Tillage Depth Effects on Soil Physical Properties,Sugarbeet Yield,and Sugarbeet Quality

Tillage depth influences the soil–water–plant ecosystem, thereby affecting crop yield and quality. The effects of tillage depth on soil physical properties and sugarbeet (Beta vulgaris L.) yield and quality were evaluated. A field study composed of two tillage depths [10 cm, referred to as shallow (ST), and 20 cm, referred to as deep (DT)] was conducted on a Lihen sandy loam soil in spring 2007 at the Agricultural Research Service (ARS) irrigated research farm near Williston, North Dakota. Soil bulk density (ρ_b), gravimetric water content (θ_w), and saturated hydraulic conductivity (Ks) were measured three times during the growing season at four depth increments to 40 cm deep. Samples were taken approximately 0.5 m apart within the crop row of irrigated sugarbeet. Soil air-filled pore volume (ε_a) was calculated from soil bulk density and water content data. Soil penetration resistance (PR) was also measured in 2.5-cm increments to a depth of 35 cm. Roots were hand-harvested from each plot, and each sample consisted of the roots within an area consisting of two adjacent rows 1.5 m long. Soil ρ_b was greater in ST than in DT, whereas Ks was greater with DT than with ST. Soil PR was significantly greater in ST than in DT at the 0- to 20-cm depth. Soil θ_w and ε_a were slightly greater in DT than those under ST. Although tillage depth had no significant effect on sugarbeet population, root yield, or sucrose content, a small difference in sucrose yield between two depths of tillage may be attributed to reduced ρ_b, increased water intake, improved aeration, and increased response to nitrogen uptake under DT than under ST. It was concluded that tillage depth enhanced soil physical quality and had little effect on sugarbeet yield or quality.     

Soil macroporosity,hydraulic conductivity and air permeability of silty soils under long-term conservation tillage in Indiana

With the increasing use of conservation tillage, many questions about the long-term effects of tillage system on soil physical properties have been raised. Studies were conducted to evaluate saturated hydraulic conductivity (K_SAT), macropore characteristics and air permeability of two silty soils as affected by long-term conservation tillage systems in the state of Indiana. Measurements were taken during the tenth year of a tillage study on a Chalmers silty clay loam (Typic Haplaquoll) and the fifth year of a study on a Clermont silt loam (Typic Ochraqualf). Tillage systems were moldboard plow, chisel, ridge till-plant, and no-till in a rotation of corn (Zea mays L.) and soya beans (Glycine max L.). Saturated hydraulic conductivity was measured on large soil columns (25 × 25 × 40 cm) before spring tillage, and macropore size and continuity were assessed with staining techniques. Intact soil cores (8 cm diam × 10 cm) were collected in early July in the row and non-trafficked interrow at three depths (10–20, 20–30, and 30–40 cm) and were analyzed for air permeability (K_air), air-filled porosity and bulk density. Saturated hydraulic conductivity values were in the order plow > chisel > ridge till > no-till for the Chalmers soil and were significantly greater in the plow treatment than in the other 3 tillage systems on the Clermont soil. Differences in K_SAT between the 2 soils were generally greater than differences among tillage systems, and coefficients of variation were lower for treatments that did not include may fall tillage operations. At the 10-cm depth on the Chalmers soil, the chisel treatment had the greatest number of stained cylindrical channels, whereas for the Clermont soil the ridge till had the greatest number at this depth. Although the no-till treatment had similar or fewer total channels, it had the most continuous channels from the 10-cm depth to the 20- and 30-cm depths on both soils. Tillage system, row position and depth all affected K_air. On the Chalmers soil, plow, chisel and ridge systems had lower K_air between rows than in the row at the 10–20-cm depth, whereas no-till had constant K_air in the row and between the row. On the Clermont soil, ridge till had the highest K_air of all treatments at the 10–20-cm depth, and no-till had the highest K_air of all treatments at the 20–30-cm depth.     

