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.     

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 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.     

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.     

Amelioration of a hardsetting Alfisol through deep mouldboard ploughing, gypsum application and double cropping. I. Soil physical and chemical properties

Contrasting soil management techniques were applied to a hardsetting red-brown earth (Alfisol) used for flood-irrigated wheat (Triticum aestivum) production at Trangie, N.S.W., Australia. The individual and combined effects of deep mouldboard ploughing to a depth of 0.45 m, gypsum application (5 t ha⁻¹) and double cropping upon aggregate stability, bulk density, porosity, cone index and the non-limiting water range were evaluated. Dispersion and slaking of the surface soil were unaffected by the treatments when measured at the end of the second year of the experiment. Approximately 60% of the soil mass in the 0–0.15 m layer slaked on wetting, whereas less than 1% of the soil dispersed. Organic carbon (OC) levels of the surface soil were not affected by double cropping or gypsum application, but were reduced by mouldboard ploughing from 0.9% to 0.6% OC. The relationship between OC and macroaggregate (more than 250 μm) stability indicated that large increases in OC beyond 0.7% OC were required for relatively small increases in aggregate stability. Mouldboard ploughing increased clay content of the upper 0.15 m of the soil from 22% to 27%. This was associated with an increase in the frequency and depth of cracking which, however, diminished over time. The non-limiting water range (NLWR) was expanded in the uppermost 0.1 m by gypsum application from 0.15–0.30 to 0.09–0.28 m³ m⁻³. Mouldboard ploughing expanded the NLWR at a depth of 0.2 m. Penetrometer resistance, on average, exceeded the critical value for wheat root growth at a water content of 0.15 m³ m⁻³, which is substantially higher than the wilting point (0.09 m³ m⁻³). Excessive resistance to penetration as opposed to inadequate aeration or water availability is the main agronomic impediment in these soils, at least in the initial stages of crop development. Penetration resistance within the 0.05–0.3 m layer was reduced during a drying cycle in the order: mouldboard ploughing>gypsum>double cropping. The reduced penetration resistance associated with mouldboard ploughing was due to higher water content to a depth of 0.2 m and reduced bulk density below this depth.     

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 conservation tillage on hydraulic properties of a Griswold silt loam soil

The effects of conservation tillage (CT) systems on crop production and erosion control have been well documented, but limited information is available concerning the effects of different CT systems on the hydraulic properties of layered soils. The effects of three CT treatments: chisel (CH), no-tillage (NT) and till-plant (TP) as compared with conventional modlboard plowing (CN) were investigated on a Griswold silt loam soil (Typic Argiudoll), formed in loess overlaying glacial till. Hydraulic properties were determined in situ. In addition, hydraulic conductivity was determined in the laboratory where more detailed hydraulic conductivity changes were monitored for the lower soil moisture tension range near soil saturation.

At or near saturation, there was no difference in hydraulic properties for all four tillage treatments. For example, mean saturated hydraulic conductivities (from laboratory determination) were 25.5, 25.1, 24.2 and 22.8 cm day⁻¹ for CN, CH, TP and NT, respectively. However under unsaturated conditions, tillage treatments and soil layering (discontinuity between surface loess and glacial till beneath) affected hydraulic properties. In situ hydraulic conductivity (K) ranked CH>CN = NT = TP for the 0.32–0.33 m³ m⁻³ moisture content range. There were no differences in K for all treatments at other moisture ranges considered and at moisture contents 0.31 m³ m⁻³, in situ specific moisture capacity was, however, significantly lower in NT than in the other three treatments. Throughout the 20-day free drainage period for in situ K determination, the effect of layering is exhibited by the mean K values at the 50-cm depth being higher than those at 25 cm. There were negligible treatment-block interaction effects on the hydraulic properties as the soil became drier. Spatial variability in hydraulic properties was also noted for all treatments and soil depths considered.     

