Strip-tillage effect on seedbed soil temperature and other soil physical properties

The no-tillage system is perceived as having lower soil temperatures, wetter soil conditions, and greater surface penetration resistance compared with conventional and other conservation tillage systems. Concerns associated with the effect of the no-tillage system on certain soil physical properties (i.e. soil temperature, moisture, and compaction) prompted this study to evaluate the effect of an alternative tillage system, strip-tillage, on these physical properties, compared with chisel plow and no-tillage systems. The study was conducted on two Iowa State University research and demonstration farms in 2001 and 2002. One site was at the Marsden Farm near Ames, where the soils were Nicollet loam (Aquic Hapludolls) and Webster silty clay loam (Typic Haplaquolls). The second site was at the Northeast Research and Demonstration Farm near Nashua, where the soils were Kenyon loam (Typic Hapludolls) and Floyd loam (Aquic Hapludolls).Soil temperature increased in the top 5 cm under strip-tillage (1.2–1.4 °C) over no-tillage and it remained close to the chisel plow soil temperature. This increase in soil temperature contributed to an improvement in plant emergence rate index (ERI) under strip-tillage compared with no-tillage. The results show no significant differences in soil moisture status between the three tillage systems, although the strip-tillage soil profile has slightly greater moisture content than chisel plow. Moisture content through the soil profile particularly at the lower depths under all tillage treatments was greater than the plant available water (PAW). However, the changes in soil moisture storage were much greater with strip-tillage and chisel plow than no-tillage from post-emergence to preharvest at 0–30 and 0–120 cm. It was observed also that most change in soil moisture storage occurred between post-emergence and tasseling. Penetration resistance was similar for both strip-tillage and no-tillage, but commonly greater than chisel plow. In general, the findings show that strip-tillage can contribute effectively to improve plant emergence, similar to chisel plowing and conserve soil moisture effectively compared with no-tillage.     

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.     

Crop yield and soil fertility response to reduced tillage under organic management

Conservation tillage (no-till and reduced tillage) brings many benefits with respect to soil fertility and energy use, but it also has drawbacks regarding the need for synthetic fertilizers and herbicides. Our objective was to adapt reduced tillage to organic farming by quantifying effects of tillage (plough versus chisel), fertilization (slurry versus manure compost) and biodynamic preparations (with versus without) on soil fertility indicators and crop yield. The experiment was initiated in 2002 on a Stagnic Eutric Cambisol (45% clay content) near Frick (Switzerland) where the average annual precipitation is 1000 mm. This report focuses on the conversion period and examines changes as tillage intensity was reduced. Soil samples were taken from the 0–10 and 10–20 cm depths and analysed for soil organic carbon (C_org), microbial biomass (C_mic), dehydrogenase activity (DHA) and earthworm density and biomass. Among the components tested, only tillage had any influence on these soil fertility indicators. C_org in the 0–10 cm soil layer increased by 7.4% (1.5 g C_org kg⁻¹ soil, p < 0.001) with reduced tillage between 2002 and 2005, but remained constant with conventional tillage. Similarly, C_mic was 28% higher and DHA 27% (p < 0.001) higher with reduced than with conventional tillage in the soil layer 0–10 cm. In the 10–20 cm layer, there were no significant differences for these soil parameters between the tillage treatments. Tillage had no significant effect on total earthworm density and biomass. The abundance of endogeic, horizontally burrowing adult earthworms was 70% higher under reduced than conventional tillage but their biomass was 53% lower with reduced tillage. Wheat (Triticum aestivum L.) and spelt (Triticum spelta L.) yield decreased by 14% (p < 0.001) and 8% (p < 0.05), respectively, with reduced tillage, but sunflower (Helianthus annuus L.) yield was slightly higher with reduced tillage. Slurry fertilization enhanced wheat yield by 5% (p < 0.001) compared to compost fertilization. Overall, C_org, C_mic, and DHA improved and yields showed only a small reduction with reduced tillage under organic management, but long-term effects such as weed competition remain unknown.     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

Effect of long-term conservation tillage on soil biochemical properties in Mediterranean Spanish areas

