No-till effects on organic matter, pH, cation exchange capacity and nutrient distribution in a Luvisol in the semi-arid subtropics

No-till (NT) system for grain cropping is increasingly being practised in Australia. While benefits of NT, accompanied by stubble retention, are almost universal for soil erosion control, effects on soil organic matter and other soil properties are inconsistent, especially in a semi-arid, subtropical environment. We examined the effects of tillage, stubble and fertilizer management on the distribution of organic matter and nutrients in the topsoil (0–30 cm) of a Luvisol in a semi-arid, subtropical environment in southern Queensland, Australia. Measurements were made at the end of 9 years of NT, reduced till (RT) and conventional till (CT) practices, in combination with stubble retention and fertilizer N (as urea) application strategies for wheat (Triticum aestivum L.) cropping.

In the top 30 cm depth, the mean amount of organic C increased slightly after 9 years, although it was similar under all tillage practices, while the amount of total N declined under CT and RT practices, but not under NT. In the 0–10 cm depth, the amounts of organic C and total N were significantly greater under NT than under RT or CT. No-till had 1.94 Mg ha⁻¹ (18%) more organic C and 0.20 Mg ha⁻¹ (21%) more total N than CT. In the 0–30 cm depth, soil under NT practice had 290 kg N ha⁻¹ more than that under the CT practice, most of it in the top 10 cm depth. Microbial biomass N was similar for all treatments. Under NT, there was a concentration gradient in organic C, total N and microbial biomass N, with concentrations decreasing from 0–2.5 to 5–10 cm depths.

Soil pH was not affected by tillage or stubble treatments in the 0–10 cm depth, but decreased significantly from 7.5 to 7.2 with N fertilizer application. Exchangeable Mg and Na concentration, cation exchange capacity and exchangeable Na percentage in the 0–10 cm depth were greater under CT than under RT and NT, while exchangeable K and bicarbonate-extractable P concentrations were greater under NT than under CT.

Therefore, NT and RT practices resulted in significant changes in soil organic C and N and exchangeable cations in the topsoil of a Luvisol, when compared with CT. The greater organic matter accumulation close to the soil surface and solute movement in these soils under NT practice would be beneficial to soil chemical and physical status and crop production in the long-term, whereas the concentration of nutrients such as P and K in surface layers may reduce their availability to crops.     

Spatial distributions of soil chemical and physical properties prior to planting soybean in soil under ridge‐, no‐ and conventional‐tillage in a maize–soybean rotation

Detailed information on the profile distributions of agronomically important soil properties in the planting season can be used as criteria to select the best soil tillage practices. Soil cores (0–60 cm) were collected in May, 2012 (before soybean planting), from soil transects on a 30‐yr tillage experiment, including no‐tillage (NT), ridge tillage (RT) and mouldboard plough (MP) on a Brookston clay loam soil (mesic Typic Argiaquoll). Soil cores were taken every 19 cm across three corn rows and these were used to investigate the lateral and vertical profile characteristics of soil organic carbon (SOC), pH, electrical conductivity (EC), soil volumetric water content (SWC), bulk density (BD), and penetration resistance (PR). Compared to NT and MP, the RT system resulted in greater spatial heterogeneity of soil properties across the transect. Average SOC concentrations in the top 10 cm layer were significantly greater in RT than in NT and MP (P = 0.05). NT soil contained between 0.8 and 2.5% (vol/vol) more water in the top 0–30 cm than RT and MP, respectively. MP soil had lower PR and BD in the plough layer compared to NT and RT soils, with both soil properties increasing sharply with depth in MP. The RT had lower PR relative to NT in the upper 35 cm of soil on the crop rows. Overall, RT was a superior conservation tillage option than NT in this clay loam soil; however, MP had the most favourable soil conditions in upper soil layers for early crop development across all treatments.     

The effects of long-term conservation tillage, crop residues and P fertilizer on soil conditions and responses of summer and winter crops on an Andosol in Japan

