Soil structure and the effect of management practices

To evaluate the impact of management practices on the soil environment, it is necessary to quantify the modifications to the soil structure. Soil structure conditions were evaluated by characterizing porosity using a combination of mercury intrusion porosimetry, image analysis and micromorphological observations. Saturated hydraulic conductivity and aggregate stability were also analysed.

In soils tilled by alternative tillage systems, like ripper subsoiling, the macroporosity was generally higher and homogeneously distributed through the profile while the conventional tillage systems, like the mouldboard ploughing, showed a significant reduction of porosity both in the surface layer (0–100 mm) and at the lower cultivation depth (400–500 mm). The higher macroporosity in soils under alternative tillage systems was due to a larger number of elongated transmission pores. Also, the microporosity within the aggregates, measured by mercury intrusion porosimetry, increased in the soil tilled by ripper subsoiling and disc harrow (minimum tillage). The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed by the higher hydraulic conductivity in the soil tilled by ripper subsoiling. Aggregates were less stable in ploughed soils and this resulted in a more pronounced tendency to form surface crust compared with soils under minimum tillage and ripper subsoiling.

The application of compost and manure improved the soil porosity and the soil aggregation. A better aggregation indicated that the addition of organic materials plays an important role in preventing soil crust formation.

These results confirm that it is possible to adopt alternative tillage systems to prevent soil physical degradation and that the application of organic materials is essential to improve the soil structure quality.     

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.     

Tillage effects on near-surface soil hydraulic properties

The processes for the formation of porosity are thought to differ between tilled and non-tilled cropping systems. The pores are created primarily by the tillage tool in the tilled systems and by biological processes in non-tilled systems. Because of the different methods of pore formation, the pore size distribution, pore continuity and hydraulic conductivity functions would be expected to differ among tillage systems. The objective of this study was to determine effects of three tillage systems — mold-board plow (MP), chisel plow (CP), and no-till (NT) — on hydraulic properties of soils from eight long-term tillage and rotation experiments. Tillage effects on saturated and unsaturated hydraulic conductivity, pore size distribution, and moisture retention characteristics were more apparent for soils with a continuous corn (CC) rotation than for either a corn-soybean (CS) rotation or a corn-oats-alfalfa (COA) rotation. Pore size distributions were similar among tillage systems for each soil except for three soils with a CC rotation. The MP system increased volume of pores >150 μm radius by 23% to 91% compared with the NT system on two of the soils, but the NT system increased the volume of the same radius pore by 50% on one other soil. The NT system had 30 to 180% greater saturated hydraulic conductivity than either the CP or MP systems. The NT system with a CC rotation showed a greater slope of the log unsaturated hydraulic conductivity; log volumetric water content relationship on two of the soils indicating greater water movement through a few relatively large pores for this system than for either the CP or MP systems.     

Wheel traffic impact on soil conditions as influenced by tillage system in Central Anatolia

The increased limiting effects of soil compaction on Central Anatolian soils in the recent years demonstrate the need for a detailed analysis of tillage system impacts. This study was undertaken to ascertain the effects of seven different tillage systems and subsequent wheel traffic on the physical and mechanical properties of typical Central Anatolian medium textured clay loam soil (Cambisol), south of Ankara, Turkey. Both tillage and field traffic influenced soil bulk density, porosity, air voids and strength significantly except the insignificant effect of traffic on moisture content. Traffic affected the soil properties mostly down to 20 cm. However, no excessive compaction was detected in 0–20 cm soil depth. The increases of bulk density following wheel traffic varied between 10–20% at 0–5 cm and 6–12% at 10–15 cm depth. In additions, traffic increased the penetration resistance by 30–74% at 0–10 cm and 7–33% at 10–20 cm. Less wheel traffic-induced effects were found on chisel tilled plots, compared to ploughed plots. Soil stress during wheel passage was highly correlated with soil strength. Also, both tillage and traffic-induced differences were observed in mean soil aggregate sizes, especially for mouldboard ploughed plots. The obtained data imply that chisel+cultivator-tooth harrow combination provides more desirable soil conditions for resisting further soil compaction.     

