Subsoil Tillage Research Articles

Soil carbon change and yield increase mechanism of conservation tillage on sloping drylands in semi-humid arid area

A long-term field experiment was conducted in the semi-humid areas of western Henan Province to study the changes of soil organic carbon (SOC), soil microbial biomass carbon (SMBC) and yield increase mechanism of wheat. The results show that SOC increases significantly under sub-soiling tillage and no-tillage, especially in cultivated soil layers. SOC (6.79 g·kg-1) is highest under sub-soiling, which is 13.8% higher than that under conventional tillage. SOC under no-tillage is 11.6% higher than conventional tillage, which also drops by 1.4% under reduced tillage. The deeper the soil layer, the lower SOC content is. SMBC content occurs in the following order: no-tillagesub-soilingconventional tillagereduced tillage; while SMBC contents under no-tillage, sub-soiling tillage and reduced tillage are 79.3%, 19.9% and-2.5% higher than that of conventional tillage. Ratio of SMBC to SOC under no-tillage and sub-soiling are 3.11% and 2.04%. Through out the field trial experiments, sub-soiling yields the highest. No-tillage increases wheat yield, except in very rainy years. No-tillage and sub-soiling tillage store more water in the soil and improve accumulation of dry matter during the later growing stage of winter wheat, postpone plant co-senescence in wheat.

Influence of Compaction and Subsoil Tillage on Soil Conditions and Pink Eye

A densely compacted soil layer has been a prevalent feature of the vegetable crop production region of Central Wisconsin, resulting in poor water drainage, increased susceptibility to tuber disease, and reduced yield and quality in potatoes. Subsoil tillage has been implemented on a wide-scale for management of problems associated with compacted soil layers. Pink eye is a tuber disorder that causes storage and processing losses. Periods of moisture stress and increased hill temperatures have been linked to pink eye incidence, but the cause of this disorder is unknown and few specific management recommendations exist. The goals of this work were to quantify the impact of compacted soils and subsoil tillage on development of potato pink eye. Small plot experiments were conducted to quantify response of soil conditions and potato pink eye to soil compaction and subsoil tillage. Compacted soils resulted in higher volumetric soil water content and extended periods of free water, especially after substantial precipitation events. Subsoil tillage allowed for more rapid movement of water following large precipitation events decreasing periods of free water. More compacted soils also had higher soil temperatures. Subsoil tillage delayed the development and progression of pink eye symptoms, but did not influence overall incidence. Increased soil moisture and temperature corresponded with more rapid development of pink eye in compacted and conventionally tilled soils. This research suggests subsoil tillage may be useful in reducing the severity of pink eye symptoms by alleviating compacted subsoil layers that limit water drainage. In addition, prevention of compaction reduced soil temperatures which limited pink eye development.

Evaluating energy efficiency of site-specific tillage in maize in NE Italy

This paper examine the efficiency of energy use of three conservation tillage practices (SST – sub-soil tillage; MT – minimum tillage; and NT – no tillage) performed within two management zones, previously identified in a field according to the stability of yield variability. Experiments were carried out in 2003 in NE Italy, on a farm near Rovigo, on a 8-ha field with clay soil, in maize (Zea mays, L.). The purpose of the paper is (i) to investigate the energy variability due to these tillage practices performed spatially within two management zones and (ii) to analyze the long-term energetic efficiency for each tillage practice. The energy balance was highest for SST with respect to MT and NT, due to labor and fuel consumption rates. The energy balance was influenced by the spatial pattern of yield, with appreciable differences between practices in terms of both the conversion index of energy for tillage (9.0, 12.6 and 22.8GJha−1 for SST, MT and NT, respectively) and the energy use efficiency for tillage (8.0, 11.6, 21.8GJha−1 for SST, MT and NT, respectively). Based on the simulated data and the calibration results, SALUS model proved to be a good tool for analyzing long-term effects of tillage practices on yield. The NT treatment showed the best efficiency over years, due to the low inputs in comparison with the output level.