A field experiment was conducted from 1983 to 1992 in Tsukuba, Japan to investigate the effects of tillage on soil conditions and crop growth in a light-colored Andosol. Three tillage methods (NT: no-tillage, RT: no-tillage for summer cropping and moldboard plowing for winter cropping, and CT: conventional rotary tillage to a depth of 15 cm) were employed in combination with crop residue application (+R, −R) and fused magnesium phosphate (FMP) fertilization (+P, −P). Under the combination of NT and +R, diurnal variation of soil temperature at a depth of 5 cm was smaller during the summer cropping season and soil temperature in the daytime was lower during the winter cropping season than under CT. Soil inorganic N concentration at a depth of 0–30 cm was +R > −R and NT > RT > CT. The early growth of summer crops was accelerated under NT in comparison with CT, and yields were higher under NT and RT in comparison with CT. On the other hand, winter crop yields were significantly reduced under NT, while they were still higher under RT in comparison with CT. Yields were higher with +R and +P application, respectively, and these effects were more pronounced in winter cropping. The positive effect of FMP fertilization was greater in combination with NT, and that of residue treatment was greater in combination with RT and NT than with CT. In conclusion, the best tillage practice for Andosols on the Kanto Plain is RT, i.e. a combination of NT for summer cropping and CT for winter cropping. The application of NT for winter cropping is not recommended, although the application of phosphate and crop residues could reduce the risk of yield reduction, because of improved soil nutrient status and moderation of diurnal soil temperature.     

Organic and inorganic phosphorus in Mollisol soil under different tillage practices

The distribution of soil phosphorus (P) between different organic and inorganic forms depends on, among other factors, the tillage systems. The evaluation of soil P fractions is essential to determine if they are related to available P. The objective was to characterize the P forms from a soil under no tillage (NT) and conventional tillage (CT). Soil samples were taken at 0–5, 5–10 and 10–20 cm depth from a fine, mixed, thermic Petrocalcic Paleoudoll, after 8 years under NT and CT. Inorganic and organic P was measured in the anion exchange membrane (AEM), NaHCO₃, NaOH, NaOH after sonication, HCl and residual fractions extracted sequentially. Microbial P was determined by fumigating with chloroform after P extraction with AEM. The tillage systems did not affect the total P content but the distribution of P among fractions changed between NT and CT. No tillage system had significantly higher microbial P at all soil depths and ranged from 34 mg P kg⁻¹ at 0–5 cm to 10 mg P kg⁻¹ at 10–20 cm. In the upper 10 cm of soil, NT tended to have higher AEM-Pi and NaHCO₃-Pi comparing to CT system. The increase in AEM-Pi was closely related to organic carbon increases and pH decreases. The was a consistently higher concentration of NaOH-Po but the increase was significant al 5–10 and 10–20 cm, and represented on average about 35% of total P. The residual P which was considered mostly organic was also an important pool in both NT and CT, and accounted for about 30% of total P. Therefore, P availability is mainly controlled by organic P which makes up a larger proportion of total P.     

Impact of tillage and crop rotation on light fraction and intra-aggregate soil organic matter in two Oxisols

It is well known that no-tillage (NT) practices can promote greater stocks of soil organic matter (SOM) in the soil surface layer compared to conventional tillage (CT) by enhancing the physical protection of aggregate-associated C in temperate soils. However, this link between tillage, aggregation and SOM is less well established for tropical soils, such as Oxisols. The objective of this study was to investigate the underlying mechanisms of SOM stabilization in Oxisols as affected by different crop rotations and tillage regimes at two sites in southern Brazil. Soils were sampled from two agricultural experiment sites (Passo Fundo and Londrina) in southern Brazil, with treatments comparing different crop rotations under NT and CT management, and a reference soil under native vegetation (NV). Free light fraction (LF) and intra-aggregate particulate organic matter (iPOM) were isolated from slaking-resistant aggregates. Of the total C associated with aggregates, 79–90% was found in the mineral fraction, but there were no differences between NT and CT. In contrast, tillage drastically decreased LF-C concentrations in the 0–5 cm depth layer at both sites. In the same depth layer of NT systems at Londrina, the concentrations of iPOM-C were greater when a legume cover crop was included in the rotation. At Londrina, the order of total iPOM-C levels was generally NV > NT > CT in the 0–5 cm depth interval, but the difference between NT and CT was much less than in Passo Fundo. At Passo Fundo, the greatest concentrations and differences in concentrations across tillage treatments were found in the fine (53–250 μm) iPOM fractions occluded within microaggregates. In conclusion, even though no aggregate hierarchy exists in these Oxisols, our results corroborate the concept of a stabilization of POM-C within microaggregates in no-tillage systems, especially when green manures are included in the rotation.     

