Effect of tillage and crop rotations on pore size distribution and soil hydraulic conductivity in sandy clay loam soil of the Indian Himalayas

Tillage management can affect crop growth by altering the pore size distribution, pore geometry and hydraulic properties of soil. In the present communication, the effect of different tillage management viz., conventional tillage (CT), minimum tillage (MT) and zero-tillage (ZT) and different crop rotations viz. [(soybean–wheat (S–W), soybean–lentil (S–L) and soybean–pea (S–P)] on pore size distribution and soil hydraulic conductivities [saturated hydraulic conductivity (K_sat) and unsaturated hydraulic conductivity {k(h)}] of a sandy clay loam soil was studied after 4 years prior to the experiment. Soil cores were collected after 4 year of the experiment at an interval of 75 mm up to 300 mm soil depth for measuring soil bulk density, soil water retention constant (b), pore size distribution, K_sat and k(h). Nine pressure levels (from 2 to 1500 kPa) were used to calculate pore size distribution and k(h). It was observed that b values at all the studied soil depths were higher under ZT than those observed under CT irrespective of the crop rotations. The values of soil bulk density observed under ZT were higher in 0–75 mm soil depth in all the crop rotations. But, among the crop rotations, soils under S–P and S–L rotations showed relatively lower bulk density values than S–W rotation. Average values of the volume fraction of total porosity with pores <7.5 μm in diameter (effective pores for retaining plant available water) were 0.557, 0.636 and 0.628 m³ m⁻³ under CT, MT and ZT; and 0.592, 0.610 and 0.626 m³ m⁻³ under S–W, S–L and S–P, respectively. In contrast, the average values of the volume fraction of total porosity with pores >150 μm in diameter (pores draining freely with gravity) were 0.124, 0.096 and 0.095 m³ m⁻³ under CT, MT and ZT; and 0.110, 0.104 and 0.101 m³ m⁻³ under S–W, S–L and S–P, respectively. Saturated hydraulic conductivity values in all the studied soil depths were significantly greater under ZT than those under CT (range from 300 to 344 mm day⁻¹). The observed k(h) values at 0–75 mm soil depth under ZT were significantly higher than those computed under CT at all the suction levels, except at −10, −100 and −400 kPa suction. Among the crop rotations, S–P rotation recorded significantly higher k(h) values than those under S–W and S–L rotations up to −40 kPa suction. The interaction effects of tillage and crop rotations affecting the k(h) values were found significant at all the soil water suctions. Both S–L and S–P rotations resulted in better soil water retention and transmission properties under ZT.     

Dynamics of soil hydraulic properties during fallow as affected by tillage

There is limited information on the effects of tillage practices on soil hydraulic properties, especially changes with time. The objective of this study was to evaluate on a long-term field experiment the influence of conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) on the dynamics of soil hydraulic properties over 3 consecutive 16–18 month fallow periods. Surface measurements of soil dry bulk density (ρ_b), soil hydraulic conductivity (K(ψ)) at −14, −4, −1 and 0 cm pressure heads using a tension disc infiltrometer, and derived hydraulic parameters (pore size, number of pores per unit of area and water-transmission porosity) calculated using the Poiseuille's Law were taken on four different dates over the fallow period, namely, before and immediately after primary tillage, after post-tillage rains and at the end of fallow. Under consolidated structured soil conditions, NT plots presented the most compacted topsoil layer when compared with CT and RT. Soil hydraulic conductivity under NT was, for the entire range of pressure head applied, significantly lower (P < 0.05) than that measured for CT and RT. However, NT showed the largest mean macropore size (0.99, 0.95 and 2.08 mm for CT, RT and NT, respectively; P < 0.05) but the significantly lowest number of water-conducting pores per unit area (74.1, 118.5 and 1.4 macropores per m² for CT, RT and NT, respectively; P < 0.05). Overall, water flow was mainly regulated by macropores even though they represented a small fraction of total soil porosity. No significant differences in hydraulic properties were found between CT and RT. In the short term, tillage operations significantly increased K (P < 0.05) for the entire range of pressure head applied, which was likely a result of an increase in water-conducting mesopores despite a decrease in estimated mesopore diameter. Soil reconsolidation following post-tillage rains reduced K at a rate that increased with the intensity of the rainfall events.     

