluated for playing qualities including visual wear tolerance, ball bounce (BB), surface hardness, and traction. Soil properties were evaluated in some years including pH, soil organic matter (SOM), soil bulk density, soil aggregate stability (SAG), and soil available P. Both MS received the same total N of 196 kg ha−1 year−1 but P applied varied with the MS (synthetic, 7.6 kg ha−1 year−1; organic, 23.2 kg ha−1 year−1). Synthetic practices provided acceptable visual wear tolerance (1–9, ≥6 acceptable) in 4 of 8 years compared to only 1 year for organic practices. Shorter cut grass (3.2 cm) consistently provided better visual wear tolerance (average = 5.6), harder surfaces (average = 51 g), and higher BB (average = 35.8%) consistent with accepted player standards. Synthetic practices afforded better tolerance to wear compared to organic practices in 5 of 8 years but little difference was observed in the other surface properties. Organic practices were consistently above 6.0 in soil pH (higher by 12%), 20% higher in soil available P, 25% higher in SOM, and with lower soil bulk density. SAG was higher following 8 years of simulated traffic by the last year of the test under organic practices. Results suggest competing benefits with synthetic practices affording better wear tolerance while organic practices promote better soil health.

Relative contribution of shade avoidance and resource competition to early-season sugar beet yield loss due to weeds

AbstractShade avoidance alters the way plants grow, usually causing them to grow taller at the expense of placing resources into leaves, roots, seeds, and other harvestable materials. Sugar beet (Beta vulgaris L.) is a rosette-forming biennial species that has limited capacity to grow tall in the first year of growth. In the context of crop–weed competition, it is mostly unknown to what extent shade avoidance reduces yield in sugar beet relative to other effects like resource competition. To determine the extent of yield loss due to shade avoidance in a field-relevant situation, sugar beets were grown alongside Kentucky bluegrass (Poa pratensis L.) sod in a field study. Roots were separated with a steel root barrier placed into the ground between the grass and beets. Four treatments included a weed-free control (no root barrier or grass), a root barrier control (with root barrier but no grass), shade avoidance (with root barrier and grass), and full competition (with grass but no root barrier). The presence versus absence of grass was the primary driver of effects on measured sugar beet growth and yield parameters, regardless of whether a root barrier was present. Leaf number and root length were also impacted by the presence of the root barrier. These results suggest that shade avoidance is at least as important as root interactions and resource depletion in the context of early-season sugar beet yield loss due to weeds.

Management, harvest, and storage characteristics of low‐input cool‐season turfgrass sod mixtures

AbstractThe lack of turfgrass diversity in cool‐season sod production is related to information inefficiencies, such as the lack of agronomic information available on improved, low‐input species, such as fine fescues (Festuca spp.). Collaborative research between Purdue University and University of Minnesota investigated the influence of cool‐season turfgrass species mixtures on the harvest (production and strength) and storage limitations of sod. Field experiments were established in 2018 in West Lafayette, IN, and in 2019 in St. Paul, MN. Treatments included 12 turfgrass species mixtures that consisted of the following five species: strong creeping red fescue (Festuca rubra L. ssp. rubra Gaudin), Chewings fescue (F. rubra ssp. commutata Gaudin), hard fescue (F. brevipila Tracey), tall fescue (F. arundinacea Schreb.), and Kentucky bluegrass (Poa pratensis L.). Data on turf cover, vertical growth rate, sod tensile strength, sod handling, and shelf‐life storage and transplant success were collected at multiple harvest timings from 10 to 24 mo after planting. The majority of the sod mixtures, especially those containing ≥33% strong creeping red fescue, produced high quality sod similar to the standard comparison of 100% Kentucky bluegrass sod and transplant success was not severely affected when stored for 24–72 h immediately following a spring or autumn harvest. Sod mixtures containing tall fescue, including “rhizomatous tall fescue,” consistently resulted in the lowest sod strength and handling. Overall, sod producers growing fine fescue sod may be able to not only reduce management inputs, but also yield good sod strength with low‐input sod mixtures.

