Chisel-plowed Plots Research Articles

Salmonella and Fecal Indicator Bacteria Survival in Soils Amended with Poultry Manure

Minimizing the risks associated with manure-borne pathogenic microorganisms requires an understanding of microbial survival under realistic field conditions. The objective of this 3-year study was to assess the fate of Salmonella (SALM) and fecal indicator bacteria (FIB), E. coli (EC) and enterococci (ENT), in glacial till-derived soils, after application of poultry manure (PM) to cornfields under chisel-plowed (CP) or no-till (NT) management. From 2010 to 2012, soil samples were obtained each spring at 0–15- and 15–30-cm depths, to determine whether over-wintering of target bacteria had occurred. Sampling was followed by application of PM at low (PM1) and high (PM2) rates, based on nitrogen application goals. In 2012, soil samples were collected 21, 42, and 158 days after manure application (DAM), to assess the effects of time, application rates, and tillage on frequency of detection and concentrations of target bacteria. Despite dry conditions, all three target organisms were detected 158 DAM in 2012, and detection of these organisms in spring soil samples from manured plots in 2011 and 2012, nearly a full year after PM application, suggests that these organisms can persist in the soil environment long after application. The highest SALM concentration (790 cfu/g dry weight) and detection rate (25%) was found in PM2 plots 42 DAM. SALM were detected more frequently in CP plots (20%) compared to NT plots (5%). In contrast, tillage practices had no apparent effect on EC or ENT survival, as indicated by both soil, and decay rates estimated from tile-water bacteria concentrations. Decay rate constants (μ) ranged from 0.044 to 0.065 day−1 for EC and 0.010 to 0.054 day−1 for ENT.

Corn stover harvest and tillage impacts on near-surface soil physical quality

Excessive harvest of corn (Zea mays L.) stover for ethanol production has raised concerns regarding negative consequences on soil physical quality. Our objective was to quantify the impact of two tillage practices and three levels of corn stover harvest on near-surface soil physical quality through the Least Limiting Water Range (LLWR). We evaluated no harvest, moderate and high stover harvest treatments within no-tillage and chisel plow plots following seven years of continuous corn production. Forty undisturbed soil samples were taken from the 0–7.5cm deep layer within each treatment and used to determine water retention curves, soil resistance to penetration and bulk density values (Bd). No-tillage plots had higher average soil bulk density and resistance to penetration values, and were more affected by stover harvest than chisel plow plots. The results confirmed that soil resistance to penetration determined the lower limit of the LLWR regardless of tillage or stover treatment, whereas soil aeration controlled the upper limit only at Bd>1.45 and Bd>1.55Mgm−3 for chisel plow and no-tillage, respectively. The LLWR was smallest for no-tillage with moderate or high corn stover harvest, indicating poor soil physical condition for plant growth, while the largest LLWR occurred with moderate stover harvest and chisel plowing. The introduction of alfalfa (Medicago sativa L.) into an extended rotation with no-tillage improved the LLWR by reducing the potential crop growth restriction due to resistance to penetration. Although bulk density values were only occasionally higher than the critical level (Bd=1.60Mgm−3 for chisel plow and Bd=1.64Mgm−3 for no-tillage), lower soil structure quality was evident with no-tillage under moderate or high stover harvest and with chisel plowing under high stover removal. The LLWR was more sensitive than available soil water content for detecting tillage and stover harvest effects on soil structural degradation.