耕作对土壤生物碳动态变化的影响

本文讨论了耕作方法对作玉米地土壤生物碳动态变化的影响。实验证明，传统耕法、短期免耕和长期免耕处理中的不同点位，土壤生物碳量分布有系统的差异。     

Use of a surface gamma-neutron gauge for in situ measurement of changes in bulk density of the tilled zone

Short-term temporal changes in bulk density and related soil-water properties of a tilled soil may appreciably influence the processes of infiltration, soil water storage, runoff and erosion. Using a properly-calibrated surface gamma-neutron gauge, the changes in bulk density and moisture content within the topsoil layer can be measured in situ and at a large number of locations, with a minimum amount of time and expense. In this study on a Bernow loam soil (Typic Paleudult), factory calibration for either the neutron or the gamma component of a Troxler gauge was found unsatisfactory when compared with soil cores. Field calibration was obtained for both these components. Two different methods tried for gamma calibration gave satisfactory and nearly the same results. These findings generally agreed with the results for two other soils, whose data were available from an earlier study. Using field calibrations, soil bulk density was measured weekly at several sites within 4 freshly-tilled plots, one left bare, two planted to corn and one to soya bean, in depth intervals of 0–10, 10–20 and 20–30 cm. The plots were irrigated 3 days before each measurement. Over a 15-week period, the major changes in bulk density occurred only within the 0–10-cm layer, and these changes were strongly correlated with the amount of water applied. The presence of crops did not significantly influence these changes measured in the interrow areas. However, some additional data in the 0–10-cm layer indicated that roots may modify soil bulk density in the crop row and interrow areas differently. Measurements of this type serve to provide important information for improving soil and water management.     

Soil microbial population and nitrogen-transforming bacteria from 11-year sorghum tillage plots

Soil tillage alters crop residue placement, soil moisture and soil physical properties, which in turn may affect soil chemical and microbial properties. The impact of tillage on microbial populations was investigated by studying soil microbiological, physical and chemical properties after 11 years of a tillage management experiment with continuous sorghum (Sorghum bicolor L. Moench) on an Orelia sandy clay loam (fine-loamy, mixed, hyperthermic Typic Ochraqualf). Soil from 0–7.5 and 7.5–15 cm depths was sampled from four replications of moldboard plow (MB), conventional till (CT), minimum till (MT) and no-till (NT) treatments in March (before planting) and May (during the growing season), 1989. Heterotrophic bacteria (HB) and actinomycete populations differed among tillage treatments before planting. Soil microbial populations differed with soil depth among all tillage treatments before the growing season (when no plants were present), but were similar among tillage treatments when counts by soil depth were composited, indicating that, although microbial distribution differed, total populations were similar. During the growing season, actinomycetes were lower in NT treatments, while HB counts were not significantly different between treatments. The similarity between treatments was attributed to drier soil conditions and the effect of plant roots in all treatments, which may have stimulated microbes similarly in all treatments. Ammonium oxidizers were lowest and dentrifiers highest in the NT soil a the 0–7.5 cm depth before planting. The sample obtained during the growing season indicated that soil nitrifier populations were usually greater in MT and NT treatments. The MB and CT treatments had significantly larger amounts of soil moisture, clay and nitrate than the NT and MT treatments, indicating that soil physical properties and nitrate levels were altered by tillage treatment. Soil nitrate was significantly correlated with nitrogen-transforming bacteria in several instances, although there was no predictable effect from soil depth or sampling date. In some instances, nitrifier counts fell and denitrifier counts increased as soil nitrate increased. HB and actinomycete population levels were not significantly correlated with the soil physical or chemical properties measured in this study. Although there were tillage treatment differences in soil physical (moisture, bulk density and clay content), chemical (nitrate-nitrogen, NO₃---N) and microbiological properties (HB, actinomycetes, and denitrifier, nitrifier and ammonium oxidizer activity), generalizations about tillage system effects on soil microbiological properties were difficult to confirm because of the temporal nature of these differences.     

