Surface Residue Cover Research Articles

Consistent plant residue removal causes decrease in minimum soil water content in a Mediterranean environment

Residue retention and no-till farming have been widely adopted to reduce erosion risk, but residue retention in particular is becoming less common due to issues with weed control, and competing markets for residue such as bioenergy production. For this reason, the impact of residue removal on soil water contents in a sandy soil in a Mediterranean-type environment was evaluated. Crop residues were removed by burning or conventional tillage annually in autumn (April or May) from 2008 until 2011. Surface residue cover and soil water contents were measured in summer (February-March) every year from 2008 until 2012, at the time of minimum soil water content (approaching air-dry). After three years of residue removal, average ground cover in the subsequent summers (2011 and 2012) decreased from 78% to 51%, and surface soil water contents decreased from 5.1% to 3.1%. Tillage also significantly decreased ground cover (from 72% to 58%) and soil water (from 4.2% to 3.9%) during the same time period. Changes in surface cover and soil water content indicate that residue removal will have implications for soil health and sustainable crop production.

Shallow mixing of surface soil and liquid dairy manure conserves nitrogen while retaining surface residue

Incorporation of spring-applied manure is known to reduce N volatilization losses and hence increase the N value of the manure. However, traditional incorporation methods are not compatible with reduced-tillage systems requiring minimum residue coverage of 30 %. Here, eight New York dairy farms participated in 2008 in a 2-year on-farm trial. This trial was designed to test the hypothesis that shallow mixing of soil involving aerator incorporation of spring-applied manure is as effective as chisel incorporation of manure in conserving manure N for corn (Zea mays, L) uptake while retaining more surface residue. The eight fields selected for this trial varied from first to third year corn after hay and had varying manure histories. All fields were subjected to a randomized complete block design with four replicates comparing surface application of manure, as control, shallow incorporation of manure with an aerator, and chisel incorporation of manure. Starter N applications were 39 kg N/ha or less, and manure application rates ranged from 51 to 112 kL/ha. Results show that shallow incorporation of manure significantly reduced soil disturbance and retained, on average, 30 % more surface residue cover than obtained with chisel incorporation. Chisel and aerator-based incorporation resulted in similar soil nitrate levels at 13 of 16 site years, suggesting similar levels of N conservation. Across all sites and years, incorporation increased silage yield by 0.9–1.5 Mg DM/ha, independent of incorporation method. Based on these results, we show that shallow mixing of soil and spring-applied manure is a suitable option for conserving N and maintaining greater surface residue coverage without compromising on yield or silage quality.

Integrating Mechanical and Reduced Chemical Weed Control in Conservation Tillage Corn

Conservation tillage for corn (Zea mays L.) production has greatly reduced the soil erosion potential in these systems, but relies heavily on herbicides to manage weeds. Overreliance on herbicides can lead to the development of herbicide‐resistant weed communities and increase the risk of ground and surface water contamination by residual herbicides. This study evaluates the integration of various mechanical soil/weed management implements and herbicide programs for surface residue cover, weed control, corn productivity, and economic net returns. A pre‐plant vertical coulter/rotary harrow tended to control small annual weeds as well as a standard burn down herbicide program, but reduced surface residue cover by 15% compared to the no‐till check treatments. The high residue rotary hoe had little effect on surface residue cover, but provided inconsistent early‐season weed control. The high residue inter‐row cultivator resulted in 23% residue cover compared to 50% in the no‐till treatments, but reduced weed biomass by 53% without any supplemental residual herbicides and 88% with a banded residual herbicide compared to the weedy check treatment. Crop productivity and net return data suggest that integrating the vertical coulter/rotary harrow, high residue cultivator, and banded residual herbicide program could reduce herbicide ai rates by 70% and still achieve similar corn yields and economic returns as the herbicide intensive systems. Such integrated mechanical‐chemical systems will increase the crop management complexity for farmers, which may hinder adoption. Soil erosion potential of the integrated systems requires further in‐depth evaluation.