Carbon loss in tile drainage and surface runoff from a clay loam soil after a half century of continuous and rotational cropping

Tile drainage and surface runoff are major pathways for pollution of water resources by agricultural nutrients and chemicals. Little is known, however, of the pathways and amounts of carbon entry into water resources from agricultural land. This paper evaluates dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) losses in tile drainage and surface runoff from a Brookston clay loam after more than a half century of monoculture maize ( Zea mays L.), continuous bluegrass sod ( Poa Pratensis L.), and maize-oat ( Avena sativa L.)–alfalfa ( Medicago sativa L.)–alfalfa rotation. Water loss in tile drainage and surface runoff accounted for 27%, 32%, and 18% of annual precipitation (876 mm) for rotation, monoculture maize, and continuous sod, respectively. Tile drainage comprised 66%–89% of water loss from rotation and continuous sod, but only 15% from monoculture maize, with the remaining 85% of water loss from monoculture maize due to surface runoff. On an annualized basis, the measured dissolved C loss was 79 and 83 kg C ha–1 yr–1) from rotation and continuous sod, respectively, while 49 kg C ha–1 yr–1 was lost from monoculture maize. As up to 9% off-gassing loss of CO2 from water samples was measured, total dissolved carbon losses in tile drainage and runoff water were likely greater. For Brookston clay loam soil, leaching into tile drains was the dominant mechanism for dissolved carbon loss from long-term continuous sod and crop rotation, while surface runoff was the dominant mechanism for dissolved carbon loss from long-term monoculture maize.

Investigation of cool‐season species, seeding rate, and nitrogen fertilization in sod production: II. Management and shelf‐life

AbstractResearch is required on sod to explore the differences in management and postharvest practices to help inform sod producers and reduce information inefficiencies that affect the supply and demand of cool‐season turfgrass sod. Replicated field experiments were conducted in Indiana and Minnesota to quantify the effect of turfgrass species (strong creeping red fescue [Festuca rubra L. ssp. rubra Gaudin], Chewings fescue [F. rubra ssp. commutata Gaudin], tall fescue [F. arundinacea Schreb.], and Kentucky bluegrass [Poa pratensis L.]), seeding rate (1, 2, and 3 pure live seed (PLS) cm−2), and N fertilization (98, 196, and 294 kg N ha−1 yr−1) on growth rate and shelf‐life storage. Turf height measurements occurred at multiple timings to calculate growth rates of treatments. Sod was harvested in the spring and autumn and stored on pallets for either 24 or 72 h and then reinstalled in its previous location and treatment effects were assessed. Seeding rate had no effect on growth rate or transplant success of sod. Differences in growth rates demonstrate potential savings for sod growers through less mowing requirement when producing fine fescue sod. Treatments did not influence internal heating of sod rolls, which were higher than, but similar to, diurnal fluctuations of air temperatures. There were minimal differences among turfgrass species and N rates, which indicates strong creeping red fescue, Chewings fescue, tall fescue, and Kentucky bluegrass sod stored for 24–72 h after a spring or autumn harvest in Indiana or Minnesota will not hinder transplant success.

Field Response of Green Ash (Fraxinus pennsylvanica) and Honey Locust (Gleditsia triacanthos) to Aminocyclopyrachlor1

AbstractField trials were conducted to assess the impact of aminocyclopyrachlor on green ash (Fraxinus pennsylvanica Marshall) and honey locust (Gleditsia triacanthos L.) trees in an urban environment. Aminocyclopyrachlor is a relatively new, selective, plant-growth-regulator herbicide in the pyrimidine carboxylic acid family. Treatments were applied to Kentucky bluegrass (Poa pratensis L.) sod growing with and without trees present. Evaluations included determination of a safe spraying distance from target trees and the effect of application timing on tree response. This multi-year study showed that green ash was highly tolerant to aminocyclopyrachlor while honey locust developed severe injury in trees closest to applications. Honey locust trees up to 7 m (23 ft) from the tree trunk to the edge of the application displayed moderate to severe injury symptoms and fall treatment in October and November had the lowest tree injury compared to all other application timings. Honey locust trees exhibiting moderate to severe cosmetic injury would not be acceptable to landowners; recovery over time was minimal. Trees located 13 m (43 ft) away displayed no injury for any treatment timing. Soil analysis demonstrated that aminocyclopyrachlor dissipation was the same underneath green ash and honey locust trees, and that dissipation was faster in the presence of growing trees. Taken together, these results provide a basic groundwork necessary for improving aminocyclopyrachlor labels, and a better understanding of this herbicide's effect on certain woody species.Index words: Herbicide injury, aminocyclopyrachlor, herbicide fate, tree safety.Species used in this study: Green ash, Fraxinus pennsylvanica Marshall, honey locust, Gleditsia triacanthos L.Chemicals used in this study: Aminocyclopyrachlor.

