Reduced Tillage Treatments Research Articles

Effects of reduced tillage on net greenhouse gas fluxes from loamy sand soil under winter crops in Denmark

The environmental consequences of changing from conventional to reduced soil tillage in winter crops are yet poorly understood under North European conditions. Soil tillage intensity may affect both crop growth and soil carbon (C) and nitrogen (N) turnover and balances, including emissions of greenhouse gases (GHG) such as CO 2 and N 2O. In this study we compared the effects of conventional tillage (CT) using mouldboard ploughing to 20 cm depth, reduced tillage (RT) using rotary harrowing to 8–10 cm depth and direct drilling (DD) with disk coulters on fluxes of CO 2 and N 2O from loamy sand soil under winter oilseed rape ( Brassica napus L.) followed by winter wheat ( Triticum aestivum L.). The measurements were conducted by use of chambers over a period from August 2003 to July 2005 in a soil tillage experiment established in Denmark in 2002. To integrate information on the C and GHG budgets for the experiment, the FASSET model was used with no recalibration in a two-step modelling procedure. First, we fitted the soil organic matter (SOM) model of FASSET to give the observed ratio of soil CO 2 respiration from the CT and DD treatments by scaling all decomposition and maintenance parameters for the DD treatment with the same value ( δ), called the “tillage factor”. Second, the complete FASSET model was run with default parameter value for ploughing depth in CT ( δ = 1.00) and the estimated value for DD ( δ = 0.57), in order to quantify the cumulated CO 2 and N 2O emissions. Both measurements and model simulations showed that the combined global warming potential (GWP) from CO 2 and N 2O emissions was lower from reduced tillage treatments (RT and DD) than from conventional tillage. Thus, compared with CT, modelled reduced soil tillage treatments decreased GHG emissions by 0.56 (RT) and 1.84 (DD) Mg CO 2-eq. ha −1 year −1. Similar differences between treatments were obtained for simulations over 30 years of observed weather for the specific site. In both cases, negative GWPs for the studied site were obtained. A sensitivity analysis showed that the simulated GHG emissions were primarily influenced by changes in SOM model parameters, whereas observed changes in soil water retention affected only N 2O emissions, and soil temperature had only minor effects.

Effects of Tillage Practices on Dissemination and Spatial Patterns of Heterodera glycines and Soybean Yield.

Two field experiments were conducted in central Iowa to assess the effects of tillage on Heterodera glycines dissemination and reproduction and soybean (Glycine max) yield. Plots in both experiments were artificially infested with equivalent numbers of H. glycines cysts. In one experiment, plots were left noninfested or received aggregated or uniform infestation, and a susceptible soybean cultivar was grown for 3 years. By the end of the first growing season and through the second, H. glycines population densities were consistently greater (P ≤ 0.05) in uniformly infested plots than in plots with aggregated infestations. No differences in soybean yield among the treatments were detected. In a second experiment, a 1-m2 area of each plot was infested with H. glycines cysts, susceptible soybeans were grown for four seasons, and crop residue was managed with either ridge-, conventional-, reduced-, or no-tillage. After 1 year, nematode population densities were significantly (P ≤ 0.05) greater in conventional- and reduced-tillage treatments than in no- and ridge-tillage treatments. After 2 years, H. glycines had been disseminated 6.9 m from the infestation site in conventional- and reduced-tillage treatments but only 0.5 and 1.4 m for no-tillage and ridge-tillage treatments, respectively. After 3 years, H. glycines population densities were 10 times greater in conventional- and reduced-tillage treatments than in the no-tillage treatment; conventional-tillage was the only treatment with yield significantly lower (P ≤ 0.05) than the noninfested control. Aggregation of H. glycines eggs was greater (P ≤ 0.05) in no- and ridge-tillage treatments than in conventional- and reduced-tillage treatments. Results indicate tillage can quickly disseminate H. glycines in newly infested fields, facilitating more rapid nematode reproduction and subsequent yield loss.