玉米农田行尺度土壤热特性变异特征及其对土壤含水量和温度的响应

农田土壤热特性受地表能量平衡、土壤特性和作物生长的影响,存在显著的时空变异性,而目前缺乏关于作物行尺度土壤热特性变异特征的研究。本研究采用定位试验,利用热脉冲技术监测了玉米农田行尺度四个位置处（1/2行间、1/4行间、棵下和棵间）两个深度（2 cm和4.5 cm）土壤热特性的时空变异规律,并分析了土壤温度和含水量对土壤热特性的影响。结果表明,在试验期间,热导率、热容量和热扩散率的变化范围分别为0.66—2.22 W/(m?K),1.46—4.49 MJ/(m3?K)和4.07×10-7—6.88×10-7 m2/s。降雨之后,热导率和热容量增加,且随着时间推移逐渐降低。2 cm深度的土壤热特性的波动较大,棵下位置土壤热导率和热容量值最大,波动最为明显;土壤热扩散率在1/2行间位置最大。在4.5 cm深度,各位置土壤热特性变化趋势基本一致,土壤热导率和热容量值在1/2行间位置最大,土壤热扩散率在棵间位置最大。综合两个土层数据得出1/4行间位置的热导率和热容量更具代表性。本研究中土壤热特性对土壤含水量的响应规律较为明显,随着土壤含水量增加,热导率和热容量线性增加,热扩散率则表现出先增加后降低的规律。在测定的土壤温度范围内,热扩散率随土壤温度增加呈上升趋势。该研究可以为农田水热管理提供理论依据。     

Plant-water relations,crop growth and grain yield of spring barley in relation to tillage methods

The influence of tillage methods on plant water status was measured in spring barley on a sandy loam soil (Wighill series) in 1976. Three methods of tillage were used: direct drilling, tine cultivation to 12.5 cm depth, and moldboard plowing to 20 cm depth. Soil bulk density was higher in the 0–5 and 5–10 cm layers of the direct-drilled plots. Soil strength was also higher in the direct-drilled plots to 22.8 cm depth compared with plowed plots, and to 15.2 cm depth compared wiht tine-cultivated plots. Thje only significant effect on soil water content (measured to 90 cm depth) was between 80 and 114 days from planting when extraction from the 0–10 cm depth was greater in the direct-drilled plots compared with the plowed plots, and at 20 cm depth greater in plowed plots than in direct-drilled plots. There were no significant differences between tillage methods in leaf water potential, above-ground dry matter produced, and grain yield.     

Soil Physical Properties and Bromide Movement in Relation to Tillage System

Abstract

Conventional (CT) and no‐tillage (NT) effects on soil physical properties and bromide (Br) movement were studied at two locations in North Carolina. The soils were a Norfolk sandy loam (fine‐loamy, siliceous, thermic Typic Paleudult) at a North American eastern Coastal Plain location and a Pacolet sandy clay loam (clayey, kaolinitic, thermic Typic Kanhapludult) at a Piedmont location. Bulk density (Db), macroporosity (Mp), and saturated hydraulic conductivity (Ks) were measured in the plant row (R) and trafficked (T) or untrafficked (N) interrow positions. Simulated rain was applied at two intensities to 1?m² plots after KBr was surface applied. The first simulated rain (30 min) consisted of a low (1.27 cm h^?1) or a high (5.08 cm h^?1) intensity applied 24 h after Br application. One week later, the high rainfall rate was repeated on all plots. Soil samples for Br determinations were taken 2 days after each rain simulation event to a depth of 40 cm and at the end of the growing season to 120 cm. Soil physical properties were affected by both tillage and position. Bulk density was greater for NT than for CT and in the T compared with R and N row positions. Mp was significantly greater in NT than CT at Coastal Plain location, but the results were opposite at the Piedmont location. Saturated hydraulic conductivity was highly variable ranging from 0.36 cm h^?1 to 14.4 cm h^?1 at the Coastal Plain location and from 0.06 cm h^?1 to 7.12 cm h^?1 at the Piedmont location. Saturated hydraulic conductivity at T position was about 100% lower than Ks at N and R positions, but the effect of tillage system was not significant on Ks. The surface 10 cm of soil contained the greatest Br concentration for both tillage systems. For the first and second sampling dates, greater Br movement occurred under NT vs. CT. However, no significant differences were observed in Br movement in the end of season sampling. Because of the coarser soil texture, greater Ks and Mp at the Coastal Plain location, Br moved, to a greater depth at this site than at the Piedmont site.     