Influence of soil tillage systems on aggregate stability and the distribution of C and N in different aggregate fractions

Soil aggregation is influenced by the tillage system used, which in turn affects the amount of C and N in the different aggregate fractions. This study assessed the impact of different tillage systems on soil aggregates by measuring the aggregate stability, the organic carbon (C_org) and the total nitrogen (N_tot) contents within different aggregate fractions, and their release of dissolved organic carbon (DOC). Soil samples were collected from the top 0 to 10 cm of a long-term tillage experiment at Fuchsenbigl (Marchfeld, Austria) where conventional tillage (CT), reduced tillage (RT), and minimum tillage (MT) treatments were applied to a Chernozem fine sandy loam. The stable aggregates (1000–2000 μm) were subject to dispersion by the soil aggregate stability (SAS or wet sieving) method after Kemper and Rosenau (1986), and the ultrasonic method of Mayer et al. (2002). Chemical analysis of the soil was obtained for the aggregate fractions 630–1000, 250–630 and 63–250 μm gathered from the ultrasonic method. Using the SAS method, CT and RT had the least amounts of stable aggregates (18.2% and 18.9%, respectively), whereas MT had twice as much stable aggregates (37.6%). Using the ultrasonic method, MT also had the highest amount of water stable aggregates in all three fractions (1.5%, 3.7%, and 35%, respectively), followed by RT (1%, 2.3%, 32.3%), and CT (0.8%, 1.7%, 29.1%). For comparison, a reference soil, EUROSOIL 7 (ES-7) was also analysed (40%, 6.7%, and 12.1%). The highest amounts of C_org and N_tot were measured under MT in all three fractions, with 8.9%, 3.8%, and 1.3% for C_org, and 0.4%, 0.3%, and 0.1% for N_tot. Apart from the fraction 630–1000 μm, the aggregates of RT and CT contained <50% of the C_org and N_tot values of MT. The C/N ratio was least favourable for CT (42.6) in the aggregate fraction 630–1000 μm. The DOC release from stable aggregates after 10 min of ultrasonic dispersion was highest from MT soil (86.7 mg l⁻¹). The values for RT and CT were 21% and 25% below this value. The results demonstrate that tillage type influences both aggregate stability and aggregate chemical composition. This research confirms that CT interferes more with the natural soil properties than RT and MT. Furthermore, MT has the highest potential to sequester C and N in this agriculturally used soil.     

Reduced tillage effects on physical properties of silt loam soils growing root crops

In the scope of the increasing concern for soil conservation, reduced tillage (RT) agriculture is growing more important in today's agriculture in Western Europe. However, crop rotations often include beets and potatoes, crops that are generally assumed to be less suitable under RT agriculture because they result in a high disturbance of the soil at the formation of the ridges and at harvest. Therefore, the short- and long-term effect of RT agriculture on bulk density (BD), water retention curve (WRC), aggregate stability and field-saturated hydraulic conductivity of silt loam soils with crop rotations including root crops was evaluated. Ten fields at seven locations representing the important RT types, applied for a different number of years, and eight fields under conventional tillage (CT) agriculture with similar soil type and crop rotation were selected. At each location, BD of the 5–10 cm layer was mostly lower in the RT fields (1.42 ± 0.05 Mg m⁻³ [average with standard deviation]) compared to the CT fields (1.44 ± 0.09 Mg m⁻³) and the water content at saturation was mostly higher (0.394 ± 0.027 m³ m⁻³ and 0.382 ± 0.021 m³ m⁻³ for RT and CT fields, respectively). No differences in BD (1.53 ± 0.03 Mg m⁻³) or WRC could be found in the 25–30 cm soil layer when comparing the RT with the CT fields. The stability index of the 0–10 cm layer measured by ‘dry and wet sieving’ [De Leenheer, L., De Boodt, M., 1959. Determination of aggregate stability by the change in mean weight diameter. Mededelingen van landbouwhogeschool en de opzoekingstations van de staat te Gent 24, 290–300] was 40% higher under RT than CT agriculture. The mean weight diameter (MWD) [Le Bissonnais, Y., 1996. Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology. Eur. J. Soil Sci. 47, 425–437] was significantly higher even after short-term RT compared to CT agriculture. The MWD after a heavy shower, a slow wetting of the soil and stirring the soil after prewetting was 19%, 38% and 34% higher for RT than CT fields, respectively. The field-saturated hydraulic conductivity tended to be higher under RT compared to the CT fields. Despite the high disturbance of the soil every 2 or 3 years of crop rotations including sugar beets or potatoes, RT agriculture had a positive effect on the investigated physical soil properties.     

Changes in soil organic carbon and its chemical fractions under different tillage practices on loess soils of the Guanzhong Plain in north‐west China