On-farm effects of tillage and crops on soil erosion measured over 10 years in Switzerland

The positive effects of soil conserving farming methods have mostly been demonstrated using small test plots. The present study is aimed at confirming that they also occur on the catchment scale. The impact of crops and soil tillage practises on the extent of soil erosion was determined in 203 crop fields over 10 years in the Swiss Midlands. Soil erosion totalled 1969t or 0.75tha−1yr−1. Most erosion took place in winter wheat fields (33%), which accounted for 22% of the crop area. Second and third most erosion was observed in potato (26%) and fallow (14%) fields. By far the highest mean soil loss was found for potatoes, at 2.87tha−1yr−1. Fallow (1.06tha−1yr−1) and winter wheat (1.05tha−1yr−1) fields were also relatively susceptible to soil erosion. In contrast, values for soil loss below mean were observed for maize (0.44tha−1yr−1), sugar beet (0.27tha−1yr−1), and rape seed (0.39tha−1yr−1). 88% of soil erosion took place on plough tilled land (PT), 9% on non-ploughed land with less than 30% surface residue cover (RT), 1% on mulch-tilled land with more than 30% surface residue cover (MT), and 2% in non-tilled or strip-tilled land with >30% soil cover (NT). At 0.07 and 0.12tha−1yr−1, respectively, the mean soil loss in MT and NT fields was more than an order of magnitude lower than that under PT (1.24tha−1yr−1). Field mappings confirmed the positive effects of the soil conserving soil tillage practises. The risk of soil erosion was significantly influenced by crop rotation. The carry-over effects should be taken into account when studying the effects of cropping methods on soil erosion.

Evaluation of the impact of surface residue cover on single and dual crop coefficient for estimating soybean actual evapotranspiration

Abstract Single and dual crop coefficient methods are used in conjunction with grass reference evapotranspiration ( ET o ) to estimate actual crop evapotranspiration ( ET c ). However, the impact of soil surface residue cover on the accuracy of ET c estimated with these methods is not well understood. The objective of this study is to evaluate and compare the accuracy of the FAO-56 single crop coefficient (single- K c ) and dual crop coefficient (dual- K c ) methods for estimating soybean [ Glycine max (L.) Merr.] ET c in a partially residue covered field. The study was conducted at the University of Nebraska-Lincoln, South Central Agricultural Laboratory (SCAL), Nebraska, during the 2007 and 2008 growing seasons. The field was under reduced-tillage (ridge till) on a silt loam soil and irrigated using a subsurface drip irrigation system. Evapotranspiration flux ( ET m ) above the crop canopy was measured using a deluxe version of a Bowen ratio energy balance system (BREBS) and ET o was calculated with the Penman–Monteith method. The single- K c and dual- K c -estimated ET c values, both unadjusted for residue cover, were compared to ET m . The unadjusted FAO-56 K c values performed poorly as the single- K c underestimated ET m during the initial crop growth stage by 21% in 2007 and 33.6% in 2008 while the dual- K c overestimated ET m during the same growth stage by 16.8% in 2007 and 16.5% in 2008. Extended simulations were conducted to determine the magnitude by which ET c is reduced for each 10% of soil surface covered with crop residue. Downward adjustments in soil water evaporation ( E s ) for every 10% of the soil surface covered with crop residue improved the accuracy of ET c estimated by the dual- K c method. The largest changes in ET c due to adjustments in E s occur during the initial stage of the growing season. The best estimates for seasonal ET c were obtained by reducing E s by 5% for every 10% of surface covered with residue in 2007 ( R 2 = 0.77, RMSD = 0.87 mm d −1 , E = 0.94) and 2008 ( R 2 = 0.83, RMSD = 0.84 mm d −1 , E = 0.95). Greater improvements in the accuracy of estimated seasonal ET c were obtained by reducing E s by 2.5% for each 10% of surface covered with residue during the initial stage and by 5% during the rest of the crop growth stage. These results suggest that the more computationally-involved dual- K c method with adjustments in E s for each 10% of surface covered with residue improves the prediction of ET c in fields with soil surface residue cover, especially during the initial growth stage. Inaccurate selection of percentage reduction in E s can result in substantial overestimation or underestimation of seasonal ET c by the dual- K c method.