Effects of soil compaction on N-mineralization and microbial-C and -N. II. Laboratory simulation

Soil compaction can affect the turnover of C and N (e.g. by changing soil aeration or by changing microbial community structure). In order to study this in greater detail, a laboratory experiment simulating total soil porosities representative of field conditions in cropped and pasture soils was set up. Soils were silty clay loams (Typic Endoaquepts) from a site that had been cropped with cereals continuously for 28 years, a permanent pasture and a site that had been cropped with maize continuously for 10 years. Soils from the three sites were compacted into cores to different total porosities (corresponding bulk densities ranging from 0.88 to 1.30 Mg m⁻³). The soil cores were equilibrated to different matric potentials (ranging from −1 to −100 kPa), yielding values for the fraction of air-filled pores of < 0.01 to 0.53 m³ m⁻³, and then incubated at 25°C for 21 days. C-mineralization was on average 15, 33 and 21 μg C g⁻¹ day⁻¹ for soils from the cropped, pasture and maize sites, respectively, and was positively correlated with soil water contents. Net N-mineralization showed a similar pattern only for well-aerated, high total porosity cores (corresponding bulk density 0.88 Mg m⁻³) from the pasture soil. Denitrification at < 0.20 m³ m⁻³ for the fraction of air-filled pores may have caused the low N-mineralization rates observed in treatments with high water content or low porosity. Microbial biomass estimates decreased significantly with increasing water contents if measured by fumigation-extraction, but were not significantly affected by water content if estimated by the substrate-induced respiration method. The degree of soil compaction did not affect the microbial biomass estimates significantly but did affect microbial activity indirectly by altering aeration status.     

Soil bulk density and porosity of homogeneous morphological units identified by the Cropping Profile Method in clayey Oxisols in Brazil

Soil structure is important to root development and crop yield. The objective of this study was to test the Cropping Profile Method in Brazilian soils, in order to evaluate the soil structure in the field. Grouped different structures determined by the Cropping Profile Method were compared to laboratory determinations for soil bulk density, total porosity and mercury porosity. The study was conducted in clayey Oxisols submitted to different uses and management including annual crops, orchards and natural forests in the State of Paraná, southern Brazil. Homogeneous morphological units (HMUs) were determined in trenches using the Cropping Profile Method, and the different structures were grouped as: (a) non-compacted; (b) compacted; (c) in-process-of-compacting. Results of field evaluation were compatible with those obtained in the laboratory. More compacted and in-process-of-compacting structures corresponded to soil bulk density values of 1.42 and 1.33 Mg m⁻³, which were significantly higher than the 1.18 Mg m⁻³ value obtained for soil bulk density in non-compacted HMU. The total porosity of compacted HMU and in-process-of-compacting HMU was 0.49 and 0.52 m³ m⁻³, respectively. These were significantly lower than the value obtained for the non-compacted HMU (0.60 m³ m⁻³). The Cropping Profile Method is useful mainly in field research works when it is important to verify the effect of management practices on soil structure.     

The effect of speed of wheeling on soil stresses, rut depth and soil physical properties in an ameliorated transitional red-brown earth

Soil stress measurements were made in an ameliorated transitional red-brown earth (Natric Palexeralf) during one pass of a heavily loaded (4 t) wheel. Different speeds (up to about 8 km h⁻¹ and soil water contents (close to the lower plastic limit) were used for measurements of total stress, final bulk density, air permeability and rut depth. Effective stresses appeared to decrease with speed. Increases of total stress caused by extra fluid pressure (i.e. pore-water pressure) at 20-cm depth were associated with fast deformation rates of the soil (up to about 3 m s⁻¹) just behind the leading edge of the tyre contact area. Shear stress changed very little with speed. Equations relating speed and water content to rut depth and resultant bulk density were also found. These predicted approximately 10% less mean rut depth or bulk density at 20-cm depth by increasing speed from 0.5 to 10 km h⁻¹ over this soil at water contents near the lower plastic limit.     