Visual Soil Structure Effects of Tillage and Corn Stover Harvest in Iowa

Core Ideas VESS detected soil structural quality changes under corn stover harvest and tillage systems. A high level of corn stover harvest had an adverse effect on the soil structural quality. Under high stover harvest, structural quality in chisel plow was worse than in no‐tillage. VESS should be further evaluated as an integrative soil quality/health indicator. High levels of corn (Zea mays L.) stover harvest for ethanol production have raised concerns regarding negative consequences on soil structure and physical quality. Visual soil structure assessment methods have the potential to help address these concerns through simple, straightforward on‐farm evaluations. Our objective was to determine if the visual evaluation of soil structure (VESS) approach could detect soil structural quality differences associated with different levels of corn stover harvest and tillage practices. We evaluated no harvest and moderate and high stover harvest levels within no‐tillage (NT) and chisel plow (CP) plots following 7 yr of continuous corn. Undisturbed 10‐ by 20‐ by 25‐cm soil samples were taken using a spade in April 2015. The thickness and structural quality (Sq) scores for the 0‐ to 5‐ (top) and 5‐ to 20‐cm (bottom) soil layers were determined, and an overall Sq was computed. The Sq values showed a significant interaction between corn stover harvest and tillage practice. Soil structural quality showed no significant differences between NT and CP systems for either the no‐ or moderate‐harvest treatments, but with a high stover harvest rate, CP structural quality was worse than NT. With NT, both moderate and high rates of stover harvest significantly increased Sq compared to no harvest; in CP, there was no significant difference between the no‐ and moderate‐harvest treatments. Only a high level of stover harvest had an adverse effect on the Sq rating. The VESS approach was sensitive for detecting the effects of corn stover harvest and tillage systems on soil structural quality and should be further evaluated as an integrative, on‐farm soil quality/health indicator.

Effects of tillage and poultry manure application rates on Salmonella and fecal indicator bacteria concentrations in tiles draining Des Moines Lobe soils

Application of poultry manure (PM) to cropland as fertilizer is a common practice in artificially drained regions of the Upper Midwest United States. Tile-waters have the potential to contribute pathogenic bacteria to downstream waters. This 3-year study (2010–2012) was designed to evaluate the impacts of manure management and tillage practices on bacteria losses to drainage tiles under a wide range of field conditions. PM was applied annually in spring, prior to planting corn, at application rates ranging from 5 to 40 kg/ha to achieve target rates of 112 and 224 kg/ha nitrogen (PM1 and PM2). Control plots received no manure (PM0). Each treatment was replicated on three chisel-plowed (CP) plots and one no-till (NT) plot. Tile-water grab samples were collected weekly when tiles were flowing beginning 30 days before manure application to 100 days post application, and additional grab samples were obtained to target the full spectrum of flow conditions. Manure and tile-water samples were analyzed for the pathogen, Salmonella spp. (SALM), and fecal indicator bacteria (FIB), Escherichia coli (EC), and enterococci (ENT). All three bacterial genera were detected more frequently, and at significantly higher concentrations, in tile-waters draining NT plots compared to CP plots. Transport of bacteria to NT tiles was most likely facilitated by macropores, which were significantly more numerous above tiles in NT plots in 2012 as determined by smoke-testing. While post-manure samples contained higher concentrations of bacteria than pre-manure samples, significant differences were not seen between low (PM1) and high (PM2) rates of PM application. The highest concentrations were observed under the NT PM2 plot in 2010 (6.6 × 103 cfu/100 mL EC, 6.6 × 105 cfu/100 mL ENT, and 2.8 × 103 cfu/100 mL SALM). Individual and 30-day geometric mean ENT concentrations correlated more strongly to SALM than EC; however, SALM were present in samples with little or no FIB.