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

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

Using the simplified falling head technique to detect temporal changes in field-saturated hydraulic conductivity at the surface of a sandy loam soil

Determining temporal changes in field-saturated hydraulic conductivity (K_fs) is important for understanding and modeling hydrological phenomena at the field scale. Little is known about temporal variability of K_fs values measured at permanent sampling points. In this investigation, the simplified falling head (SFH) technique was used for an approximately 2-year period to determine temporal changes in K_fs at 11 permanent sampling points established at the surface of a sandy loam soil. Additional K_fs measurements were obtained by the single-ring pressure infiltrometer (PI) technique to also compare the SFH and PI techniques. The lowest mean values of K_fs, M(K_fs), were detected in December and January (20.5 ≤ M(K_fs) ≤ 146.2 mm h⁻¹), whereas higher results (190.5 ≤ M(K_fs) ≤ 951.9 mm h⁻¹) were obtained in the other months of the year. The K_fs values were higher and less variable in the dry soil (θ_i ≤ 0.21 m³ m⁻³, M(K_fs) = 340.6 mm h⁻¹, CV(K_fs) = 106%) than in the wet one (θ_i > 0.21 m³ m⁻³, M(K_fs) = 78.4 mm h⁻¹, CV(K_fs) = 185%). Both wet and dry soil were less conductive at the end of the study period than at the beginning one but a more appreciable change was detected for the dry soil (K_fs decreasing by 83.4%) than for the wet one (K_fs decreasing by 63.0%). The simple SFH technique yielded K_fs results similar to the more laborious and time-consuming PI technique (i.e., mean values differing at the most by a factor of two). It was concluded that (i) the soil water content was an important factor affecting the K_fs results obtained in a relatively coarse-textured soil, (ii) the impact of time from the beginning of the experiment on the saturated hydraulic conductivity was larger for a repeated sampling of dry soil than of wet soil and (iii) the SFH technique yielded reliable K_fs results in a relatively short period of time without the need for extensive instrumentation or analytical methodology.     

Effect of tillage treatments on soil thermal conductivity for some Jordanian clay loam and loam soils

Soil thermal conductivity determines how a soil warms or cools with exchange of energy by conduction, convection, and radiation. The ability to monitor soil thermal conductivity is an important tool in managing the soil temperature regime to affect seed germination and crop growth. In this study, the temperature-by-time data was obtained using a single probe device to determine the soil thermal conductivity. The device was used in the field in some Jordanian clay loam and loam soils to estimate their thermal conductivities under three different tillage treatments to a depth of 20 cm. Tillage treatments were: no-tillage, rotary tillage, and chisel tillage. For the same soil type, the results showed that rotary tillage decreased soil thermal conductivity more than chisel tillage, compared to no-tillage plots. For the clay loam, thermal conductivity ranged from 0.33 to 0.72 W m⁻¹ K⁻¹ in chisel plowed treatments, from 0.30 to 0.48 W m⁻¹ K⁻¹ in rotary plowed treatments, and from 0.45 to 0.78 W m⁻¹ K⁻¹ in no-till treatments. For the loam, thermal conductivity ranged from 0.40 to 0.75 W m⁻¹ K⁻¹ in chisel plowed treatments, from 0.34 to 0.57 W m⁻¹ K⁻¹ in rotary plowed treatments, and from 0.50 to 0.79 W m⁻¹ K⁻¹ in no-till treatments. The clay loam generally had lower thermal conductivity than loam in all similar tillage treatments. The thermal conductivity measured in this study for each tillage system, in each soil type, was compared with independent estimates based on standard procedures where soil properties are used to model thermal conductivity. The results of this study showed that thermal conductivity varied with soil texture and tillage treatment used and that differences between the modeled and measured thermal conductivities were very small.     

Effect of deep tillage for vineyard establishment on soil structure: A case study in Southern France

Deep tillage that is used before vine plantation to remove old vine roots and loosen subsoil may induce physical soil degradation that could affect soil structure and vine water supply. The objective of the study was to experimentally evaluate the effect of deep tillage on soil structure. The impacts on soil structure of two deep tillage techniques, i.e. deep ploughing and ripper, and two contrasted soil water conditions were compared in a experimental field by combining morphological observations, bulk density and saturated hydraulic conductivity measurements. These three methods were found very complementary to analyse and discriminate the impact of the different treatments. The proportion of compacted zones and mean bulk density increased from the initial plot (0.15 m² m⁻², 1.45 Mg m⁻³) to a maximum in the case of the deep ploughing under wet conditions plot (0.60 m² m⁻², 1.60 Mg m⁻³). The main results showed that (i) a significant soil compaction was observed after wet conditions only, (ii) deep ploughing produced more soil compaction than ripper because of a greater volume of soil affected by wheeling in the former operation and (iii) a specific response of soils is significatively observed in the case of deep ploughing only with an increase of compacted zones fragmentation in relation to a decrease of clay content.     