Soil CO2 flux from a norfolk loamy sand after 25 years of conventional and conservation tillage

Tillage affects the ability of coarse-textured soils of the southeastern USA to sequester C. Our objectives were to compare tillage methods for soil CO₂ flux, and determine if chemical or physical properties after 25 years of conventional or conservation tillage correlated with flux rates. Data were collected for several weeks during June and July in 2003, October and November in 2003, and April to July in 2004 from a tillage study established in 1978 on a Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults). Conventional tillage consisted of disking to a depth of approximately 15 cm followed by smoothing with an S-tined harrow equipped with rolling baskets. Conservation tillage consisted of direct seeding into surface residues. Flux rates in conservation tillage averaged 0.84 g CO₂ m⁻² h⁻¹ in Summer 2003, 0.36 g CO₂ m⁻² h⁻¹ in Fall 2003, 0.46 g CO₂ m⁻² h⁻¹ in Spring 2004, and 0.86 g CO₂ m⁻² h⁻¹ in Summer 2004. Flux rates from conventional tillage were greater for most measurement times. Conversely, water content of the surface soil layer (6.5 cm) was almost always higher with conservation tillage. Soil CO₂ flux was highly correlated with soil water content only in conventional tillage. In conservation tillage, no significant correlations occurred between soil CO₂ flux and soil N, C, C:N ratio, pH, bulk density, sand fraction, or clay fraction of the surface 7.5 cm. In conventional tillage, sand fraction was positively correlated, while bulk density and clay fraction were negatively correlated with soil CO₂ flux rate, but only when the soil was moist. Long-term conservation tillage management resulted in more uniform within- and across-season soil CO₂ flux rates that were less affected by precipitation events.     

Effects of mechanical energy inputs on soil respiration at the aggregate and field scales

Cultivation machinery applies large amounts of mechanical energy to the soil and often brings about a decrease in soil organic carbon (SOC). New experiments on the effects of mechanical energy inputs on soil respiration are reported and the results discussed. In the laboratory, a specific energy, K, of 150 J kg⁻¹, similar to that experienced during typical cultivation operations, was applied to soil aggregates using a falling weight. Respiration (carbon dioxide, CO₂ emission) of the samples was then measured by an electrical conductimetric method. Basal respiration (when K=0) measured on Chromic Luvisol aggregates, was found to increase with increasing SOC, from 1.88 μg CO₂ g⁻¹ h⁻¹ for a permanent fallow soil (SOC=11 g kg⁻¹) to 8.25 μg CO₂ g⁻¹ h⁻¹ for a permanent grassland soil (SOC=32 g kg⁻¹). Basal respiration of a Calcic Cambisol, more than doubled (2.0–5.2 μg CO₂ g⁻¹ h⁻¹) with increasing gravimetric soil water contents. Mechanical energy inputs caused an initial burst of increased respiration, which lasted up to 4 h. Over the following 4–24 h period, arable soils with lower SOC contents, (11–21 g kg⁻¹), respiration rates dropped back to a level, approximately 1.14 times higher than the basal value. However, grassland soils with higher SOC contents (28–32 g kg⁻¹), increases in this longer-term respiration rate following 150 J kg⁻¹ of energy, were negligible. A field experiment, in which CO₂ was measured by infra-red absorption, also showed that tillage stimulated increased levels of soil respiration for periods ranging from 12 h to more than one week. The highest respiration rates, 80 mg CO₂ m⁻² h⁻¹ were associated with high energy, powered tillage on clay soils. On the same soil, low energy draught tillage resulted in a respiration rate of approximately half this value. The results of these experiments are discussed in relation to equilibrium levels of soil organic matter. The application of known quantities of mechanical energy to soil aggregates under laboratory conditions, in order to simulate the effect of different cultivation practices, when combined with the subsequent measurement of soil respiration, can provide useful indication of the likely consequences of soil management on SOC.     