Tillage Affects Imazamox Carryover in Yellow Mustard

Farmers grow crops in the dryland region of the Pacific Northwest (PNW) using tillage practices ranging from moldboard plowing to no-tillage. The objective of this study was to determine the effect of tillage on persistence of imazamox herbicide in intermediate and high precipitation zones of the inland PNW. Along with a nontreated control, imazamox was applied to imidazolinone-tolerant winter wheat in the fall and spring at one, two, and three times the maximum labeled rate at locations near Genesee, ID, Davenport, WA, and Pendleton, OR. Moldboard plow, chisel plow, and no-till tillage treatments were implemented soon after wheat harvest and yellow mustard was planted the following season to determine crop response. Experiments were conducted at each location in 2005 to 2007 and 2006 to 2008. There were significant location by year and year and location interactions. There was no significant tillage by imazamox rate interaction, except at Pendleton in year 2, for all measured yellow mustard responses (crop injury, biomass, and yield). Genesee was colder than Pendleton and had more precipitation than Davenport, resulting in more injury to yellow mustard at Genesee than at Pendleton but less than at Davenport. Davenport had greater injury than the other two locations, likely due to lower soil pH, higher organic matter (OM), and cooler, drier climate, which allowed imazamox to persist longer in the soil. Overall, Pendleton had the least yellow mustard injury, which likely was related to its warmer, wetter climate and the concomitant rapid soil dissipation of imazamox. Tillage did not reduce the persistence of imazamox. Yellow mustard had the lowest injury and had greater mature biomass and seed yield in no-till seeded plots when averaged across imazamox rates compared to moldboard and chisel-plowed plots.

Tillage and Nutrient Source Effects on Water Quality and Corn Grain Yield from a Flat Landscape

Beneficial effects of leaving residue at the soil surface are well documented for steep lands, but not for flat lands that are drained with surface inlets and tile lines. This study quantified the effects of tillage and nutrient source on tile line and surface inlet water quality under continuous corn (Zea mays L.) from relatively flat lands (<3%). Tillage treatments were either fall chisel or moldboard plow. Nutrient sources were either fall injected liquid hog manure or spring incorporated urea. The experiment was on a Webster-Canisteo clay loam (Typic Endoaquolls) at Lamberton, MN. Surface inlet runoff was analyzed for flow, total solids, NO(3)-N, NH(4)-N, dissolved P, and total P. Tile line effluent was analyzed for flow, NO(3)-N, and NH(4)-N. In four years of rainstorm and snowmelt events there were few significant differences (p < 0.10) in water quality of surface inlet or tile drainage between treatments. Residue cover minimally reduced soil erosion during both snowmelt and rainfall runoff events. There was a slight reduction in mineral N losses via surface inlets from manure treatments. There was also a slight decrease (p = 0.025) in corn grain yield from chisel-plow plots (9.7 Mg ha(-1)) compared with moldboard-plow plots (10.1 Mg ha(-1)). Chisel plowing (approximately 30% residue cover) alone is not sufficient to reduce nonpoint source sediment pollution from these poorly drained flat lands to the extent (40% reduction) desired by regulatory agencies.

Soil organic carbon changes after 12 years of no-tillage and tillage of Grantsburg soils in southern Illinois

Many factors including management history, soil type, climate, and soil landscape processes affect the dynamics of soil organic carbon (SOC). The primary objective of this research was to determine the effects of no-tillage and tillage systems on the SOC content after 12 years of controlled treatments. A tillage experiment with three treatments (no-till (NT), chisel plow (CP) and moldboard plow (MP)) was initiated in the spring of 1989 in southern Illinois. The plot area was previously in a tall fescue hayland for 15 years and had a 6% slope. Maize ( Zea mays L.) and soybean ( Glycine max L. Merr.) were grown in the plot area on a yearly rotation system starting with maize. Periodically, the SOC content of various soil layers, to a depth of either 30 or 75 cm, was measured and expressed on both a gravimetric and volumetric basis. After 12 years, the 0–15 cm surface soil layer of MP was significantly lower in SOC than the NT and CP plots. For all but 2 values, the significance of findings did not change with the form of expression (gravimetric versus volumetric). The surface layer (0–15 cm), subsoil (15–75 cm), and rooting zone (0–75 cm) of all treatments had reduction in SOC on a volumetric basis when compared to the pre-treatment values for sod. At the end of the 12-year study, the MP system had significantly less SOC in the surface layer, subsurface layer and rooting zone than the NT system at comparable depths. After 12 years of tillage under a maize–soybean rotation, the NT treatment sequestered or maintained more SOC stock (47.0 Mt ha −1) than the CP (43.7 Mt ha −1) and MP (37.7 Mt ha −1) treatments. The annual rate of SOC stock build up in the root zone (0–75 cm), above the MP system base, was 0.71 Mt ha −1 year −1 for the NT system and 0.46 Mt ha −1 year −1 for the CP system. For land coming out of the Conservation Reserve Program and returning to row crop production, NT and CP systems would maintain more SOC stock than MP system and reduce CO 2 emissions to the atmosphere.