Modification of soil structural and hydraulic properties after 50 years of imposed chaparral and pine vegetation

Although biotic communities have long been recognized as important factors in soil development, especially of A horizons, few studies have addressed their influence on soil physical properties in nonagricultural settings. A biosequence of 50-year-old soils supporting near monocultures of Coulter pine (Pinus coulteri), scrub oak (Quercus dumosa), and chamise (Adenostoma fasciculatum) was used to determine the relative influence of vegetation type and associated soil organisms on the development of soil structural characteristics and water flow. Total porosity ranged from a high of 51% in the heavily worm-worked A horizon under oak to a low of 39% within the 35- to 50-cm depth under pine, where earthworms were absent. Macroporosity (pores with diameters >300 μm) was highest in the A horizon under oak (15.6%) and lowest under pine (9.5%). Saturated hydraulic conductivity of surface soils ranged from 10.8 cm h⁻¹ under oak to 3.2 cm h⁻¹ under pine. Soil under chamise, which had fewer earthworms than that under oak, had K_sat and bulk density values intermediate between oak and pine. Root and macrofauna distributions suggest that roots are the dominant factor in the development of macroporosity under pine, while earthworms have had the greatest effect under oak. Porosity has increased at an average rate of 0.22% per year in the 0- to 7-cm depth under oak (from 41% to 56%), but has not been significantly altered within the same depth under pine. Below the 7-cm depth, porosity values are similar for each vegetation type and the original parent material. Available water capacity (AWC) within the first 0- to 7-cm depth has increased from the original values (about 0.11 m³ m⁻³) to 0.17 m³ m⁻³ under oak, 0.16 m³ m⁻³ under chamise, and 0.13 m³ m⁻³ under pine. The data show that the presence of burrowing macrofauna, which is determined by litter palatability and therefore indirectly controlled by vegetation, can significantly influence porosity, increasing the water-holding capacity of a soil.     

Moisture conservation for rainfed wheat production with alternative mulches and conservation tillage in the hills of north-west India

In the hills of north–west India, maize (Zea mays L.)-wheat (Triticum aestivum L.) is the dominant cropping system. However, rainfed wheat suffers from lack of optimum moisture at sowing. Field experiments were conducted for 3 years on a silty clay loam (Typic Hapludalf) to evaluate the effectiveness of mulches and conservation tillage for rainfed wheat in mitigating this problem. The treatments were ten factorial combinations of five mulch-tillage practices and two nitrogen levels (N₆₀ and N₁₂₀ kg ha⁻¹). Mulch treatments consisted of application of 10 Mg ha⁻¹ (dry weight basis), to previous standing maize, of either wild sage (Lantana camara L.) or eupatorium (Eupatorium adenophorum Sprengel) in combination with either conventional or conservation (minium) tillage prior to wheat sowing. These alternative practices were compared to the conventional farmer practice of soil tillage after harvest of maize with no mulch. The application of these weed mulches to standing maize maintained friable soil structure owing to a five fold higher mean population of earthworms underneath mulch. Mulches resulted in 0.06–0.10 m³ m⁻³ higher moisture in the seed-zone when wheat was sown compared with the conventional farmer practice of soil tillage after maize harvest. Mulch-conservation tillage treatments favourably moderated the hydro-thermal regime for growing a wheat crop. The mean root mass density under these treatments at wheat flowering was higher by 1.27–1.40 times over the conventional farmer practice during the 3 year study. Conservation tillage holds promise because it does not require elaborate tillage and may ultimately reduce animal draught in the hilly regions. Recycling available organic materials having no fodder value coupled with conservation tillage may help enrich the soil environment in the long-term. The practice also offers gainful use of these obnoxious weeds that cause great menace in grass and forest lands in the region.     