Tillage Effects on Soil Organic Carbon Fractions in Mediterranean Dryland Agroecosystems

Under semiarid conditions, soil quality and productivity can be improved by enhancing soil organic matter content by means of alternative management practices. In this study, we evaluated the feasibility of no‐till (NT) and cropping intensification as alternative soil practices to increase soil organic C (SOC). At the same time, we studied the influence of these management practices on two SOC fractions (particulate organic matter C, POM‐C, and the mineral‐associated C, Min‐C), in semiarid agroecosystems of the Ebro River valley. Soil samples were collected from five soil layers (0–5‐, 5–10‐, 10–20‐, 20–30‐, 30–40‐cm depth) during July 2005 at three long‐term tillage experiments located at different sites in the Ebro River valley (northeast Spain). Soil bulk density, SOC concentration and content, SOC stratification ratio, POM‐C, and Min‐C were measured. Higher soil bulk density was observed under NT than under reduced tillage (RT), subsoil tillage (ST), or conventional tillage (CT). At the soil surface (0–5‐cm depth), the highest total SOC concentration, POM‐C, and Min‐C were measured under NT, followed by RT, ST, and CT, respectively. In the whole soil profile (0–40 cm), similarly, slightly greater SOC content was measured under NT than under CT with the exception of the Selvanera site, where deep subsoil tillage combined with moldboard plowing accumulated more SOC than NT. In semiarid Mediterranean agroecosystems where CT consists in moldboard plowing, NT is a viable management practice to increase SOC.

In-Row Subsoil Tillage and Planting Depth Influence on Corn Plant Population and Yield on Sandy-Textured Mid-Atlantic Coastal Plain Soils

In-Row Subsoil Tillage and Planting Depth Influence on Corn Plant Population and Yield on Sandy-Textured Mid-Atlantic Coastal Plain Soils

Banco de sementes do solo de margem viária dominada por capim-annoni-2 e sujeito ao controle com distúrbios no solo e introdução de gramíneas

Os impactos das ações antrópicas nas rodovias favorecem um ecossistema diferenciado do seu entorno, facilitando o estabelecimento de espécies oportunistas, como o capim-annoni-2 (Eragrostis plana Nees). No Rio Grande do Sul os acostamentos de rodovias encontram-se invadido por esta espécie, constituindo-se como centro dispersor. Com este estudo objetivou-se descrever o tamanho e a composição do banco de sementes do solo (BSS) deste ambiente, e demonstrar o seu potencial para recompor a florística campestre de acostamentos degradados e invadidos através do estimulo do BSS. O experimento foi estabelecido à margem de uma estrada municipal, anexa à sede da Fazenda São Lucas, no município de Rio Pardo RS, no período de janeiro de 2005 a maio de 2006. O delineamento foi em blocos casualizados com parcelas subdivididas e com três repetições. Os tratamentos das parcelas foram: uso de subsolador e de subsolador mais grade com aplicação de calcário e fósforo. Nas subparcelas, foram semeadas Megathyrsus maximus, Setaria sphacelata, mistura de três espécies nativas de Paspalum ssp e exclusão (testemunha). A ocorrência de sementes de espécies exóticas representou 20% do BSS, destacando-se o capim-annoni-2. As espécies inibidoras do BSS do capim-annoni-2 foram Megathyrsus maximus e Setaria sphacelata, associadas à operação de subsolagem, gradagem e adubação. O tamanho e a riqueza do BSS indicam alto potencial de regeneração da vegetação herbácea nativa em acostamentos de rodovias invadidos por capim-annoni-2.