Over the past 20 years, conservation tillage has been used on the loess plateau of north‐west China to improve the sustainability of local agriculture. There had been particular concern about loss of soil organic matter associated with traditional tillage. We examined the influence of four tillage treatments: conventional tillage (CT), subsoiling tillage (SST), rotary tillage (RT) and no‐tillage (NT), with two straw residue management treatments (return and removal) on the distribution with soil depth (0–20 cm, 20–40 cm) of total organic carbon, labile organic carbon (KMnO₄‐C) and bound organic carbon. The study was carried out on a Loutu soil (Earth‐cumuli‐Orthic Anthrosol) over seven consecutive years of a winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) crop rotation. By the end of this period, conservation tillage (SST, RT and NT) led to greater storage of soil organic carbon (SOC) (22.7, 14.9 and 16.3% with straw return in contrast to 21.4, 15.8 and 12.3% with no straw return, respectively) compared with CT in the surface soil (0–20 cm). The reduced tillage treatments (SST and RT) both increased significantly the highly labile organic carbon (HLOC) content of the surface soil (50% in both SST and RT) and mildly labile organic matter (MLOC) (49.4 in SST and 53.5% in RT) when straw was removed. The largest pool of bound carbon was observed in the Humin‐C pool, and the smallest in the free humic acids C (FHA‐C) in each tillage treatment. Conservation tillage led to an increased content of FHA‐C and CHA‐C. Results from correlation analyses indicate that SOC enrichment might have resulted from the increase in HLOC, MLOC, FHA‐C and CHA‐C over a short period. Labile organic carbon was associated with the organic carbon that was more loosely combined with clay (FHA‐C and CHA‐C). We conclude that both SST and RT are effective in maintaining or restoring organic matter in Loutu soils in this region, and the effect is greater when they are used in combination with straw return.     

Changes in soil chemical characteristics with different tillage practices in a semi-arid environment

We examined the effects of various tillage intensities: no-tillage (NT), minimum tillage with chisel plow (MT), conventional tillage with mouldboard plow (CT), and zone-tillage subsoiling with a paraplow (ZT) applied in alternate years in rotation with NT, on the topsoil profile distribution (0–30 cm) of pH, soil organic carbon (SOC), organic N and available nutrients on a semi-arid soil from Central Spain. The equivalent depth approach was used to compare SOC, N and nutrient stocks in the various tillage treatments. Measurements made at the end of 5 years showed that in the 0–30 cm depth, SOC and N had increased under NT and ZT compared with MT and CT. Most dramatic changes occurred within the 0–5 cm depth where plots under NT and ZT had respectively 7.0 Mg ha⁻¹ and 6.2 Mg ha⁻¹ more SOC and 0.5 Mg ha⁻¹ and 0.3 Mg ha⁻¹ more N than under MT or CT. No-tillage and ZT plots, however, exhibited strong vertical gradients of SOC and N with concentrations decreasing from 0–5 to 20–30 cm. In the 0–20 cm layer, higher concentrations of P and K under NT and ZT than under MT or CT were also found. Soil pH under NT and ZT was 0.3 units lower than under MT or CT at a depth of 0–5 cm. This acidifying effect was restricted at the surface layer and in the 20–30 cm interval, pH values under NT and ZT were higher than in MT and CT plots. These results suggest that in the soil studied, ZT in rotation with NT maintain most advantages associated with NT, and present a definite potential for use as a partial-width rotational tillage practice.     

Soil porosity and water infiltration as influenced by tillage methods

The relations between soil pore structure induced by tillage and infiltration play an important role in flow characteristics of water and solutes in soil. In this study, we assessed the effect of long-term use of various tillage systems on pore size distribution, areal porosity, stained (flow-active) porosity and infiltration of silt loam Eutric Fluvisol. Tillage treatments were: (1) ploughing to the depth of 20 cm (conventional tillage (CT)); (2) ploughing to 20 cm every 6 years and to 5 cm in the remaining years (S/CT); (3) harrowing to 5 cm each year (S); (4) sowing to the uncultivated soil (no tillage (NT)), all in a micro-plot experiment. Equivalent pore size distribution was derived from the water retention curve, areal porosity – from resin-impregnated blocks (8 cm × 9 cm × 4 cm) and stained porosity – from horizontal sections (every 2 cm) of column samples (diameter: 21.5 cm, height: 20 cm) taken after infiltration of methylene blue solution. The pore size distribution curves indicated that the textural peaks of the pore throat radius of approximately 1 μm were mostly defined under NT, whereas those in the structural domain of radii of 110 μm radius—under CT. The differences among the tillage treatments were more pronounced at depth 0–10 cm than 10–20 cm. At both depths, the differences in pore size distribution between the tillage treatments were relatively greater in structural than those in the matrix domain. CT soil had the greatest areal porosity and stained porosity. The stained porosity as a function of depth could be well described by logarithmic equations in all treatments. Cumulative infiltration (steady state) as measured by the double ring infiltrometer method was the highest under CT (94.5 cm) and it was reduced by 62, 36 and 61% in S/CT, S and NT soil, respectively. Irrespective of tillage method, cumulative infiltration rates throughout 3 h most closely correlated with stained porosity in top layers (0–6 cm). Overall, the results indicate that soil pore system under CT with higher contribution of large flow-active pores compared to reduced and no tillage treatments enhanced infiltration and water storage capacity.     