In semi-arid Mediterranean areas, studies of the performance of conservation tillage systems have largely demonstrated advantages in crop yield, soil water storage and soil protection against wind and water erosion. However, little attention has been given to interactions between soil biochemical properties under different tillage practices. Biochemical properties are useful tools to assess changes caused by different soil tillage systems in long-term field experiments. This study deals with the effect of long-term tillage practices (reduced tillage and no-tillage vs. traditional tillage) on soil chemical properties and microbial functions in three different sites of Spain (two of them located in the Northeast and one in the Southwest) under semi-arid Mediterranean conditions. Soil biological status, as index of soil quality, was evaluated by measuring microbial biomass carbon (MBC) and dehydrogenase (an oxidoreductase) and protease (a hydrolase) activities at three soil depths (0–5, 5–10 and 10–25 cm). In the three experimental areas, increases in soil organic matter content, MBC and enzymatic activities were found at the superficial layers of soil under conservation tillage (reduced tillage and no-tillage) in comparison with traditional tillage. Values of the stratification ratio of some biochemical properties were significantly correlated with yield production in Northeast sites.Conservation tillage has proven to be an effective strategy to improve soil quality and fertility in Mediterranean areas of Spain.     

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.     

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.     

Carbon sequestration in a long-term conventional versus conservation tillage experiment

The impact of conservation tillage practices on carbon sequestration has been of great interest in recent years. Changes in the soil organic carbon (SOC) as influenced by tillage, is more noticeable under long-term rather than short-term tillage practices. This experiment analyzed the organic carbon status of soils sampled at depth increments from 0 to 60 cm after 25 years of five tillage treatments in a silt loam soil. Zero tillage (ZT) treatment was compared to conventional tillage practices of mouldboard and chisel plow operations conducted either during the fall or spring season in a randomized complete block design with four replications. The SOC was calculated on depth and equivalent soil mass bases. Contrast analysis showed a significantly (5%) higher soil bulk density for zero versus fall and zero versus chisel tillage operations at 5–10 cm soil depth. The SOC concentration was dependent on the depth of tillage operation and followed the trend of higher SOC for zero, chisel, and mouldboard tillage at 0–5, 5–10, and 20–40 cm depth, respectively. There were more significant differences in the SOC storage when expressed on depth compared to an equivalent soil mass basis. SOC storage was significantly higher for ZT at the 0–5 cm soil depth compared to conventional tillage practices. Contrast analysis on an equivalent mass basis showed that SOC storage was significantly higher for spring tillage compared to fall tillage at 0–60 cm depth. In conclusion, ZT practices increased SOC concentration and storage compared to conventional tillage operations only for the surface layer but not for the entire soil profile.     

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.     

Carbon and nitrogen sequestration and soil aggregation under sorghum cropping sequences

Management practices, such as no tillage (NT) and intensive cropping, have potential to increase C and N sequestration in agricultural soils. The objectives of this study were to investigate the impacts of conventional tillage (CT), NT, and cropping intensity on soil organic C (SOC) and N (SON) sequestration and on distribution within aggregate-size fractions in a central Texas soil after 20 years of treatment imposition. Tillage regime and cropping sequence significantly impacted both SOC and SON sequestration. At 0–5 cm, NT increased SOC storage compared to CT by 33% and 97% and SON storage by 25% and 117% for a sorghum/wheat/soybean (SWS) rotation and a continuous sorghum monoculture, respectively. Total SOC and SON storage at both 0–5 and 5–15 cm was greater for SWS than continuous sorghum regardless of tillage regime. The majority of SOC and SON storage at 0–5 cm was observed in 250-m to 2-mm aggregates, and at 5–15 cm, in the >2-mm and 250-m to 2-mm fractions. Averaged across cropping sequences at 0–5 cm, NT increased SOC storage compared to CT by 212%, 96%, 0%, and 31%, and SON storage by 122%, 92%, 0%, and 37% in >2-mm, 250-m to 2-mm, 53- to 250-m, and <53-m aggregate-size fractions. No tillage and increased cropping intensity improved soil fertility by increasing soil organic matter levels and potential nutrient supply to crops.     

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.     