Review Article: Remote Sensing, Surface Residue Cover and Tillage Practice

A growing world population and possible liquid fuel energy shortages are likely to result in worldwide agricultural intensification, and the possible expansion of non-sustainable practices. The adoption of non-sustainable practices could result in the loss of currently productive land, with potential impacts on human welfare and economic viability. One of the easiest techniques to maintain productivity is to maintain surface soil organic matter. However, developing reliable, cost effective and accurate methods for quantifying and monitoring crop residue cover (a major source of soil organic matter) that remains on top of the soil over large spatial extents constitutes a significant challenge. This article reviews potential remote sensing approaches for estimating surface residue cover with a view to mapping tillage practice.

Manure Composition and Incorporation Effects on Phosphorus in Runoff Following Corn Biomass Removal

Greater demand for corn ( L.) stover for bioenergy use may lead to increased corn production acreage with minimal surface residue cover, resulting in greater risk for soil erosion and phosphorus (P) losses in runoff. A rainfall simulation study was conducted to determine the effects of spring-applied dairy cow () manure (none, in-barn composted, and exterior walled-enclosure pit) with >200 g kg organic solids content following fall corn biomass removal with and without incorporation (chisel plow [CP] and no-till [NT]) on sediment and P in runoff. Runoff was collected from a 0.83-m area for 60 min following the onset of rainfall simulation (76 mm h), once in spring and once in fall. Runoff dissolved reactive P (DRP) and dissolved organic P (DOP) concentrations were positively correlated with manure P rate and were higher in NT compared with CP. Conversely, sediment and particulate P (PP) concentrations in runoff were inversely correlated with manure P rate (and manure solids) and were higher in CP compared with NT. Runoff volume where no manure was applied was higher in NT than in CP in spring but similar in fall. The addition of manure reduced runoff volumes by an average of 82% in NT and 42% in CP over spring and fall. Results from this study indicate that surface application of dairy manure with relatively high solids content may reduce sediment and PP losses in runoff without increasing the risk of increased DRP and DOP losses in the year of application where corn biomass is harvested.

Infiltration, Runoff, and Export of Dissolved Organic Carbon from Furrow-Irrigated Forage Fields under Cover Crop and No-Till Management in the Arid Climate of California

Development of best management practices (BMPs) such as conservation tillage and winter cover crop to mitigate runoff and reduce dissolved chemicals in irrigation runoff is an important objective for controlling surface water pollution attributable to agricultural activities. In this study, the effect of standard tillage (ST), STwith winter cover cropping (STCC), and no-till (NT) management practices on infiltration, runoff, and dissolved organic carbon (DOC) export from furrow-irrigated fields of 244-m length was investigated for summer 2007 and 2008 irrigations. The practices were implemented for 2 years. The average surface residue cover was 11, 44, and 32% for ST, STCC, and NT, respectively, for 2007 and 11, 59, and 61%, respectively, in the following year of the study. Two irrigations in each year were considered for the analysis. The runoff samples were collected from each tillage treatment using ISCO autosamplers at regular time intervals. The infiltration and runoff were estimated using a volume balance model (VBM) by considering a 0.2-m irrigation requirement. Converting from ST to STCC increased the infiltration by 14 and 43% and reduced the runoff by 48 and 43% in 2007 and 2008 irrigations, respectively; whereas, converting ST to NT enhanced the infiltration by 4% in both years and decreased the runoff by 19 and 23% in 2007 and 2008 irrigations, respectively. The authors observed only slightly higher DOC concentrations in STCC, but there was a 24% increase for NT in 2007 irrigations, and both compared to with ST ranged from 3.98 to 5:46 mg=L. The DOC concentration was not significantly different among the treatments in 2008 irrigations (3.48 to 4: 6m g=L). Combining the runoff and DOC concentration effects, the DOC export for STCC was decreased by 55% in both years; whereas, it was decreased by 4 and 27% for NT in 2007 and 2008 irrigations, respectively, compared with ST. Although STCC and NT have higher concentrations, the reduction in export in these treatments is attributable to lower runoff. These results suggest that DOC export can be controlled with STCC practice. No-till showed the same trend, although these results must be confirmed after extended implementation of this practice. DOI: 10.1061/(ASCE)IR.1943-4774.0000385. © 2012 American Society of Civil Engineers.