Chemical and spectroscopic characteristics of humic acid from a clay loam soil in Ontario after 52 years of consistent fertilization and crop rotation

Long-term fertilization and crop rotation can influence both organic C sequestration as well as the C composition of soils and the more resistant organic C compounds contained in humic acid (HA). This study examined the effects of fertilization and cropping type (monoculture corn (MC) and Kentucky bluegrass sod (KBS) and corn-oat-alfalfa-alfalfa rotation (RC)) on the HA composition of soil from a 52-year field study in southern Ontario, Canada. Humic acid samples were extracted from soil, and elemental analysis, infrared spectroscopy, solid state 13 C nuclear magnetic resonance spectra, and electron paramagnetic resonance methods were used to determine the influence of the cropping type on the characteristics of HA. Both fertilization and cropping type affected the chemical characteristics of HA. Fertilization led to a 5.9% increase in C, a 7.6% decrease in O, and lower O/C and (N + O)/C ratios in HA as compared to the corresponding non-fertilized treatments. Rotation resulted in a lower proportion of C (48.1%) and a greater (N + O)/C ratio (0.7) relative to monoculture cropping. Infrared spectroscopy analysis showed that HA contained more C-O groups in fertilized soil than in non-fertilized soil under MC and KBS. Fertilization increased the O-alkyl-C, phenolic-C, and free radical contents of HA relative to non-fertilization treatments. Rotation decreased the aliphatic and carboxyl groups and increased the O-alkyl, carbohydrate, aryl, and phenolic groups and free radicals, relative to MC and KBS. Both long-term crop rotation and fertilization dramatically modified the soil HA composition. Significant relationships were observed between the molecular composition of HA and soil organic C. Hence, humic acid characterization could be used as an indicator of the long-term sustainability of crop management practices.

Legacy Phosphorus After 45 Years With Consistent Cropping Systems and Fertilization Compared to Native Soils

Agricultural practices affect the status of legacy phosphorus (P) in soils and consequently the P bioavailability and susceptibility of losses to water resources. Previous studies have primarily assessed P status within agro-ecosystems and rarely have these results been compared to virgin conditions. We evaluated the effects of long-term (45 years) consistent cropping (continuous corn, CC; corn-oats-alfalfa-alfalfa rotation, CR,; and continuous bluegrass sod, CB) with and without P fertilization on changes in P fractions of different bioavailability in a Brookston clay loam, as compared to an adjacent virgin forest. Soil P was separated into various inorganic P (Pi) and organic P (Po) fractions using a modified sequential fractionation method. Phosphorus in virgin soil was predominated by moderately labile Po (NaOH-Po), 44%, followed by moderately stable Pi (HCl-P), 26%. Compared to the virgin soil, consistent cropping without P fertilization significantly decreased all P fractions except for water extractable Po, with the largest decrease in labile Pi (water-Pi + NaHCO3-Pi) and moderately labile Po of 65 and 73 mg kg-1, respectively, over 45 years. Consistent cropping with fertilization retained comparable amount of total P in CC and RC, but increased total P in CB, relative to the virgin soil. Averaged over cropping systems, labile Pi, NaOH-Pi, and HCl-P increased by 129, 74 and 20 mg kg-1, respectively, whereas, labile Po and moderately labile Po decreased by 8 and 60 mg kg-1, respectively, compared to the virgin soil. This study indicates that long-term cropping significantly enhanced the rate of moderately labile Po mineralization, irrespective of fertilization. The increased total P and Po in the fertilized CB plots suggests that P accumulation in long-term grass fields is a concern as far as potential P contamination in surface waters.

