No-till Plots Research Articles

Tillage management to mitigate herbicide loss in runoff under simulated rainfall conditions

Conservation tillage mitigates soil loss in cropland because plant residues help protect the soil, but effects on pesticide movement in surface runoff are not as straightforward. Effects of soil disturbance on surface runoff loss of chlorimuron and alachlor were evaluated utilizing runoff trays. Soil in the trays was either disturbed (tilled) and kept bare or was not tilled, and existing decomposed plant residue was left on the surface. Rainfall (25 mm, 20 min) was simulated 1 d after alachlor (2.8 kg ha −1) or chlorimuron (54 g ha −1) application, and runoff was collected. Runoff fractions were analyzed for herbicide and sediment. Total alachlor loss from bare plots was greater than that in no-tillage plots (4.5% vs. 2.3%, respectively). More than one-third of total alachlor lost from bare plots occurred in the first l of runoff, while no-tillage plots had less runoff volume with a more even distribution of alachlor concentration in the runoff during the rainfall simulation and subsequent runoff period. In contrast, more chlorimuron was lost from no-tillage plots than bare plots (12% vs. 1.5%) even though total runoff volume was lower in the no-tillage plots (10.6 mm vs. 13.6 mm). This was attributed to dense coverage with partially decomposed plant residue in no-tillage plots (1652 kg ha −1) that intercepted chlorimuron. It was likely that chlorimuron, a polar compound, was more easily washed off surface plant residues and transported in runoff.

Monitoring corn and soybean agroecosystems after establishing no-tillage practices in Québec, Canada

The conversion to no-tillage (NT) may seem risky to some producers who rely on tillage to control weeds, some insect pests and disease-causing pathogens that can reduce crop yield. Weeds, arthropods, and disease incidence were monitored in silage corn (Zea mays L.) and soybean (Glycine max L. Merr.) agroecosystems with CT and newly established NT plots in Ste-Anne-de-Bellevue, Québec. During the first 2 establishment years, there were more annual grass and fewer annual broadleaf weeds in NT than in CT plots, but the surface area covered by weeds (broadleaf,grasses and perennials) was greater in CT than NT plots. Foliar arthropods were more numerous in soybean than corn plots in both years, but were unaffected by tillage. There were more ground-dwelling generalist predators, especially Coleoptera and Carabidae, in CT than NT plots, while spiders and harvestmen (Araneae and Opiliones) were dominant in NT plots. Crop damage from insect pests and diseases was below economic thresholds, but 5 yr of yield monitoring (2000–2004) revealed a trend of greater silage corn and soybean yields in CT than NT plots. The reduction in crop yield after establishing NT practices at this site was probably due to rooting constraints from inadequate seedbed preparation in the NT system, rather than from weed competition, insect damage or crop diseases. Key words: Arthropods, crop disease, silage corn, soybean, tillage, weed control

Tillage and Soybean Canopy Effects on Common Cocklebur (Xanthium strumarium) Emergence

Field experiments were conducted in Pendleton, SC, in 2004 and 2005, to determine the influence of tillage with or without soybean on common cocklebur emergence. Treatments included no-till/no soybean (NTNS), no-till plus soybean (NTS), tillage/no soybean (TNS), and tillage plus soybean (TS). Emergence was monitored from an artificial seed bank in 2004 and a natural seed bank in 2005. Overall, common cocklebur emerged from early May through late October and presented multiple emergence. In no-till plots with or without soybean, initial emergence was delayed 7 d in both years. In TNS plots, major emergence (daily emergence > mean emergence plus standard deviation) of common cocklebur occurred from early May to late July. In NTNS plots, major emergence occurred from late May through late August. No-till reduced total common cocklebur emergence by 59 to 69% compared with tillage. At the V5 to V6 soybean growth stage, the daily soil thermal fluctuation at 2.5 cm soil depth diminished from approximately 15 to 5 C and reduced common cocklebur emergence by 84 to 91% for the rest of the growing season. Common cocklebur emergence was higher when the mean soil temperature was > 15 C, and the daily thermal fluctuation was > 7.5 C. This study suggests that strategies that promote early crop canopy development and minimum tillage should reduce common cocklebur emergence.