Tillage and rotation effect on corn–soybean energy balances in eastern Nebraska

Data from a field experiment conducted in eastern Nebraska over 16 years (1986–2001) were used to determine the energy balance of corn ( Zea mays L.) and soybean ( Glycine max L.) as affected by tillage treatments and rotation. Tillage treatments included chisel plow, tandem disk, moldboard plow, ridge-tillage, no-till and subsoil tillage. Crop sequences were continuous corn, continuous soybean, corn in a corn–soybean rotation and soybean in a soybean–corn rotation. The energy balance was assessed by comparing the parameters: energy gain (net energy output), energy intensity (energy input per unit grain equivalent, GE) and output/input ratio. Changes in plant density, crop production practices and machinery over the course of the study were taken into account in the analysis. Averaged across years, the no-till treatment required lower energy input (7.34 GJ ha −1) than tandem disk (7.65 GJ ha −1), ridge-till (7.69 GJ ha −1), chisel plow (7.83 GJ ha −1), subsoil-tillage (7.96 GJ ha −1) and moldboard plow (8.72 GJ ha −1). The energy input was lower for soybean systems than corn. Hence, the lowest energy input was required for soybean with no-tillage (5.43 GJ ha −1) and highest for corn systems with moldboard plow tillage (10.6 GJ ha −1). Within a rotation the tillage treatment had a small effect on energy output with energy efficiency being more strongly affected by crop rotation than by tillage method. Moldboard plow tillage maximized the energy gain while reduced tillage (ridge-till, no-till) minimized energy intensity and maximized output/input ratio. Within crops and crop rotations, the highest energy gain (98 GJ ha −1) and lowest energy intensity (162.4 GJ GE −1) occurred in corn production. For both corn and soybean, the energy gain was greater for crop rotations (92.8 GJ ha −1) than monocultures (78.0 GJ ha −1). The output/input ratio was greatest for rotated corn (14.0) and lowest for continuous soybean (9.9). Crop rotations that include legumes and reduced tillage improve the energy efficiency of crop production systems.

Influence of subsoiling on direct-seeded cereals in southeastern Idaho

The influence of shallow (20 cm deep) subsoil tillage on cereals planted with a no-till planter was investigated for 3 years at two locations in southeastern Idaho. Among Fusarium spp., F. culmorum was the primary fungus isolated from diffuse brown-black root lesions in the wetter location (Ririe), while F. semitectum, F. reticulatum, F. equiseti, and F. acuminatum were the dominant species isolated at the drier location (Arbon Valley). Increased yields resulting from methyl bromide fumigation indicated that biological factors were limiting the yield. However, subsoiling did not influence nematode populations or fungal root rots. The primary parasitic nematode found at both locations was Pratylenchus neglectus. Subsoiling had a tendency to increase soil moisture at depths between 61 and 90 cm, to increase organic matter, and to decrease nitrogen. Yield increased by 8% or more with subsoil tillage at both locations the first year. Yield increases were not significant in other years, when moisture was particularly limiting or abundant. Subsoiling may prove favorable for cereals planted in a soil-conservation tillage system, but the risk of fungal root rots may increase with such a practice. Additional study is warranted, as subsoil-tillage practices may increase yield and desirable soil parameters without compromising the benefits associated with cereal production in a soil-conservation tillage system.

Effects of conservation tillage practices on winter wheat water-use efficiency and crop yield on the Loess Plateau, China

