Explore the vast range of titles available.

Addition of an overwintering cereal rye (Secale cereale L.) cover crop (CC) to midwestern maize (Zea mays L.)‐based systems offers several environmental benefits, but the long‐term effects of this practice on soil hydrological properties are not well understood. We utilized four long‐term (10+ yr) trials (two commercial fields, two research plots) in Iowa that included a replicated winter rye CC and no‐cover treatment in no‐till maize/soybean [Glycine max (L.) Merr.] systems. We took intact 7.62‐cm diam. soil samples from a 10‐to‐18‐cm depth shortly after cash crop planting in the spring. We measured the soil water retention curve using matric potentials ranging from saturation to –500 cmH2O. In addition, we measured organic matter, textural composition, and bulk densities of the soil samples. At the depth sampled, CCs did not meaningfully affect bulk density, water contents at saturation, or air‐entry potentials at any trial, nor increase the percentage of macropores. At two trials, soil water content at field capacity (–100 cmH2O) in the CC treatments was 2.5 vol% (SE: 1.2%; commercial field) and 2.4 vol% (SE: 1.3%; research plot) higher compared with the no‐cover treatments. This increase could meaningfully reduce the amount of water drained from a field after a saturating rain and should be considered when assessing CC impacts on landscape hydrology. The presence or absence of a CC effect on field capacity was not related to CC aboveground biomass production, previous cash crop, or soil texture at the trial sites. Based on our results, a causal model, and previous literature we hypothesize CC root characteristics are key to understanding variable effects of CCs on soil water storage. Our results indicate it is possible for CCs to meaningfully affect soil water storage, but more research is needed on the mechanisms by which these changes occur. Core ideas · Cover crop effects on soil water storage at 10‐to‐18‐cm soil depth were not consistent. · Cover crops increased water held at field capacity in two of four trials. · Cover crops did not affect water held at saturation or increase percentage of macropores. · Causal model suggests cover crop roots may be a key driver of variable results.

Core Ideas Cover crop mixtures did not provide benefits beyond cover crop monocultures. Cover crops did not influence soil temperature, soil P or K concentrations, or corn yield. Cover crops did not influence weed density or weed community in subsequent corn. The use of cover crops can decrease soil erosion, weed density, and nitrate leaching while improving soil quality. We investigated nine cover crops, winter rye (Secale cereale L.), winter triticale (× Triticosecale Wittm. ex A. Camus), two winter canola (Brassica napus L.), winter camelina [Camelina sativa (L.) Crantz], spring barley (Hordeum vulgare L.), spring oat (Avena sativa L.), turnip (B. rapa L.), and hairy vetch (Vicia villosa Roth), as sole crops and selected binary and trinary mixtures and their influences on subsequent corn (Zea mays L.) productivity. A control treatment of no cover crop was included. Cover crops were no‐till drilled immediately after soybean [Glycine max (L.) Merr] harvest. The study was a randomized complete block conducted in five environments over 2013–2014 and 2014–2015. Across environments, rye and rye mixtures produced the greatest spring aboveground biomass (758 kg ha−1), C, and N accumulation, had some of the lowest spring soil nitrate concentrations, and generally produced the lowest corn leaf chlorophyll. Rye accounted for more than 79% of spring aboveground biomass accumulation in rye mixtures. Triticale and camelina monoculture produced approximately 50% less biomass than rye or mixtures with rye. Cover crops in monoculture and mixtures did not influence surface soil temperature, soil P or K concentrations, weed density, weed community, or corn yield. Cover crops had limited influence on volumetric soil water content. Cover crop mixtures had no advantages over monocultures except for increasing fall stand density. Turnip and vetch had limited winter survival while barley, oat, and canola winterkilled.