Effects of tillage systems on energy and carbon balance in north-eastern Italy

An energy analysis of three cropping systems with different intensities of soil tillage (conventional tillage, CT; ridge tillage, RT; no tillage, NT) was done in a loamy-silt soil (fulvi-calcaric Cambisol) at Legnaro, NE Italy (45°21′N, 11°58′E, 8 m above sea-level (a.s.l.), average rainfall 822 mm, average temperature 11.7°C). This and measurements of the evolution of the organic matter content in the soil also allowed the consequences to be evaluated in terms of CO₂ emissions.

The weighted average energy input per hectare was directly proportional to tillage intensity (CT > RT > NT). Compared with CT, total energy savings per hectare were 10% with RT and 32% with NT. Average energy costs per unit production were fairly similar (between 4.5 and 5 MJ kg⁻¹), with differences of 11%. The energy outputs per unit area were highest in CT for all crops, and lowest in NT. The RT outputs were on average more similar to CT (−12%). The output/input ratio tended to increase when soil tillage operations were reduced, and was 4.09, 4.18 and 4.57 for CT, RT and NT, respectively. As a consequence of fewer mechanical operations and a greater working capacity of the machines, there was lower fuel consumption and a consistently higher organic matter content in the soil with the conservation tillage methods.

These two effects result in less CO₂ emission into the atmosphere (at 0°C and pressure of 101.3–103 kPa) with respect to CT, of 1190 m³ ha⁻¹ year⁻¹ in RT and 1553 m³ ha⁻¹ year⁻¹ in NT. However, the effect owing to carbon sequestration as organic matter will decline to zero over a period of years.     

Effects of tillage and nitrogen management on soil chemical and physical properties after 23 years of continuous sorghum

Long-term tillage and nitrogen (N) management practices can have a profound impact on soil properties and nutrient availability. A great deal of research evaluating tillage and N applications on soil chemical properties has been conducted with continuous corn (Zea Mays L.) throughout the Midwest, but not on continuous grain sorghum (Sorghum bicolor (L.) Moench). The objective of this experiment was to examine the long-term effects of tillage and nitrogen applications on soil physical and chemical properties at different depths after 23 years of continuous sorghum under no-till (NT) and conventional till (CT) (fall chisel-field cultivation prior to planting) systems. Ammonium nitrate (AN), urea, and a slow release form of urea were surface broadcast at rates of 34, 67, and 135 kg N ha⁻¹. Soil samples were taken to a depth of 15 cm and separated into 2.5 cm increments. As a result of lime applied to the soil surface, soil pH in the NT and CT plots decreased with depth, ranging from 6.9 to 5.7 in the NT plots and from 6.5 to 5.9 in the CT plots. Bray-1 extractable P and NH₄OAc extractable K was 20 and 49 mg kg⁻¹ higher, respectively, in the surface 2.5 cm of NT compared to CT. Extractable Ca was not greatly influenced by tillage but extractable Mg was higher for CT compared to NT below 2.5 cm. Organic carbon (OC) under NT was significantly higher in the surface 7.5 cm of soil compared to CT. Averaged across N rates, NT had 2.7 Mg ha⁻¹ more C than CT in the surface 7.5 cm of soil. Bulk density (Δ_b) of the CT was lower at 1.07 g cm⁻³ while Δ_b of NT plots was 1.13 g cm⁻³. This study demonstrated the effect tillage has on the distribution and concentration of certain chemical soil properties.     

Short-term responses of soil physical properties to corn tillage-planting systems in a humid maritime climate

The fertile, but naturally poorly drained soils of the western Fraser Valley in British Columbia, Canada are located in an area subject to about 1200 mm of rainfall annually. These soils were under intensive conventional tillage practices for years, which contributed to their poor infiltrability, low organic matter, and overall poor structure. Development of tillage practices that incorporate winter cover crops and reduce traffic in spring is required to reduce local soil degradation problems. The objective of this study was to determine short-term responses of soil physical properties to fall and spring tillage (ST) and fall and no spring tillage (NST) systems, both using spring barley (Hordeum vulgare L.) and winter wheat (Triticum aestivum L.) as winter cover crops. Field experiments were conducted for 3 years following seeding of the winter cover crops in fall 1992 on a silty clay loam Humic Gleysol (Mollic Gleysol in FAO soil classification). Average aeration porosity was 0.15 m³ m⁻³ on NST and 0.22 m³ m⁻³ on ST, while bulk density was 1.22 Mg m⁻³ on NST and 1.07 Mg m⁻³ on ST at the 0–7.5 cm depth. Neither of these two soil properties should limit seedling and root growth. After ST, mechanical resistance was consistently greater for 500–1000 kPa in NST than in ST, but never reached value of 2500 kPa considered limiting for root growth. The NST system did not increase soil water content relative to ST, with soil water contents being similar at 10 and 40 cm depth in all years. In 2 out of 3 years NST soil was drier at the 20 cm depth than was ST soil. Three years of NST did not result in a significant changes of aggregate stability relative to ST. This experiment showed that limiting tillage operations to the fall did not adversely affect soil physical conditions for plant growth in a humid maritime climate.     