Rainfall and tillage effects on soil structure after alfalfa conversion to maize on a clay loam soil in New York

Soil degradation is accelerated when perennial crops are converted to annual row crops, primarily due to increased soil disturbance from tillage. Subsequent heavy rainfall may induce soil settling, reduce macroporosity and increase hardsetting upon drying. An experiment involving plow and no-tillage and two simulated rainfall treatments (‘wet’ and ‘dry’) was conducted on Kingsbury clay loam soil in northern New York in 1992 and 1993 to study their effects on soil structure under maize (Zea mays L.) after conversion from alfalfa (Medicago sativa L.), and to evaluate the use of spectral analysis of micropenetrometer observations for studying soil aggregation. Undisturbed soil cores were collected from the row and trafficked and non-trafficked interrow positions at the 0.05 and 0.15 m depths and used for laboratory measurement of soil strength and pore system properties. These well-structured soils show a high contribution (up to 0.15 m³ m⁻³) of macropores to the total porosity of the soil. Soil strength was generally slightly higher for no-till (NT) than plow till (PT), although only significant in 1992. Soil strength in the surface layer did not change significantly with drying. Spectral density patterns did not show strong treatment effects, although distinct peaks reflect 3.0–3.5 mm stable structural units within macroaggregates. Simulated rainfall treatments and tillage treatments generally did not strongly affect measured soil properties, presumably due to stable soil structure. Structurally stable clay loam soils show little effect of tillage or settling on soil physical properties in the first years after alfalfa to maize conversion, and have good potential for long-term annual crop production if properly managed.     

Soil Hydraulic Properties: Influence of Tillage and Cover Crops

Understanding the effects of cover crops and tillage on soil physical properties is important for determining soil productivity. This study was conducted at Lincoln University's Freeman Center, USA to evaluate the effects of tillage and cover crop management on soil hydraulic properties. The field site included three replicate blocks in a randomized complete block design with each plot measuring 21.3 m in length and 12.2 m in width. Treatment factors were tillage at two levels(moldboard plow tillage vs. no tillage) and cover crop at two levels(cereal rye(Secale cereal) cover crop vs. no cover crop). Soil samples were collected in late spring/early summer from each treatment at 10-cm depth increments from the soil surface to a depth of 40 cm using cores(76.2-mm diameter and 76.2-mm length). Soil bulk density was 13% lower with tillage compared with no-tillage. Volumetric water content was significantly higher at 0.0 and -0.4 k Pa pressures with tillage compared with no tillage. Tillage increased the proportion of coarse mesopores by 32% compared with no tillage, resulting in 87% higher saturated hydraulic conductivity(K_(sat)). Cover crop increased the proportion of macropores by 24% compared with no cover crop; this can potentially increase water infiltration and reduce runoff. As a result of higher macroporosity, Ksat was higher under cover crop compared with no cover crop. This study demonstrated that tillage can benefit soil hydraulic properties in the short term, but these effects may not persist over time. Cover crops may slightly improve soil hydraulic properties, but longer term studies are needed to evaluate the long-term effects.     

Soil compressibility and penetrability of an Oxisol from southern Brazil, as affected by long-term tillage systems