Dynamics of soil biota at different depths under two contrasting tillage practices

One aim of conservation tillage is to preserve soil biological properties. This study was conducted to examine the effects of two contrasting tillage treatments on soil biota at different depths. We investigated the population dynamics and vertical distributions of microbes and several soil faunal groups for 2 years in field Andosols in northeastern Japan. The experimental plots were under no tillage (NT) or conventional tillage (CT, rotary tilled to 20 cm) management. In the 0–10-cm soil layer, bacterial and fungal substrate-induced respiration (SIR) and the population density of enchytraeids were higher under NT than under CT, but the population densities of protozoa, mites, and collembolans did not differ significantly. In contrast, at 10–20 cm, both SIR values were higher under CT, where larger populations of mites and collembolans were recorded. At both depths, nematodes were more abundant under CT. Thus, the effects of tillage on these soil organisms differed according to soil depth, and negative impacts of tillage were smaller in the deeper layer. Larger amounts of earthworm casts at the soil surface in NT plots showed a greater biomass of earthworms than in CT. To evaluate the activities of soil biota, we buried litterbags with three different mesh sizes at the two depths and examined the rate of decomposition. The daily decay constant of litter in the surface soil layer (1.5–8.5 cm) was greater under NT. We suppose that the activities of soil biota in this layer were stimulated under NT, and that especially microbes and enchytraeids, which were abundant at 0–10 cm, contributed greatly to the decomposition.

EFFECTS OF TILLAGE ON NORFLURAZON SORPTION, DEGRADATION AND MOBILITY IN A MISSISSIPPI DELTA SOIL

The fate of pesticides in agricultural systems and impact on water quality remain important environmental issues. Recent studies have found the herbicide norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3-(2H)-pyridiazone] in groundwater and surface water. Although there are data on the sorption, degradation, and mobility of this compound in different soils, none address effects of tillage on its fate. Also, the accuracy of independent sorption and degradation data for predicting norflurazon mobility has not been assessed. This study compared sorption, degradation, and mobility of norflurazon in Dundee (fine-silty, mixed, thermic, Aeric Ochraqualfs) soil from conventional-tillage (CT) and no-tillage (NT) plots of a long-term tillage experiment. Sorption was determined for the 0- to 10-, 10- to 20-, and 20- to 30-cm depths of these soils in a 24-h batch equilibration study. Sorption was well-described by the Freundlich model and related to soil organic C, being greater in surface NT than CT soil and generally decreasing with depth. Degradation was tracked in dosed (0.256 μmol/25 g; 14C-labeled) soil samples for 14, 28, 56, and 112 days, followed by methanol extraction and high-performance liquid chromatography analysis. Norflurazon degraded with formation of desmethyl-norflurazon, nonextractable 14C residue, and loss of 14CO2. Degradation rate was adequately described by first-order models and decreased with depth but was not affected by tillage. Rate constants ranged from 0.012 to 0.005 day−1. Mobility in intact cores (~30 cm long) of CT and NT soil showed less mass eluted from and greater retention in NT cores, consistent with greater sorption. Transport showed preferential flow (Br tracer) that was described by a mobile/immobile water model. Norflurazon mobility could be reasonably well described using the batch sorption and degradation data.