Short-term changes in nitrogen availability, gas fluxes (CO2, NO, N2O) and microbial biomass after tillage during pasture re-establishment in Rondônia, Brazil

Anthropogenic conversion of primary forest to pasture for cattle production is still frequent in the Amazon Basin. Practices adopted by ranchers to restore productivity to degraded pasture have the potential to alter soil N availability and N gas losses from soils. We examined short-term (35 days) effects of tillage prior to pasture re-establishment on soil N availability, CO₂, NO and N₂O fluxes and microbial biomass C and N under degraded pasture at Nova Vida ranch, Rondônia, Brazilian Amazon. We collected soil samples and measured gas fluxes in tilled and control (non tilled pasture) 12 times at equally spaced intervals during October 2001 to quantify the effect of tillage. Maximum soil NH₄⁺ and NO₃⁻ pools were 13.2 and 6.3 kg N ha⁻¹ respectively after tillage compared to 0.24 and 6.3 kg N ha⁻¹ in the control. Carbon dioxide flux ranged from 118 to 181 mg C–CO₂ m² h⁻¹ in the control (non-tilled) and from 110 to 235 mg C–CO₂ m² h⁻¹ when tilled. Microbial biomass C varied from 365 to 461 μg g⁻¹ in the control and from 248 to 535 μg g⁻¹ when tilled. The values for N₂O fluxes ranged from 1.22 to 96.9 μg N m⁻² h⁻¹ in the tilled plots with a maximum 3 days after the second tilling. Variability in NO flux in the control and when tilled was consistent with previous measures of NO emissions from pasture at Nova Vida. When tilled, the NO/N₂O ratio remained <1 after the first tilling suggesting that denitrification dominated N cycling. The effects of tilling on microbial parameters were less clear, except for a decrease in qCO₂ and an increase in microbial biomass C/N immediately after tilling. Our results suggest that restoration of degraded pastures with tillage will lead to less C matter, at least initially. Further long-term research is needed.     

Alternative tillage and crop residue management in wheat after rice in sandy loam soils of Indo-Gangetic plains

A 3-year field study was conducted to evaluate the effect of three tillage practices (conventional, zero and reduced/strip) with two nitrogen levels (120 and 150 kg N ha⁻¹) applied in primary strips and three crop residue management practices (removal, burning and incorporation) in secondary strips in wheat after rice. Reduced tillage resulted in significantly higher overall mean wheat yield (5.10 Mg ha⁻¹) compared to conventional (4.60 Mg ha⁻¹) and zero tillage (4.75 Mg ha⁻¹). Residue incorporation resulted in highest mean yield (5.86 Mg ha⁻¹) during third year. Maximum mean yield (6.1 Mg ha⁻¹) was obtained in reduced tillage followed by conventional tillage (5.8 Mg ha⁻¹) under residue incorporation in third year. The weed dry weight recorded at 30 days after sowing was highest (0.3 Mg ha⁻¹) under zero tillage and lowest under conventional tillage (0.16 Mg ha⁻¹). Among crop residue management practices, the highest dry weight of weeds (0.22 Mg ha⁻¹) was recorded under residue incorporation. The highest infiltration rate (1.50 cm h⁻¹) was recorded in residue incorporation followed by residue burning (1.44 cm h⁻¹) whereas; the lowest (0.75 cm h⁻¹) in zero tillage. Soil bulk density was the highest (1.69 Mg m⁻³) under zero tillage and the lowest in residue incorporation (1.59 Mg m⁻³). There were no changes in soil available P and K after each crop sequence in relation to tillage practices during first 2 years. Higher organic carbon (5.1–5.4 g kg⁻¹) was measured under zero tillage compared to other treatments. Residue incorporation increased soil organic carbon and available P while higher available K was monitored in burning treatment during the third year. These results suggest that reduced tillage and in situ incorporation of crop residues at 5 Mg ha⁻¹ along with 150 kg N ha⁻¹ were optimum to achieve higher yield of wheat after rice in sandy loam soils of Indo-Gangetic plains of India.     

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.     

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.     