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

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

Characterization of soil physical properties and organic matter under long-term primary tillage in a humid climate

Chisel ploughing is considered to be a potential conservation tillage method to replace mouldboard ploughing for annual crops in the cool-humid climate of eastern Canada. To assess possible changes in some soil physical and biological properties due to differences in annual primary tillage, a study was conducted for 9 years in Prince Edward Island on a Tignish loam, a well-drained Podzoluvisol, to characterize several mouldboard and chisel ploughing systems (at 25 cm), under conditions of similar crop productivity. The influence of primary tillage on the degree of soil loosening, soil permeability, and both organic matter distribution throughout the soil profile and organic matter content in soil particle size fractions was determined. At the time of tillage, chisel ploughing provided a coarser soil macrostructure than mouldboard ploughing. Mouldboard ploughing increased soil loosening at the lower depth of the tillage zone compared to chisel ploughing. These transient differences between primary tillage treatments had little effect on overall soil profile permeability and hydraulic properties of the tilled/non-tilled interface at the 15–30 cm soil depth. Although soil microbial biomass, on a volume basis, was increased by 30% at the 0–10 cm soil depth under chisel ploughing, no differences were evident between tillage systems over the total tillage depth. Mouldboard ploughing increased total orgainc carbon by 43% at the 20–30 cm soil depth, and the carbon and nitrogen in the organic matter fraction ≤ 53 μm by 18–44% at the 10–30 cm soil depth, compared to chisel ploughing.     

Predicting the saturated hydraulic conductivity of compacted subsoils using the non-similar media concept

It is widely recognized that saturated hydraulic conductivity is dominated by the micromorphology of soil pores rather than by the merely total porosity or dry bulk density. Nevertheless, some researchers are reporting that the decrease in saturated hydraulic conductivity of subsoil is simply associated with the decrease in soil porosity or increase in dry bulk density. Based on these understandings in published papers and on our preliminary field investigation, we assumed that micromorphology of soil pores in topsoils is subjected to be destroyed with continuous disturbance by frequent tillage while subsoils tend to be compacted without serious changes of micromorphology of soil pores. Thus, we focused on finding the dependence of saturated hydraulic conductivity on dry bulk density by separating the soils into tilled layer and compacted layer. The objective of this study was to describe the relationship between saturated hydraulic conductivity and dry bulk density using a theoretical model, the non-similar media concept (NSMC) model, capable of predicting saturated hydraulic conductivities of soils with different values of dry bulk densities. The study area was located near the Tone River in Saitama Prefecture, Japan, where the soils were classified into Haplic Brown Lowland Soils according to the Classification of Cultivated Soils in Japan (Eutric Fluvisol according to FAO/UNESCO). Two sites, where the topsoils were seasonally tilled while the subsoils were sustained as it is, and another site where the topsoil was seasonally tilled, too, but extra deep tillage (1 m tillage depth) had been done, were chosen for the measurements. The saturated hydraulic conductivities and dry bulk densities of undisturbed soil cores from different depths were measured in the laboratory. The NSMC model was carefully applied only when the soil textures were the same among samples. The well-known conventional equations formulated by Kozeny–Carman and by Campbell, were used to compare the applicabilities with the NSMC model. The NSMC model succeeded in predicting the saturated hydraulic conductivities in the compacted subsoils. On the other hand, the NSMC model was not applicable to the tilled topsoils and to the deeply tilled subsoil. The saturated hydraulic conductivity of tilled topsoils and deeply tilled subsoil was always lower than that of compacted subsoils at the same dry bulk densities. The Kozeny–Carman and Campbell equations both failed in the prediction of saturated hydraulic conductivity in subsoil. It was concluded that the saturated hydraulic conductivity of subsoils under compaction without extreme disturbance is well related with its dry bulk density by the NSMC model.     