Long‐term Cropping Effects on Partitioning of Water Flow and Nitrate Loss between Surface Runoff and Tile Drainage

Surface runoff and tile drainage are the main pathways for water movement and entry of agricultural nitrate into water resources. The objective of this 5-yr study was to characterize the partitioning of water flow and nitrate loss between these pathways for a humid-temperate Brookston clay loam soil under 54 to 59 yr of consistent cropping and fertilization. Cropping treatments included monoculture corn ( L., MC), continuous bluegrass ( L.) sod (CS), and a corn-oat-alfalfa ( L.)-alfalfa rotation (RC-RO-RA1-RA2). Fertilization treatments included annual fertilizer addition (F) and no fertilizer addition (NF). Tile drainage and surface runoff occurred primarily during the nongrowing season (November-April), and they were highly correlated with the mean saturated hydraulic conductivity of the near-surface soil profile. Tile drainage accounted for 69 to 90% of cumulative water flow and 79 to 96% of cumulative nitrate loss from fertilized rotation and CS, whereas surface runoff accounted for the majority of the nitrate losses in MC (i.e., 75-93% of water flow and 65-96% of nitrate loss). Cumulative nitrate losses were highest in the RC-F (152 kg N ha), RC-NF (101 kg N ha), RA2-F (121 kg N ha), and RA2-NF (75 kg N ha) plots, and these high losses are attributed to N mineralization from the plowed alfalfa and fertilization (if applicable). Fertilization increased cumulative nitrate loss in tile drainage from all treatments, whereas no fertilization increased cumulative nitrate loss in surface runoff from the rotation. Cropping system and fertilization on clay loam soil changed how water flow and nitrate loss were partitioned between tile drainage and surface runoff.

The Effect of Wear and Soil Compaction on Kentucky Bluegrass Sod Rooting and Plant Recovery

Damage areas in sport fields from wear are often sodded before complete rooting. The objective of this study was to examine the influence of traffic (the combined effects of wear and soil compaction) on sod rooting. Poa pratensis L. sod was installed in September 2008 and 2009 on a silt loam and a sand rootzone at the University of Massachusetts‐Amherst. Treatments included a compaction and noncompaction soil and wear and nonwear treatments, which were evaluated under the influence of two soils. Compaction was applied using a plate Vibro‐Tamper prior to sodding and wear was applied with a steel brush. Wear was initiated 4 wk after sod installation in both years and applied six times. Wear injury and recovery was assessed using a 1 to 9 rating scale (9 = no injury), root initiations were measured by counts, and sod rooting strength was determined by lifting force. Wear significantly reduced sod rooting strength compared with nonwear. New root initiations and root biomass were significantly reduced by wear. Soil compaction significantly reduced root biomass below 7.5‐cm soil depth with no effect observed at the 0‐ to 7.5‐cm depth. Wear applied to sod on the silt loam achieved full recovery 45 d earlier in both years than sod grown on the sand rootzone. The effects of traffic on newly placed sod in the repair of damaged areas on athletic fields indicate that wear is the major stress limiting sod rooting, while soil compaction is secondary.

Biosolids as an Alternative Fertilizer for Kentucky Bluegrass Sod Production in Wisconsin

Land application of biosolids holds the potential to reduce or eliminate the need for synthetic fertilizer applications. The objective of this study was to evaluate the agronomic impacts of using biosolids to produce Kentucky bluegrass (Poa pratensis L.) sod on a silt loam soil in Wisconsin. Anaerobically digested biosolids cake and biosolids cake mixed with sand and sawdust in a 2:1:1 ratio by volume (MetroMixTM) were produced by and obtained from the Madison Metropolitan Sewerage District. Each material was applied at three rates based on their estimated supply of plant‐available nitrogen (PAN). The control treatment mimicked conventional sod maintenance techniques using synthetic fertilizer applied at 309 kg N ha−1 over the 20‐mo production cycle. All biosolids treatments improved or exhibited similar establishment cover compared with the conventional practice. However, generally the lowest rate of cake and the two lowest rates of the MetroMix underperformed the conventional production in terms of visual quality throughout harvest and into transplanting. Cake had superior visual quality compared with MetroMix when applied at equivalent PAN rates. Optimization modeling determined that a biosolids cake application rate of 425 kg PAN ha−1 would likely meet agronomic standards (quality, color, sod strength, etc.) of the conventional practice. Repeated applications decreased the optimized biosolids rate to from 425 to 325 and 285 kg PAN ha−1, depending on number of previous applications. These results suggest that biosolids‐based sod production has the potential to replace or supplement traditional fertilization practices to meet current agronomic goals for sod production in Wisconsin.