Agricultural studies of GM maize and the field experimental infrastructure of ECOGEN

Summary Within the ECOGEN project, long-term field experiments with genetically modified maize, Zea mays L. were conducted to study agro-ecological effects on the soil fauna and agro-economic implications of the technology. Here, we describe the study-sites, experimental layout and results of agro-economic relevance. Experiments were conducted during 2002–2005 in Denmark (Foulum), northern France (Varois) and the Midi-Pyrenees region of southern France (Narbons). MON810 Bacillus thuringiensis ( Bt )-varieties expressing the Cry1Ab protein, and a T25 glufosinate-ammonium (Basta) tolerant variety expressing the pat-gene encoding phosphinotrinacetyl-transferase were compared with near-isogenic non- Bt varieties, and conventional maize varieties. At Foulum, the maize was harvested for silage. There were no significant differences in yield between Bt -maize and a near-isogenic non- Bt variety, while a small difference in N-concentration of dry matter was detected in 1 year in a range of a measured quality parameters. Similar yield and quality were found in ploughed and reduced tillage treatments in all varieties. At Varois, the maize was harvested at ripeness and no significant differences in grain yield between Bt -maize and near-isogenic non- Bt varieties were found. These results were expected, as only Narbons harbours significant corn-borer populations. At Narbons, the number of Sesamia and Ostrinia corn-borer larvae were significantly lower in the Bt -maize than in a near-isogenic non- Bt variety and for Sesamia even less than in conventional varieties sprayed with pesticides to control corn-borer infestation. Here, Bt -maize produced a higher grain yield and grain size than a near-isogenic non- Bt variety or allowed a significant reduction in pesticide use. Concentrations of Cry1Ab in the Bt -varieties were sufficient to effectively control corn-borer larvae. In soil, Cry1Ab was close to the limit of detection and the protein did not accumulate in the soil year on year.

Characterizing Soil Water‐Conducting Macro and Mesoporosity as Influenced by Tillage Using Tension Infiltrometry

Knowledge of soil water conductive porosity is of paramount importance for understanding the water and solute movement in soil. The objective of this study was to describe and evaluate an alternative pore index, i.e., the representative mean pore radius for two consecutive soil water tensions (λΔΨ), for characterizing the water‐transmitting macro‐ and mesoporosity of soil. The hydraulic conductivity (K) and related hydraulic parameters were measured using a tension disk infiltrometer at −14, −4, −1, and 0 cm water pressure heads at a soil depth of 2 cm on a long‐term conservation tillage experiment (after 9 yr of trial) under conventional tillage (CT), reduced tillage (RT), and no‐tillage (NT) treatments. The soil was loam (Xerollic Calciorthid). The measurements were performed within the first half of a 16‐ to 18‐mo‐long fallow period. Unlike the model based on the classical capillary rise theory, which assumes no differences between measurement sites (e.g., tillage treatments) for the corresponding equivalent pore radius (C0) for macro‐ and mesopores, significant differences in λΔΨ values for macro‐ and mesopores were found between the three tillage systems tested. The number of water‐transmitting macro‐ and mesopores per unit area estimated by means of the capillary rise approach was significantly greater than that calculated using the λΔΨ pore index. Although significantly higher values of λΔΨ for both macro‐ and mesopores were observed under NT, a significantly lower near‐saturation K was found under NT than CT and RT treatments due to the lower density of water‐transmitting macro‐ and mesopores.

Effect of different methods of land preparation on runoff, soil and nutrient losses from a Vertisol in the Ethiopian highlands