Corn Yield Response to Deficit Irrigation

Because dwindling water supplies are limiting crop production, a field study was conducted during 2005-2009 in southwest Kansas to determine the yield response of corn to irrigation and evapotranspiration (ETc), and to document plant growth parameters and soil water use. Corn was grown in a five-year rotation of corn-corn-wheat-grain sorghum-sunflower. Results from the corn after sunflower and corn after corn are presented here. Six irrigation treatments were produced by applying 25 mm of irrigation every 5 to 17 days. Year-to-year grain yields averaged over irrigation and crop sequence appeared to be correlated with leaf area index, which possibly reflected the severity of hail events that occurred in four of the five years of the study. However, dry matter accumulation per plant did not vary across irrigation treatments. Surface residue coverage from the previous year's crop was 38% for sunflower and 61% for corn. ETc and productivity, also known as water use efficiency (WUE), decreased significantly as irrigation decreased. The deficit irrigation treatments used more of the previous non-growing season precipitation than the fully irrigated treatment due to greater soil water storage capacity in the drier soil profile. Furthermore, these treatments extracted more soil water during the growing season as irrigation decreased. Linear models of ETc predicted grain and dry matter yields with R2 values of 0.67 and 0.59, respectively. The relationship of relative grain yield and ETc was also linear and more pronounced, with an R2 value of 0.82. In contrast, the relationship of relative yield and irrigation followed a curvilinear model. During the five-year study, variability in yields increased as irrigation decreased, illustrating a greater income risk with less irrigation. Yield response to irrigation, especially over multiple years, is essential information to build economic studies of cropping alternatives, deficit irrigation management, and income risk. These relationships need to be developed regionally to characterize the effects of environmental factors, especially precipitation.

Comparison of Fallow Tillage Methods in the Intermediate Rainfall Inland Pacific Northwest

Winter wheat (Triticum aestivum L.) is usually grown in the Pacific Northwest (PNW) intermediate rainfall zone following tilled or chemical summer fallow. Studies were conducted near Davenport, WA and Helix, OR over two fallow–winter wheat cycles to evaluate the efficacy of reduced or no‐tillage fallow compared to conventional fallow and compare the efficacy of herbicides applied using a light‐activated sensor‐controlled (LASC) applicator to broadcast applications. Six treatments included conventional primary tillage followed by rodweeding; sweep‐tillage followed by rodweeding, broadcast, or LASC herbicide application; and no‐tillage followed by broadcast or LASC herbicide application. Broadcast and LASC herbicide applications controlled weeds similarly in no‐tillage treatments. However, LASC applications used from 45 to 70% less herbicide than broadcast applications to attain similar weed control. No‐tillage or sweep‐tillage systems with herbicide application had from 15 to 30% greater surface residue cover than the conventional tillage system. Available soil moisture in both the root‐zone and seed‐zone soil profiles at time of planting was similar among tillage systems. There were no differences in wheat quality parameters across treatments. The conventional tillage system had similar wheat grain yield as sweep‐tillage systems followed by rodweed or broadcast herbicide application, but yields were up to 21% greater than sweep‐tillage with LASC applied herbicides and no‐tillage systems. Reduced tillage systems using sweep‐tillage and broadcast herbicide application could potentially replace more tillage intensive fallow systems in the PNW.

Dependence of effective hydraulic conductivity on rainfall intensity: loamy agricultural soils

AbstractEffective hydraulic conductivity (Ke) can be estimated with statistical models derived from datasets of field measured conductivities. Pedotransfer functions (PTFs) estimate constant Ke values, but suffer from large prediction errors because the functions usually do not account for soil structural heterogeneities. Rainfall‐runoff data have shown that the effective hydraulic conductivity, defined as final infiltration rate at steady state given ponding, is dependent on rainfall intensity. In this study a statistical approach to establish functions for rainfall intensity‐dependent Ke values is presented, including some specific functions for Western European loamy agricultural soils. Steady‐state rainfall experiments have been conducted with a drip‐type rainfall simulator at multiple intensities on small plots, installed on fields covered by four typical crops of the central part of the Belgian loess belt. A mixed linear model has been applied to temperature standardized and ln‐transformed values of apparent steady‐state infiltration rate and rainfall intensity data for the determination of significant explanatory variables and their parameters. Crop type was a necessary classification effect that accounts for much of the variation that could not be explained by continuous variables of soil and surface properties. However, soil surface bulk density, silt and sand content, tortuosity in surface microtopography, plant and residue cover (RC) were predictors that improved predictions combined with crop effect. Model efficiency (ME) values were between 0·81 and 0·97 for calibration and between 0·75 and 0·95 for validation. The application of the functions is limited to sloping, loamy agricultural soils in a Western European climate, during the spring and early summer growing phase, with not fully developed canopy cover and an RC of less than 20%. These limitations bound field conditions that are vulnerable to severe erosion events. A dynamic Ke could be applied in infiltration models, changing runoff and erosion response in hillslope models. Copyright © 2010 John Wiley & Sons, Ltd.