Effects of farmyard manure and tillage systems on soil physical properties and corn yield in central Iran

Tillage management and manure application are among the important factors affecting soil physical properties and crop yield. A 2-year field experiment was conducted on a silty clay loam soil (fine-loamy, mixed, thermic Typic Haplargids). Effects of two tillage systems (moldboard plowing as conventional tillage (T₁) and disk harrowing as reduced tillage (T₂)) at three farmyard manure rates (zero (M₁), 30 (M₂), 60 (M₃) Mg ha⁻¹) were studied on the soil physical properties and corn (Zea mays L.) yield. The experiment was carried out in split block design with three replications. Organic matter (OM) content, bulk density (BD), saturated hydraulic conductivity (K_S), aggregate mean weight diameter (MWD) and dry biomass yield (DBY) were measured after harvesting in the second year. Manure application increased OM on both the row and inter-row tracks significantly. Manure application rate of 60 Mg ha⁻¹ increased MWD (0.33, 0.40 and 0.75 mm for M₁, M₂ and M₃, respectively) at the 0–5 cm soil layer, but the effect was not significant below 5 cm depth. Adding manure significantly decreased soil BD on the row tracks (1.39, 1.22 and 1.17 Mg m⁻³ for M₁, M₂ and M₃ treatments, respectively), but did not have any significant effect on the inter-row tracks. Hydraulic conductivity was improved by manure applications both on the row and inter-row positions. Manure treatments M₂ and M₃ increased DBY compared to the M₁ treatment. Although moldboard plowing increased the depth of root penetration significantly (43 cm for T₁ and 30 cm for T₂), the effect of tillage systems on yield and soil physical properties was not significant.     

Soil-water and soil physical properties under contour hedgerow systems on sloping oxisols

Hedgerows planted along the contour on steep lands in the humid tropics reduce soil erosion and build terraces over time. The objectives of this study in two Hapludoxes in the Philippines were to evaluate changes after 4 years in soil properties and soil water relations on transects perpendicular to the cropped alleys between four grass and tree hedgerow systems and a control. Hedgerow plants included Gliricidia sepium, Paspalum conjugatum, and Penisetum purpureum. Soil properties evaluated as a function of position in the alley (upper, middle, or lower elevation in an alley) included bulk density, mechanical impedance, soil water transmissivity, water retention, soil water pressure, and soil water content. In general, soil properties were not affected by hedgerow system, but were affected by position in the alley. Nearness to the hedgerow, but not hedgerow species, affected soil water distribution (P = 0.05). Plant available water at the 10–15 cm depth was 0.16 m³ m⁻³, 0.13 m³ m⁻³, and 0.08 m³ m⁻³ for the lower, middle, and upper alley position, respectively. Water transmissivity decreased from 0.49 mm s⁻¹ in the lower alley to 0.12 mm s⁻¹ in the upper alley. The lower soil water contents and soil water pressures in and near the hedgerows confirmed competition for water between the hedgerow species and the food crop in the alley, a condition that is expected to suppress food crop production.     

Tillage and mulch effects on soil physical environment, root growth, nutrient uptake and yield of maize and wheat on an Alfisol in north-west India

Field experiments were conducted for 6 years on a silty clay loam to study the effect of soil management on soil physical properties, root growth, nutrient uptake and yield of rainfed maize (Zea mays L.) and wheat (Triticum aestivum L.) grown in a sequence. Treatments were: no-tillage (NT), NT+pine needle mulch at a rate of 10 t ha⁻¹ (NT+M), conventional tillage (CT), CT+pine needle mulch at a rate of 10 t ha⁻¹ (CT+M) and deep tillage (DT). The soil is classified as a Typic Hapludalf and has compact sub-surface layers. The NT treatment increased the bulk density of the surface layer but this problem was not observed in the no-tilled treatment having mulch at the surface (NT+M). The CT+M and NT+M treatments favourably moderated the hydro-theregime resulting in greater root growth, nutrient uptake and grain yields of maize and wheat. The DT treatment, imposed only once, at the beginning of the study, also enhanced root growth and grain yields. The yields were similar to the mulched treatments for maize and somewhat less than the mulched treatments for wheat. Mulched treatments generally showed significantly greater total uptake of N, P and K than corresponding unmulched ones. Since NT+M was comparable to CT for maize and superior for wheat, the latter is preferable since it does not require ellaborate tillage.     