Abstract. Vertisols are among the most common, high-potential soils in the central highlands of Ethiopia, where over 88% of human and 77% of the livestock population are located. Productivity from these soils is constrained by severe waterlogging due to their physical properties and intensive rainfall in summer. Traditionally, farmers plant late in the season to avoid the waterlogging, which results in harvest yields that are far below optimal. To bridge this yield gap, the broad-bed and furrow system for surface drainage has been introduced. Despite reported yields of various crops, little is known of the on-site and off-site impacts of this system. Consequently, four land preparation methods viz. (i) broad-bed and furrow (BBF), (ii) green manure (GM), (iii) the traditional system of ridge and furrow (RF) and (iv) reduced tillage (RT) were compared on standard runoff plots for 5 years (1998–2002) at Caffee Doonsaa in the central Highlands of Ethiopia. Runoff, sediment, organic carbon and nutrient (organic nitrogen and available phosphorus) losses were determined during the last two years (2001 and 2002). Over 50% of the seasonal rainfall was lost as runoff, regardless of the treatment, with significantly more of the excess water running off BBF and RT treatments in both years. The BBF system drained 67% and 54% of rainfall as runoff in 2001 and 2002, respectively, compared with 61% and 53% from the RT system during the measurement period. Although not statistically significant, the largest sediment and total nutrient losses tended to be from the BBF. The effect of the treatments on total nutrient loss and enrichment ratio was inconsistent. The nutrient concentration in the eroded sediment was greater than that of the originating surface soil but was strongly correlated. The effect of the land preparation methods was significant and varied with crops. Recommended options for best crop productivity are BBF for lentil and RT for wheat and tef.

Influence of cultivation methods on suspended solids and phosphorus concentrations in surface runoff on clayey sloped fields in boreal climate

Abstract Methods for decreasing agricultural phosphorus (P) loadings to surface waters are needed to achieve good water quality. To reliably find out the efficiency of different methods in changing hydrological conditions, long-term experiments are of invaluable importance. Here the effects of various cultivation methods on total suspended solids (TSS) and P concentrations in – and the volume of – plough layer runoff (PLR) were studied in a sloping experimental field in southwest Finland during a 9-year period. Yearly means of PLR and flow-weighted mean concentrations from the treatment plots were compared with a control, winter wheat ( Triticum aestivum ) treatment (WW), of which the values assigned were equal to 1. No major differences were found in PLR for cultivation methods up and down slope, except for the cross-ploughing treatment (0.49). Normal ploughing and cultivation treatments produced the highest TSS concentrations (1.38 and 1.18, respectively), whereas values between 0.44 and 0.53 were measured for three treatments with reduced (or no) tillage. Particle-bound P (PP) concentrations closely followed those of TSS. Dissolved reactive P (DRP) showed contrasting behaviour, with the greatest treatment effects from the three reduced tillage treatments (1.58–2.29). This study showed that by changing over from intensive autumn tillage to permanent vegetation cover, erosion and PP loss were markedly decreased. Methods employing no autumn tillage and leaving an undisturbed soil surface during winter showed particularly high reductions in loading. The simultaneous increase in DRP loss is an undeniable drawback that should be resolved separately. This study, as a part of a wider complex of integrated studies, will be utilized in a decision-making tool for the assessments of loading effects and load reduction possibilities in terms of cultivation methods.

Reduced Tillage Alternatives for Machine-harvested Cucumbers

Cucumber (Cucumis sativus L.) is grown using intensive tillage practices, which increase the cost of production and may lead to an increase in soil and water erosion. Research on alternative tillage practices for cucumber production has been limited primarily to exploring the benefits of no tillage. Alternative tillage practices, such as disking (one pass with a tandem disk) and zone tillage (one pass with a Trans-till) have not been investigated. Thus, the objective of this study was to compare the influence of reduced tillage practices on the growth, development, and yield of cucumbers. Seedling emergence varied between years, but was unaffected by a reduction in tillage, while cucumber leaf number, leaf area index, and vine growth were reduced by no tillage (P ≤ 0.05). Total dry matter accumulation and days to 50% open flower varied with tillage. No-tillage plots produced an average of 34 g·m-2 of dry matter compared to 47 g·m-2 for conventional tillage plots and took 1 day longer to reach 50% flower. Although growth differences were observed under all reduced tillage treatments, no reduction in total yield was observed when compared with conventional tillage yields. Alternative reduced tillage practices, such as disking or zone tillage, were found to be viable options for successful cucumber production. These alternative practices will reduce the cost of production, provide growers with greater time flexibility and ease of land preparation, and reduce the potential for water and wind erosion.