In the semi-humid to arid loess plateau areas of North China, water is the limiting factor for rain-fed crop yields. Conservation tillage has been proposed to improve soil and water conservation in these areas. From 1999 to 2005, we conducted a field experiment on winter wheat ( Triticum aestivum L.) to investigate the effects of conservation tillage on soil water conservation, crop yield, and water-use efficiency. The field experiment was conducted using reduced tillage (RT), no tillage with mulching (NT), subsoil tillage with mulching (ST), and conventional tillage (CT). NT and ST improved water conversation, with the average soil water storage in 0–200 cm soil depth over the six years increased 25.24 mm at the end of summer fallow periods, whereas RT soil water storage decreased 12 mm, compared to CT. At wheat planting times, the available soil water on NT and ST plots was significantly higher than those using CT and RT. The winter wheat yields were also significantly affected by the tillage methods. The average winter wheat yields over 6 years on NT or ST plots were significantly higher than that in CT or RT plots. CT and RT yields did not vary significantly between them. In each study year, NT and ST water-use efficiency (WUE) was higher than that of CT and RT. In the dry growing seasons of 1999–2000, 2004–2005 and the low-rainfall fallow season of 2002, the WUE of NT and ST was significantly higher than that of CT and RT, but did not vary significantly in the other years. For all years, CT and RT showed no WUE advantage. In relation to CT, the economic benefit of RT, NT, and ST increased 62, 1754, and 1467 yuan ha −1, respectively, and the output/input ratio of conservation tillage was higher than that of CT. The overall results showed that NT and ST are the optimum tillage systems for increasing water storage and wheat yields, enhancing WUE and saving energy on the Loess Plateau.

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.

Short-term tillage effects on soil cone index and plant development in a poorly drained, heavy clay soil

Soil compaction is a big challenge in managing poorly drained clay soils. An on-farm field study was conducted over 2 years in a poorly drained, heavy clay soil, Red River Valley, Manitoba, Canada, where soil compaction, crop growth and root development were perceived as serious concerns. To address these concerns, no-tillage and sub-soiling tillage were proposed and compared with the traditional tillage system in which light-duty field cultivators were used at tillage depths ranging from 50 to 75 mm. Measurements of soil cone index indicated that a hardpan existed at approximately 175 mm soil depth in each fall as a result of wheel traffic during the growing season. It may not be necessary to break the hardpan with fall tillage operations in the studied region, as the hardpan was naturally removed over winter. Effects of tillage practices were evaluated using seeding performance and plant development. No-tillage resulted in the similar speed of emergence, plant population and crop yield, but more uniform seeding depth and more roots in the topsoil layer (0–75 mm), when compared with the conventional tillage. Sub-soiling promoted much faster crop emergence, higher plant populations and crop yield as well as deeper root penetration than the conventional tillage. However, the draft force required for sub-soiling was four times that of the conventional tillage.

Soil structure and the saturated hydraulic conductivity of subsoils

The saturated hydraulic conductivity, K sat, was measured on soil samples collected from the plough layer and the subsoil. A range of naturally occurring soil bulk densities was obtained by sampling in different years, with different crops and within and without wheel-tracks, etc. It was found that, for the plough layer, quite good linear relationships exist between the logarithm of K sat and the bulk density. However, for the subsoils, the value of K sat usually lies above the regression line for found for the corresponding plough layer. This “excess” hydraulic conductivity of subsoils is attributed to the presence of biopores, especially root channels. The lower hydraulic conductivity of the plough layer, relative to the subsoil, is attributed to the destruction of these biopores by tillage. A simple model for the separate contributions of soil texture and root channels to the overall value of K sat is presented. It is concluded that subsoil tillage could cause significant reductions in K sat with potentially serious environmental consequences unless it is repeated periodically.

