Reducing Tillage Intensity Research Articles

Clay soil moisture in spring cereal cultivation as related to tillage management

Conservation tillage with crop covered soil surface has been found to reduce the risk of erosion and nutrient leaching. The reduction of tillage intensity changes topsoil structure affecting soil physical conditions relevant to crop growth. In this study, the effects of autumn tillage management on soil moisture during the growing season of spring barley ( Hordeum vulgare ) was examined on two fi eld experiments on clay soils (Vertic Cambisol, Eutric Cambisol) in southwestern Finland in 2004–11. The objective of the study was to investigate the effects of reduced tillage intensity on soil moisture conditions of two different clay soils in different weather conditions. Autumn mouldboard ploughing (to 20–25 cm depth, P) was compared to stubble cultivation (10–15 cm, S) and zero tillage (N). During the growing season, soil moisture was determined once a week at the depth of 0−30 cm with a TRASE system I (Time Domain Refl ectometry (TDR)). Daily weather conditions (precipitation, air temperature) were also determined. Zero tilled soil stayed moister than the soil in other tillage treatments. When the beginning of the growing season was dry, higher soil moisture content in zero tilled soil improved the growth conditions of barley. In an unexceptional rainy beginning of growing season, the wetness of clay soils in zero tilled treatment hampered the crop growth and yield production clearly.

Effects of tillage and fallow period management on soil physical behaviour and maize development

Abstract Effects of two tillage treatments and two fallow period managements under continuous maize cropping on soil temperature, soil water dynamics and maize development were evaluated over a 4-year period (2005–2008). Tillage treatments were conventional tillage with mouldboard ploughing and conservation tillage with disk harrowing. The fallow period managements were bare soil or soil sown with a cover crop after maize harvest. For each year, topsoil temperature (0–20 cm-depth) was lower under conservation tillage systems at sowing, from 0.8 to 2.8 °C. This difference persisted several weeks after sowing, and disappeared afterwards. Under conservation tillage, higher soil water content was generally measured at sowing and during the growing season strong fluctuations were observed at 40 cm-depth. Under conventional tillage, soil water content varied mainly in the tilled layer (20 cm-depth). Tillage and fallow period management affected water flow rate at 40 cm-depth. During the maize growing season, the lowest drainage volumes were measured in 2006 and 2008 under conservation tillage in cover cropped plots. No effect of fallow period management on maize development and yield was observed but significantly higher yields were measured under conservation tillage in 2005 and 2007. From this 4-year experiment under continuous maize cropping, using cover crop and reducing tillage intensity enhanced water use efficiency while maintaining or increasing maize yields.

Cultivation Intensity in Relation to Organic Matter and Related Properties in a Vertisol in Southern Turkey

As most of the organic carbon (C) in the biosphere resides in the soil in the form of soil organic matter (SOM), tillage practices can potentially increase C losses to the atmosphere as carbon dioxide, thus contributing to greenhouse gases that exacerbate climate change. In the past century, conventional tillage, involving plowing and secondary cultivation, has unwittingly decreased C stocks in arable soils in North America, Europe, and Australia. The information on the effects of tillage on soil C and related properties in the Mediterranean region is scant, with evidence of resilience being even rarer. While long-term trials that directly measure tillage effects are rare in the Mediterranean, the alternative is a retrospective based on soil management history. In this study of a Vertisol in southern Turkey, we sampled sections of a field that had been intensively cultivated for about 20 years and 40 years, as well as a section left undisturbed in native vegetation for 14 years following years of conventional tillage. The SOM and total nitrogen (N) values were inversely related to cultivation intensity or duration, while the highest values were from the uncultivated site. Labile biomass C and N values followed the same trends with cultivation, whereas available P increased with cultivation time; in contrast, the percentage of water-stable aggregates decreased with cultivation duration. The study showed that such clay soils show a high degree of resilience and can recover in a relatively short time period if left uncultivated or in fallow. While preservation or set aside of arable crop land is not a viable option for farmers, reducing tillage intensity is feasible. The study suggests that minimum tillage or no-till could promote resilience and mitigate the adverse soil effects of conventional tillage that have already occurred.

Soil Organic Carbon Change Monitored Over Large Areas

Soils account for the largest fraction of terrestrial carbon (C) and thus are critically important in determining global C cycle dynamics. In North America, conversion of native prairies to agriculture over the past 150 years released 30–50% of soil organic carbon (SOC) stores [Mann, 1986]. Improved agricultural practices could recover much of this SOC, storing it in biomass and soil and thereby sequestering billions of tons of atmospheric carbon dioxide (CO2). These practices involve increasing C inputs to soil (e.g., through crop rotation, higher biomass crops, and perennial crops) and decreasing losses (e.g., through reduced tillage intensity) [Janzen et al., 1998; Lal et al., 2003; Smith et al., 2007].Managing agricultural soils to increase SOC storage is an immediately available, cost‐competitive option for mitigating CO2 emissions [Smith et al., 2007; Thomson et al., 2008], with a technical potential to offset as much as 800 teragrams of CO2 per year in the United States (∼13% of U.S. CO2 emissions) [Lal et al., 2003] and 5000 teragrams per year globally (∼17% of global CO2 emissions) [Smith et al., 2007]. Managing soils to sequester organic C also brings attendant benefits such as increased and sustainable crop productivity; improved quality of soil, water, and air; reduced energy inputs; and reduced vulnerability to climate change [Lal, 2004].