Surface versus incorporated residue effects on water-stable aggregates

Reduced tillage methods for field crop production result in less disruption of soil structure and often increased amounts of crop residue maintained on the soil surface. The combination of these two factors produces increased surface soil aggregation. This study was conducted in the field and within pots to determine whether surface residue by itself improves soil aggregation within a short period of time. The soil was a silt loam loess deposit in the Pacific Northwest, USA, where summers are hot and dry, and most precipitation (420 mm) is received during the mild winters. Two pot studies were conducted over winter, one under a shelter with controlled irrigations (183 mm), and the other outdoors receiving natural precipitation (77 mm). In both pot studies 640 g m −2 wheat ( Triticum aestivum L.) residue was either placed on the surface of the soil or thoroughly mixed into the soil. The field study was conducted on plots where, for the past 7 years, wheat crop residues were either incorporated through chisel/disk tillage or removed before tillage and replaced on the surface after tillage. The field study included plots where wheat was grown with no tillage. In the pots, there was no significant effect due to residue treatment on aggregate mean weight diameter, measured monthly for 4 winter months. This was true despite dissolved organic carbon being leached from the surface residue. In the 7-year-old field plots, replacing residues on the surface resulted in slightly greater mean weight diameter of aggregates at 5–10 cm depth compared to the mixed residue treatment. The no-till plots had significantly greater mean weight diameter at 0–5 cm depth than either tilled treatment. Our conclusion is that surface residue by itself failed to increase aggregation of tilled surface soil within the first rainy season after tillage.

Dynamics of soil hydraulic properties during fallow as affected by tillage

There is limited information on the effects of tillage practices on soil hydraulic properties, especially changes with time. The objective of this study was to evaluate on a long-term field experiment the influence of conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) on the dynamics of soil hydraulic properties over 3 consecutive 16–18 month fallow periods. Surface measurements of soil dry bulk density ( ρ b), soil hydraulic conductivity ( K( ψ)) at −14, −4, −1 and 0 cm pressure heads using a tension disc infiltrometer, and derived hydraulic parameters (pore size, number of pores per unit of area and water-transmission porosity) calculated using the Poiseuille's Law were taken on four different dates over the fallow period, namely, before and immediately after primary tillage, after post-tillage rains and at the end of fallow. Under consolidated structured soil conditions, NT plots presented the most compacted topsoil layer when compared with CT and RT. Soil hydraulic conductivity under NT was, for the entire range of pressure head applied, significantly lower ( P < 0.05) than that measured for CT and RT. However, NT showed the largest mean macropore size (0.99, 0.95 and 2.08 mm for CT, RT and NT, respectively; P < 0.05) but the significantly lowest number of water-conducting pores per unit area (74.1, 118.5 and 1.4 macropores per m 2 for CT, RT and NT, respectively; P < 0.05). Overall, water flow was mainly regulated by macropores even though they represented a small fraction of total soil porosity. No significant differences in hydraulic properties were found between CT and RT. In the short term, tillage operations significantly increased K ( P < 0.05) for the entire range of pressure head applied, which was likely a result of an increase in water-conducting mesopores despite a decrease in estimated mesopore diameter. Soil reconsolidation following post-tillage rains reduced K at a rate that increased with the intensity of the rainfall events.

Farm Management Effects on Rhizosphere Colonization by Native Populations of 2,4-Diacetylphloroglucinol-Producing Pseudomonas spp. and Their Contributions to Crop Health

ABSTRACT Analyses of multiple field experiments indicated that the incidence and relative abundance of root-colonizing phlD+ Pseudomonas spp. were influenced by crop rotation, tillage, organic amendments, and chemical seed treatments in subtle but reproducible ways. In no-till corn plots, 2-year rotations with soybean resulted in plants with approximately twofold fewer phlD+ pseudomonads per gram of root, but 3-year rotations with oat and hay led to population increases of the same magnitude. Interestingly, tillage inverted these observed effects of cropping sequence in two consecutive growing seasons, indicating a complex but reproducible interaction between rotation and tillage on the rhizosphere abundance of 2,4-diacetlyphloroglucinol (DAPG) producers. Amending conventionally managed sweet corn plots with dairy manure compost improved plant health and also increased the incidence of root colonization when compared with nonamended plots. Soil pH was negatively correlated to rhizosphere abundance of phlD+ pseudomonads in no-till and nonamended soils, with the exception of the continuous corn treatments. Chemical seed treatments intended to control fungal pathogens and insect pests on corn also led to more abundant populations of phlD in different tilled soils. However, increased root disease severity generally was associated with elevated levels of root colonization by phlD+ pseudomonads in no-till plots. Interestingly, within a cropping sequence treatment, correlations between the relative abundance of phlD and crop stand or yield were generally positive on corn, and the strength of those correlations was greater in plots experiencing more root disease pressure. In contrast, such correlations were generally negative in soybean, a difference that may be partially explained by difference in application of N fertilizers and soil pH. Our findings indicate that farming practices can alter the relative abundance and incidence of phlD+ pseudomonads in the rhizosphere and that practices that reduce root disease severity (i.e., rotation, tillage, and chemical seed treatment) are not universally linked to increased root colonization by DAPG-producers.