Reduced tillage increases residue groundcover in subsequent dry pea and winter wheat crops in the Palouse region of Idaho

Crop management practices are needed that increase crop residue groundcover and reduce soil erosion after winter wheat ( Triticum aestivum L. emend. Thell.) planting in the Palouse region of northern Idaho and eastern Washington. This experiment investigates if reduced tillage leaves more residue groundcover from two spring small grain crops following different tillage practices and increases crop performance in subsequent dry pea ( Pisum sativum L. subsp. sativum) crops, and into winter wheat crops. In 1996 and 1997, two 3-year trials (spring cereal–dry pea–winter wheat rotation) were seeded to spring wheat and barley ( Hordeum vulgare L.) crops as sub-plot treatments. Plow, chisel, and paratill tillage, and no-till main-plot tillage treatments were applied to silt loam soils after the spring small grain crops. Spring small grain residue persisted from fall tillage through pea planting with little change over winter averaging 44% groundcover in 1997 and 74% groundcover in 1998 for the no-till treatment after pea planting. In 1998 pea yield in no-till was highest (1835 kg ha −1), whereas pea yield was lowest in the plow treatment (1605 kg ha −1). Pea residue mass collected after harvest was not different across treatments, but the carryover spring small grain residue mass was highest in no-till at 3010 kg ha −1 for barley and 2160 kg ha −1 for wheat. After winter wheat seeding in 1997, only the no-till treatment had over the minimum 30% groundcover recommended for erosion control. In 1998, all reduced tillage treatments left more than 30% groundcover and the next year no-till had 46% groundcover after winter wheat seeding. Winter wheat yields were not different in 1998, but in 1999 were highest in the chisel and paratill treatment and averaged 5150 kg ha −1. Residue groundcover can be increased by reduced tillage and good yields can be obtained if plant stand is achieved and pest problems are well managed.

Effects of agronomic practices on the soil carbon storage potential in arable farming in Austria

According to the Kyoto-Protocol for carbon dioxide mitigation the direct human induced sequestration potential of carbon in agricultural soils may in the future be included for calculating net changes in greenhouse gas emissions. Therefore we used long-term experiments on arable land in Austria differing strongly in climate and soil conditions to explore the effects of agronomic practices on changes in soil organic carbon content. Optimal mineral N fertilizer input increased the carbon stocks on an average to 2.1 t ha−1compared with no N fertilization in a 36 years period. Additional farm yard manure application (10 t ha−1 y−1) enhanced carbon storage to about 5.6 t ha−1 after 21 years. Site-specific influences must be considered. Losses of 2.4 t carbon per ha were caused by additional irrigation of sugar beet and maize in a rotation with cereals in a 21 years period. The incorporation of all crop residues resulted in an increase of 3.4 t ha−1 organic carbon in topsoil after 17 years. In the uppermost soil layer (0–10 cm) minimum and reduced tillage treatment enhanced carbon stocks to about 4.7 t ha−1 and 3.2 t ha−1 compared to conventional soil management within a decade. Based on these results, only a limited soil carbon sequestration potential can be inferred: Manuring and incorporation of crop residues are well-proven practices on arable land and therefore no additional human induced carbon sequestration might be achieved. The adoption of minimum tillage on Phaeozems, Chernozems and Kastanozems could, roughly calculated, result in a supplementary carbon storage of about 0.6% of the entire present annual carbon dioxide emission in Austria. However, the storage of carbon in topsoil means only a mid-term sequestration. By changing practices in short-terms, these amounts of carbon might be a source of additional carbon dioxide in the future.