The precompression stress value defines the transition from the reloading curve to the virgin compression line in the stress–strain curve, which can be used to quantify the highest load or the most intense predrying previously applied to the soil. Thus, in soils with well-defined structured soil horizons, each layer can be characterized by such mechanical strength. Penetration resistance measurements, on the other hand, can be used to determine total soil strength profiles in the field. The effect of long-term tillage systems on physical and mechanical properties was determined in undisturbed and remolded samples collected at 5 and 15 cm depth, 6 months after applying no-till (NT), chisel plow (CP), and conventional tillage (CT) treatments, along with the application of mineral fertilizer and poultry litter. The compressibility tests were performed under confined conditions, with normal loads varying from 10 to 400 kPa after a defined predrying to −6 or −30 kPa. Penetration resistance was determined in the field, after seeding, in three positions: seeding row (SR), untrafficked interrow (UI), and recently trafficked interrow (TI). No-till system showed greater soil resistance to deformation than tilled treatments, as determined by the higher precompression stress and lower coefficient of compressibility. When original soil structure was destroyed (remolded samples), smaller differences were found. The application of extra organic matter (poultry litter) resulted in a reduction of precompression stress in undisturbed samples. Penetration resistance profiles showed greater differences among tillage treatments in the upper layer of the untrafficked interrow, where NT system showed the higher values. Smaller differences were found in the seeding row (with lower values) and in recently trafficked interrow (with higher values), showing that even traffic with a light tractor after soil tillage reduced drastically the effect of previous tillage by loosening up the soil. On the other hand, the tool used to cut the soil and to open the furrow for seeding, incorporated in the direct seeding machine, was sufficient to realleviate surface soil compaction.     

Effect of planting date and tillage system on soybean root growth

Soil erosion and moisture retention are major concerns of soybean growers. Conservation tillage provides residue cover to reduce soil loss and water evaporation. This study was conducted on a Tiptonville silt loam near Portageville, MO, USA. to determine the effect of tillage system and planting date on soybean [Glycine max (L.) Merrill] root growth and distribution. Tillage systems were conventional (clean) tillage, ridge tillage, and no‐tillage. ‘Essex’ soybean was planted on 14 May, 15 June, and 7 July in 1992 and 12 May, 2 June, and 21 June in 1993. Roots were observed 30 and 60 days after emergence (DAE) using a minirhizotron system. Stand density was not affected by tillage in either year or by planting date in 1992. Tillage did not effect rooting depth in either year. In 1992, rooting depth 30 DAE was greater for the 14 May planting date than for either of the other two planting dates. No other planting date effects on rooting depth were found. Among soil depths, root length density (RLD) was greatest for the 14 to 26 cm depth in 1992 and for the 0 to 13 cm depth in 1993. Neither tillage system nor planting date affected RLD in either year and there was no interaction between these main effects and soil depths. The largest changes in RLD (CRLD) were observed in the 14 to 26 cm and 27 to 39 cm depths in 1992 and the 0 to 13 cm depth in 1993. Tillage did not planting date in 1992 and the 12 May and 2 June planting dates in 1993 produced the highest yields. Tillage did not affect yield and there was no interaction between tillage and planting date.     

Long-term cultivation effects on hydraulic properties of a Walla Walla silt loam

Hydraulic properties of a Walla Walla silt loam were significantly changed by 50 years or more of cultivation under either a wheat-peas rotation (tillage depth 30 cm) or a wheat-summerfallow rotation (tillage depth 15 cm) as compared with no cultivation. Soil pH was reduced to depths as great as 60 cm in the cultivated sites; dry bulk density was increased to depths as great as 40 cm. Expressions of these changes were greater in the wheat-peas rotation because tillage was deeper than in the wheat-summerfallow rotation. Small reductions in soil organic matter were also noted in the cultivated sites. In the 60- to 90-cm depth, all three sites had similar bulk density, pH, cation exchange capacity, soil texture, desorption water characteristic, and hydraulic conductivity. In the upper 40-cm layer the desorption water characteristic showed that cultivation produced more smaller pores at the expense of large pores; in the upper 30-cm layer of the cultivated soils hydraulic conductivity was reduced at least 10-fold for water potentials > −100 cm of H₂O. Steady-state drainage profiles and associated assumptions suggest that long-term cultivation increased the hydraulic gradient in the upper 35 cm, and that the low saturated conductivity of the 0- to 15-cm layer had an overall drying effect on the 15- to 35-cm layer. In the cultivated soils increased runoff and denitrification in the plow layer should both be expected and water relations in the 15- to 35-cm layer should favor microorganisms sensitive to high water potentials. Simulations suggested that long-term cultivation decreased evaporation rates an estimated 40% and in wet soil, increased the drying time needed to attain optimum moisture for tillage.     