Survival and Inoculum Production of Gibberella zeae in Wheat Residue.

Survival and inoculum production of Gibberella zeae (Schwein.) Petch (anamorph Fusarium graminearum (Schwabe)), the causal agent of Fusarium head blight of wheat and barley, was related to the rate of wheat (Triticum aestivum L.) residue decomposition. Infested wheat residue, comprising intact nodes, internodes, and leaf sheaths, was placed in fiberglass mesh bags on the soil surface and at 7.5- to 10-cm and 15- to 20-cm depths in chisel-plowed plots and 15 to 20 cm deep in moldboard-plowed plots in October 1997. Residue was sampled monthly from April through November during 1998 and every 2 months through April to October 1999. Buried residue decomposed faster than residue placed on the soil surface. Less than 2% of the dry-matter residue remained in buried treatments after 24 months in the field, while 25% of the residue remained in the soil-surface treatment. Survival of G. zeae on node tissues was inversely related to the residue decomposition rate. Surface residue provided a substrate for G. zeae for a longer period of time than buried residue. Twenty-four months after the initiation of the trial, the level of colonization of nodes in buried residue was half the level of colonization of residue on the soil surface. Colonization of node tissues by G. zeae decreased over time, but increased for other Fusarium spp. Ascospores of G. zeae were still produced on residue pieces after 23 months, and these spores were capable of inducing disease. Data from this research may assist in developing effective management strategies for residues infested with G. zeae.

Soil compaction and root distribution for okra as affected by tillage and vehicle parameters

Many soil physical properties and crop yield are affected by compaction and tillage systems. The effect of three different factors, i.e. tillage treatments (no-tillage, chisel plowing, and moldboard plowing), axle load (6 and 16 t/axle vehicle), and tire inflation pressure (120 and 350 kPa inflation pressures) on okra ( Abelmoschus esculentus) root density and soil physical properties (bulk density and cone penetration resistance) was studied. This study was initiated in April 2000 on a loam soil (42% sand, 36% silt, 22% clay) at an experimental farm in Irbid, a district in the northern part of Jordan. Response to the above factors was measured down to 48 cm. Axle load and tire inflation pressure caused an increase in bulk density (BD) and cone penetration (CI) resistance from the soil surface down to 48 cm. The loaded vehicle with 350 kPa tire inflation pressure on no-tillage plots had the greatest effect soil physical properties measured while the unloaded vehicle with 120 kPa tire inflation pressure on chisel-plowed plots had the least effect. Plants in the no-tillage and moldboard-plowed treatments had a higher concentration of roots near the base of the plant compared to the plants in the chisel-plowed treatment.

Phosphorus runoff: effect of tillage and soil phosphorus levels.

Continued inputs of fertilizer and manure in excess of crop requirements have led to a build-up of soil phosphorus (P) levels and increased P runoff from agricultural soils. The objectives of this study were to determine the effects of two tillage practices (no-till and chisel plow) and a range of soil P levels on the concentration and loads of dissolved reactive phosphorus (DRP), algal-available phosphorus (AAP), and total phosphorus (TP) losses in runoff, and to evaluate the P loss immediately following tillage in the fall, and after six months, in the spring. Rain simulations were conducted on a Typic Argiudoll under a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Elapsed time after tillage (fall vs. spring) was not related to any form of P in runoff. No-till runoff averaged 0.40 mg L(-1) and 0.05 kg ha(-1) DRP and chisel-plow plots averaged 0.24 mg L(-1) and 0.02 kg ha(-1) DRP concentration and loads, respectively. The relationship between DRP and Bray P1 extraction values was approximated by a logistic function (S-shaped curve) for no-till plots and by a linear function for tilled plots. No significant differences were observed between tillage systems for TP and AAP in runoff. Bray P1 soil extraction values and sediment concentration in runoff were significantly related to the concentrations and amounts of AAP and TP in runoff. These results suggest that soil Bray P1 extraction values and runoff sediment concentration are two easily measured variables for adequate prediction of P runoff from agricultural fields.