Effects of zone-tillage in rotation with no-tillage on soil properties and crop yields in a semi-arid soil from central Spain

A limiting factor to the no-tillage system in arid and semi-arid regions is the possibility of soil densification from lack of tillage. This research examines the extent and duration of the effects of periodic (rotational) zone-tillage over 2 years, on selected soil physical and chemical properties and crop yields. In the first year four tillage treatments were applied: conventional tillage with mouldboard plow (CT), minimum tillage with chisel plow (MT), no-tillage (NT) and zone-tillage subsoiling with a paraplow (ZT). In the second year, the ZT plots were returned to NT to follow the residual effects of ZT. The soil was a loamy sand (Calcic Haploxeralf) from semi-arid Central Spain and the crop rotation was grey pea ( Pisum sativum L.)–barley ( Hordeum vulgare L.). Crop residues on the soil surface after sowing grey pea were 85% in NT plots, 55% in ZT plots and 15% in MT plots. When comparing NT and ZT, the immediate effects of subsoiling on soil physical properties were significant ( P < 0.05). Soil strength as measured by cone index approached 3.0 MPa in NT and was reduced to <1.0 MPa by ZT over 300 mm sampling depth. Soil moisture content and bulk density were improved by ZT. No-till and ZT favoured surface accumulation of soil organic carbon (SOC), total N and available P and K. Stratification ratio of SOC was not different among tillage systems, but soil N stratification ratio followed the order NT > ZT > MT > CT. Grey pea yields were reduced by 3 Mg ha −1 in the NT and MT compared with ZT. Crop residues on the soil surface after barley sowing were 80% in NT, 56% in ZT, and 12% in MT. At the end of the second year, soil strength, soil moisture and bulk density in ZT declined to NT levels at all soil depths. The positive effect of ZT in increasing SOC in the top layer had also disappeared. However, total N, and available P and K concentrations under NT and ZT were still significantly higher than in MT and CT. Stratification ratios of SOC under NT and ZT were >2 and more than two-fold those under MT and CT. Nitrogen stratification ratio under ZT increased and no significant differences between NT and ZT could be reported. Barley yield was 0.6 Mg ha −1 higher in ZT compared with NT. Our results suggest that ZT improved the physical and chemical condition of the soil studied in months following subsoiling. These positive effects, however, diminished with time and only some residual effects on total N and available P and K content in the top-layer were still evident after 2 years.

Tillage and cover effects on soil microbial properties and fluometuron degradation

This research concerns the influence of no tillage (NT) or conventional tillage (CT) and a ryegrass (Lolium multiforum Lam.) cover crop in a cotton (Gossypium hirsutum L.) production system on soil and ryegrass microbial counts, enzyme activities, and fluometuron degradation. Fluorescein diacetate hydrolysis, aryl acylamidase, and colony-forming units (CFUs) of total bacteria and fungi, gram-negative bacteria, and fluorescent pseudomonads were determined in soil and ryegrass samples used in the degradation study. Fluometuron (14C-labelled herbicide) degradation was evaluated in the laboratory using soil and ryegrass. The CT and NT plots with a ryegrass cover crop maintained greater microbial populations in the upper 2 cm compared to their respective no-cover soils, and CT soils with ryegrass maintained greater bacterial and fungal CFUs in the 2–10 cm depth compared to the other soils The highest enzymatic activity was found in the 0–2 cm depth of soils with ryegrass compared to their respective soils without ryegrass. Ryegrass residues under NT maintained several hundred-fold greater CFUs than the respective underlying surface soils. Fluometuron degradation in soil and ryegrass residues proceeded through sequential demethylation and incorporation of residues into nonextractable components. The most rapid degradation was observed in surface (0 to 2 cm) soil from CT and NT–ryegrass plots. However, degradation occurred more rapidly in CT compared to NT soils in the 2 to 10 cm depth. Ryegrass cover crop systems, under NT or incorporated under CT, stimulated microbiological soil properties and promoted herbicide degradation in surface soils.