Farm-level profitability analysis of alternative tillage systems on clay soils

Crop yields, production costs, and net returns for seven alternative conservation tillage (including five reduced tillage and two no-till) treatments were compared with a conventional tillage (CT) treatment for a corn (Zea mays L.) – soybean (Glycine max L. Merr) rotation for two clay soils in southwestern Ontario. There was no significant difference in corn and soybean yields between the CT and the conservation tillage systems at either location, although actual yields tended to be highest for CT management. Tillage treatments that used a common set of machinery for corn and soybean production generated savings in annual machinery costs. Variable costs were lowest for the reduced-tillage treatments and highest for the two no-till treatments due to higher equipment expenditures and additional herbicide requirements. For a given location, there was often no significant difference in net returns between CT and the conservation tillage treatments, although average net returns for the corn–soybean cropping systems tended to be highest for CT and lowest for no-till. Key words: Net returns analysis, conservation tillage systems, clay soils, corn, soybeans

Effects of Soil Tillage and Nitrogen on Winter Wheat Yield and Weed Biomass

In a three year study (1994-96) reduced soil tillage variants proved satisfactory for winter wheat grown on Humogley soil in Eastern Croatia in the absence of herbicides. During the experiment the conventional tillage (ploughing, disk-harrowing, standard sowing) did not give significantly higher yields compared to the reduced tillage treatments (disk-harrowing ; tillage by multitiller with chisels ; seedbed preparation (rototiller) + sowing by rotosem ; and ploughing, seedbed preparation + sowing by rotosem). Production of weed biomass at the conventional tillage equalled the treatment tillage by rototiller + sowing by rotosem, but was significantly lower than in other tillage treatments. Totally, nitrogen fertilisation had a significant influence upon wheat yield increase at each N level (140, 170, and 200 kg/ha), whereas the efficacy of fertilisation upon yields was higher at reduced tillage treatments without ploughing than at the conventional tillage. The correlation between crop yield and weed biomass decreased along with the increase of N level. Winter wheat had a higher N optimum than its weed component, which points out that for this crop N fertilisation at reduced tillage systems can be used as a measure for weed control. The reduced tillage variant with rototiller + sowing by rotosem turned out to be entirely competitive with the conventional tillage regarding yield and weed biomass, as well as a higher resistance to weather conditions.

Dynamics of the mycorrhizal symbiosis of corn ( Zea mays L.): effects of host physiology, tillage practice and fertilization on spatial distribution of extra-radical mycorrhizal hyphae in the field

Tillage and fertilization may reduce the abundance of indigenous arbuscular mycorrhizal (AM) fungi in agricultural field soils. The dynamics of hyphal abundance in soil were studied over two growing seasons at a site in eastern Canada in a corn crop grown in a sandy loam soil and over one growing season in a corn crop grown in a clay soil. Experimental plots in a long-term tillage experiment, had been managed under no-tillage (NT), reduced tillage (RT) and conventional tillage (CT) for 11 years. Soil receiving each of these tillage treatments also received either inorganic (N and K) or organic (liquid dairy manure) fertilizer. Soil samples were collected from different places within each plot: on the plant row, at 18.75 cm from the row (quarter of the inter-row distance) and in between two rows (mid-row, i.e., 37.5 cm from the adjacent rows). Plant and soil samples were taken at the 12–14 leaf stage of corn (June), at silking stage (August) and at harvest (October), in order to measure the fluctuation in soil hyphal densities and plant nutrients concentrations during the season. Densities of total and viable AM hyphae were greatest in the row and lowest in the mid-row. Hyphal density on the row increased steeply from 12–14 leaf stage to silking stage and decreased thereafter. No significant fluctuation of hyphal abundance was observed in the mid-row, suggesting a prevalence of AM hyphae on the row. Hyphal densities were higher in NT soil than in CT soil, while RT soil contained intermediate hyphal densities. The highest corn P, Zn and Cu concentrations were observed in NT and RT treatments concurrently with the highest hyphal densities. Concentrations of K, Ca and Mg did not change with tillage or fertilization type. Manure application significantly increased the densities of total and viable hyphae in the clay soil.