Effects of Soil Tillage and Post-Emergence Weed Control on Weed Biomass and Maize Yield

The three-year study was carried out on lessive pseudogleic soil in North-eastern Croatia. Effects of tillage intensity (mouldboard-, chisel plough, disk harrowing) and sulfonylurea herbicide combinations were evaluated on dry biomass of certain life cycle weed groups and on maize grain yield. Annual grass of Echinochloa crus-galli (L.) PB. was the main species in all years, with dry biomass reaching from 175 to 305 g m-2. E. crus-galli biomass was significantly greater in chisel plow and disk harrowed plots than in mouldboard plow plots. No significant tillage effect was recorded for biomass of annual broad-leaved and perennial weeds. The differences in total weed biomass between mouldboard ploughing and reduced tillage practices as well between years were considerable. All herbicide combinations provided consistent biomass control of annual grass weeds (91-98%) and annual broad-leaved weeds (86-95%) but inadequate control of perennials (45-87%) on average. Nicosulfuron + 50% prosulfuron & 30% primisulfuron-methyl gave the best total weed control effect, followed by rimsulfuron + thifensulfuron-methyl and rimsulfuron + 50% prosulfuron & 30% primisulfuron-methyl without any significant effect on the yield. Maize yields were significantly affected by year and tillage. Tillage, which included mouldboard ploughing, gave significantly higher yields and showed higher resistance to weather conditions than less intensive tillage.

CROPPING SYSTEM EFFECTS ON NO3–N LOSS WITH SUBSURFACE DRAINAGE WATER

An appropriate combination of tillage and nitrogen management practices will be necessary to develop sustainable farming practices. A six–year (1993–1998) field study was conducted on subsurface–drained Clyde–Kenyon–Floyd soils to quantify the impact of two tillage systems (chisel plow vs. no tillage) and two N fertilizer management practices (preplant single application vs. late–spring soil test based application) on nitrate–nitrogen (NO3–N) leaching loss with subsurface drain discharge from corn (Zea mays L.) soybean (Glycine max L.) rotation plots. Preplant injected urea ammonium nitrate solution (UAN) fertilizer was applied at the rate of 110 kg ha–1 to chisel plow and no–till corn plots, while the late–spring N application rate averaged 179 and 156 kg ha–1 for the no–till and chisel plow corn plots, respectively. Data on subsurface drainage flow volume, NO3–N concentrations in subsurface drainage water, NO3–N loss with subsurface drainage flow, and crop yield were collected and analyzed using a randomized complete block design. Differences in subsurface drainage flow volume due to annual variations in rainfall significantly (P = 0.05) affected the NO3–N loss with subsurface drainage flows. High correlation (R2 = 0.89) between annual subsurface drainage flow volume and the annual NO3–N leaching loss with subsurface drainage water was observed. The flow–weighted average annual NO3–N concentrations varied from a low of 6.8 mg L–1 in 1994 to a high of 13.9 mg L–1 in 1996. Results of this study indicated that NO3–N losses from the chisel plow plots were 16% (16 vs. 19 kg–N ha–1) lower in comparison with no–till plots, while corn grain yield was 11% higher in the chisel plow plots (8.3 vs. 7.5 Mg ha–1). Late–spring N application applied as a sidedress resulted in 25% lower NO3–N leaching losses with subsurface drainage water in comparison with preplant single N application and also significantly (P = 0.5) higher corn grain yield by 13% (8.4 vs. 7.4 Mg ha–1). These results clearly demonstrate that chisel plow tillage with late–spring soil test based N application for corn after soybean can be a sustainable farming practice for the northeast part of Iowa.