Soil physical properties and soybean (Glycine max, Merrill) root abundance in conventionally- and zero-tilled soils in the humid Pampas of Argentina

In the humid Pampas of Argentina soybean is cultivated in different soil types, which were changed from conventional- to zero tillage systems in the last decade. Little is known about the response of soybean roots to these different soil physical environments. Pasture, and conventionally- and zero-tilled field lots cropped to soybean (R1 and R2 ontogenic stages) were sampled in February–March 2001 in a sandy clay loam and two silty clay loam Mollisols, and in a clayey Vertisol. In the 0–0.05 m layer of conventionally- and zero-tilled lots soil organic carbon represented 53–72% of that in pasture lots, and showed an incipient recovery after 4–11 years of continuous zero tillage. Soil aggregate stability was 10.1–46.8% lower in conventionally-tilled than in pasture lots, and recovered completely in zero-tilled lots. Soil relative compaction ranged 60.8–83.6%, which was below the threshold limit for crop yields (>90%). In change, soil porosity >50 μm ranged 0.91–5.09% soil volume, well below the minimum critical limit for root aeration and elongation (>10%, v/v). The threshold of soil resistance (about 2–3 MPa) was only over passed in an induced plough pan in the conventionally-tilled Bragado soil (5.9 MPa), and in the conventionally- and zero-tilled Ramallo soils (3.7–4.2 MPa, respectively). However, neither the low macroporosity nor the high soil resistances impeded soybean roots growth in any site. According to a fitted polynomial function, root abundance was negatively related to clay content in the subsoil (R² = 0.84, P < 0.001). Soybean roots were only abundant in the subsoil of the sandy clay loam Mollisol, which had <350 g kg⁻¹ clay. Results show that subsoil properties, and not tillage systems, were the primary effect of root growth of soybean.     

Economics of tillage systems for spring wheat production in southwestern Saskatchewan (Canada)

The economic performance of continuous wheat (Triticum aestivum L.) and fallow-wheat rotations grown under conventional, minimum- and zero-tillage management practices on silt loam, sandy loam and heavy clay in southwestern Saskatchewan was determined during the relatively dry period of 1982–1988. The costs and returns for each rotation-tillage system were evaluated annually based on 1989–1990 price and cost conditions, and for various other plausible scenarios. Gross returns on silt loam were higher for continuous wheat (average 228 $ ha⁻¹) than for fallow-wheat systems (average 155 $ ha⁻¹). On the sandy loam, gross returns were similar for all cropping systems (average 112 $ ha⁻¹); on the heavy clay, they were higher for fallow-wheat than for continuous wheat (139 versus 119 $ ha⁻¹). Conservation tillage management increased gross returns over that obtained with conventional tillage only in years when growing season temperatures were high and precipitation was poorly distributed, or when the 21-month summerfallow period was droughty. On silt loam, gross returns were significantly lower with conservation tillage in as many as 3 of 7 years. On silt loam, net returns were highest for conventionally tilled continuous wheat when wheat prices were> 175 $ t⁻¹; at lower wheat prices, conventionally tilled fallow-wheat was the most profitable. On the other soils, minimum- and zero-tillage fallow-wheat provided the highest net returns at all wheat prices tested, with minimum tillage being slightly better at low wheat prices, but at these sites conventionally tilled fallow-wheat was not studied. The cost of production was highest for continuous wheat and for zero-tillage management. For fallow-wheat systems, conservation tillage required lower expenditures than conventional tillage for fuel, labor, machine repair and machine overheads; costs for minimum tillage averaged 9 $ ha⁻¹ and for zero tillage 15 $ ha⁻¹ lower on the silt loam. These savings were more than offset by increased herbicide costs which averaged 26 and 64 $ ha⁻¹ higher for minimum-tillage and zero-tillage systems, respectively. We concluded that producers in southwestern Saskatchean who are motivated primarily by short-term profit will find little incentive to adopt conservation tillage systems for spring wheat production, unless they are situated on soils that have already incurred severe soil loss or the soils are highly prone to further erosion losses.     