PREDICTING NITRATE-N LEACHING UNDER DIFFERENT TILLAGE SYSTEMS USING LEACHM AND NTRM

Two simulation models LEACHM-N and NTRM were used to estimate nitrate-nitrogen (NO3 –N) leaching in a sandy loam soil under no-till (NT), reduced tillage (RT), and conventional tillage (CT) practices, for conditions with residue (R) and without residue (NR) in undisturbed soil columns. LEACHM-N generally overestimated NO3 –N mass below 0.4 m in RT and CT treatments. However it underestimated NO3 –N concentration ([NO3 –N]) measured immediately after fertilizer application, particularly at the lower depths, showing a deviation of up to 50%. LEACHM-N overpredicted [NO3 –N] in the top 0.2 m soil layers in all treatments. Overall, model predictions were within one standard deviation of observed data. NTRM performed well at depths below 0.4 m, but underpredicted NO3 –N movement at shallower depths. No significant differences were shown among tillage and residue treatments by NTRM. Both models still require improvement to accurately predict [NO3 –N] in the soil.

Growth, yield and water use efficiency of winter barley in response to conservation tillage in a semi-arid region of Spain

In the semi-arid areas of Aragón (NE Spain), dryland crop production is limited by low and variable precipitation. Conservation tillage has been proposed as a promising strategy to improve soil and water conservation in these areas. A long-term field research project to determine the feasibility of conservation tillage was initiated in 1989 at four locations, three on loam to silt loam soils (Xerollic Calciorthid) and one on a silty clay loam (Fluventic Ustochrept), receiving between 300 and 600 mm of average annual rainfall. This study compared, under both continuous cropping and cereal-fallow rotation, the effects of conventional tillage (mouldboard plough) and two conservation tillage systems, reduced tillage (chisel plough) and no-tillage, on winter barley ( Hordeum vulgare L.) growth and yield, and water use efficiency during the first two growing seasons. Whereas a similar crop response between the conventional and reduced tillage treatments was generally found at all locations, poor performance with no-tillage was observed at the most arid sites. At these sites, lower early growth of barley with no-tillage resulted in a 53% reduction in grain yield, compared to conventional tillage. This unfavourable crop response to no-tillage was due to a lower crop water use, mainly starting with the stem elongation stage (20% lower than the tilled treatments), and a larger proportion of total water use lost as evaporation (69% compared to 50% of tilled treatments). Values of water use efficiency for grain production (0.7–17.0 kg ha −1 mm −1) and transpiration efficiency (7.4–23.8 kg ha −1 mm −1) were within the ranges reported for cereal crops in Mediterranean environments. Fallowing in the cereal-fallow rotation proved to be an inefficient practice for improving soil water storage and subsequent crop yield, under both conventional and conservation management. Based on the study, we conclude that, up to now, only reduced tillage provides an alternative to conventional tillage to maintain crop production in the dryland cereal-growing areas of Aragón.

Temporal dynamics of microbial biomass, xylanase activity, N-mineralisation and potential nitrification in different tillage systems

Three methods of tilling soil were employed (conventional, reduced and minimum tillage) to determine their effects on substrate-induced respiration (SIR), xylanase activity, N-mineralisation and potential nitrification in a fine-sandy Haplic Chernosem. The top soil layer (0–10 cm) under minimum and reduced tillage systems showed significantly higher SIR rates than conventionally tilled soil. The stratification of soil microbial biomass within the profile of reduced and minimum tillage systems is suggested to be the major mechanism for higher xylanase and N-mineralisation near the soil surface compared with conventional tillage. The localisation of microorganisms and their activities in the soil profile may influence the efficiency of pesticides, the fate of nitrogen fertiliser and the immobilisation of nitrogen. Lack of water in summer caused a significant decline in all microbial activities, and during this time no significant effects of tillage treatment were detected. The ratio of biomass C to organic C fluctuated throughout the year within the range previously reported by other authors. The turnover rates of biomass C ranged from 0.79 to 1.58 year −1 and were clearly dependent on the different tillage treatments and soil depth. The slightly higher soil density, higher water capacity and lower air circulation might have caused the significantly lower biomass C turnover rate (0.99 year −) of the minimum tillage treatment versus the reduced (1.58 year −1) and conventional (1.50 year- −1) treatments. At a soil depth of 20–30 cm, xylanase activity and N-mineralisation were significantly higher in conventional treatments than in minimum or reduced tillage treatments due to buried organic substrates after ploughing. The likelihood of nitrate leaching when the soil surface is bare is therefore increased in conventionally ploughed soils. The type of soil cultivation influenced the spatial distribution as well as the quantity of N-mineralisation and xylanase activity in the entire activity. Minimum and reduced tillage systems tended toward higher N-mineralisation and xylanase activity in the entire 0–30 cm soil layer. After 4 years of different tillage treatments, only slight changes in organic matter content were detected and there was no effect on water content.