Can Frequent Measurement of Normalized Difference Vegetative Index and Soil Nitrate Guide Nitrogen Fertilization of Kentucky Bluegrass Sod?

Objective approaches to guide N fertilization of turfgrass sod crops are lacking. This study was conducted to determine the relationships among normalized difference vegetative index (NDVI), frequently‐measured soil NO3–N concentrations, and peak‐shear force of predominately Kentucky bluegrass (Poa pratensis L.) sod, and to evaluate if those relationships could help guide N fertilization. Ramp calibration strips (RCS) with varying N rates were established within production sod fields in Rhode Island across three consecutive years. At 2‐wk intervals during each growing season, soil NO3–N concentrations and NDVI readings were recorded and correlated. Biweekly relative NDVI readings plateaued when soil NO3–N concentrations ranged between 5 and 12 mg kg–1. Mean relative NDVI plateaued at 196 kg N ha–1 yr–1. Relative sod peak‐shear force was negatively correlated to soil NO3–N concentrations and the total amount of N applied per year. Relative peak‐shear force was maximized when mean relative NDVI readings ranged from 0.969 to 0.982, but declined as mean relative NDVI increased towards 1.0. The results suggest that frequently measured NDVI and soil NO3–N concentrations show promise as guides for N fertilization of predominately Kentucky bluegrass sod. Further research will be required to validate these approaches on larger‐scale sod fields.

Matching Subjective Assessments of Sod Strength to Quantitative Measurements of Peak Shear Force with Predominately Kentucky Bluegrass Sod

Adequate turfgrass sod strength for harvesting and handling is typically determined by the producer’s past experience and subjective appraisal. This study was conducted to determine the relationship between producer subjective sod-strength assessments and quantitative shear-strength measurements with predominantly kentucky bluegrass (Poa pratensis L.) turf. Across three consecutive growing seasons, 93 samples were collected from sod fields in Rhode Island and assessed for sod strength by subjective and quantitative methods. Producer subjective ratings of sod strength were significantly (P < 0.0001) associated with quantitative measurements of peak force required to shear a sod strip. Minimally acceptable strength occurred most frequently when peak shear force was between 55 and 85 kg·m−1 width of sod; whereas preferred sod strength occurred most frequently when peak shear force was between 70 and 140 kg·m−1 width of sod. Once peak force exceeded 58 and 86 kg·m−1, there was a > 50% probability that sod strength would be judged at least adequate and at preferred strength, respectively, up to a peak force of 140 kg·m−1. The results suggest that quantitative measurements of shear strength can be related to producer subjective assessments, and provide unbiased benchmark values to guide management decisions for kentucky bluegrass sod production.

Impacts of 49–51 years of fertilization and crop rotation on growing season nitrous oxide emissions, nitrogen uptake and corn yields