Soil physical responses to cattle grazing cover crops under conventional and no tillage in the Southern Piedmont USA

Grazing of cover crops in grain cropping systems can increase economic return and diversify agricultural production systems, but the environmental consequences of this intensified management have not been well documented, especially under different tillage systems. We conducted a multiple-year investigation of how cover crop management (grazed and ungrazed) and tillage system [conventional (CT; initial moldboard plowing and thereafter disk tillage) and no tillage (NT)] affected soil physical properties (bulk density, aggregation, infiltration, and penetration resistance) on a Typic Kanhapludult in Georgia. Responses were determined in two cropping systems: summer grain/winter cover crop and winter grain/summer cover crop. Soil bulk density was reduced (P = 0.02) with CT compared with NT to a depth of 30 cm at the end of 0.5 year, but only to a depth of 12 cm at the end of 2, 2.5, and 4.5 years. Grazing of cover crops had little effect on soil bulk density, except eventually with 4.5 years of management. Water-stable macroaggregation was reduced (P ≤ 0.01) with CT compared with NT to a depth of 12 cm at all sampling times during the first 2.5 years of evaluation. Stability of macroaggregates in water was unaffected by grazing of cover crops in both tillage systems. Across 7 sampling events during the first 4 years, there was a tendency (P = 0.07) for water infiltration rate to be lower with grazing of cover crops (5.6 mm min⁻¹) than when ungrazed (6.9 mm min⁻¹), irrespective of tillage system. Across 10 sampling events, soil penetration resistance was greater under NT than under CT at a depth of 0–10 cm (P = 0.001) and the difference was greater in ungrazed than in grazed systems (P = 0.06). Biannual CT operations may have alleviated any surface degradation with animal traffic, but the initially high level of soil organic matter following long-term pasture and conversion to cropland with NT may have buffered the soil from any detrimental effects of animal traffic. Overall, the introduction of cattle to consume the high-quality cover crop forage did not cause substantial damage to the soil.     

Physical, chemical and microbiological properties of an Andisol as related to land use and tillage practice

The effects of land use and management practice on soil physical, chemical and microbiological properties may provide essential information for assessing sustainability and environmental impact. This study compared the effects of 41 years of no-tillage (NT) with continuous apple orchard, with those of conventional tillage (CT) with wheat–soybean rotation and another of puddling (PD) with continuous rice on the characteristics of a pumice Andisol in a temperate region of northern Japan. Higher values for bulk density, penetration resistance, pH, C/N ratio, exchangeable Na (X-Na), Fe, and Mn were observed for PD than NT and CT. On the other hand, organic matter, EC, N, exchangeable K (X-K), exchangeable Ca (X-Ca) and Cu were significantly higher for NT than CT and PD. Highest content of Zn was found in CT compared to other practices. The three-phase composition at pF 2.0 was significantly affected by land use and tillage practices. The solid phase and liquid phase were greater under PD than under NT and CT, while air phase was greater under CT than under NT and PD. Significantly higher values for saturated hydraulic conductivity was found in CT than NT and PD. Total phospholipid fatty acid (PLFA) and PLFA for bacteria, aerobes and cyanobacteria were remarkably higher in NT than CT and PD, regardless of depth. On the other hand, PLFA for methane-oxidizing bacteria, sulfate-reducing bacteria and mycorrhizae were significantly higher in CT than NT and PD. PLFA for fungi was significantly higher in surface (0–10 cm) soils than subsurface (10–20 cm) soils regardless of treatments. Highest bacterial and fungal diversity evaluated by DNA band number in DGGE analysis based on PCR amplification of 16S rDNA and 18S rDNA fragments, respectively, were observed in surface soil of PD. The result suggests a linkage between microbial community and tillage practices in temperate Andisol. This study also justifies the need of measuring soil characteristics based on soil microbial communities.     

The influence of 12 years of tillage and crop rotation on total and labile organic carbon in a sandy loam soil