Evaluation of temporal, spatial, and tillage-induced variability for parameterization of soil infiltration

Model simulation of water and chemical transport requires information on soil hydraulic properties. Recently, independent parameterization methods have been developed to characterize soil type, tillage, temporal and spatial effects of soils. This study determines the relative magnitude of tillage-induced, temporal (yearly and seasonal), and spatial (within fields and between rows) variability in a combined analysis of soil infiltration in an agricultural field and evaluates the appropriateness of various parameterization scenarios. Infiltration measurements were obtained in the row and interrow position under plow-tilled and ridge-tilled corn (Zea mays L.) in four replicates on multiple dates in a wetter (1990) and dryer year (1991). Measurements exhibited significant temporal variability within a growing season, especially in a dry year under plow till when soil cracking resulted in higher infiltration. Position with respect to the row was the most significant source of variability under ridge till, but not under plow till. Row and interrow differences in a ridge-tilled soil are the result of dense soil and lack of disturbance in the interrow. Yearly variations and field variability were relatively low. Differences between tillage practices were primarily expressed in variable susceptibility to spatial and temporal variation. Adequate parameterization of soil infiltration on agricultural fields requires recognition of various sources of variability under different tillage management systems, weather and climatic conditions, and soil types. High intrinsic variability of soil infiltration must be accounted for through increased sampling (e.g. duplicate measurements) and the use of stochastic methods.     

Spatial and temporal variability of some soil physical properties following tillage of a Nigerian Paleustult

The objective of this study was to evaluate quantitatively the magnitude of the spatial and temporal variation for 7 soil physical properties on a conventionally-tilled Nigerian Paleustult. A 0.4-ha plot was disc-ploughed, disc-harrowed twice, subjected to tractor-wheel traffic at regular space intervals and then seeded to maize (Zea mays, L.). There were significant differences in the physical properties owing to tillage position (spatial variability) and date of sampling (temporal variability), more so in the 0–10-cm layer than in the 10–20-cm layer. In the surface layer, bulk density (Db) and penetrometer resistance (PR) were significantly higher (P ⩽ 0.01) along the tyre marks (maximum Db = 1.76 Mg m⁻³) than in the uncompacted crop row (maximum Db = 1.35 Mg m⁻³) and interrow positions (maximum Db = 1.46 Mg m⁻³). Saturated hydraulic conductivity (K_sat), total porosity (TP) and macroporosity (M) were significantly lower along the tyre mark than in the crop row and interrow positions. K_sat ranged from 0.6 to 42.8 cm h⁻¹, TP, from 0.34 to 0.50 cm³ cm⁻³ and M from 0.06 to 0.25 cm³ cm⁻³ along the tyre mark and crop row positions, respectively. Significant temporal changes were noticed only in K_sat, soil moisture content (MC) and PR. K_sat increased steadily with time along the tyre mark, but showed an irregular trend in the other two positions. PR did not change with time along the tyre marks but it increased significantly with time along the other two positions. MC changed according to the periodicity of rainfall. Only TP varied, owing to tillage position × date interaction. The 10–20-cm layer was spatially less variable but temporally more viarable than the surface layer. Only K_sat and PR showed significant changes owing to the tillage positions, but Db, K_sat, PR and moisture retained at 10 kPa suction (τv10) showed significant temporal changes. Only τv110 varied owing to position × date interaction in this layer.     