Tillage alters corn root distribution in coarse-textured soil

Root responses to tillage vary and the driving factors are not well understood. Characterization of root response is requisite to optimize fertilizer placement and to understand limitations to no-till production. Corn (Zea mays L.) root length and weight were measured in the top 0.3 m of coarse-textured soil (Psammentic Hapludalf) in southwestern Ontario, Canada after 5, 6 and 7 yr of conventional and no-till management. Root length density in the top 0.1 m was greater under no-till (17 km m⁻³) than under conventional till (7 km m⁻³) 2 yr out of 3. Root length density was 4 km m⁻³ lower under no-till than under conventional till in the 0.15 to 0.3 m layer 1 yr out of 3, but otherwise root growth below 0.1 m was unaffected by tillage. Each year, root length and weight were distributed more horizontally under no-till than under conventional till. Corn grain yields did not vary with tillage, even though soil water content was often greater under no-till. The increase in soil water (of between 0.01 and 0.03 m³ m⁻³) was partly due to increased water holding capacity—water held between −8 and −200 kPa matric potential was usually greater under no-till (0.07 m³ m⁻³) than under conventional till (0.06 m³ m⁻³) in the top 0.15 m. The shift in root distribution was apparently driven by soil structure because variation in bulk density with tillage and depth followed the same trends as variation in root length. Bulk density was greater under no-till (1.5 Mg m⁻³) than under conventional till (1.4 Mg m⁻³) in the top 0.15 m. In the top 0.075 m, the proportion of the total space occupied by capillary pores (<36 μm diameter) was greater under no-till (17%) than under conventional till (15%), there were more dry-stable aggregates under no-till (9% of total soil in the 0.85–5.7 mm size fraction) than under conventional till (7%), and a greater proportion of these aggregates were water-stable under no-till (25%) than under conventional till (16%). Greater bulk density may trigger formation of lateral roots, and greater aggregation contribute to the more superficial development by deflecting roots from their gravitropic pathway. Given the more superficial root distribution under no-till, shallower placement of downwardly mobile nutrients such as nitrogen may be more efficient than knife-injection.     

In situ and potential CO2 evolution from a Fluventic Ustochrept in southcentral Texas as affected by tillage and cropping intensity

Quality of agricultural soils is largely a function of soil organic matter. Tillage and crop management impact soil organic matter dynamics by modification of the soil environment and quantity and quality of C input. We investigated changes in pools and fluxes of soil organic C (SOC) during the ninth and tenth year of cropping with various intensities under conventional disk-and-bed tillage (CT) and no tillage (NT). Soil organic C to a depth of 0.2 m increased with cropping intensity as a result of greater C input and was 10% to 30% greater under NT than under CT. Sequestration of crop-derived C input into SOC was 22±2% under NT and 9±4% under CT (mean of cropping intensities ± standard deviation of cropping systems). Greater sequestration of SOC under NT was due to a lower rate of in situ soil CO₂ evolution than under CT (0.22±0.03 vs. 0.27±0.06 g CO₂–C g⁻¹ SOC yr⁻¹). Despite a similar labile pool of SOC under NT than under CT (1.1±0.1 vs. 1.0±0.1 g mineralizable C kg⁻¹ SOC d⁻¹), the ratio of in situ to potential CO₂ evolution was less under NT (0.56±0.03) than under CT (0.73±0.08), suggesting strong environmental controls on SOC turnover, such as temperature, moisture, and residue placement. Both increased C sequestration and a greater labile SOC pool were achieved in this low-SOC soil using NT and high-intensity cropping.     