Drury, C. F., Reynolds, W. D., Tan, C. S., McLaughlin, N. B., Yang, X. M., Calder, W., Oloya, T. O. and Yang, J. Y. 2014. Impacts of 49–51 years of years of fertilization and crop rotation on growing season nitrous oxide emissions, nitrogen uptake and corn yields. Can. J. Soil Sci. 94: 421–433. A field study was established in 1959 to evaluate the effects of fertilization and crop rotation on crop yields, soil and environmental quality on a Brookston clay loam. There were two fertilizer treatments (fertilized and not-fertilized) and six cropping treatments including continuous corn (CC), continuous Kentucky bluegrass sod and a 4-yr rotation of corn–oat–alfalfa–alfalfa with each phase present each year. We measured N2O emissions, inorganic N and plant N uptake over three growing seasons (2007–2009) in the corn phase. Nitrous oxide emissions varied over the 3 yr as a result of the seasonal variation in precipitation quantity, intensity and timing and differences in crop growth and N uptake. Fertilized CC lost, on average, 7.36 kg N ha−1 by N2O emissions, whereas the not-fertilized CC lost only 0.51 kg N ha−1. Fertilized rotation corn (RC) lost 6.46 kg N ha−1, which was 12% lower than fertilized CC. The not-fertilized RC, on the other hand, emitted about half as much N2O (2.95 kg N ha−1) as the fertilized RC. Fertilized RC had corn grain yields that averaged 10.0 t ha−1 over the 3 yr followed by fertilized CC at 5.48 t ha−1. Not-fertilized RC corn had yields that were 61% lower (3.93 t ha−1) than fertilized RC, whereas the not-fertilized CC had yields that were 75% lower (1.39 t ha−1) than fertilized CC. Nitrous oxide emissions were found to be dramatically affected by long-term management practices and crop rotation had lower emissions in the corn phase of the rotation even though the N input from fertilizer addition and legume N fixation was greater. These N2O emission and yield results were due to both factors that are traditionally used to describe these processes as well as long-term soil quality factors, which were created by the long-term management (i.e., soil organic carbon, soil physical parameters such as bulk density, and porosity, soil fauna and micro-flora) and that influenced crop growth, N uptake and soil water contents.

Water movement and fate of nitrogen during drip dispersal of wastewater effluent into a semi-arid landscape

Drip dispersal of partially treated wastewater was investigated as an approach for onsite water reclamation and beneficial reuse of water and nutrients in a semi-arid climate. At the Mines Park Test Site in Golden, Colorado, a drip dispersal system (DDS) was installed at 20- to 30-cm depth in an Ascalon sandy loam soil profile. Two zones with the same layout were established to enable study of two different hydraulic loading rates. Zones 1 and 2 each had one half of the landscape surface with native vegetation and the other with Kentucky bluegrass sod. After startup activities, domestic septic tank effluent was dispersed five times a day at footprint loading rates of 5 L/m2/d for Zone 1 and 10 L/m2/d for Zone 2. Over a two-year period, monitoring included the frequency and volume of effluent dispersed and its absorption by the landscape. After the first year of operation in October a 15N tracer test was completed in the sodded portion of Zone 1 and samples of vegetation and soil materials were collected and analyzed for water content, pH, nitrogen, 15N, and bacteria. Research revealed that both zones were capable of absorbing the effluent water applied at 5 or 10 L/m2/d. Effluent water dispersed from an emitter infiltrates at the emitter and along the drip tubing and water movement is influenced by hydrologic conditions. Based on precipitation and evapotranspiration at the Test Site, only a portion of the effluent water dispersed migrated downward in the soil (approx. 34% or 64% for Zone 1 or 2, respectively). Sampling within Zone 1 revealed water filled porosities were high throughout the soil profile (>85%) and water content was most elevated along the drip tubing (17–22% dry wt.), which is also where soil pH was most depressed (pH 4.5) due to nitrification reactions. NH4+ and NO3− retention occurred near the dispersal location for several days and approximately 51% of the N applied was estimated to be removed by plant uptake and denitrification. Heterotrophic bacteria levels were elevated (up to 1 log) in the subsurface within the DDS but there was effective elimination of effluent fecal coliform and Escherichia coli bacteria.

Effects of long-term and recently imposed tillage on the concentration and composition of amino sugars in a clay loam soil in Ontario, Canada