Hydraulic conductivity, residue cover and soil surface roughness under different tillage systems in semiarid conditions

The objective of this study was to investigate the effect of tillage and cropping system on near-saturated hydraulic conductivity, residue cover and surface roughness to improve soil management for moisture conservation under semiarid Mediterranean conditions. Three tillage systems were compared (subsoil tillage, minimum tillage and no-tillage) under three field situations (continuous crop, fallow and crop after fallow) on two soils (Fluventic Xerochrept and Lithic Xeric Torriorthent). Soil under no-tillage had lower hydraulic conductivity (5.0 cm day⁻¹) than under subsoil tillage (15.5 cm day⁻¹) or minimum tillage (14.3 cm day⁻¹) during 1 of 2 years in continuous crop due to a reduction of soil porosity. Residue cover at sowing was greater under no-tillage (60%) than under subsoil or minimum tillage (<10%) in continuous crop. Under fallow, residue cover was low (10%) at sowing of the following crop for all tillage systems in both soils. Surface roughness increased with tillage, with a high value of 16% and decreasing following rainfall. Under no-tillage, surface roughness was relatively low (3–4%). Greater surface residue cover under no-tillage helped conserve water, despite indications of lower hydraulic conductivity. To overcome the condition of low infiltration and high evaporation when no-till fallow is expected in a cropping sequence, either greater residue production should be planed prior to fallow (e.g. no residue harvest) or surface tillage may be needed during fallow.     

TILTH MELLOWING

Effects of weathering action, mainly wetting and drying cycles, on the strength of the clods produced by tillage are studied. Experiments were carried out on sandy loam soils at two sites in South Australia, and on silt loam and clay soils at Wye College, England. It is found that tillage increases the amplitude of soil water content fluctuations. These bigger soil water content fluctuations resulted in a decrease in the clod strength and this in turn modified the size distribution of the clods produced by tillage in the South Australian soils. The decrease in clod strength, as measured by the drop shatter test, was followed by an increase in the proportion of the smaller aggregate size fraction produced by a second implement pass. It is suggested that, for soils in which the increase in the soil water content fluctuations after the first tillage implement pass decreases clod strength, a further implement pass should be delayed for several days. By doing this, the soil can be tilled with minimum energy and cost to produce a good seed bed.     

Persistence of soil compaction due to high axle load traffic. II. Long-term effects on the properties of fine-textured and organic soils

The long-term effects of high axle load traffic on soil structure were investigated in three field experiments. Two of the experiments were located on fine-textured mineral soils (Vertic Cambisol). The clay soil had 48 g clay (particle size less than 2 μm) per 100 g in the topsoil and 65 g per 100 g in the subsoil, and the loam soil had clay contents of 30 g and 42 g per 100 g in the topsoil and subsoil, respectively. One experiment was located on an organic soil (Mollic Gleysol) consisting of well-decomposed sedge peat mixed with clay from 0.2 to 0.4–0.5 m depth, and underlain by gythia (organic soil with high clay content). In the autumn of 1981, one pass and four repeated passes with a heavy tractor-trailer combination compacted the soils to 0.4–0.5 m depth. The trailer tandem axle load was 19 Mg on the clay and 16 Mg on the other soils.

For 9 years after the experimental traffic, the main crops grown were spring cereals. During this time, the maximum axle load applied during field operations was 5 Mg and the maximum tyre inflation pressure was 150 kPa. The clay and loam froze to 0.5 m depth for 6 and 2 years, respectively. During several growing seasons all three soils dried and cracked. In the ninth year after the loading, soil penetrometer resistance, saturated hydraulic conductivity (K_sat), macroporosity and number and area of cylindrical biopores were measured and the visual structure of the soils examined.