Information on which management practices can enhance soil organic matter (SOM) content and quality can be useful for developing sustainable crop production systems. We tested the influence of 12 years of no-till (NT) versus conventional tillage (CT), and four crop sequences on the organic C pools of a Grey Luvisolic sandy loam soil in northwestern Alberta, Canada. The crop sequences were: continuous wheat (Triticum aestivum L.), field pea (Pisum sativum L.)–wheat–canola (Brassica rapa L.)–wheat, red clover (Trifolium pratense L.) green manure–wheat–canola–wheat/red clover and fallow–wheat–canola–wheat. Soil samples from 1992, when the study was initiated, and 1996, 2000 and 2004 were analyzed for total organic C (TOC), the light fraction (LF) and its C content, and water-soluble and mineralizable C. Total organic C in the top 15 cm of soil was higher in the red clover rotation than either the pea or fallow rotation by 1996. The tillage effect became significant only in 2004 with NT having a higher TOC than CT. The LF dry matter (DM) increased from 6.9 g kg⁻¹ soil in 1992 to a range of 10–13 g kg⁻¹ in 2000 and 2004. It was higher under NT than CT in 2 of 3 years and in the red clover rotation than the pea or fallow rotation in 1 of 3 years. The LF C content exhibited a similar trend as LF DM. The water-soluble and mineralizable C pools were not affected by tillage but decreased with time. Among crop rotations, the red clover rotation tended to result in higher levels of hot water-soluble and mineralizable C. It is concluded that tillage had a greater influence than crop rotation on the LF DM and LF C (as indicators of C storage), whereas the converse effect applied to mineralizable C and, to a lesser degree, hot water-soluble C (as indicators of SOM quality).     

Physico-chemical indicators and microarthropod communities as influenced by no-till, conventional tillage and nitrogen fertilisation after four years of continuous maize

A multidisciplinary study was carried out over four years in Northern Italy on a silt loam under continuous maize. The experimental design was a split-plot with four replicates; the main factor was the soil management system, conventional tillage (CT) or no-tillage (NT), while the secondary factor was N fertilisation. At the end of the trial, soil samples were taken from all plots at four depths (from 0 to 20 cm). In these samples the following were determined: pH, soil organic carbon (SOC), total N, available P, exchangeable K, cation exchange capacity (CEC), electrical conductivity (EC) and water aggregate stability (WAS). Soil compaction was measured during the last three years, after maize harvesting. To study the microarthropod community, soil samples (0–10 cm depth) were taken six times over the four years. Our results show that NT significantly increased SOC (+15.8%), total N (+9.6%), C/N (+5.3%), exchangeable K (+37.1%) and WAS (+64.8%). The stratification ratio for exchangeable K reached 2.15 for NT plots. N fertilisation, on the other hand, had no significant effect on most of the physico-chemical indicators, except for pH, CEC and EC. Soil compaction was significantly higher for NT compared with CT up to a depth of 25–30 cm. During the last year, interesting reductions in soil penetration resistance for NT were measured, up to 300–430 kPa in the 2.5–12.5 cm layer. As for the microarthropods, Acari were more sensitive to tillage compared with Collembola, and the Wardle V index proved to be a good indicator of the response to tillage. N fertilisation with 300 kg N ha⁻¹ had a negative effect on the total microarthropod abundance. The Shannon diversity index gave fluctuating and significantly different results: over the years results were split alternately between the two tillage systems. The QBS-ar index, calculated for all the four years of the study, ranged between 48 and 72, values typical of intensively cultivated soils. The results obtained suggested that it was not influenced by the tillage system. Therefore, this index seems to be unsuitable for detecting the influence of tillage management and N fertilisation on the microarthropod community.     

Dynamics of soil biota at different depths under two contrasting tillage practices

One aim of conservation tillage is to preserve soil biological properties. This study was conducted to examine the effects of two contrasting tillage treatments on soil biota at different depths. We investigated the population dynamics and vertical distributions of microbes and several soil faunal groups for 2 years in field Andosols in northeastern Japan. The experimental plots were under no tillage (NT) or conventional tillage (CT, rotary tilled to 20 cm) management. In the 0–10-cm soil layer, bacterial and fungal substrate-induced respiration (SIR) and the population density of enchytraeids were higher under NT than under CT, but the population densities of protozoa, mites, and collembolans did not differ significantly. In contrast, at 10–20 cm, both SIR values were higher under CT, where larger populations of mites and collembolans were recorded. At both depths, nematodes were more abundant under CT. Thus, the effects of tillage on these soil organisms differed according to soil depth, and negative impacts of tillage were smaller in the deeper layer. Larger amounts of earthworm casts at the soil surface in NT plots showed a greater biomass of earthworms than in CT. To evaluate the activities of soil biota, we buried litterbags with three different mesh sizes at the two depths and examined the rate of decomposition. The daily decay constant of litter in the surface soil layer (1.5–8.5 cm) was greater under NT. We suppose that the activities of soil biota in this layer were stimulated under NT, and that especially microbes and enchytraeids, which were abundant at 0–10 cm, contributed greatly to the decomposition.     