Single‐ and Twin‐Row Peanut Production within Narrow and Wide Strip Tillage Systems

Increased production costs and potential benefits of maintaining surface residue has renewed interest in conservation tillage systems for peanut (Arachis hypogaea L.) production. We determined surface residue cover from rye (Secale cereale L.) or oat (Avena sativa L.) cover crops after two strip tillage systems (narrow vs. wide) and planting operations with different row configurations (single vs. twin). We also compared plant populations, yields, and total sound mature kernels for three peanut cultivars (‘ANorden’, ‘AP‐3’, and ‘Georgia‐02C’) across each treatment combination. Seven site‐years were examined across similar soil types in Alabama and northern Florida during the 2004 to 2006 growing seasons. The highest surface residue counts were for the narrow tillage system planted in single rows. Final plant stands were influenced by an interaction between cultivar and row configuration, with ‘ANorden’ planted in single rows below recommended rates. Peanut yields were affected by strip tillage system and row configuration, but differences among cultivars were also observed. Twin‐row peanut yields were 5% greater than single‐row peanut yields in the narrow strip tillage system but were similar across strip tillage systems. Cultivars ‘AP‐3’ and ‘Georgia‐02C’ yielded 20% higher than ‘ANorden’. Total sound mature kernels were only affected by peanut cultivar, with the cultivar ‘Georgia‐02C’ producing the highest‐quality peanut, followed by ‘ANorden’ and ‘AP‐3’. These results indicate that growers interested in using twin rows for peanut production can also take advantage of a narrow strip tillage system that maximizes surface residue coverage and subsequent benefits.

Conservation tillage to effectively reduce interrill erodibility of highly-weathered Ultisols

Highly weathered Southeastern soils traditionally cropped under conventional tillage systems are drought-prone and susceptible to runoff and soil loss. We quantified differences in infiltration, runoff, soil loss, and interrill erodibilities (Ki) for three soils: Compass loamy sand, Decatur silt loam, and Tifton loamy sand managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems with and without a residue cover (rye [Secale cerale L.]) (+C/-C) and with and without paratilling (+P/-P). Duplicate plots (1 m2 [~10 ft2]) on each tillage treatment received simulated rainfall (50 mm h-1 [2 in hr-1] for two hours). Runoff and sediment yields were continuously measured, and Ki values were calculated from measured data. The Water Erosion Prediction Project (WEPP) model was used to extend experimental data to long-term annual trends. For the Compass soil, NT-C plots increased runoff by as much as 43% and sediment yields by as much as 10-fold compared to NT+C plots. The NT+P+C plots decreased runoff by as much as 70% and sediment yields by 24-fold compared to CT-P-C. For the Decatur soil, NT+P plots decreased runoff by as much as 71% and sediment yields by as much as 2.7-fold compared to NT-P plots. The NT+P+C plots decreased runoff by as much as 73% and sediment yields by as much as 11.8-fold compared to CT-P-C. For the Tifton soil, ST+P+C plots decreased runoff by as much as 44% and sediment yields by as much as 2.7-fold compared to CT-P-C plots. Calculated Ki values for the Compass, Decatur, and Tifton soils were 0.37, 0.40, and 0.24, respectively. Residue cover decreased effective interrill erodibilities (Kieff) values by 11%, 2-fold, and 2.6-fold for the Decatur, Tifton, and Compass soils, respectively; Paratilling decreased Kieff values by 3-fold for the Compass and Decatur soils. The NT and/or ST systems had lower Kieff values than Ki values from corresponding CT-P-C treatments (Compass = 4- to 37-fold; Decatur = 4- to 13-fold; Tifton = 2-fold). Converting from a CT to a NT or ST system reduced predicted runoff (Compass = 1.7-fold; Decatur = 10% to 17%; Tifton = 1.6- to 2.3-fold) and sediment yields (Compass = 10- to 12-fold; Decatur = 6- to 33-fold; Tifton = 7.3- to 12.1-fold). The most benefit of NT or ST, as quantified by the maximum difference in 100-year predicted runoff and sediment yields, was for the Compass (78%) and Tifton (75%) soils for runoff and for the Compass (10.3-fold) and Decatur soils (9.7-fold) for sediment. Conservation tillage systems (NT, ST) coupled with surface residue cover and/or paratilling are effective in reducing runoff and sediment yields from highly-weathered soils by lowering effective Ki values.