A comparison between seasonal changes in soil water storage and penetration resistance under conventional and conservation tillage systems in Aragón

Low and extremely variable precipitations limit dryland crop production in the semi-arid areas of Aragón (NE Spain). These areas are also affected by high annual rates of topsoil losses by both wind and water erosion. A long-term experiment to determine the feasibility of conservation tillage in the main winter barley production areas of Aragón was initiated in 1989 at four locations, three on loam to silt loam soils (Xerollic Calciorthid) and one on a silty clay loam (Fluventic Ustochrept), receiving between 300 and 600 mm of average annual rainfall. In this study, we compared, under both continuous cropping and cereal-fallow rotation, the effects of conventional tillage (mouldboard plough) and two conservation tillage systems, reduced tillage (chisel plough) and no-tillage, on soil water content and penetration resistance during the first two growing seasons. Whereas reduced and conventionally tilled treatments generally had similar soil water content during the experimental period, the effects of no-tillage were inconsistent. No-tilled plots had from 26% less to 17% more stored soil water (0–80 cm) than conventional tilled plots at the beginning of the growing season. In contrast to the conventional and reduced tillage treatments, penetration resistances were between 2 and 4 MPa after sowing in most of the plough layer (0–40 cm) under no-tillage at all sites. Fallow efficiencies in moisture storage in the cereal-fallow rotation, when compared with the continuous cropping system, ranged from −8.7 to 12%. The highest efficiencies were recorded when the rainfall in the months close to primary tillage exceeded 100 mm. Since this event is very unlikely, long fallowing (9–10 months) appears to be an inefficient practice for water conservation under both conventional and conservation management. Our results suggest that, up to now, only reduced tillage could replace conventional tillage without adverse effects on soil water content and penetration resistance in the dryland cereal-growing areas of Aragón.

Tracing Nitrogen Movement in Corn Production Systems in the North Carolina Piedmont: Analysis of Nitrogen Pool Size

AbstractThe fate of N in North Carolina Piedmont corn (Zea mays L.) was traced using N pool size analysis. In 1989 and 1990, selected N pools [corn; weeds; surface residues; and soil NH+4 NO‐3, and potentially mineralizable N (No)] were sequentially sampled in four reduced chemical input systems: (i) crimson clover (Trifolium incarnatum L.) with conventional tillage (clover‐till), (ii) no cover crop with conventional tillage and 70 kg N ha−1 as NH4NO3 (fertilizer‐till), (iii) crimson clover with strip‐tillage (clover‐strip), and (iv) no cover crop with no tillage and 70 kg N ha−1 as NH4NO3 (fertilizer‐no‐till). The largest of the repeatedly measured N pools was soil No, which accounted for <10% of the total Kjeldahl soil N. Soil No was highest in the clover‐till treatment, and had large seasonal fluctuations: 170 to 255 kg N ha−1 in clover‐ till, and 117 to 210 kg N ha−1 in other treatments. Fertilizer treatments had higher inorganic N levels than did clover treatments only immediately after fertilizer application. Although clover shoots contained 97 to 134 kg N ha−1 yr−1, more than the N applied to fertilizer treatments, no significant differences among treatments in plant (corn + weed) aboveground N accumulation (38 to 132 kg N ha−1) were observed. Of these totals, weed N accounted for 5 to 30 kg N ha−1. Surface residue N content was highest in reduced tillage treatments. In reduced chemical input systems such as these, N transfers among soil No, weed, and residue pools may be as large or larger than N transfers among soil inorganic and crop pools.