Root growth dynamics of spring cereals with discontinuation of mouldboard ploughing

A vigorous root system is essential for efficient use of plant nutrients. This paper focuses on root growth and its response to tillage changes in the most fertile soil horizon, 0–40 cm depth. The field experiment was established in 1995 on clay soil, with 45–50% clay and 5.5% organic matter in the topsoil. Three tillage treatments were mouldboard plough to a depth of 20 cm (conventional), field cultivator to a depth of 8 cm, and no primary tillage (conservation). The field had an oat (Avena sativa L.)–barley (Hordeum vulgare L.) crop rotation. In 1997–1998 and 2000, root distribution during the growing season was evaluated by a non-destructive minirhizotron (MR) and video recording method. Root length density and root diameter were also measured once a season (1997 and 1998) by destructive root sampling and image analysis of washed roots. At shoot elongation, root numbers increased more under conventional than conservation tillage, at soil depth of 10–25 cm. The effect was clear for both barley (1997) and oat (2000) with maximum root numbers of 175 and 210 per 100 cm² by mouldboard ploughing, but 120 and 170 per 100 cm² under unploughed conditions (in the whole 0–0.4 m region). The suboptimal condition of unploughed soil was also indicated by lower shoot nutrient contents at tillering (studied in 1997) and by higher penetrometer resistance (studied in 1998, 2000) and lower macroporosity (studied in 2000) at 10–25 cm soil depth. Root growth dynamics were similar for both plant species. Root diameter was not significantly affected by the tillage treatments. Discontinuation of mouldboard ploughing reduced root growth (P<0.05) within this clay soil 5 years after the tillage change, although conservation tillage preserved more water for plant use. The data show that a clay soil can be too dense for optimal rooting during the 3rd–6th-years after discontinuation of ploughing.     

No tillage and crop rotation effects on soil aggregation and organic carbon in a Rhodic Ferralsol from southern Brazil

In Brazil, no tillage (NT) is a soil conservation practice now widely adopted by farmers, including smallholders. The effect of NT and conventional tillage (disc ploughing followed by two light disc harrowings, CT) was investigated on the aggregation properties of a clayey Rhodic Ferralsol from southern Brazil under different crop rotations. The same soil type under secondary forest was used as reference. Macro- and microaggregate classes were separated by wet sieving using a series of eight sieves (8, 4, 2, 1, 0.5, 0.25, 0.125, 0.053 mm) at four sampling layers (0–5, 5–10, 10–20, 20–30 cm). The soil in general had high structural stability. At 0–5 cm, meanweight diameter (MWD, 11.1 mm) and total organic C in macroaggregates (TOC, 39 g kg⁻¹ soil) were highest for the forest soil. Soil under NT had a more similar distribution of aggregate size classes and TOC to the forest soil than CT. The most pronounced difference between tillage systems was observed in the surface soil layer (0–5 cm). In this layer, NT had higher aggregate stability (AS_NT: 96%; AS_CT: 89%), had higher values of aggregate size distribution (MWD_NT: 7.9 mm, MWD_CT: 4.3 mm), and had on average 28% greater TOC in all aggregate size classes than CT. Soil under NT had greater TOC in macroaggregates (NT: 22 g kg⁻¹; CT: 13 g kg⁻¹). Crop rotation did not have a significant effect on soil aggregate distribution and TOC. By increasing macroaggregation NT increased organic carbon accumulation in soil.     

The influence of tillage systems on soil organic matter and soil hydrophobicity

Management practices including various tillage systems influence quantity and composition of soil organic matter (SOM). Parameters for evaluating both the SOM quantity (organic C [C_ox], total N [N_t]) and quality (microbial biomass C, hydrophobic and hydrophilic organic components) were determined in soil samples, taken from two soil depths (0–0.1 m and 0.1–0.3 m) in a field experiment in the period 2001–2007, with different tillage systems. The experiment, founded in 1995 in Prague-Ruzyně, includes conventional soil tillage (CT) plus some selected methods of conservation tillage: (a) no tillage (NT), (b) no tillage + mulch (NTM), and (c) minimum tillage with pre-crop residues incorporated (MTS). C_ox and microbial biomass C contents increased significantly with conservation tillage as compared to CT in 0–0.1 m layer, non-significant increase was found in 0.1–0.3 m layer. N_t increased non-significantly in both layers. Along with the depth of sampling, the content of the characterized parameters decreased in all variants; but the decrease in the conventionally tilled variant was, for the most part, lower than in the conservation tillage. The functional hydrophobic and hydrophilic groups of soil organic matter were identified by Fourier transform infrared (FTIR) spectroscopy, and the hydrophobic/hydrophilic group intensities ratio was calculated as the parameter of soil hydrophobicity. A higher soil hydrophobicity existed in all three conservation tillage treatments compared to CT due to the significantly higher content of hydrophobic organic components. C_ox correlated significantly with microbial biomass C, N_t, hydrophobic components, and soil hydrophobicity (R = 0.552–0.654; P < 0.05). Hydrophilic components did not correlate with other soil characteristics, with the exception of hydrophobic components. These data show that shifting from CT to the conservation tillage systems increased the content of SOM in top soil layer in relatively short time, improved the SOM quality and increased soil hydrophobicity in the condition of experiment.     