Compaction in the plough layer was alleviated by ploughing and natural processes, whereas in the subsoil the effects of the compaction were still measurable, in all experiments, in the ninth year after the high axle load traffic. In the clay soil in the 0.3–0.5 m layer and in the organic soil in the 0.28–0.4 m layer, the penetrometer resistance was 22–26% greater and the soil structure more massive in the plots compacted with four passes than in the control plots. In the 0.4–0.55 m layer in all soils, the loading with four passes decreased K_sat by 60–98% and macroporosity (diameter greater than 300 μm) by 37–70%. In the fine-textured mineral subsoils, cylindrical biopores were found in all treatments. The trend of the results was, however, for biopores to be fewer in compacted than in control plots.     

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.     

Twenty years of conservation tillage research in subarctic Alaska: II. Impact on soil hydraulic properties

Soil management practices are needed in the subarctic that stabilize the soil against the forces of wind and water as well as conserve soil water for crop production. There is a paucity of information, however, regarding the long-term effects of conservation tillage on soil hydraulic properties in subarctic Alaska. The objective of this study was therefore to characterize infiltration, water retention, and saturated hydraulic conductivity of a soil 20 years after establishing tillage and straw management treatments in interior Alaska. The strip plot experimental design, established on a silt loam and maintained in continuous barley (Hordeum vulgare L.), included tillage as the main treatment and straw management as the secondary treatment. Tillage treatments included no tillage, autumn chisel plow, spring disk, and intensive tillage (autumn and spring disk) while straw treatments included retaining or removing stubble and loose straw from the soil surface after harvest. Soil properties were measured after sowing in spring 2004; saturated hydraulic conductivity was measured by the falling-head method, infiltration was measured using a double-ring infiltrometer, and water retention was assessed by measuring the temporal variation in in-situ soil water content. No tillage resulted in greater saturated hydraulic conductivity and generally retained more water against gravitational and matric forces than other tillage treatments. Infiltration was greater in autumn chisel plow than other tillage treatments and was presumably suppressed in no tillage by an organic layer overlying mineral soil. Infiltration was also enhanced by retaining straw on rather than removing straw from the soil surface after harvest. No tillage is not yet a sustainable management practice in this region due to lack of weed control strategies. In addition, the formation of an organic layer in no tillage has important ramifications for the soil hydrological and thermal environment. Therefore, minimum tillage (i.e., autumn chisel plow or spring disk) appears to be a viable management option for maximizing infiltration in interior Alaska.     

Surface versus incorporated residue effects on water-stable aggregates

Reduced tillage methods for field crop production result in less disruption of soil structure and often increased amounts of crop residue maintained on the soil surface. The combination of these two factors produces increased surface soil aggregation. This study was conducted in the field and within pots to determine whether surface residue by itself improves soil aggregation within a short period of time. The soil was a silt loam loess deposit in the Pacific Northwest, USA, where summers are hot and dry, and most precipitation (420 mm) is received during the mild winters. Two pot studies were conducted over winter, one under a shelter with controlled irrigations (183 mm), and the other outdoors receiving natural precipitation (77 mm). In both pot studies 640 g m⁻² wheat (Triticum aestivum L.) residue was either placed on the surface of the soil or thoroughly mixed into the soil. The field study was conducted on plots where, for the past 7 years, wheat crop residues were either incorporated through chisel/disk tillage or removed before tillage and replaced on the surface after tillage. The field study included plots where wheat was grown with no tillage. In the pots, there was no significant effect due to residue treatment on aggregate mean weight diameter, measured monthly for 4 winter months. This was true despite dissolved organic carbon being leached from the surface residue. In the 7-year-old field plots, replacing residues on the surface resulted in slightly greater mean weight diameter of aggregates at 5–10 cm depth compared to the mixed residue treatment. The no-till plots had significantly greater mean weight diameter at 0–5 cm depth than either tilled treatment. Our conclusion is that surface residue by itself failed to increase aggregation of tilled surface soil within the first rainy season after tillage.     