Italian Ryegrass (Lolium Multiflorum) Management Options in Winter Wheat in Oklahoma

An experiment was conducted at three sites in central Oklahoma to compare the efficacy of Italian ryegrass management options in no-till (NT) and conventional tillage (CT) winter wheat. The Italian ryegrass management options included selected herbicide treatments, wheat-for-hay, and a rotation consisting of double-crop soybean seeded immediately after wheat harvest, followed by early season soybean, and then by wheat. In continuous wheat, before application of glyphosate or tillage, Italian ryegrass plant densities in mid-September were 12,300 to 15,000 plants/m2in NT plots vs. 0 to 500 plants/m2in CT plots. When applied POST, diclofop controlled more Italian ryegrass than tralkoxydim or sulfosulfuron. In continuous wheat, yields were greater in CT plots than in NT plots at two of three sites. None of the Italian ryegrass management options consistently reduced Italian ryegrass density in the following wheat crop. Of the Italian ryegrass control strategies applied to continuous wheat, three herbicide treatments in NT at Chickasha and all treatments in NT at Perry reduced Italian ryegrass density in the following wheat crop. Italian ryegrass plant density in November and spike density were highly related to wheat yield at two and three sites, respectively. No management options were more profitable than rotation to soybean.

Short-term changes in soil properties under tillage systems and their effect on sweet potato (Ipomea batatas L.) growth and yield in an Ultisol in south-eastern Nigeria

Tillage influences soil quality via its effects on soil physical, chemical, and biological properties, which in turn affect crop productivity. This study evaluates the effects of conventional (CT) and no-till (NT) systems on (1) soil temperature, bulk density, soil gravimetric water content (GWC), saturated hydraulic conductivity (Ksat), soil organic carbon content (SOC), and total nitrogen (N), and (2) growth and yield of 3 sweet potato (Ipomoea batatas) (L) Lam varieties (87/00/87, ex-Igbariam, and 8164). A field experiment was conducted in 2005 and 2006 on a Typic paleudult in south-eastern Nigeria. The experimental plots comprised 6 treatments (CT 87/00/87 variety, CT ex-Igbariam, CT 8164, NT 87/00/87 variety, NT ex-Igbariam, NT 8164 variety) laid out in the field using randomised complete block design replicated 3 times. Soil temperature was 1–2°C higher in CT plots during early stages of crop development. CT plots had significantly lower soil dry bulk density (1.30–1.35 Mg/m3) than NT plots. Soil GWC was higher, whereas Ksat was lower, in NT plots than CT plots at 35 and 65 days after planting (DAP) for both planting seasons. NT plots had a 0.22–0.26-fold increase in SOC and 16–27% higher N content compared with CT plots at 35 and 65 DAP. The 3 varieties of sweet potato used did not significantly influence soil properties at the different times after planting. Sweet potato yield obtained in CT 87/00/87 variety (21.7–24.9 Mg/ha) for both seasons was higher (P &lt; 0.05) than sweet potato tuber yield obtained from NT ex-Igbariam plots (which had the lowest yield) by about 88%. For each variety, CT plots has significantly higher yield than NT plots. This study showed that although NT practices conserved soil moisture, decreased soil temperature, reduced water infiltration, and increased SOC and soil total N content when compared to CT plots, the reduction in soil compaction at the early stages of crop development (0–65 DAP) in CT plots had a more positive impact on tuber yield and masked the positive effect of other soil productivity parameters for this crop.