Continuous Corn Response to Residue Management and Nitrogen Fertilization

Harvesting corn (Zea mays L.) residue in continuous corn (CC) may require changes in crop management for increased efficiency. Experiments were conducted in Illinois to determine how residue removal and tillage affect surface residue after planting and the response of CC to N fertilization. Partial removal of residue left 21 to 26% surface residue coverage with a chisel plow system, compared with 53 to 65% with no‐till. Across 2 yr with 92 to 128 mm rainfall during June and July, grain yield only responded to N fertilization with no‐till. When compared with full removal of residue in no‐till, no removal increased the economically optimum N fertilizer rate (EONR) by 58% and yield at the EONR from 8.6 to 10.3 Mg ha−1. Across five environments with 201 to 264 mm rainfall during June and July, yields with full removal of residue were 13.1 Mg ha−1 with no‐till and 13.4 Mg ha−1 with tillage. With partial and no residue removal, yields were 5 and 12% greater with the chisel plow than with the no‐tillage system, respectively. Across tillage systems in these environments, retaining all residue increased the EONR by 13% and decreased yield at the EONR by 4% when compared to full or partial removal of residue. On productive soils with adequate rainfall, removal of residue has the potential to raise yields and to lower N fertilizer requirements in the short term. This advantage, however, needs to be balanced against the need to retain adequate soil cover to maintain soil productivity.

Residue impacts on runoff and soil erosion for different corn plant populations

The year to year carry-over effects of biomass additions under different plant populations on runoff and erosion are unclear. The objective of this study was to quantify the impact of different plant populations on residue cover to elucidate the effects of residue cover on runoff and erosion. The residue management system involved shredding of corn (maize) biomass after harvest, incorporating the residue in the spring, and leaving the land fallow until it was no-till planted the following spring. Runoff and soil losses were measured on 18 runoff plots with plots arranged in two areas with each having three randomized treatments (0%, 50%, and 100% plant population) with three replications. The two areas were managed as a fallow/no-till corn rotation in two cycles of alternating years. Surface residue cover was highly dynamic with significant changes between cycles and seasons in response to the management practices. The annual soil losses were reduced by 47% and 54% for the 50% and 100% plant populations, respectively compared to the control. However, the annual soil loss even for the 100% plant population was still nearly seven times the tolerable soil loss limit of 7 ton ha −1. The normal erosion protection afforded by no-till practices was lost by the incorporation of residue the previous year.

A heuristic model to predict earthworm biomass in agroecosystems based on selected management and soil properties