Snowmelt runoff, sediment, and phosphorus losses under three different tillage systems

In cold climates, snowmelt runoff often exceeds rainfall runoff during the year. Conservation tillage practices may be effective in reducing runoff during the cropping season but not during the snowmelt period. A plot study was conducted on a cropped hillslope to assess how tillage practices affect snowmelt runoff and the associated losses of sediment, phosphorus (P), and chemical oxygen demand (COD). Tillage systems were fall moldboard and chisel plowing with spring disking, and a ridge till system utilizing only the tillage associated with summer row cultivation. Tillage and planting were done up and down the slope. Ridge tilled plots had higher fall residue cover, retained more snow, had less surface roughness, and consequently produced more runoff than the moldboard plow treatment. The amount of runoff from chisel plowed plots was similar to runoff from ridge tilled plots despite a relatively rough surface and moderate amount of residue cover. Phosphorus losses in runoff were higher for the ridge till and chisel plow systems than for the moldboard plow system. For all tillage systems, soluble P represented a major portion (75%) of the total P loss in snowmelt runoff. Although erosive losses in snowmelt were low, the P losses were substantial and merit consideration in studies evaluating management systems impact on surface water quality in regions where snowmelt runoff is important.

Atrazine and alachlor concentrations under ridge tillage and chisel-plow tillage in an alluvial plain soil

Although agricultural fertilizers and herbicides have significantly improved crop yields during the past 30 years, there is concern regarding the presence of these chemicals within certain environments. Atrazine and alachlor presence in an alluvial plain soil in south-central Ohio, USA, was evaluated over a 5-year period under ridge- and chisel-plow-tillage systems. The ridge-tillage plots included one large field-scale plot, 10 ha in size, and nine 0.4 ha plots used for replicating each phase of the corn ( Zea mays L.)–soybean ( Glycine max L.)–wheat ( Triticum aestivuum L.) rotation every year; three plots for corn, three plots for soybean, and three plots for wheat. The chisel plowed plots with continuous corn included one large field-scale plot, 10 ha in size, and three 0.4 ha plots used for replicated studies. Soil cores were taken from all plots, approximately biweekly during the growing season and monthly during the non-growing season, from under the row for the period from 1991 to 1993. Soil cores were taken approximately monthly during the growing season from under the row and between the rows in 1994 and 1995. Measured concentrations of atrazine and alachlor were similar in soil samples taken from under the row in the chisel-plowed, continuous-corn and ridge-tilled, corn–soybean–wheat systems. Atrazine and alachlor concentrations measured under the row, and between the row, were generally significantly different (42 of 54 sampling events) in the ridge-tillage system because a banded application of herbicides was used. Movement of herbicides from the ridge position to the valley position was not evident. Herbicide usage was reduced by 66% because of the banding operation in the ridge-tillage cropping system. A similar reduction in herbicide usage could occur in the chisel-plow system if herbicides were applied in a band and cultivation was used to control weed pressure between the rows. Chisel-plow tillage with a banded application of herbicides may be a favorable alternative for farm operators wishing to reduce herbicide usage without converting to the controlled traffic, ridge-tillage system.