004 WINTER COVER CROPS FOR WEED CONTROL IN SUSTAINABLE VEGETABLE PRODUCTION

A three-year study determined the effect of winter cover crops on weeds and vegetable crops in a vegetable production system. Winter rye and hairy vetch were interseeded in the fall of 1990, 1991 and 1992 at 112 and 34-kg ha-1, respectively. The cover crops were killed by ether applying glyphosate at 1.1 kg a.i ha-1 [reduced tillage(RT)] or mowing and disking the cover crop (Disked). The conventional tillage (CT) was bare ground with a preplant incorporated application of 0.84 kg a.i ha-1 of trifluralin. During the three years, the greatest snap bean yields were in the CT; total yields of cabbage and tomato varied between the years; and were not affected by management systems. Weed control was similar in the RT and CT treatments during the three years. Disked cover crop treatments tended to have greater weed numbers than either RT or CT treatments.

Soil physical and chemical changes due to tillage and their implications for erosion and productivity

A seven-year tillage trial was conducted in central New South Wales, Australia to measure the effect and extent of conservation tillage practices on soil physical and chemical properties. Three tillage treatments, traditional tillage (TT), reduced tillage (RT) and direct drilling (DD) were imposed on hardsetting red-brown earths at Cowra and Grenfell. A fourth treatment, direct drilling without grazing (NT) was imposed at Cowra only. At Cowra there was a significant trend of reduced total runoff in the DD and NT treatments but not in the RT treatment. Runoff significantly increased in the TT treatment. At Grenfell, runoff decreased in all treatments but only significantly in the DD and RT treatments. Similar trends in total sediment loss were measured at both sites. Associated physical measurements of saturated hydraulic conductivity, sorptivity and bulk density confirmed that the changes in runoff were due to the creation of macroporosity greater than 0.75 mm diameter. The relationship between macroporosity, organic carbon and aggregate stability is discussed. Conclusions were that in these soil types runoff and sediment loss were affected more by destruction of macroporosity due to cultivation than changes in organic carbon from residue retention. To achieve these soil improvements using conservation tillage a continuous cropping period of four years was necessary to obtain significant and consistent trends. Soil chemical data showed that total nitrogen increased with conservation tillage practices. Available phosphorus changes due to tillage were not observed because of more than adequate fertiliser applied. Soil pH decreased significantly in the DD and NT treatments at Cowra only. The implications of these chemical changes are discussed.

Tillage-Induced Differences in Organic Matter of Particle-Size Fractions and Microbial Biomass

Tillage can modify the quantity and vertical distribution of organic matter in soils. Its effects on the composition of organic matter is less well documented, however. The objective of this study was to determine the effects of tillage practices in silage corn (Zea mays L.) production on some characteristics of organic matter of a Neubois silt loam (fine-loamy, mixed, frigid Aeric Haplaquept). Carbon and N contents of particle-size separates and microbial biomass C were determined on soil samples collected in three soil layers (0–8, 8–16, and 16–24 cm) from three tillage systems (moldboard plow, minimum tillage, and ridge tillage) that had been established for 11 yr. There were no detectable differences in total organic C among tillage treatments at any depth. The organic C of the sand-size separates, however, accounted for 7% of the total C in the moldboard plow system and up to 19% in the reduced tillage treatments. There was little difference in the organic C content of the silt- and clay-size fractions among the tillage treatments. Nitrogen contents of the size fractions generally mirrored those observed for C. Microbial biomass C accounted for 1.2 to 1.4% of the organic C in the moldboard plow treatment, 2.4 to 3.9% in the ridge tillage treatment, and 3.5 to 5.1% in the minimum tillage treatment. This study demonstrated that, even in a cropping system that involves almost no return of aboveground residue to the soil, such as silage corn production, reducing tillage intensity can result in the maintenance or increase of the more labile fractions of soil organic matter.