Long-term impact of reduced tillage and residue management on soil carbon stabilization: Implications for conservation agriculture on contrasting soils

Residue retention and reduced tillage are both conservation agricultural management options that may enhance soil organic carbon (SOC) stabilization in tropical soils. Therefore, we evaluated the effects of long-term tillage and residue management on SOC dynamics in a Chromic Luvisol (red clay soil) and Areni-Gleyic Luvisol (sandy soil) in Zimbabwe. At the time of sampling the soils had been under conventional tillage (CT), mulch ripping (MR), clean ripping (CR) and tied ridging (TR) for 9 years. Soil was fully dispersed and separated into 212–2000 μm (coarse sand), 53–212 μm (fine sand), 20–53 μm (coarse silt), 5–20 μm (fine silt) and 0–5 μm (clay) size fractions. The whole soil and size fractions were analyzed for C content. Conventional tillage treatments had the least amount of SOC, with 14.9 mg C g⁻¹ soil and 4.2 mg C g⁻¹ soil for the red clay and sandy soils, respectively. The highest SOC content was 6.8 mg C g⁻¹ soil in the sandy soil under MR, whereas for the red clay soil, TR had the highest SOC content of 20.4 mg C g⁻¹ soil. Organic C in the size fractions increased with decreasing size of the fractions. In both soils, the smallest response to management was observed in the clay size fractions, confirming that this size fraction is the most stable. The coarse sand-size fraction was most responsive to management in the sandy soil where MR had 42% more organic C than CR, suggesting that SOC contents of this fraction are predominantly controlled by amounts of C input. In contrast, the fine sand fraction was the most responsive fraction in the red clay soil with a 66% greater C content in the TR than CT. This result suggests that tillage disturbance is the dominant factor reducing C stabilization in a clayey soil, probably by reducing C stabilization within microaggregates. In conclusion, developing viable conservation agriculture practices to optimize SOC contents and long-term agroecosystem sustainability should prioritize the maintenance of C inputs (e.g. residue retention) to coarse textured soils, but should focus on the reduction of SOC decomposition (e.g. through reduced tillage) in fine textured soils.     

Effect of straw and plastic film management under contrasting tillage practices on the physical properties of an erodible loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and surface cover management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of straw and plastic film management under contrasting tillage practices (no tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) which had been under conventional management for hundred of years in the northwestern Loess Plateau, China. Surface soil (0–10 cm) under no tillage with straw cover had the highest water stability of macro-aggregates (>250 μm) and the highest saturated hydraulic conductivity. Compared with straw cover, plastic film cover did not change macro-aggregate stability and the soil had the lowest saturated hydraulic conductivity (K_sat) but the highest % <50 μm soil particles. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indication the importance of the latter on soil structural development. No tillage on its own (without straw cover) was not sufficient to improve structural stability probably due to lack of organic carbon input. While use of plastic film cover might lead to short term yield increases, results indicated that it did little to improve soil physical fertility. On the other hand, no tillage with straw cover management should lead to long-term improvement of physical quality of this structurally fragile soil.     