Tillage disturbance influences soil microorganisms and consequently the production and decomposition of microbial residues such as amino sugars. However, our understanding is still limited with respect to the changes in amino sugars which occur in soil after tillage operations. In this study, changes in amino sugars in a clay loam soil (mesic Typic Argiaquoll) in Ontario, Canada were tracked in long-term (29 years) no-tillage (NT), long-term conventional moldboard plow tillage (MP), and long-term bluegrass (Poa pratensis L.) sod (BG) as well as when long-term (13 years) NT was converted to MP, long-term MP was converted to NT, and long-term BG was converted to MP. Our objective was to determine if the quantity of amino sugars in the soil as well as their composition (i.e. whether they originate from bacterial or fungal residues) would respond to changes in tillage practices. We also wanted to evaluate the effects of converting from grassland to arable cropping (corn and soybean) on the amino sugar composition of soils. Soil samples were collected at depths of 0–5, 5–10, and 10–20cm after 1 (1997), 6 (2002), 11 (2007), and 16 (2012) years following tillage conversion. Concentrations of amino sugars were much greater under long-term BG than under both long-term NT and MP treatments. In the 0–5cm depth, long-term NT significantly increased total amino sugars and fungal-derived glucosamine (GluN) by 18 and 25%, respectively, compared with long-term MP whereas long-term NT had 26% lower MurA concentrations than long-term CT. Concentrations of total amino sugars in the 0–5cm depth were reduced significantly within the first year after conversion of long-term NT and BG to MP, due primarily to decreases in the GluN concentrations. On the other hand, concentrations of amino sugars in soil accumulated gradually after conversion of long-term MP to NT. The results confirmed our hypothesis that loss of soil amino sugars is rapid and substantial when MP is initiated after NT and BG, while their recovery is gradual when NT is initiated after MP.

Nitrogen Fertilization Influences Shear Strength and Quality of Kentucky Bluegrass Sod Grown on Clay

Shipment costs and easiness of handling sometimes make it necessary to produce sod on non‐ideal soils, such as clay. The objective of this study was to test the effects of N rate and N‐application timing, seeding rate, and mowing height on sod shear strength of Kentucky bluegrass (Poa pratensis L.) produced on a clayey soil under the climate conditions of the upper Midwest in the United States. A blend of four Kentucky bluegrass cultivars were seeded at 50 or 100 kg ha−1 in 2004 and 2005 and maintained at 4.5‐ or 7.5‐cm mowing height. Annual N rates of 120 or 210 kg ha−1 were applied from April to September in different splits. Sod was harvested at 14 or 23 mo after seeding. By 14 mo after seeding, all N treatments had turfgrass visual quality above 6.0 except the unfertilized control and the 120 kg ha−1 yr−1 rate applied mainly in summer or spring. Sod shear strength reached a minimum acceptable level of 0.9 kg m−2 ×104 about 23 mo after seeding. Highest sod shear strength (1.18–1.36 kg m−2 ×104) with acceptable visual quality could be achieved through an N program of 8, 16, 24, 32, and 40 kg ha−1 in May, June, July, August, and September, respectively. Based on a 23‐mo production time line, a seeding rate at 50 kg ha−1 and a 7.5‐cm mowing height is recommended for economic reasons. Applying more than 40 kg ha−1 of N in June and July is not recommended.

Optimal soil physical quality inferred through structural regression and parameter interactions

Soil physical quality (SPQ) is assessed by comparing values of “indicator” soil properties (e.g. bulk density, air capacity) to “ideal ranges” established in the literature. These ideal ranges may not be optimal for any particular soil or field site, however, as they are only “guidelines” based on broad soil types. The objective of this study was to determine if more relevant estimates of optimal indicator ranges can be obtained by using structural (Model II) regression to account for soil/site-specific indicator behaviour and interactions among the indicator parameters. The indicator parameters included relative water capacity (RWC), organic carbon content (OC), bulk density (BD), bulk soil air capacity (AC B), soil matrix air capacity (AC M), macroporosity (POR P), matrix porosity (POR M), field capacity (FC), plant-available water capacity (PAWC), and saturated hydraulic conductivity ( K S). The indicators were determined using intact soil cores collected from the top 10 cm of a uniform, cool, humid clay loam soil under maize–soybean cropping, continuous bluegrass sod, and virgin soil. The structural regression analysis was applied by regressing RWC, OC, AC B, AC M, POR P, POR M, FC, PAWC and K S against BD using the “least squares bisector” method. Structural regression predicted soil/site-specific optimal ranges of 3 ≤ OC ≤ 4 wt.%, 1.10 ≤ BD ≤ 1.23 Mg m − 3 , 0.16 ≤ AC B ≤ 0.22 m 3 m − 3 , 0.07 ≤ AC M ≤ 0.10 m 3 m − 3 , and 0.09 ≤ POR P ≤ 0.13 m 3 m − 3 , which are either narrower than the corresponding literature guidelines, or partially overlapping the guidelines. The regressions also provided information that is not currently available in the literature, including a possible optimal range for FC (0.30 ≤ FC ≤ 0.35 m 3 m − 3 ), and plausible “upper limits” to the optimal ranges for AC B, AC M and POR P (see above). Optimal ranges were not obtainable for POR M and PAWC because they were effectively constant among the cropping and sod treatments. A questionably high optimal range was obtained for K S (8 × 10 − 2 ≤ K S ≤ 7 × 10 − 1 cm s − 1 ), and this was attributed to the perturbing effects of large, highly water-conductive macropores. The overall SPQ at the field site was judged by structural regression to be “poor” for maize–soybean cropping, “good” for bluegrass sod, and “fair” for virgin soil. It was concluded that structural regression is useful for determining soil/site-specific optimal ranges for SPQ indicators.