Contrasting response to cropping of populations of earthworms and predacious nematodes in four soils

The activities of many soil animals make a positive contribution to soil processes and they should be considered for inclusion in indices of ‘soil quality'. To assess the potential use of nematodes and earthworms as indicators, the relationships between populations of earthworms (Lumbricidae), total number of nematodes and predacious nematodes (Mononchoidea) and six soil physical factors, soil carbon and pH were investigated in four New Zealand soils. In each, soil treatments ranged from 5–90 year pastures to cropping with maize or barley for 11–29 years. With increasing cultivation, trends in bulk density, total porosity, aggregate stability and concentration of total carbon were similar in all four soils. In Manawatu (Dystric Fluventic Eutrochrept) and Kairanga (Typic Endoaquept) soils earthworm populations were negligible under continuous cropping while Mononchoidea were abundant (11 600 and 34 100 m⁻²). In contrast, in Moutoa (Fluvaquentic Endoaquoll) and Wakanui (Aquic Ustochrept) soils earthworms persisted under cultivation, while Mononchoidea were less abundant (300 and 2500 m⁻²). At these two latter sites, aggregate stability was higher (1.14 and 0.92 mm mean weight diameter (MWD)) than in Manawatu and Kairanga soils (0.38 and 0.35 mm MWD). These relationships between aggregate stability, earthworm abundance and predacious nematodes show not only that some potential indicators may have a local rather than national application, but also that there are important interactions between soil physical properties and soil fauna which require further investigation.     

Water infiltration and soil structure related to organic matter and its stratification with depth

Soil organic matter is a key attribute of soil quality that impacts soil aggregation and water infiltration. Two soils (Typic Kanhapludults), one under long-term management of conventional tillage (CT) and one under long-term management of no tillage (NT), were sampled to a depth of 12 cm. Soil cores (15 cm diameter) were either left intact or sieved and repacked to differentiate between short-term (sieving) and long-term (tillage management) effects of soil disturbance on water infiltration, penetration resistance, soil bulk density, macroaggregate stability, and soil organic carbon (SOC). Mean weekly water infiltration was not different between sieved and intact cores from long-term CT (22 cm h⁻¹), but was significantly greater in intact (72 cm h⁻¹) than in sieved (28 cm h⁻¹) soil from long-term NT. The stratification ratio of SOC (i.e., of 0–3 cm depth divided by that of 6–12 cm depth) was predictive of water infiltration rate, irrespective of short- or long-term history of disturbance. Although tillage is used to increase soil porosity, it is a short-term solution that has negative consequences on surface soil structural stability, surface residue accumulation, and surface-SOC, which are critical features that control water infiltration and subsequent water transmission and storage in soil. The stratification ratio of SOC could be used as a simple diagnostic tool to identify land management strategies that improve soil water properties (e.g., infiltration, water-holding capacity, and plant-available water).     

花江喀斯特石漠化区不同经济型植物的土壤蓄水特征

选择贵州省花江喀斯特石漠化综合治理区分布广泛的几种典型生态经济型种植模式花椒、金银花、砂仁、火龙果、构树、花椒金银花混交林为研究对象,以荒草地为对照,对各植物的土壤物理性质和蓄水性能进行了对比研究。结果表明:（1）研究区土壤容重的浮动范围为1.09～1.40 g/cm³,并随土层深度增加而增加;孔隙度随土层深度增加而减小,上层土壤的蓄水性能和通透性能优于下层。（2）与荒草地相比,构树、火龙果、花椒金银花混交林、花椒、金银花的土壤容重和孔隙度状况都优于荒草地,只有砂仁比荒草地差。（3）从土壤含水量和0—30 m总蓄水量来看,混交林土壤含水量最大（37.69%）,分别比金银花、火龙果、构树、花椒、荒草地、砂仁高3.18%,4.33%,4.83%,7.49%,10.15%,13.18%;总蓄水量表现为花椒金银花混交林（1 769.54 t/hm²） > 火龙果（1 732.94 t/hm²） > 构树（1 722.14 t/hm²） > 花椒（1 698.43 t/hm²） > 金银花（1 655.58 t/hm²） > 荒草地（1 640.79 t/hm²） > 砂仁（1 428.75 t/hm²）。（4）相关分析表明土壤容重和毛管孔隙度与最大持水率及毛管持水率均呈极显著相关（p < 0.01）,相关系数分别为-0.931,0.897,-0.915,0.890。因此,在花江喀斯特石漠化植被恢复过程中应优先考虑以花椒金银花为代表的混交林与火龙果模式。