A study of some tillage practices for sustainable crop production in India

Soil tilth has been defined in terms of a ‘Physical Index’ based on the product of the ratings of eight physical properties — soil depth, bulk density, available water storage capacity, cumulative infiltration or apparent hydraulic conductivity, aggregation or organic matter, non-capillary pore space, water table depth and slope. The Physical Index and a tillage guide were used to identify the tillage requirements of different soils varying in texture from loamy sand to clay in the semi-arid tropics. The physical index was 0.389 for a loamy sand, 0.518 for a black clay loam and 0.540 for a red sandy loam soil and the cumulative rating indices in summer and winter seasons were 45 and 44 for loamy sand, 52 and 51 for red sandy loam and 54 and 52 for black clay loam soils, respectively. The compaction of the loamy sand by eight passes of a 490 kg tractor-driven roller (0.75 m diameter and 1.00 m length) increased the physical index to 0.658 and chiselling of the red sandy loam and black clay loam increased the physical indices to 0.686 and 0.729, respectively. The grain yields of rainfed pearl millet and guar and irrigated pearl millet, wheat and barley increased significantly over the control (no compaction) yields by compaction.

The chiselling of the soils varying in texture from loamy sand to clay at 50 to 120-cm intervals up to 30–40 cm depth, depending upon the row spacing of seedlines and depth of the high mechanical impedance layer, increased the grain yields of rainfed and irrigated maize on alluvial loamy sand, rainfed maize on alluvial sandy loam and red sandy loam, rainfed sorghum on red sandy loam and black clay loam, irrigated sorghum on black clay loam and rainfed black gram on red sandy loam, pod yield of rainfed groundnut, tuber yield of irrigated tapioca and fresh fruit yield of rainfed tomato on red sandy loam and sugarcane yield on black clay soil, significantly over the yields of no-chiselling systems of tillage such as disc harrow and country plough.     

Tillage methods and soil and water conservation in eastern Africa

This paper reviews some research studies on tillage methods influencing soil and moisture conservation in the eastern African countries of Kenya, Tanzania, Malawi and Ethiopia during the past four decades. Most of these studies were conducted in marginal rainfall (semi arid) areas and on shallow soils of various textures (sandy clay loam, sandy clay, clay and loam). The studies were meant to establish the effects of tillage and residue management practices on physico-chemical soil properties (i.e. structure, bulk density, soil moisture and organic matter contents), runoff and infiltration.

This review emphasizes the importance of appropriate tillage and residue management methods (contour bunds and terraces, minimum tillage, tied ridging, mulching and conventional tillage) in providing soil conditions favourable for soil moisture conservation and subsequent crop performance and yield on smallholder farms.     

Contrasting development of soil microbial community structure under no-tilled perennial and tilled cropping during early pedogenesis of a Mollisol

A range of agricultural practices influence soil microbial communities, such as tillage and organic C inputs, however such effects are largely unknown at the initial stage of soil formation. Using an eight-year field experiment established on exposed parent material (PM) of a Mollisol, our objectives were to: (1) to determine the effects of field management and soil depth on soil microbial community structure; (2) to elucidate shifts in microbial community structure in relation to PM, compared to an arable Mollisol (MO) without organic amendment; and (3) to identify the controlling factors of such changes in microbial community structure. The treatments included two no-tilled soils supporting perennial crops, and four tilled soils under the same cropping system, with or without chemical fertilization and crop residue amendment. Principal component (PC) analysis of phospholipid fatty acid (PLFA) profiles demonstrated that microbial community structures were affected by tillage and/or organic and inorganic inputs via PC1 and by land use and/or soil depth via PC2. All the field treatments were separated by PM into two groups via PC1, the tilled and the no-tilled soils, with the tilled soils more developed towards MO. The tilled soils were separated with respect to MO via PC1 associated with the differences in mineral fertilization and the quality of organic amendments, with the soils without organic amendment being more similar to MO. The separations via PC1 were principally driven by bacteria and associated with soil pH and soil C, N and P. The separations via PC2 were driven by fungi, actinomycetes and Gram (−) bacteria, and associated with soil bulk density. The separations via both PC1 and PC2 were associated with soil aggregate stability and exchangeable K, indicating the effects of weathering and soil aggregation. The results suggest that in spite of the importance of mineral fertilization and organic amendments, tillage and land-use type play a significant role in determining the nature of the development of associated soil microbial community structures at the initial stages of soil formation.