Soil N(2)O emissions from three corn (Zea mays L.)--soybean [Glycine max (L.) Merr.] systems in central Iowa were measured from the spring of 2003 through February 2005. The three managements systems evaluated were full-width tillage (fall chisel plow, spring disk), no-till, and no-till with a rye (Secale cereale L. 'Rymin') winter cover crop. Four replicate plots of each treatment were established within each crop of the rotation and both crops were present in each of the two growing seasons. Nitrous oxide fluxes were measured weekly during the periods of April through October, biweekly during March and November, and monthly in December, January, and February. Two polyvinyl chloride rings (30-cm diameter) were installed in each plot (in and between plant rows) and were used to support soil chambers during the gas flux measurements. Flux measurements were performed by placing vented chambers on the rings and collecting gas samples 0, 15, 30, and 45 min following chamber deployment. Nitrous oxide fluxes were computed from the change in N(2)O concentration with time, after accounting for diffusional constraints. We observed no significant tillage or cover crop effects on N(2)O flux in either year. In 2003 mean N(2)O fluxes were 2.7, 2.2, and 2.3 kg N(2)O-N ha-1 yr-1 from the soybean plots under chisel plow, no-till, and no-till + cover crop, respectively. Emissions from the chisel plow, no-till, and no-till + cover crop plots planted to corn averaged 10.2, 7.9, and 7.6 kg N(2)O-N ha-1 yr-1, respectively. In 2004 fluxes from both crops were higher than in 2003, but fluxes did not differ among the management systems. Fluxes from the corn plots were significantly higher than from the soybean plots in both years. Comparison of our results with estimates calculated using the Intergovernmental Panel on Climate Change default emission factor of 0.0125 indicate that the estimated fluxes underestimate measured emissions by a factor of 3 at our sites.

Nitrate in water from tile drained corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] fields in the U.S. Midwest contributes to nitrate contamination of surface waters. Denitrification-based biofilters are a promising strategy for reducing nitrate concentrations, but these systems require an external carbon supply to sustain denitrification. The ability of four organic materials to serve as carbon substrates for denitrification biofilters was evaluated in this laboratory study. Wood chips, wood chips amended with soybean oil, cornstalks, and cardboard fibers were mixed with subsoil (oxidized till) and incubated anaerobically for 180 d. Periodically, 15NO3-N was added to maintain nitrate N concentrations between 10 and 100 mg L-1. All of the materials stimulated NO3-N removal and the degree of removal from highest to lowest was: cornstalks, cardboard fibers, wood chips with oil, and wood chips alone. Analysis of 15N showed that immobilization and dissimilatory nitrate reduction to ammonium accounted for <4% of NO3-N removal in all treatments, therefore denitrification was the dominant NO3-N removal process. Cardboard fibers, wood chips and oil, and wood chips alone did not support as much denitrification as cornstalks, but their rates of NO3-N removal were steady and would probably continue longer than cornstalks. The addition of soybean oil to wood chips significantly increased denitrification over wood chips alone.

Subsurface drainage in agricultural watersheds exports a large quantity of nitrate-nitrogen (NO3-N) and concentrations frequently exceed 10 mg L-1. A laboratory column study was conducted to investigate the ability of a wood chip bioreactor to promote denitrification under mean water flow rates of 2.9, 6.6, 8.7 and 13.6 cm d-1 which are representative of flows entering subsurface drainage tiles. Columns were packed with wood chips and inoculated with a small amount of oxidized till and incubated at 10°C. Silicone sampling cells at the effluent ports were used for N2O sampling. 15Nitrate was added to dosing water at 50 mg L-1 and effluent was collected and analyzed for NO3-N, NH4-N, and dissolved organic carbon. Mean NO3-N concentrations in the effluent were 0.0, 18.5, 24.2, and 35.3 mg L-1 for the flow rates 2.9, 6.6, 8.7, and 13.6 cm d-1, respectively, which correspond to 100, 64, 52, and 30% efficiency of removal. The NO3-N removal rates per gram of wood increased with increasing flow rates. Denitrification was found to be the dominant NO3-N removal mechanism as immobilization of 15NO3-N was negligible compared with the quantity of 15NO3-N removed. Nitrous oxide production from the columns ranged from 0.003 to 0.028% of the N denitrified, indicating that complete denitrification generally occurred. Based on these observations, wood chip bioreactors may be successful at removing significant quantities of NO3-N, and reducing NO3-N concentration from water moving to subsurface drainage at flow rates observed in central Iowa subsoil.