Crop Yield and Nitrogen Accumulation Response to Tillage of a Coastal Plain Soil

Delineation of the benefit derived from either surface or subsoil tillage is important for the advancement of soil‐conserving crop production systems in the Coastal Plain. The objective of this experiment was to measure the impact of surface and subsoil tillage of a sandy Coastal Plain soil (fine‐loamy, siliceous, thermic Typic Kandiudult) on grain yield and nitrogen accumulation for a 2‐yr rotation of corn (Zea mays) and wheat–double‐cropped soybean {(Triticum aestivum L.) and [Glycine max (L.) Merr.]}. Soils of the experimental plots initially possessed different surface residue and organic matter characteristics because they had received in‐row subsoiling with either surface‐disking tillage or no surface tillage for the previous 18‐consecutive years. The current experiment was conducted from 1997 to 2001, which was an exceptionally dry period. Thus, results of this experiment provide insight into how these cropping and tillage treatments performed during one of the driest 5‐yr periods of the last half century. In each year, both phases of the crop rotation were grown in plots with the following tillage treatments: (i) neither surface nor subsoil tillage, (ii) paratill subsoiling without surface tillage, (iii) surface tillage without subsoiling, and (iv) both surface tillage and paratill subsoiling. Soybean was not significantly affected by any tillage treatment. With subsoiling, corn grain yields (4‐yr means) were not significantly different with surface‐disking tillage versus no surface tillage (4.98 and 4.92 Mg ha−1, respectively). Without subsoiling, corn yields were higher with no surface tillage (4.24 Mg ha−1) than with surface‐disking tillage (3.51 Mg ha−1). Likewise, with subsoiling, wheat grain yields (5‐yr means) were not significantly different with surface‐disking tillage versus no surface tillage (3.12 and 3.24 Mg ha−1, respectively). Without subsoiling, wheat grain yields were higher with no surface tillage (2.80 Mg ha−1) than with surface‐disking tillage (2.59 Mg ha−1). Nitrogen accumulations in both shoot dry matter and grain generally followed the treatment responses of grain yield. Thus, during this dry period, surface no‐till and the associated accumulation of organic matter could only somewhat compensate for the need to subsoil. With or without surface tillage, paratill subsoiling was very beneficial for corn and wheat yields.

On-farm assessment of organic matter and tillage management on vegetable yield, soil, weeds, pests, and economics in California

In intensive vegetable production, low organic matter (OM) inputs and leaching of nitrate (NO3 − -N) decrease soil quality with time. Four management regimes were compared for their effects on soils and on production issues in a cooperative research project with a commercial vegetable grower in the Salinas Valley, California, USA, on an 8.3 ha field: minimum tillage with OM (+OM) inputs; minimum tillage with no OM (−OM) inputs; conventional tillage +OM inputs; and conventional tillage −OM inputs. Minimum tillage retained the same raised beds for the 2-year study (four crop cycles), and tilled to approximately 20 cm depth. Conventional tillage used many passes for surface and subsoil tillage, and disturbed the soil to approximately 50 cm depth. In +OM, compost was added two times per year, with a rye (Secale cereale) cover crop in the fall or winter, whereas −OM treatments followed the typical practice of only incorporating crop residues. Addition of cover crops and compost increased microbial biomass C (MBC) and N (MBN), reduced bulk density, and decreased the NO3 − -N pools in the 0–90 cm profile, so that leaching potential was lower compared to −OM treatments. Tillage practices had generally similar effects on soils except that surface soil moisture and NO3 − -N in the deep profile were consistently lower with minimum tillage. Minimum tillage tended to decrease lettuce (Lactuca sativa) and broccoli (Brassica oleracea) yields, but was not associated with increased pest problems. Weed density of shepherd’s purse (Capsella bursa-pastoris) and burning nettle (Urtica urens) were occasionally lower in the +OM treatments. Disease and pest severity on lettuce was slight in all treatments, but for one date, corky root disease (caused by Rhizomonas suberifaciens) was lower in the +OM treatments. The Pea Leafminer, Liriomyza huidobrensis, was unaffected by management treatments. Economic analysis of the three lettuce crops showed that net financial returns were highest with minimum tillage −OM inputs, despite lower yields. Various tradeoffs suggest that farmers should alternate between conventional and minimum tillage, with frequent additions of OM, to enhance several aspects of soil quality, and reduce disease and yield problems that can occur with continuous minimum tillage. © 2004 Elsevier B.V. All rights reserved.