耕作方式对土壤螨类群落结构的影响

土壤螨类是土壤生态系统中重要的指示生物之一。为探讨耕作方式对土壤螨类数量、类群数、群落结构以及垂直分布的影响, 试验选取位于东北黑土区中国科学院海伦农田生态系统国家野外科学观测研究站中5种耕作方式(免耕耕作、少耕耕作、平翻耕作、组合耕作和旋耕耕作)试验区内土壤螨类为研究对象, 采用改良干漏斗(Modified Tullgren)法, 于2009年5月、6月和7月3个时期分离0~15 cm土层中的土壤螨类。结果表明: 耕作方式对土壤螨类数量和类群数存在显著影响, 3个时期共捕获土壤螨类2 441只, 免耕耕作、少耕耕作、组合耕作、旋耕耕作和平翻耕作分别捕获土壤螨类366只、436只、553只、819只和267只, 分别隶属于13科、18科、13科、14科和11科。传统的旋耕耕作具有最高的土壤螨类个体数量, 而保护性耕作中的少耕耕作具有最高的土壤螨类类群数。不同时期耕作方式对土壤螨类垂直分布的影响不同, 5月除免耕耕作外其他4种耕作方式均较好地保持了土壤螨类垂直分布的表聚特征, 即0~5 cm土层中土壤螨类的数量显著(P<0.05)高于其他两层(5~10 cm, 10~15 cm), 其中组合耕作和少耕耕作在3个时期中均较好地保持了土壤螨类的表聚特征, 且少耕耕作较好地保持了土壤螨类的多样性。MGP分析结果表明: 土壤甲螨群落随季节的变化在组成上发生变化, 从最初的高等甲螨为优势类群转化为低等甲螨为优势类群, 免耕和少耕的这种趋势较其他耕作方式更为明显, 少耕耕作3个时期土壤甲螨的组成类型分别为P型、G型和O型, 而免耕耕作3个时期土壤甲螨的组成类型分别为P型、O型和G型。少耕和免耕两种保护耕作方式较其他耕作方式更有利于土壤螨类群落结构的稳定性及多样性的保持, 有利于农田土壤生态环境的保护。     

Improving animal drawn tillage system in Ethiopian highlands

In most smallholder farms in Ethiopian highlands, farmers still use the wooden ard plough (Maresha). This study was undertaken to understand and optimise the traction forces provided by the draught animals. An ard plough equipped with three load cells (one on the beam and one on each side of the yoke) was implemented to measure traction forces required for tillage of four Vertisol fields under wet and dry conditions. Tillage was performed at three different depths of shallow (0–5 cm), medium-deep (5–10 cm) and deep (10–15 cm). The interpretation of force measurement was done for equally and unequally strong pair of oxen. After tillage, soil samples were taken for the determination of bulk density and moisture content. The cross-section area of furrow profile (CSAFP) and depth were also measured.With the measurement of equally strong oxen, each ox provided 50% of the total traction force required for tillage. However, with unequally strong oxen, different contributions of each ox to the total traction force were found. The stronger ox moved faster than the weaker ox, creating an asymmetric position of the yoke. In this situation, the weaker ox had to work harder to overcome the force transferred from the strong ox and correct the asymmetric position of the yoke. Thus, the weaker ox had to provide a larger force to the total traction force compared to the stronger ox. A larger traction force was measured with the yoke asymmetric position for smaller depth, speed and CSAFP. Therefore, farmers in the Ethiopian highlands can improve the tillage efficiency of the Ethiopian ard plough by using equally strong pairs of oxen. However, with unequally strong oxen the weaker ox should be enhanced to walk a head of the stronger ox, allowing the latter to provide the larger required traction force.     

The role of tephra covers on soil moisture conservation at Haleakala's crater (Maui, Hawai'i)

The influence of tephra covers on soil water was studied in Haleakala (Maui, Hawai'i) during two summers; eight sites with tephra layers and silverswords (Argyroxiphium sandwicense DC.) were sampled at 2415–2755 m. At each site, eight paired-sample sets were obtained in bare soils and under adjacent tephra, at three depths. Tephra were sharply separated from underlying soils and showed prominent vertical stratification. Tephra clast size-distribution was assessed by photosieving and on interstitial-gravel samples; stones included 45.6% cobbles, 29.4% pebbles, and 25% blocks.Moisture content increased with depth in both positions, but soils below tephra had more water at all depths than exposed areas. Surface soils beneath tephra contained 83% more water than bare ground. Soils at 5–10 cm had  106% greater moisture under rocks, but only  70% at 10–15 cm. Differences between plots were statistically significant ( p < 0.001) for surface soils, but less pronounced for subsoils. Soils above 2650 m had greater water content than at lower elevations, and moisture disparity between sample pairs increased with altitude.All soils were coarse, with  20% gravel and  94% sand; most fine material (≤ 0.063 mm) was silt, as clay content was negligible. Organic-matter percentage was low (1.65%). Bulk density and porosity were associated with moisture variation both in tephra-insulated and bare soils; 80% of field moisture was statistically (p < 0.001) accounted for by pore space. Air and soil temperatures were recorded at three sites during  one-week periods prior to moisture sampling. Tephra substantially decreased soil maxima and daily thermal amplitude in underlying soils, but did not noticeably affect nightly minima. Thin (5–6 cm) tephra layers were nearly as effective as thicker (9–15 cm) deposits in depressing soil maxima. Possible water-conservation mechanisms under tephra include: decreased evaporation due to ground shielding and lower maxima; reduced capillary flow; greater infiltration depth; nocturnal dew condensation; and fog interception by blocks.     