Earthworm burrows can be significant preferential flow paths for water and contaminants to move to subsurface drainage networks and groundwater. Thus earthworm biomass could serve as an indicator of such transport potential, and therefore, inform risk assessments associated with water contamination resulting from land application of fertilizer amendments. In this study, we evaluated relationships and interactions between earthworm biomass, soil properties (bulk density, particle size, organic matter, surface residue), land management (crop type, tillage approach), and soil hydraulic properties (field saturated hydraulic conductivity and air-entry tension) for the purpose of building regionally based models to predict earthworm biomass. Data were collected from 43 fields distributed throughout eastern Ontario, Canada. Earthworm biomass was measured using “hot mustard” methods (early autumn) and in situ soil hydraulic properties were determined using pressure infiltrometers (late summer/early fall). Classification and Regression Tree (CART) data mining techniques were used to develop tree-structured models to predict biomass from site environmental data. CART regression tree models had coefficients of determination between 0.50 (not including soil hydraulic properties) and 0.55 (including soil hydraulic properties). Both regression trees split all earthworm biomass data ( N = 243) into two groupings defined on the basis of tillage treatment. No-tilled field biomass averaged 192.1 g m −2 (S.D. = 71.5 g m −2), and biomass data for conventionally tilled sites subdivided into terminal groupings on the basis of “higher surface residue cover” (biomass average = 107.9 g m −2 (S.D. = 81.1 g m −2) and ‘lower surface residue cover’ (62.4 g m −2 (S.D. = 54.6 g m −2)) classes. Soil physical and hydraulic data were not important predictors of biomass for tilled datasets; whereas they were more important for no-tilled datasets. For both regression trees, no-till biomass stratified into terminal biomass groupings defined on the basis of bulk density, clay content, and silt content; and for the model including soil hydraulic properties, additionally by soil air-entry tension and surface residue cover. However, bulk density was deemed in the model to be a proxy for years a field was in no-tillage; a positive relationship existed between bulk density and biomass. Overall, the terminal tree groups with the highest average earthworm biomasses were for no-till soils with bulk densities >1.4 g cm −3 (longer term no-tillage). Regression tree variance reductions associated with the in situ measurements of field saturated hydraulic conductivity and air-entry tension were insignificant or small. Generally, empirical models predicting earthworm biomass at large spatial scales in agroecosystems using soils and land management information, should consider utilizing variables that express tillage practice, surface residue coverage, years in no-tillage, and soil particle size; however, variable interactions should be considered.

Crop Residue Coverage of Soil Influenced by Crop Sequence in a No‐Till System

Field research was conducted to determine the influence of crop and crop sequencing on crop residue coverage of soil with 10 crops [buckwheat (Fagopyrum esculentum Moench), canola (Brassica napus L.), chickpea (Cicer arietinum L.), corn (Zea mays L.), dry pea (Pisum sativum L.), grain sorghum [Sorghum bicolor (L.) Moench], lentil (Lens culinaris Medik.), oil seed sunflower (Helianthus annuus L.), proso millet (Panicum miliaceum L.), and hard red spring wheat (Triticum aestivum L.)]. Crop residue production was obtained. Crop residue coverage of the soil surface was measured with a transect technique at the time of seeding spring wheat. Crop residue coverage varied and was more clearly associated with the second‐year crop than with the first‐year crop of a 2‐yr crop sequence. Crop sequences composed of spring wheat, proso millet, and grain sorghum had higher crop residue coverage compared with sequences composed of the other crops. When these three crops and three crops that provide lower crop residue coverage of soil the subsequent year (lentil, chickpea, and sunflower) were analyzed as a subset to compare various sequences of crops providing a range of residue coverage, for example, lower (first yr)/lower (second yr), the surface residue coverage ranged from 65% for the lower/lower combination to 93% for the higher/higher combination in 2004 and from 56 to 94% in 2005, respectively. A producer operating on more fragile soil and concerned about reducing soil erosion hazards would be advised to grow crops that provide higher residue coverage in the year before crops that provide lower residue coverage.

Soil erosion estimation in conservation tillage systems with poultry litter application using RUSLE 2.0 model

Soil erosion is a major threat to global economic and environmental sustainability. This study evaluated long-term effects of conservation tillage with poultry litter application on soil erosion estimates in cotton ( Gossypium hirsutum L.) plots using RUSLE 2.0 computer model. Treatments consisting of no-till, mulch-till, and conventional tillage systems, winter rye ( Secale cereale L.) cover cropping and poultry litter, and ammonium nitrate sources of nitrogen were established at the Alabama Agricultural Experiment Station, Belle Mina, AL (34°41′N, 86°52′W), beginning fall 1996. Soil erosion estimates in cotton plots under conventional tillage system with winter rye cover cropping declined by 36% from 8.0 Mg ha −1 year −1 in 1997 to 5.1 Mg ha −1 year −1 in 2004. This result was largely attributed to cumulative effect of surface residue cover which increased by 17%, from 20% in 1997 to 37% in 2004. In conventional tillage without winter rye cover cropping, soil erosion estimates were 11.0 Mg ha −1 year −1 in 1997 and increased to 12.0 Mg ha −1 year −1 in 2004. In no-till system, soil erosion estimates generally remained stable over the study period, averaging 0.5 and 1.3 Mg ha −1 year −1with and without winter rye cover cropping, respectively. This study shows that cover cropping is critical to reduce soil erosion and to increase the sustainability of cotton production in the southeast U.S. Application of N in the form of ammonium nitrate or poultry litter significantly increased cotton canopy cover and surface root biomass, which are desirable attributes for soil erosion reduction in cotton plots.