Comparative effects of annual and permanent dairy pastures on soil physical properties in the Tsitsikamma region of South Africa

Abstract. The effects of grazed, annual ryegrass pasture (annually tilled with a rotary cultivator) and permanent kikuyu pasture were compared with that of undisturbed native vegetation at four sites in the Tsitsikamma region, South Africa. Soil organic carbon content, aggregate stability, saturated hydraulic conductivity, air permeability, root length density and rooting depth were all less under ryegrass than kikuyu pasture. There was, however, no consistent effect of pasture‐type on pore size distribution or penetrometer resistance. Differences in penetrometer resistance were most obvious in the 10–30 cm layer with subsurface compaction being evident at some sites under both types of pasture. This was attributed to the treading effects of grazing cattle plus formation of a compacted layer at the depth of tillage under ryegrass pastures. Subsoil tillage of a ryegrass pasture resulted in a substantial reduction in penetrometer resistance in the compacted 10–20 cm layer and increases in hydraulic conductivity, air permeability, root length density and rooting depth. We conclude that conversion from conventional to zero tillage is a potential way of improving the sustainability of annual pasture production and that the extent of subsoil compaction under both pasture types needs further investigation.

Modeling the soil water balance based on time-dependent hydraulic conductivity under different tillage practices

A simulation model with time-dependent hydraulic conductivity parameters was used to predict the effects of three different tillage practices: conventional tillage (CT), no-tillage (NT) and subsoiling tillage (ST) on the components of the soil water balance during the summer maize growing season. The predictive capability of the model was improved, particularly for the subsoiling tillage case. The simulation results show that temporal changes in soil hydraulic conductivity induced by different tillage practices can affect percolation, water storage, transpiration and evaporation. Differences in the simulated components of the water balance were found to be small between CT and NT practices, but larger in the ST case. Compared with the conventional and no-tillage methods, subsoiling promotes infiltration and deep percolation, thereby favoring a possible recharge of the groundwater. Actual evaporation is always lower in the subsoiled plots, whatever the hydrological year. Transpiration is similar for the three treatments, suggesting no significant differences in water availability, except in wet years where it is higher in subsoiled soils.

Response of Soybean Sudden Death Syndrome to Subsoil Tillage.

The soilborne pathogen Fusarium solani f. sp. glycines causes sudden death syndrome (SDS) of soybean. Previous research indicated that soil compaction related directly to disease foliar symptoms. Therefore, we hypothesized that decreasing soil compaction would increase soil porosity and provide a more aerated root zone that would hinder root infection by the fungus and decrease SDS foliar symptom severity. Two experimental areas (110 by 120 m) were established to evaluate the relationship between soil variables and SDS. Across the experimental area, strips (9.14 m wide) were subsoiled perpendicular to soybean rows to a depth of 40 to 45 cm, which alternated with strips that were not tilled. In both 1999 and 2000, subsoiling dramatically reduced foliar symptoms of SDS. Compared with no-till plots, subsoiled plots had lower soil bulk density, greater soil porosity, and less soil moisture. In areas where SDS occurs and soil compaction exists, the use of subsoiling can be used to reduce severity of foliar symptoms of SDS.

Soil Bulk Density and Penetration Resistance under Different Tillage and Crop Management Systems and Their Relationship with Barley Root Growth

To study the effects of fallow and tillage on soil physical properties and barley (Hordeum vulgare L.) root growth, an experiment was conducted for several years on two soils of contrasting depth: deep, a Fluventic Xerochrept of 120‐cm depth, and shallow, a Lithic Xeric Torriorthent of 30‐cm depth. Subsoil tillage (ST), minimum tillage (MT), and no‐tillage (NT) were compared in the deep soil and MT and NT in the shallow soil. Bulk density (BD), penetration resistance, gravimetric water content, gravel content, and root length density were determined at several times during the year. In the deep soil, BD was lower in the fallow and crop‐after‐fallow plots (1.26 Mg m−3) than in the continuous‐crop plots (1.32 Mg m−3). In this soil, NT showed the largest bulk densities (mean of 1.34 Mg m−3), followed by MT (mean of 1.27 Mg m−3) and ST (mean of 1.22 Mg m−3). Larger penetration resistance was found in NT than in ST and MT in both soils soon after tillage operations. However, root length density profiles sometimes showed greater values for NT than for the other tillage systems, revealing a good soil condition for root growth under NT. Therefore, an increase in soil strength is observed under NT in the first years after its introduction that does not greatly affect root growth in well‐structured soils. Fallow reduces soil strength due to the effect of tillage and natural loosening factors like drying and wetting cycles or fauna activity. This effect extends to the following crop.