Cumulative effect of annually repeated passes of heavy agricultural machinery on soil structural properties and sugar beet yield under two tillage systems

The aim of this study was to determine potential cumulative effects of repeated passes with current heavy agricultural machinery on topsoil (0–0.3 m) and subsoil (below 0.3 m) physical properties of a Luvisol as affected by long-term tillage (annual mouldboard ploughing to 0.3 m depth (MP), shallow-mixing conservation tillage to 0.1 m depth (SM) with a wing-bladed rigid tine cultivator). Moreover, sugar beet yield was determined. Wheeling was conducted with a six-row self-propelled sugar beet harvester representing contemporary heavy agricultural machinery (wheel load 7.8–11.7 Mg, average ground contact pressure 100–145 kPa). Wheeling was applied once per year over three consecutive years after harvest of sugar beet, cereal and cereal, and moreover, independent from regular plot management with light experimental machinery. Soil moisture at wheeling (0–0.6 m depth) was around 100% field capacity in most years, which was secured by irrigation before wheeling if necessary.Repeated wheeling negatively affected penetration resistance, macropore volume (equivalent diameter >50 μm) and air permeability of topsoil (0.05–0.1 m, 0.18–0.23 m) and subsoil (0.4–0.45 m) layers, while biopore number and surface water infiltration remained unaffected. SM compared to MP tillage increased penetration resistance while decreasing macropore volume and air permeability in the 0.18–0.23 m layer, whereas reverse effects occurred in 0.4–0.45 m depth. Sugar beet yield was decreased by wheeling and SM tillage compared to the control treatments. No significant interactions between wheeling and tillage occurred in any parameter investigated.Conclusively, SM tillage did not provide better subsoil resistance against compaction compared to MP treatment under wheeling and soil conditions prevalent in our experiment. Repeated wheeling with heavy agricultural harvest machinery is obviously at risk to exceed the bearing capacity of susceptible soils. Although (i) under regular harvest conditions just small parts of arable fields (except headlands) are wheeled with high loads, (ii) harvest is by far not every year conducted under high soil moisture, and (iii) effects in the subsoil were small, such risks have to be taken into account. Reduction of tillage depth to <0.1 m is not recommended for high yielding sugar beet crops grown on loessial soils.     

Conservation of soil moisture by different stone covers on alpine talus slopes (Lassen, California)

This study reports on the influence of stone covers with different clast sizes on the soil moisture of alpine talus slopes in Lassen (California). Fifteen four-plot sets were sampled in the dry season (July 1990) in sandy areas and in talus covered with pebbles, cobbles, or blocks between 2740 and 2775 m. Three depths (0–5, 5–10, 10–15 cm) were sampled. Field moisture content increased gradually with depth in all soil profiles, and also in plots covered by increasingly larger rocks. Surface soils in sand areas were very dry, but under rocks had water contents 6 to 14 times greater. Differences among plots decreased with depth, but subsoil samples in sand were still drier than those beneath any stone cover at similar depths. Blocks were most effective in conserving moisture; water content below them was higher than even in deep (10–15 cm) sand soils. Soil temperatures were recorded in sand and under blocks for an 11-day period. Minima were not significantly different, but average maxima were 5.6°C lower under blocks than in sand, which reached highs 4.4°C lower than the air. Differences in soil moisture among talus types are ascribed to lower evaporation losses under stones, due to both disruption of capillarity by the coarse particles, which prevented water flow to the talus surface, and to their efficient reduction of maximum temperatures. An irrigation experiment was conducted at 2110 m on a steep talus on the Chaos Crags from July 18 to Aug. 2, 1993. Four 100×75 cm plots with the same surface types than at Lassen received 22.5 mm water; moisture content was then periodically sampled. Watering produced similar water distributions among soil depths and talus types to those in Lassen. Evaporation occurred quickly in bare soils due to high air and soil temperatures. The sand surface was already dry 2 days after watering, but stone-covered plots remained moist until day 15, when soils under blocks still retained 77–97% of the water content (percent by weight) at the start of the test.     