Parâmetros relacionados com a erosão hídrica sob taxa constante da enxurrada, em diferentes métodos de preparo do solo

O preparo do solo altera as suas condições físicas de superfície e subsuperfície e, conseqüentemente, influencia os valores dos fatores que se relacionam com a erosão hídrica. Considerando estes aspectos, realizou-se um experimento de erosão em campo, sob a ação de chuva simulada, entre outubro de 1999 e maio de 2000, na região do Planalto Sul Catarinense, tendo por objetivo a avaliação de alguns fatores relacionados com a erosão hídrica do solo na condição de equilíbrio do escoamento superficial, em três métodos de preparo do solo. No estudo, utilizou-se Nitossolo Háplico alumínico de textura argilosa, apresentando, no local do experimento, 0,14 m m-1 de declividade. Os tratamentos avaliados foram: (a) preparo reduzido (escarificação + gradagem); (b) preparo convencional tradicional (aração + duas gradagens), e (c) preparo convencional alterado (aração + duas gradagens + duas rastelagens), os dois primeiros em solo continuamente cultivado e o último em solo mantido continuamente sem cultivo (tratamento-testemunha). Os tratamentos foram caracterizados em termos de rugosidade ao acaso e cobertura superficiais do solo, as quais foram avaliadas imediatamente antes e depois do preparo, no dia anterior à aplicação da chuva simulada. O teste de chuva foi realizado por ocasião da semeadura da soja, na intensidade constante de 64 mm h-1 e com duração variável (até alcançar 30 min de enxurrada constante, em cada tratamento). O preparo do solo aumentou a rugosidade superficial ao acaso e diminuiu a cobertura por resíduo cultural em graus diferenciados, dependendo do método de preparo empregado. O preparo reduzido foi o tratamento mais eficaz no aumento da rugosidade superficial do solo ao acaso e na manutenção da cobertura por resíduo cultural. Os tempos de início e equilíbrio da enxurrada foram relativamente altos e pouco afetados pelos métodos de preparo do solo estudados. A velocidade da enxurrada, a concentração e o tamanho dos sedimentos, bem como a taxa de perda de solo, aumentaram com a diminuição da rugosidade e da cobertura superficiais do solo, enquanto a taxa de infiltração da água da chuva diminuiu. A taxa de descarga e o coeficiente de enxurrada - parâmetro C da Fórmula Racional -, aumentaram com a diminuição da rugosidade e da cobertura superficiais do solo.

Hydraulic conductivity, residue cover and soil surface roughness under different tillage systems in semiarid conditions

The objective of this study was to investigate the effect of tillage and cropping system on near-saturated hydraulic conductivity, residue cover and surface roughness to improve soil management for moisture conservation under semiarid Mediterranean conditions. Three tillage systems were compared (subsoil tillage, minimum tillage and no-tillage) under three field situations (continuous crop, fallow and crop after fallow) on two soils (Fluventic Xerochrept and Lithic Xeric Torriorthent). Soil under no-tillage had lower hydraulic conductivity (5.0 cm day −1) than under subsoil tillage (15.5 cm day −1) or minimum tillage (14.3 cm day −1) during 1 of 2 years in continuous crop due to a reduction of soil porosity. Residue cover at sowing was greater under no-tillage (60%) than under subsoil or minimum tillage (<10%) in continuous crop. Under fallow, residue cover was low (10%) at sowing of the following crop for all tillage systems in both soils. Surface roughness increased with tillage, with a high value of 16% and decreasing following rainfall. Under no-tillage, surface roughness was relatively low (3–4%). Greater surface residue cover under no-tillage helped conserve water, despite indications of lower hydraulic conductivity. To overcome the condition of low infiltration and high evaporation when no-till fallow is expected in a cropping sequence, either greater residue production should be planed prior to fallow (e.g. no residue harvest) or surface tillage may be needed during fallow.