Cover crops can offer erosion protection as well as soil and environmental quality benefits. Cereal rye (Secale cereale L.) is the most commonly used winter cover crop in corn–soybean rotations in the upper Midwest of the USA because of its superior winter hardiness and growth at cool temperatures. Cereal rye cover crops, however, can occasionally have negative impacts on the yield of a following corn crop, which discourages broader adoption and introduces substantial risk for corn farmers employing cover crops. We hypothesized that because cereal rye shares some pathogens with corn, it may be causing increased disease in corn seedlings planted soon after cereal rye termination. To test this, we performed a series of experiments in a controlled environment chamber to assess the response of corn seedlings with and without a commercial fungicide seed treatment to the presence of cereal rye or other species of cover crops that were terminated with herbicide prior to corn planting. Our results indicate that under cool and wet conditions, cereal rye reduces corn seedling growth performance and increases incidence of corn seedling root disease. Fungicide seed treatment had limited efficacy in preventing these effects, perhaps because environmental conditions were set to be very conducive for disease development. However, hairy vetch (Vicia villosa Roth) and winter canola (Brassica napus L.) cover crops had fewer negative impacts on corn seedlings compared with cereal rye. Thus, to expand the practice of cover cropping before corn, it should become a research priority to develop alternative management practices to reduce the risk of corn seedling root infection following cereal rye cover crops. Over the longer term, testing, selection and breeding efforts should identify potential cover crop species or genotypes that are able to match the winter hardiness, growth at cool temperatures and the conservation and environmental quality benefits of cereal rye, while avoiding the potential for negative impacts on corn seedlings when environmental conditions are suitable for disease development.

Carbon dioxide flux from the soil to the atmosphere is an important component of terrestrial C cycling, and accurate estimates of CO 2 –C fluxes are critical in estimating C budgets. Accurate estimation of daily C loss from infrequent measurements of CO 2 flux requires characterization of the temporal variability associated with this processes. We investigated the relationships between diurnal CO 2 flux and temperature at two locations, corresponding to two soil types (a sandy loam and a clay loam) in a residue covered no‐till corn ( Zea mays L.)/soybean field ( Glycine Max L. Merr.). Automated chambers provided hourly measurements of CO 2 flux from 4 Mar. through 6 June 2000. Hourly soil temperature measurements were made at the surface and at the 0.05‐m depth, along with air temperature and soil water content measurements. Time series analysis showed that the temporal dynamics of CO 2 flux were more closely related to air temperature than to soil temperature, perhaps because a substantial portion of the CO 2 originated from surface residues. Exponential temperature correction algorithms ( Q 10 ) were evaluated using a range of Q 10 factors applied to both air and soil temperatures. We found that a Q 10 = 2 relationship when applied to a 0.05‐m soil temperature performed poorly in this regard, however, air temperature based Q 10 relationships ( Q 10 = 1.5 or 1.25) performed better in that they reduced time‐of‐day estimation biases from 28 to <4%. Knowledge of the efficacy of temperature correction algorithms and application of the appropriate temperature measurements should improve the accuracy of cumulative C flux estimates from short‐term measurements.

Unacceptable levels of NO3 leaching to ground water and drainage systems can occur under corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotations. Cover crops have the potential to reduce NO3 leaching, but this process has not been well documented. Lysimeters utilizing large soil monoliths are an excellent approach for studying NO3 leaching because inputs can be controlled and outputs accurately measured. The objective of this study was to see if fall cover crops could reduce NO3 leaching from large soil monoliths. We used three (1 by 1 by 1.5 m deep) monoliths in each of two controlled climate chambers with oat (Avena sativa L.) or rye (Secale cereale L.) fall cover crop interplanted into soybean in mid‐August. The study was continued for two cover crop cycles in each chamber. In Chamber 1, drainage was significantly reduced due to oat or rye cover crops for the fall through summer of Years 1 and 2 (first cover crop cycle), and NO3 loss was reduced for most of the same time period. In Chamber 2, NO3 loss was reduced for the spring‐summer season of the second year (first cover crop cycle). Although drainage was less under cover crops for Chamber 1, the soil water content was not consistently lower because of replenishment by watering. The soil monoliths were useful for showing that oat and rye cover crops in a corn–soybean rotation can reduce NO3 leaching from lysimeters and suggest that the same trend would be true in the field.