The effect of light during and after soil cultivation with different tillage implements on weed seedling emergence

The purpose of this study was to investigate the role of sunlight perceived by weed seeds during and after soil cultivation with moldboard and chisel plows on induction of seed germination. Daytime cultivation with a moldboard plow increased weed seedling emergence by as much as 200% above the levels recorded following nighttime cultivation; however, the magnitude of this promotion varied depending on season and field history, and occasionally it was nil. In contrast, when a chisel plow was used in primary tillage, no differences in seedling emergence were observed between daytime and nighttime cultivation. The absolute germination level in plots cultivated with a chisel plow was at least 200% greater than in plots cultivated with a moldboard plow. This observation suggests that microenvironmental factors other than light played an important role in promoting seed germination in chisel-plowed plots. Covering moldboard-plowed plots with opaque plastic immediately after cultivation did not reduce weed seedling emergence compared to plots that were either covered with transparent film or left uncovered. Our results suggest that only the light stimulus perceived by the seeds during soil cultivation is effective in triggering germination.

RZWQM SIMULATION OF NITRATE CONCENTRATIONS IN SUBSURFACE DRAINAGE FROM MANURED PLOTS

The Root Zone Water Quality Model (RZWQM, V 3.25) was used to simulate the effect of swine manureapplications on nitrate-nitrogen (NO3-N) concentrations in subsurface drain water from continuous corn for Iowa soils.Measured values of subsurface drain flow, NO3-N concentrations in drainage water, and residual NO3-N in the soil profilefrom three chisel plow plots were available for the growing seasons of 1993 and 1995. The measured values were used toevaluate the RZWQM. Several parameters of RZWQM were calibrated to provide satisfactory subsurface drain flow,nitrate in drainage water and nitrate in soil profile for the growing season of 1993. The calibrated parameters were thenused to simulate subsurface drain flows, its NO3-N concentrations, and residual NO3-N content in the soil profile asaffected by manure application for the growing season of 1995. Simulated subsurface drain flows, NO3-N concentrations,and total residual NO3-N contents were compared with the measured values. Predicted daily subsurface drain flows bythe RZWQM were close to the observed flows. Annual total subsurface drain flows predicted by the model were also closeto the observed values (difference over two years was 3.9%). The predicted NO3-N concentrations in subsurfacedrainage water followed the observed trends well for years 1993 and 1995 for all three plots. The annual average NO3-Nconcentrations predicted by the RZWQM were also in close agreement with the measured values for 1993 and 1995(within a difference of 3.0%). Linear regression (zero interception) between the predicted values for the pooled data(average of three plots for two years) and the measured data gave an R2 value of 0.88 with a slope of 0.96. The predictedsoil NO3-N contents in 0-1.2 m soil profile were also in close agreement with the measured values in the field. The overallresults of this study indicate that RZWQM is capable of simulating various rate of manure applications in differentweather and soil conditions.

Characterization and Use of Nitrogen Contained in Sweet Corn Silage Waste in Cropping Systems

Sweet corn silage waste is ≈18% dry matter and contains 1.2% N and 0.26% P on a dry-weight basis. Silage waste in rates of 0 to 448 T·ha–1 was applied to a previously harvested sweet corn field in late summer. Beginning the following spring, soil samples were periodically collected to follow the rate of N mineralization. Field corn was planted to the site the following spring as the test crop. At harvest, grain, stover, and silage yields were recorded and N removal from the system was followed through grain and tissue sampling. Additional studies were also conducted to evaluate the impact of primary tillage method on subsequent N mobilization from sweet corn silage waste and to assess the residual N release potential beyond the first year following silage waste application. Results suggest that land application of sweet corn silage waste at 224 T·ha–1 would be environmentally responsible, provided that adequate nitrogen credit from the silage waste is integrated into the total nitrogen needs of the subsequent crop. Greater mineralization is achieved when the silage waste is moldboard plowed compared to chisel plowing. Chisel plowing could result in greater residual N carryover during the year following silage waste application. Seedling emergence rates were faster and grain yield was superior in some years in moldboard-plowed plots compared to chisel-plowed plots. Further calibration of additional N fertilizer on land that received silage waste is necessary for improved production efficiency and sweet corn silage waste use in production systems.