Abundance, production and stabilization of microbial biomass under conventional and reduced tillage

Soil tillage practices affect the soil microbial community in various ways, with possible consequences for nitrogen (N) losses, plant growth and soil organic carbon (C) sequestration. As microbes affect soil organic matter (SOM) dynamics largely through their activity, their impact may not be deduced from biomass measurements alone. Moreover, residual microbial tissue is thought to facilitate SOM stabilization, and to provide a long term integrated measure of effects on the microorganisms. In this study, we therefore compared the effect of reduced (RT) and conventional tillage (CT) on the biomass, growth rate and residues of the major microbial decomposer groups fungi and bacteria. Soil samples were collected at two depths (0-5 cm and 5-20 cm) from plots in an Irish winter wheat field that were exposed to either conventional or shallow non-inversion tillage for 7 growing seasons. Total soil fungal and bacterial biomasses were estimated using epifluorescence microscopy. To separate between biomass of saprophytic fungi and arbuscular mycorrhizae, samples were analyzed for ergosterol and phospholipid fatty acid (PLFA) biomarkers. Growth rates of saprophytic fungi were determined by [¹⁴C]acetate-in-ergosterol incorporation, whereas bacterial growth rates were determined by the incorporation of ³H-leucine in bacterial proteins. Finally, soil contents of fungal and bacterial residues were estimated by quantifying microbial derived amino sugars. Reduced tillage increased the total biomass of both bacteria and fungi in the 0-5 cm soil layer to a similar extent. Both ergosterol and PLFA analyses indicated that RT increased biomass of saprophytic fungi in the 0-5 cm soil layer. In contrast, RT increased the biomass of arbuscular mycorrhizae as well as its contribution to the total fungal biomass across the whole plough layer. Growth rates of both saprotrophic fungi and bacteria on the other hand were not affected by soil tillage, possibly indicating a decreased turnover rate of soil microbial biomass under RT. Moreover, RT did not affect the proportion of microbial residues that were derived from fungi. In summary, our results suggest that RT can promote soil C storage without increasing the role of saprophytic fungi in SOM dynamics relative to that of bacteria.     

Conservation tillage: Short- and long-term effects on soil carbon fractions and enzymatic activities under Mediterranean conditions

Short- and long-term field experiments are necessary to provide important information about how soil carbon sequestration is affected by soil tillage system; such systems can also be useful for developing sustainable crop production systems. In this study, we evaluated the short- and long-term effects of conservation tillage (CT) on soil organic carbon fractions and biological properties in a sandy clay loam soil. Both trials consisted of rainfed crop rotation systems (cereal–sunflower–legumes) located in semi-arid SW Spain. In both trials, results were compared to those obtained using traditional tillage (TT). Soil samples were taken in flowering and after harvesting of a pea crop and collected at three depths (0–5, 5–10 and 10–20 cm). The soil organic carbon fractions were measured by the determination of total organic carbon (TOC), active carbon (AC) and water soluble carbon (WSC). Biological status was evaluated by the measurement of soil microbial biomass carbon (MBC) and enzymatic activities [dehydrogenase activity (DHA), o-diphenol oxidase activity (DphOx), and β-glucosidase activity (β-glu)].The contents of AC and MBC in the long-term trial and contents of AC in the short-term trial were higher for CT than TT at 0–5 cm depth for both sampling periods. Furthermore, DHA and β-glucosidase values in the July sampling were higher in the topsoil under conservation management in both trials (short- and long-term). The parameters studied tended to decrease as depth increased for both tillage system (TT and CT) and in both trials with the exception of the DphOx values, which tended to be higher at deeper layers.Values of DHA and β-glu presented high correlation coefficients (r from 0.338 to 0.751, p ≤ 0.01) with AC, WSC and TOC values in the long-term trial. However, there was no correlation between either TOC or MBC and the other parameters in the short-term trial. In general, only stratification ratios of AC were higher in CT than in TT in both trials. The results of this study showed that AC content was the most sensitive and reliable indicator for assessing the impact of different soil management on soil quality in the two experiments (short- and long-term).Conservation management in dryland farming systems improved the quality of soil under our conditions, especially at the surface layers, by enhancing its storage of organic matter and its biological properties, mainly to long-term.