Remediation of subsoil compaction and compaction effects on corn N availability by deep tillage and application of poultry manure in a sandy-textured soil

Subsoil compaction may reduce the availability and uptake of water and plant nutrients thereby lowering crop yields. Among the management options for remediating subsoil compaction are deep tillage and the selection of crop rotations with deep-rooted crops, but little is known of the effects of applications of organic amendments on subsoil compaction. The objectives of this study were to determine the effects of subsoil compaction on corn yield and N availability in a sandy-textured soil and to evaluate the use of deep tillage and surface applications of poultry manure to remediate subsoil compaction. A field experiment planted to corn ( Zea mays L.) was conducted from 2000 to 2001 on a Reelfoot fine sandy loam (fine-silty, mixed thermic Aquic Argiudolls) formed in silty alluvium located in southeast Missouri near the Mississippi River. Treatments were arranged in a factorial design with three levels of subsoil compaction and subsoiling and four rates (averaging 0, 6, 11 and 18 Mg ha −1) of poultry manure. Subsoil tillage to a depth of 30 cm had multiple effects, including overcoming a natural or tillage-induced dense layer or pan and increasing volumetric soil water content and crop N uptake, especially in the 2001 cropping year with low early season precipitation. N recovery efficiency (NRE) was significantly higher in the subsoil treatment compared to the highest compaction treatment in 2001. No significant interactions between manure rates and compaction and subsoiling treatments were observed for corn grain and silage yields, N uptake and NRE. Average increases in corn grain yields over all manure rates due to subsoil tillage of compacted soil were 2002 kg ha −1 in 2000 and 3504 kg ha −1 in 2001. Application of poultry manure had a consistent positive effect on increasing grain yields and N uptake in 2000 and 2001 but did not significantly alter measured soil physical properties. The results of this study suggest that deep tillage and applications of organic amendments are management tools that may overcome restrictions in both N and soil water availability due to subsoil compaction in sandy-textured soils.

Soil Bulk Density and Penetration Resistance under Different Tillage and Crop Management Systems and Their Relationship with Barley Root Growth

To study the effects of fallow and tillage on soil physical properties and barley (Hordeum vulgare L.) root growth, an experiment was conducted for several years on two soils of contrasting depth: deep, a Fluventic Xerochrept of 120-cm depth, and shallow, a Lithic Xeric Torriorthent of 30-cm depth. Subsoil tillage (ST), minimum tillage (MT), and no-tillage (NT) were compared in the deep soil and MT and NT in the shallow soil. Bulk density (BD), penetration resistance, gravimetric water content, gravel content, and root length density were determined at several times during the year. In the deep soil, BD was lower in the fallow and crop-after-fallow plots (1.26 Mg m−3) than in the continuous-crop plots (1.32 Mg m−3). In this soil, NT showed the largest bulk densities (mean of 1.34 Mg m−3), followed by MT (mean of 1.27 Mg m−3) and ST (mean of 1.22 Mg m−3). Larger penetration resistance was found in NT than in ST and MT in both soils soon after tillage operations. However, root length density profiles sometimes showed greater values for NT than for the other tillage systems, revealing a good soil condition for root growth under NT. Therefore, an increase in soil strength is observed under NT in the first years after its introduction that does not greatly affect root growth in well-structured soils. Fallow reduces soil strength due to the effect of tillage and natural loosening factors like drying and wetting cycles or fauna activity. This effect extends to the following crop.