Influence of long-term wheat residue management on organic matter in an Avalon soil

This study was initiated to determine the influence of different wheat residue management practices, that were sustained for about 20 years, on the organic matter content of an Avalon soil in a long-term trial near Bethlehem in the Eastern Free State. The treatments were two methods of straw disposal (burned and unburned) × three methods of tillage (ploughing, stubble mulch and no tillage) × two methods of weed control (mechanical and chemical). Soil samples were collected at various depth intervals and organic C and total N, as indices of organic matter, were determined on these samples. The effect of either straw burning or weeding method on organic matter was small compared to that of tillage practice. A slightly higher organic C and lower total N content were measured in the unburned than burned plots to a depth of 450 mm. The tillage practices affected organic C and total N significantly in a similar manner to 100 mm depth with no-tilled plots having the highest organic matter content, followed in decreasing order by the mulched and ploughed plots. The organic matter content of the chemically-weeded plots was significantly higher than that of the mechanically-weeded plots to 100 mm depth, as indicated by organic C and total N. Significant interactions between the treatments on either organic C or total N were virtually absent. However, no tillage combined with chemical weeding resulted in the highest organic matter content. The latter combination is therefore recommended to maintain and even increase the organic matter content of this Avalon soil when cropped annually with wheat.

SENSITIVITY OF ATRAZINE PARTITION COEFFICIENT ON PESTICIDE ROOT ZONE MODEL PREDICTION OF SOIL'S ATRAZINE RESIDUE DISTRIBUTION WITHIN THE CROP ROOT ZONE

Previous applications of the Pesticide Root Zone Model (PRZM) comparing predicted distributions of pesticides in the soil profile to the measured values suggest that PRZM prediction capability may be improved by selecting proper representation of the distribution coefficient values that directly influence atrazine-soil interactions. The objective of this study was to observe the variation in the predicted distribution of atrazine in the soil profile as the coefficient of distribution (Kd) was varied in one or more soil horizons using the PRZM-2 model. The goal was to identify if more attention should be devoted to understanding the atrazine-soil sorption issues better, or whether discrepancies in field data and model output are explained by the difficulties in assessing the preferential transport of atrazine. The PRZM-2 predicted atrazine distribution was compared with measured values for no-till (NT) and conventional-till (CT) corn plots. Results indicate that reducing Kd by 70% in NT plots reduced the predicted atrazine recovery in Horizon 1 (0-10 cm) by 31%, 34%, and 87% for simulations performed 2, 4, and 8 weeks after application (WAA). Reducing Kd in only the upper soil horizon improved predictions for the upper horizon but overpredicted atrazine concentrations in the second horizon. Reducing Kd throughout the profile reduced predicted atrazine concentrations in the upper horizon and increased predicted concentrations in lower horizons. Improvement in the correlation between predicted and measured atrazine concentrations was greatest for NT plots; however, discrepancies between predicted and measured data still exist and may be due to improper characterization of the atrazine degradation or dissipation parameters. These results suggest that although preferential flow appears to influence atrazine distribution, it may not be the only process influencing our ability to model atrazine fate and transport. Future research on atrazine degradation and dissipation under field conditions seems to be necessary to simulate atrazine fate and transport under preferential flow conditions.

Comparison of modeling approaches to quantify residue architecture effects on soil temperature and water

RZ-SHAW is a hybrid model, comprised of modules from the Simultaneous Heat and Water (SHAW) model integrated into the Root Zone Water Quality Model (RZWQM) that allows more detailed simulation of different residue types and architectures that affect heat and water transfer at the soil surface. RZ-SHAW allows different methods of surface energy flux evaluation to be used: (1) the SHAW module, where evapotranspiration (ET) and soil heat flux are computed in concert with a detailed surface energy balance; (2) the Shuttleworth–Wallace (S–W) module for ET in which soil surface temperature is assumed equal air temperature; and (3) the PENFLUX module, which uses a Penman transformation for a soil slab under incomplete residue cover. The objective of this study was to compare the predictive accuracy of the three RZ-SHAW modules to simulate effects of residue architecture on net radiation, soil temperature, and water dynamics near the soil surface. The model was tested in Akron, Colorado in a wheat residue-covered (both standing and flat) no-till (NT) plot, and a reduced till (RT) plot where wheat residue was incorporated into the soil. Temperature difference between the soil surface and ambient air frequently exceeded 17 °C under RT and NT conditions, invalidating the isothermal assumption employed in the S–W module. The S–W module overestimated net radiation ( R n) by an average of 69 Wm −2 and underestimated the 3-cm soil temperature ( T s3) by 2.7 °C for the RT plot, attributed to consequences of the isothermal assumption. Both SHAW and PENFLUX modules overestimated midday T s3 for RT conditions but underestimated T s3 for NT conditions. Better performances of the SHAW and PENFLUX surface energy evaluations are to be expected as both approaches are more detailed and consider a more discretized domain than the S–W module. PENFLUX simulated net radiation slightly better than the SHAW module for both plots, while T s3 was simulated the best by SHAW, with a mean bias error of +0.1 °C for NT and +2.7 °C for RT. Simulation results for soil water content in the surface 30 cm ( θ v30) were mixed. The NT conditions were simulated best by SHAW, with mean bias error for θ v30 within 0.006 m 3 m −3; RT conditions were simulated best by the PENFLUX module, which was within 0.010 m 3 m −3.