The effect of mulching and tillage on the water and temperature regimes of a loess soil: Experimental findings and modeling

Crop residues and tillage are being advocated for their potential effectiveness to modify the soil hydrothermal regime. This study was carried out to quantify the effect of straw mulching and rotary hoeing on the soil water and thermal regimes of a loess soil. The field experiment consisted of four treatments: (1) no mulching and no rotary hoeing as control, (2) rotary hoeing, (3) wheat straw mulching, and (4) wheat straw mulching with rotary hoeing. During the study period from 5 August to 20 September 2002, soil water content and pressure head were measured daily at five soil depths (0.05, 0.15, 0.30, 0.45 and 0.60 m). Soil temperatures were measured at hourly resolution at three depths (0.05, 0.15 and 0.30 m). Mulching decreased soil water loss on an average by 0.39 mm d⁻¹ and rotary hoeing increased water loss on an average by 0.12 mm d⁻¹ as compared to control. Volumetric soil water contents at pF 1, 1.8 and 2.5 up to 30 cm depth were highest (0.418, 0.390, and 0.360 m³ m⁻³, respectively) with the application of wheat straw mulch and lowest (0.393, 0.363, and 0.333 m³ m⁻³, respectively) with the rotary hoeing. Soil thermal conductivity measured at pF 1, 1.8, 2.5, 3, and 3.7 decreased with increasing suctions in all the treatments. However, the tillage and mulching did not affect the soil thermal conductivity. Further, compared with the control, mulching reduced average soil temperatures by 0.74, 0.66, 0.58 °C at 0.05, 0.15, and 0.30 m, respectively, during the study period. The rotary hoeing tillage slightly increased the average soil temperature by 0.21 °C at 0.05 m depth compared to control. The tillage effect did not transmit to deeper depths. The numerical model Hydrus-1D was used to simulate the water and temperature regimes of the treatments. Simulations with hydraulic parameters derived from laboratory measurements did not yield satisfactory results. Only when the hydraulic parameters were optimized by the inverse method, simulations performed well. The largest deviations were observed in the wheat straw mulching treatment. Simulations were further improved by adjusting the potential evaporation rate from the measured data which was achieved by linking the inversion code UCODE to the Hydrus-1D. Soil temperatures at 0.05 and 0.15 m in all the treatments were modeled well, yielding root mean square errors between 0.3 and 1.7 °C. As for soil water, the largest temperature deviations were found for the mulching treatment. All simulations underestimated soil temperatures at 0.30 m. In conclusion, crop residue can be utilized as mulching to improve the soil hydrothermal regime and the Hydrus-1D model can be used as a tool for analyzing water and heat transport processes and for estimating hydraulic transport parameters under field conditions.     

Soil physical responses to novel rice cultural practices in the rice–wheat system: Comparative evidence from a swelling soil in Nepal

Soil puddling in advance of rice (Oryza sativa L.) transplanting disperses surface aggregates and generates compaction at depth. As a management scheme for rice, puddling is typically considered advantageous for maximizing resource availability and yield. However, some experimental findings suggest a conflict between edaphic conditions created by this establishment technique and the performance of subsequent non-rice crops like wheat (Triticum aestivum L.). At a site in the mid-hills region of Nepal on a silt loam soil with vertic characteristics, we compared the impact of six rice tillage (surface tillage—T₁, shank subsoiler—T₂, shank subsoiler + moldboard plough—T₃) and establishment (soil puddling + transplanting—TPR, direct seeding—DSR) combinations on soil physical properties over two cycles of the rice–wheat rotation. For the rice season, 0–20 cm saturated hydraulic conductivity (K_sat) in the DSR plots was 2.6 and 4.3 times higher than their TPR counterparts in the first (Y₁) and second (Y₂) years, respectively (TPR-Y₁ = 93 mm day⁻¹, DSR-Y₁ = 241 mm day⁻¹, TPR-Y₂ = 133 mm day⁻¹, DSR-Y₂ = 582 mm day⁻¹), whereas tillage method did not significantly influence K_sat in this soil layer. The impact of rice establishment method was reflected in higher TPR bulk densities in the 5–10 (DSR = 1.19 g cm⁻³, TPR = 1.24 g cm⁻³) and 10–15 cm (DSR = 1.24 g cm⁻³, TPR = 1.29 g cm⁻³) depth increments in the wet season. Although none of the treatments significantly influenced the position or thickness of the plough sole, penetration resistance profiles suggest that vertical fractures with reduced soil strength were created within the pan region by deep tillage (T₂ and T₃), although these features were not associated with higher hydraulic conductivities from 20 to 50 cm. As the soils dried at the end of the rice season, crack propagation in the deep tilled plots (T₂ and T₃) was more pervasive. During the wheat season, comparable bulk density profiles and soil moisture retention characteristics across the treatments suggest that many of the edaphic changes induced by contrasting rice tillage and establishment practices did not persist in the self-mulching, vertic soils at our site. Conversely, significant increases in K_sat among the DSR plots from Y₁ to Y₂ (Y₁ = 241 mm day⁻¹, Y₂ = 582 mm day⁻¹) imply a temporal element to soil structural regeneration with adoption of direct seeding.     