Use of an instrumented disc coulter for mapping soil mechanical resistance

A soil mechanical resistance sensor with a large-diameter disc coulter was developed to delineate areas of differing soil strength across agricultural fields. The instrumented disc coulter consisted of a 76.2 cm disc with two depth-measuring sensors (rotary potentiometer and ultrasonic proximity sensor) along with a global positioning system (GPS) receiver to georeference operating depth measurements. The consistency and repeatability of the system response were evaluated by making six passes across long-term tillage comparison plots with different degrees of soil disturbance, including: 20 cm plowing, 15 cm disking, 30 cm chiseling, and no-till in several combinations. At the time of testing, standard soil cone penetrometer measurements were taken. The relationship between the average cone index in the 0–30 cm soil profile (CI_0–30 cm) and the disc operating depth was evaluated. In addition, the cumulative energy density of the given depth of penetration defined as specific cone penetration energy (J m⁻² or N cm⁻¹) for each tillage plot was calculated using the cone index profiles. The average measured depth in each tillage plot was compared to the average predicted depth (d_ci) of a fixed specific cone penetration energy (P_ci). Static calibration tests on the depth sensors showed excellent linearity with coefficients of determination (R²) greater than 0.99. The results showed that, on the average, the changes in the depth measured with the rotary potentiometer were 44 and 68% of the changes in the depth measured with the ultrasonic proximity sensor while the disc coulter was passing across, or along, the tillage plots. This difference was primarily due to the sinkage of the tractor wheels. The depth measured with the ultrasonic sensor had significant correlation with both CI_0–30 cm and d_ci. This was partially due to the fact that a significantly high correlation (R² = 0.97) between the CI_0–30 cm and d_ci was observed, which was not expected and originated from the type of soil profiles present. The instrumented disc coulter is a low soil disturbance system and could be used as an inexpensive and simple sensor to obtain information about the mechanical condition of the soil for spot tillage or other management decisions.     

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.     

Tillage and no-tillage effects on physical and chemical properties of an Argiaquoll soil under long-term crop rotation in Buenos Aires,Argentina

No-tillage systems are able to reduce the negative effects of agricultural intensification on soil properties. However, knowledge of long-term impacts of no-tillage systems on soil properties is insufficient. It is essential to know which soil quality indicators are the most sensitive to management practices in each particular environment. Therefore, the objective of this work is to determine which soil quality properties are more sensitive to the impact of two tillage systems in a vertic Argiaquoll soil from Buenos Aires, Argentina. This work started in 2006 and included crop rotation and tillage systems, including both tillage and no-tillage. Physical and chemical properties were measured in three consecutive years (2013–2015) at two depths (0–10 cm and 10–20 cm). The tillage system modified soil physical and chemical properties, mainly in the surface layer. No-tillage showed significantly higher bulk density (2013–2015 p < 0.05), gravimetric moisture (2013; 2014 p < 0.05), organic carbon (2013–2015 p < 0.05), and aggregates stability in the face of a heavy rain (2013; 2015 p < 0.05), than soil under tillage. Soil saturation (or total porosity) was significantly greater under tillage. The tillage system did not affect hydraulic conductivity, total nitrogen and extractable phosphorus from the surface, nor physical and chemical properties from the second depth. No-tillage alleviates, but is not enough to mitigate, the loss of soil organic carbon and aggregate stability caused by continuous cropping in this vertic Argiaquall. Bulk density, organic carbon, aggregates stability and saturation are indicators for future studies performed in environments with similar soil and climate conditions.     

Recovery of enchytraeid populations after severe drought events

The potential impact of changes in precipitation patterns associated with climate changes was investigated in Enchytraeidae (Oligochaeta) in a Danish heathland. The amount of precipitation was manipulated during spring and summer in an experimental field site in order to reveal effects of three different drought regimes: weak drought (WD), medium drought (MD) and high drought (HD). Enchytraeids were sampled every six to eight weeks (0–9 cm depth) for more than the eight months and soil water potential (SWP) and soil water content (SWC) was measured on a regular basis for five months.The enchytraeid communities were generally reduced due to a natural drought spell. The HD treatment significantly reduced the moisture level of the soil further with SWP below −15 bar (5 and 10 cm depth) and SWC around 5% (v/v) for more than two months. As a result almost no enchytraeids were found in HD plots after two months with high drought stress. Nevertheless, the HD-treated enchytraeid communities recovered within two months, as there was no significant difference in biomass and density of the different treatments at that time. During periods with extreme low SWP enchytraeids were practically absent in the top soil (0–3 cm), but a few animals were found in 3–6 cm. During this period SWP was around −15 bar even in 20 cm depth, indicating that active stages could not have survived. Thus, we suggest that the species present must be dependent on a drought tolerant stage, as vertical migration could not have supported the observed recovery.SWP and SWC were both significantly correlated with the total density and biomass of enchytraeids. However, density was better correlated with the SWP and SWC compared to biomass, which can be due to hatching of cocoons and increased fragmentation rate.