Land management effects on the near-surface physical quality of a clay loam soil

Although agricultural land management is known to affect near-surface soil physical quality (SPQ), the characteristics of these affects are poorly understood, and diagnostic SPQ indicators are not well-developed. The objective of this study was to measure a suite of potential SPQ indicators using intact soil cores and grab samples collected from the 0–10 cm depth of a clay loam soil with the treatments: (i) virgin soil (VS); (ii) long-term continuous bluegrass sod (BG); (iii) long-term maize ( Zea mays L.)—soybean ( Glycine max (L.) Merr.) rotation under no-tillage (NT); (iv) long-term maize–soybean rotation under mouldboard plough tillage (MP); (v) short-term (1–4 years) NT after long-term MP; (vi) short-term MP after long-term BG; (vii) short-term MP after long-term NT. Organic carbon content, dry bulk density, air capacity, relative water capacity and saturated hydraulic conductivity appeared to be useful SPQ indicators because they were sensitive to land management, and proposed optimum or critical values are available in the literature. Soil macroporosity was also sensitive to land management, but optimum or critical values for this parameter are not yet established. Soil matrix porosity and plant-available water capacity did not respond substantially or consistently to changes in land management, and were thus not useful as SPQ indicators in this study. Converting long-term BG to MP caused overall SPQ to decline to levels similar to long-term MP within 3–4 years. Converting long-term NT to MP or vice versa caused only minor changes in overall SPQ. With respect to the measured SPQ indicators and their optimum or critical values, both VS and BG produced “good” overall SPQ in the near-surface soil, while long-term maize–soybean rotation under NT and MP produced equally “poor” SPQ.

Effects of Commercial Diazinon and Imidacloprid on Microbial Urease Activity in Soil and Sod

Diazinon [O,O-diethyl O-2-isopropyl-6-methyl(pyrimidine-4-yl) phosphorothioate] and imidacloprid [1-(1-[6-chloro-3-pyridinyl]methyl)-N-nitro-2-imidazolidinimine] are applied to lawns for insect control simultaneously with nitrogenous fertilizers such as urea, but their potential effect on urease activity and nitrogen availability in turfgrass management has not been evaluated. Urease activity in enzyme assays, washed cell assays, and soil slurries was examined as a function of insecticide concentration. Intact cores from field sites were used to assess the effect of insecticide application on urease activity in creeping bentgrass (Agrostis palustris Huds.) and bluegrass (Poa pratensis L.) sod. Bacterial urease from Bacillus pasteurii and plant urease from jack bean [Canavalia ensiformis (L.) DC.] were unaffected by the insecticides. Both insecticides inhibited the growth of Proteus vulgaris, a urease-producing bacterium, but only diazinon significantly reduced urease activity in washed cells; neither insecticide inhibited urease activity in sonicated cells. Neither diazinon nor imidacloprid inhibited urease activity in Woolper soil (fine, mixed, mesic Typic Argiudoll) slurries, but diazinon slightly inhibited urease activity in Maury soil (fine, mixed, semiactive, mesic Typic Paleudalf) slurries. Imidacloprid had no effect on urease activity in creeping bentgrass or bluegrass sod at up to 10 times the commercial application rate. Diazinon briefly, but significantly, reduced urease activity in bluegrass sod. Co-application of imidacloprid and urea appears to be benign with respect to urease activity in soil and sod. Diazinon, in contrast, appears to have a significant, short-term, inhibitory effect on the microbial urease-producing community, but that effect depends on soil type.