Surface-soil responses to paraplowing of long-term no-tillage cropland in the Southern Piedmont USA

The type of conservation-tillage management employed could impact surface-soil properties, which could subsequently affect relationships between soil and water quality, as well as with soil C sequestration and greenhouse gas emissions. We determined soil bulk density, organic C and N fractions, plant-available N, and extractable P on Typic Kanhapludults throughout a 7-year period, in which four long-term (>10 years), no-tillage (NT) water catchments (1.3–2.7 ha each) were divided into two treatments: (1) continuation of NT and (2) paraplowing (PP) in autumn (a form of non-inversion deep ripping) with NT planting. Both summer [cotton (Gossypium hirsutum L.), maize (Zea mays L.), sorghum (Sorghum bicolor L. Moench), soybean (Glycine max L. Merr.)] and winter [wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.)] crops were NT planted throughout the study under each management system. Soil bulk density was reduced with PP compared with NT by as much as 0.15 Mg m⁻³, but the extent of reduction was inversely related to the time lag between PP operation and sampling event. Soil organic C became significantly enriched with time during this study under NT (0.49 Mg C ha⁻¹ year⁻¹), but not under PP, in which poultry litter was applied equivalent to 5.7 Mg ha⁻¹ year⁻¹ to all water catchments. Soil maintained a highly stratified depth distribution of organic C and N fractions and extractable P under both NT and PP. Inability to perform the PP operation in the last year of this study resulted in rapid convergence of soil bulk density between tillage systems, suggesting that PP had <1-year effectiveness on soil loosening. The high energy cost of PP (ca. 30 kW shank⁻¹) and the lack of sustained improvement in surface-soil properties put into question the value of PP for improving upon long-term NT management in sandy loam and sandy clay loam Ultisols of the Southern Piedmont USA, unless large effects on crop yield, water quality, or other ecosystem processes warrant its use.     

Soil quality response to tillage and crop residue removal under subarctic conditions

Little is known about the long-term effects of tillage and crop residue management on soil quality and organic matter conservation in subarctic regions. Therefore, we quantified wet aggregate stability, bulk density, pH, total organic C and N, inorganic N, microbial biomass C and N, microbial biomass C:N ratio, microbial quotient, and potential C and N mineralization for a tillage/crop residue management study in central Alaska. Soil from no-till (NT), disked once each spring (DO), and disked twice (DT, spring and fall) treatments was sampled to 20 cm depth in spring and fall of the 16th and 17th years of the study. Crop residues were either retained or removed after harvest each year. Reducing tillage intensity had greater impact on most soil properties than removing crop residues with the most notable effects in the top 10 cm. Bulk density was the only indicator that showed significant differences for the 10–20 cm depth, with values of 0.74 Mg m⁻³ in the surface 10 cm in NT compared to 0.86 in DT and 1.22 Mg m⁻³ in NT compared to 1.31 in DT for the 10–20 cm depth. Wet aggregate stability ranged from 10% in DT to 20% in NT. Use of NT or DO conserved soil organic matter more than DT. Compared to measurements made in the 3rd and 4th years of the study, the DT treatment lost almost 20% of the soil organic matter. Retaining crop residues on the soil conserved about 650 g m⁻² greater C than removing all residues each year. Soil microbial biomass C and mineralizable C were highest in NT, but the microbial C quotient, which averaged only 0.9%, was not affected by tillage or crop residue treatment. Microbial biomass C:N ratio was 11.3 in DT and 14.4 in the NT, indicating an increasing predominance of fungi with decreasing tillage intensity. Barley grain yield, which averaged 1980 kg ha⁻¹ over the entire 17 years of the study, was highest in DO and not significantly different between NT and DT, but weeds were a serious problem in NT. Reduced tillage can improve important soil quality indicators and conserve organic matter, but long-term NT may not be feasible in the subarctic because of weed problems and build up of surface organic matter.