Nitrate and Water Present in and Flowing from Root‐Zone Soil

AbstractFrom 1990 through 1992, we studied water and nitrate‐nitrogen (NO3‐N) present in the soil and flowing into a subsurface drainage system. Tillages were chisel plow (CP), moldboard plow (MB), no‐till (NT), and ridge‐till (RT). Crops were continuous corn (Zea mays L.) and a corn‐soybean [Glycine max (L.) Merr.] rotation. Tillage and crop only slightly influenced soil NO3‐N and water. Drainage water flows were highest for treatments that minimized soil disturbance and maximized crop residues produced during the previous year. The 3‐yr total flows by crop were 38 cm water for rotation‐corn plots, 56 for rotation soybean, and 59 for continuous corn. Flows by tillage were 41 cm water for MB plots, 52 for RT, and 55 for both CP and NT. In continuous corn, NT plots had more monthly water drainage than MB plots for most of 1990. Ridge‐till and CP plots had more drainage than MB plots for part of 1991. Crop rotation had the greatest effect on NO3‐N drainage loss. The 3‐yr total NO3‐N losses were 77 kg ha−1 for rotation corn plots, 84 for rotation soybean, and 164 for continuous corn. Tillage losses were 95 kg ha−1 for RT, 102 for MB, 106 for NT, and 131 for CP. No‐till and RT plots always had the lowest NO3‐N concentrations in drainage water; their yearly NO3‐N losses were usually smallest. Leaching can be best minimized by applying fertilizer in amounts to just meet crop N demand and at times closest to peak uptake.

Tillage and Fungicide Management of Foliar Diseases in a Spring Wheat Monoculture

Enthusiasm over conservation tillage in wheat (Triticum aesdivum L.) monoculture has been tempered by concern about the carryover of foliar diseases on the surface residue. A 3-yr study evaluated the effects of foliar diseases on wheat production with different methods of primary tillage and with fungicide control treatments. Plots with chisel plowing (2x) as the primary tillage had higher surface residue and higher foliar severity in the early growth stages compared with moldboard plowing or with moldboard plowing preceded by burning. Early season differences in severity between moldboard plowing treatments with and without burning were mostly insignificant. The effect of chisel plowing on early season foliar disease did not consistently carry over to late season foliar ratings. In 1991, chisel plowing resulted in the highest late-season foliar disease as indicated by the area under disease progress curve (AUDPC). In 1992, there was no significant difference in AUDPC between tillage treatments, and in 1993, chisel plowed plots had the lowest AUDPC. In this study, yields were not significantly affected by any tillage-related foliar disease effect. Foliar fungicides consistently reduced foliar severity, but in all 3 yr, the fungicide treatments were not economical at 1991-1993 market prices.

Conservation and contour tillage for corn and soybeans in the Tama silt loam soil: the hydrologic response

Simulated rainfall was applied to a Tama silt loam soil under four tillage treatments, two crops (corn and soybeans), two crop stages (at planting and one month later), and two row orientations (on the contour and up-and-down the slope). Contouring significantly increased the quantity of rainfall applied before the initiation of runoff for all tillage treatments. However, after a drainage pattern was established, contouring had little effect on runoff. Depth of runoff was usually greatest from moldboard-plowed plots and least from the strip-till plots, and differences between these two treatments were usually statistically significant at the 95% level of probability. Runoff depths from the chisel-plowed plots were usually less than the moldboard-plowed plots but the differences were never statistically significant. Runoff depths from the no-till plots were often significantly less than the moldboard-plowed plots, particularly in the year following soybean production. As the soil approached saturation, steady runoff rates were an average of 7 mm h −1 greater when the previous crop was soybeans for all tillage treatments, except for the no-till. Greater runoff following soybeans could be partially explained by less soil residue following soybeans, since runoff depths and steady runoff rates from the tilled soils were negatively correlated with residue cover. The relationship between residue cover and runoff for the no-till following corn appeared to be different from all other treatments. The least runoff rates were observed from plots which had been recently tilled yet retained high levels of soil residue cover.