Effects of in-row and interrow subsoiling and time of nitrogen application on growth, stomatal conductance and yield of strip-tilled corn

The use of in-row subsoilers in conservation tillage systems in soils underlaid by tillage pans increases rooting depth, root proliferation and water infiltration. Interrow subsoiling 5 weeks after planting, to coincide with sidedress nitrogen applications, might be a practical method for further increasing infiltration of water from irrigation and high-intensity showers. Corn (Zea mays L.) was strip-till planted and grown under irrigation for 2 years at one location and 1 year at another to study the effects of subsoiling, placement and timing of nitrogen application (157 kg ha⁻¹) on plant growth, stomatal conductance and yield. Treatments included (1) not subsoiled, N applied at planting; (2) subsoiled in-row at planting, N applied at planting; (3) not subsoiled, N applied 5 weeks after planting; (4) subsoiled in-row at planting, N applied 5 weeks after planting; (5) subsoiled interrow, and N applied 5 weeks after planting; and (6) subsoiled in-row at planting and interrow 5 weeks after planting, N applied 5 weeks after planting. Nitrogen applied 5 weeks after planting resulted in higher yields than when applied at planting. In-row subsoiling at planting, interrow subsoiling 5 weeks after planting and subsoiling in-row at planting plus interrow 5 weeks later resulted in increased stomatal conductance between irrigations. Delaying N application resulted in decreased stomatal conductance in treatments that were in-row subsoiled at planting. Grain yields were lower without than with subsoiling, especially when N was applied at planting. When water was not limiting, subsoiling interrow 5 weeks after planting was as effective in increasing grain yield as in-row subsoiling at planting. In one test, the highest grain yield (9.96 t ha⁻¹) resulted from the cumulative effect of subsoiling in-row at planting plus interrow 5 weeks later.     

Soil penetrometer resistance and bulk density relationships after long‐term no tillage

Abstract

Soil penetrometer resistance (SPR) and bulk density (p) measurements can be used for assessing soil strength or density. Results from this research add to the understanding of residual soil compaction of sandy soils by answering three questions: What are the long term effects of no‐tillage on SPR and p in a double‐cropping rotation? Where in the soil profile are maximum SPR and p values found? How much of the variations in SPR are accounted for by the regression of p? Compaction was evaluated at the end of an 8‐yr oat (Avena sativa L.)/Bragg soybean [Glycine max (L.) Merr.] double‐cropping tillage experiment. The soil was Arredondo fine sand (Grossarenic Paleudults). The four treatments (replicated four times) included no‐tillage (NT), conventional tillage (CT), no‐tillage plus in‐row subsoiling (NTPS), and conventional tillage plus in‐row subsoiling (CTPS). Forty days after planting soybeans the soil was irrigated to field capacity. Readings were taken to a depth of 60 cm at five positions in the row and at 15 and 30 cm from the row on both traffic and no traffic sides of four rows. Samples for p and soil water content (6) were collected at three positions and 12 depths. The SPR data were analyzed as a split‐split‐split plot design and the p and 8 data as split‐split‐plot design. The most significant overall long‐ term effect of no‐tillage compared to conventional tillage occurred at the 15‐cm depth for SPR and in the 5‐ to 10‐cm depth for p. The increases were 19% for SPR and 11% for p. Maximum SPR (3.1 MPa) and p (1.6 Mg/m³) occurred in the 25‐ to 35‐cm depth. Wheel traffic increased SPR more than 35% in the upper 25 cm of soil, whereas p was increased less than 3%. This indicates SPR was 10 times more sensitive as an indicator of soil compaction than was p. Penetrometer resistance was predicted from an equation, in which p accounted for 24%, depth 30%, and depth‐squared 25% of the variation in SPR. The R² for the model was 0.82 (P < 0.01).     

Least limiting water range for different soil management practices in dryland farming in Iran

Integrated evaluation of soil physical properties using the least limiting water range (LLWR) approach may allow a better knowledge of soil water availability. We determined the LLWR for four tillage practices consisted of conventional tillage (CT), reduced tillage (RT), no-tillage (NT) and fallow no-tillage (NT_f). In addition, LLWR was determined for abandoned soils (i.e. control), compacted soils, ploughed compacted soils and abandoned soils with super absorbent polymers (SAPs) application. Soil water retention, penetration resistance (PR), air-filled porosity and bulk density were determined for the 0–5 and 0–25-cm depths. Mean LLWR (0.07–0.08 cm³ cm^?3) was lower in compacted soils than the soils under CT, NT, NT_f, RT, tilled, abandoned and SAP practices but it was not different among tillage practices. The values of LLWR were 0.12 cm³ cm^?3 for NT and CT. LLWR for tilled plots (0.12 cm³ cm^?3) became greater than compacted soils by 1.3 times. Analysis of the lower and upper limits of the LLWR further indicated that PR was the only limiting factor for soil water content, but aeration was not a limiting factor. The LLWR was more dependent on soil water content at permanent wilting point and at PR.     