Eight years of annual no-till cropping in Washington's winter wheat-summer fallow region

The tillage-based winter wheat ( Triticum aestivum L.)-summer fallow (WW-SF) cropping system has dominated dryland farming in the Pacific Northwest USA for 125 years. We conducted a large-scale multidisciplinary 8-year study of annual (i.e., no summer fallow) no-till cropping systems as an alternative to WW-SF. Soft white and hard white classes of winter and spring wheat, spring barley ( Hordeum vulgare L.), yellow mustard ( Brassica hirta Moench), and safflower ( Carthamus tinctorius L.) were grown in various rotation combinations. Annual precipitation was less than the long-term average of 301 mm in 7 out of 8 years. Rhizoctonia bare patch disease caused by the fungus Rhizoctonia solani AG-8 appeared in year 3 and continued through year 8 in all no-till plots. All crops were susceptible to rhizoctonia, but bare patch area in wheat was reduced, and grain yield increased, when wheat was grown in rotation with barley every other year. Remnant downy brome ( Bromus tectorum L.) weed seeds remained dormant for 6 years and longer to heavily infest recrop winter wheat. There were few quantifiable changes in soil quality due to crop rotation, but soil organic carbon (SOC) increased in the surface 0–5 cm depth with no-till during the 8 years to approach that found in undisturbed native soil. Annual no-till crop rotations experienced lower average profitability and greater income variability compared to WW-SF. Yellow mustard and safflower were not economically viable. Continuous annual cropping using no-till provides excellent protection against wind erosion and shows potential to increase soil quality, but the practice involves high economic risk compared to WW-SF. This paper provides the first comprehensive multidisciplinary report of long-term alternative annual no-till cropping systems research in the low-precipitation region of the Pacific Northwest.

Long-term continuous cropping in the Pacific Northwest: Tillage and fertilizer effects on winter wheat, spring wheat, and spring barley production

Conventional tillage winter wheat ( Triticum aestivum) (WW)–summer fallow reduces soil productivity and increases soil erosion. Conservation tillage management, together with intensive cropping may have the potential to reverse these sustainability concerns. The objective of this study was to determine the effects of conventional tillage (CT) and no-tillage (NT) systems on grain yield of long-term annual cropping of monoculture WW, spring wheat (SW), and spring barley ( Hordeum vulgare) (SB) grown with or without fertilizer, in the Pacific Northwest region of the USA. In unfertilized crops, grain yield of WW, SW, and SB was 15%, 25%, and 50% higher, respectively, in CT than in NT plots, an indication of the involvement of yield limiting factors under the NT cropping system. When fertilized, there were no significant differences in grain yield of WW. Yields of SW and SB, however, remained 21% and 15% higher, respectively, in CT than in NT, an indication that factors other than fertility were involved. These results suggest that in order for NT management to be widely adopted by area growers, the yield-limiting factors need to be addressed.