Contrasting grain crop and grassland management effects on soil quality properties for a north-central Missouri claypan soil landscape

Abstract

Crop management has the potential to either enhance or degrade soil quality, which in turn impacts on crop production and the environment. Few studies have investigated how crop management affects soil quality over different landscape positions. The objective of the present study was to investigate how 12 years of annual cropping system (ACS) and conservation reserve program (CRP) practices impacted soil quality indicators at summit, backslope and footslope landscape positions of a claypan soil in north-central Missouri. Claypan soils are particularly poorly drained because of a restrictive high-clay subsoil layer and are vulnerable to high water erosion. Three replicates of four management systems were established in 1991 in a randomized complete block design, with landscape position as a split-block treatment. The management systems were investigated: (1) annual cropping system 1 (ACS1) was a mulch tillage (typically ≥ 30% of soil covered with residue after tillage operations) corn (Zea mays L.)–soybean (Glycine max (L.) Merr.) rotation system, (2) annual cropping system 2 (ACS2) was a no-till corn–soybean rotation system, (3) annual cropping system 3 (ACS3) was a no-till corn–soybean–wheat (Triticum aestivum L.) rotation system, with a cover crop following wheat, (4) CRP was a continuous cool-season grass and legume system. In 2002, soil cores (at depths of 0–7.5, 7.5–15 and 15–30 cm) were collected by landscape position and analyzed for physical, chemical and biological soil quality properties. No interactions were observed between landscape and crop management. Relative to management effects, soil organic carbon (SOC) significantly increased with 12 years of CRP management, but not with the other management systems. At the 0–7.5-cm soil depth in the CRP system, SOC increased over this period by 33% and soil total nitrogen storage increased by 34%. Soil aggregate stability was approximately 40% higher in the no-till management systems (ACS2 and ACS3) than in the tilled system (ACS1). Soil aggregation under CRP management was more than double that of the three grain-cropping systems. Soil bulk density at the shallow sampling depth was greater in ACS3 than in ACS1 and ACS2. In contrast to studies on other soil types, these results indicate only minor changes to claypan soil quality after 12 years of no-till management. The landscape had minor effects on the soil properties. Of note, SOC was significantly lower in the 7.5–15-cm soil depth at the footslope compared with the other landscape positions. We attribute this to wetter and more humid conditions at this position and extended periods of high microbial activity and SOC mineralization. We conclude that claypan soils degraded by historical cropping practices will benefit most from the adoption of CRP or CRP-like management.     

科学耕作与留茬改良小麦-玉米两熟农田土壤物理性状及增产效果

为了探讨不同覆盖耕作方式对农田土壤物理性状及作物产量的影响,该试验研究了免耕、常规2种耕作方式和4种留茬高度的玉米秸秆还田处理,对麦-玉两熟农田土壤含水率、容重、孔隙度以及作物产量的影响。结果表明:在0～40cm土层内,秸秆还田的集雨和保水效果显著,免耕留茬0.5m还田处理的含水率比免耕无覆盖处理增加了15.95%。秸秆还田量对0～40cm内土壤贮水量的影响不同。耕作措施显著影响了土壤容重,小麦播种前常规留茬1m还田、常规全量还田处理容重低至1.0g/cm3左右。秸秆还田能增加土壤总孔隙度、降低毛管与非毛管孔隙度的比值。单一免耕处理降低了作物产量,而免耕覆盖能增产,其留茬1m还田处理比无还田处理增产22.44%,比常规留茬0.5m还田处理高3.64%。因此,免耕留茬1m还田处理在改善农田土壤物理性状和增加作物产量方面显著,该研究可为农田管理过程中耕作措施和秸秆还田量的选择提供参考依据。