Earthworm dynamics and soil physical properties in the first three years of no-till management

Earthworms are often referred to as ecosystem engineers due to their ability to alter the soil environment. Since earthworms influence a wide range of critical chemical and physical soil properties it is important to understand how their populations are impacted by soil management. Earthworms were sampled during the spring and summer of 2001, 2002, and 2003 from conventional tillage (CT) and no-till (NT) plots established in 2000. Although there was a strong trend for higher earthworm density in NT plots in 2001 ( p = 0.08) and 2002 ( p = 0.19), statistically significant differences were not detected between tillage treatments until 2003 ( p = 0.04) when mean earthworm density was 37.7 individuals m −2 in CT and 149.9 individuals m −2 in NT during spring and 17.1 individuals m −2 in CT and 58.4 individuals m −2 in NT in summer. A high mortality rate between spring and summer, combined with greater cocoon production under NT suggests that the earthworm population turns over rapidly in NT plots. Data also suggest that adverse soil environmental conditions will limit earthworm density in these dryland agroecosystems. Despite significantly higher earthworm density after three years of NT management, soil bulk density, saturated hydraulic conductivity, and aggregate stability of the 0.5- to 1-mm size fraction were not different between the two tillage treatments. The apparent lack of impact of reduced disturbance and increased earthworm density on soil physical properties may be due to the short time this soil has been under NT management, limited seasonal earthworm activity due to environmental conditions, or differences in the scale at which soil physical properties have been affected after three years of NT management and the scale at which our measurements were made.

Effects of tilling no-till soil on losses of atrazine and glyphosate to runoff water under variable intensity simulated rainfall

Herbicides released through agricultural activities to surface waters and drinking water systems represent a risk to human and environmental health, as well as a cost to municipalities for removal. This study focuses on the viability of glyphosate tolerant cropping systems as an alternative to atrazine-based systems, and the impact of tilling historically no-till ground on the runoff pollution potential of these systems. Variable intensity field rainfall simulations were performed on 2 m long × 1 m wide plots within a field in first-year disk and harrow following no-till (CT), and within a long-term no-tilled (NT) field, both treated with atrazine and glyphosate according to label. Rainfall sequence was: 50 mm h −1 for 50 min followed by 75 mm h −1 for 15 min, 25 mm h −1 for 15 min, and 100 mm h −1 for 15 min. Runoff was collected at regular time intervals during two simulated rainfall events and analyzed for herbicide concentration, sediment content, and volume. Maximum glyphosate concentration in runoff was 233 μg L −1 for NT and 180 μg L −1 for CT (approximately 33% and 26% of the maximum contaminant limit (MCL) for glyphosate (700 μg L −1), respectively, while maximum atrazine concentrations in runoff was 303 μg L −1 for NT and 79 μg L −1 for CT (approximately 100 times and 26 times the atrazine MCL (3 μg L −1)). Atrazine concentration and loading were significantly higher in runoff from NT plots than from CT plots, whereas glyphosate concentration and loading were impacted by tillage treatment to a much lesser degree. Results suggest that glyphosate-based weed management may represent a lower drinking water risk than atrazine-based weed management, especially in NT systems.

137Cs profiles in erosion plots with different soil cultivation

Cesium-137 methodology has been successfully used to assess soil erosion. Seven erosion plots were sampled to determine the 137Cs profile and to assess the erosion rates. Cesium-137 profile for native pasture plot showed an exponential decline below 5 cm depth, with little 137Cs activity in the superficial layer (0-5 cm). Cesium-137 profile for wheat-soybean rotation plot in conventional tillage showed a uniform distribution with depth. For this plot, the soil loss occurs more in middle than upper and lower level. Cesium-137 profile for wheat-soybean rotation and wheat-maize rotation plots in no-tillage showed a similar result to the native pasture, with a minimum soil loss in the superficial layer. Cesium-137 profile for bare soil and cultivated pasture plots are similar, with a soil erosion rate of 229 t ha-1 year -1 . In the plots with a conventional tillage a greater soil loss occur in middle than upper and lower level. In no-tillage cultivation plots occurs soil loss in lower level, but no sign of soil loss neither gain in the upper level is observed. Cesium-137 methodology is a good tool to assess soil erosion and the 137Cs profile gives possibility to understand the soil erosion behavior in erosion plots.