Effects of compost input and tillage intensity on soil microbial biomass and activity under Mediterranean conditions

Organic amendment and tillage reduction are two common practices to contrast soil organic matter decline, thus promoting sustainable cropping and carbon sequestration. In a horticultural land use system under Mediterranean climate, we evaluated the 9-year effects of two compost inputs (15 and 30 t ha−1 y−1, low and high input, respectively) and two tillage intensities (intensive and reduced) on soil macronutrients concentration, microbial biomass and activity. Total organic C, total N and POlsen were smaller in plots amended at low input, whilst intensive tillage decreased them at both compost inputs. These decreases in intensively tilled plots was ascribed to the disruption of soil aggregates, with consequent microbial degradation of the physically protected organic matter by oxidative processes. On the contrary, reduced tillage increased the extractable C, likely due to a higher protection of the most labile soil C fraction from the mineralization. Similarly, microbial biomass C and N increased following both doubling compost input and reducing tillage intensity, with a greater effect by the first factor. The higher values of cumulative 10-day basal and 20-h glucose-induced respiration, and metabolic quotient in intensively tilled plots suggested that high tillage favoured soil aggregate disruption and C accessibility. This was also confirmed by higher values of dehydrogenase activity/total organic C in those plots. Intensive tillage caused a higher soil aeration and organic substrates accessibility to microflora, thus undoing the fertility benefits provided by the high compost input. However, also a low compost input coupled to reduced tillage seemed to accomplish soil sustainability needs.

Energy use efficiency in different tillage systems for winter wheat on a clay and silt loam in Sweden

The energy efficiency of different implements and tillage systems for winter wheat in Sweden was examined. Mouldboard ploughing was compared with different ploughless tillage systems (chisel plough, disc, disc-press) and direct drilling on a clay and a silt loam soil during three years. Fuel consumption was measured for all tillage operations, including seedbed preparation and sowing. Energy balances were calculated, based on the direct and indirect use of fossil fuels in crop production. Specific draught (draught per cross-sectional area of soil) was highest for the disc-press implement, while mouldboard ploughing gave the lowest specific surface (surface area per kg soil). Total energy requirement for tillage ranged from 0.6 to 2.8 GJ ha −1 on the clay soil and 0.5 to 1.5 GJ ha −1 on the silt loam. Yield of winter wheat in the ploughless tillage and mouldboard ploughing systems was similar when oats or barley were grown as preceding crops. Growing winter wheat after winter wheat caused yield losses in treatments with reduced tillage intensity, especially direct drilling. Overall energy use in tillage as a proportion of total energy use for crop production ranged from 5% for direct drilling on the silt loam soil to 25% for mouldboard ploughing on the clay. The energy input in tillage was low compared with the energy in the harvested crop and thus energy efficiency, expressed as energy gain, depended mainly on crop yield and not on tillage intensity. For Swedish conditions, a small increase in energy gain might be expected for ploughless tillage compared with mouldboard ploughing when winter wheat is grown with a good preceding crop, but a lower energy gain when winter wheat is grown after winter wheat.

Effects of tillage and nitrogen fertilisation on triticale grain yield, chemical composition and nutritive value

Given the interest in the development of cultivation systems with low agronomic input and environmental impact, the aim of this study was to determine the influence of tillage system (conventional tillage (CT), two-layer tillage (TT), surface tillage (ST) and minimum tillage (MT)) and nitrogen (N) fertilisation rate (0, 50 and 100 kg ha(-1)) on triticale grain and protein yields, chemical composition and nutritive value. There were no significant differences among tillage treatments in grain and protein yields. ST resulted in significantly higher crude protein (CP) and true soluble protein (TSP) contents as well as in vitro crude protein digestibility (CPD). Neutral detergent fibre concentration was significantly higher with ST than with MT, and this led to a small reduction (2 g kg(-1) dry matter (DM)) in in vitro true DM digestibility (IVTDMD). N fertilisation significantly increased grain and protein yields as well as CP, non-protein nitrogen and TSP contents and CPD. IVTDMD was significantly lower with 0 kg N ha(-1) than with 50 and 100 kg N ha(-1). Reducing tillage intensity improved the CP content and CPD of triticale grain. The application of 50 kg N ha(-1) resulted in good grain quality parameters and grain and protein yields.

Tillage management effects on pesticide fate in soils. A review

Reducing tillage intensity through the implementation of conservation practices is a way to reach a more sustainable agriculture. Reducing tillage is indeed an efficient way to control soil erosion and to decrease production costs. Nonetheless, the environmental impact of reduced tillage is not well known because conservation techniques may induce strong changes in soil physicochemical properties and biological activity. Knowledge on the fate of applied pesticides under conservation practices is particularly important from this point of view. We review here the advances in the understanding, quantification and prediction of the effects of tillage on pesticide fate in soils. We found the following major points: (1) for most dissipation processes such as retention, degradation and transfer, results of pesticide behaviour studies in soils are highly variable and sometimes contradictory. This variability is partially explained by the multiplicity of processes and contributive factors, by the variety of their interactions, and by their complex temporal and spatial dynamics. In addition, the lack of a thorough description of tillage systems and sampling strategy in most reports hampers any comprehensive interpretation of this variability. (2) Implementation of conservation tillage induces an increase in organic matter content at the soil surface and its gradual decrease with depth. This, in turn, leads to an increase in pesticide retention in the topsoil layer. (3) Increasing retention of pesticides in the topsoil layer under conservation tillage decreases the availability of the pesticides for biological degradation. This competition between retention and degradation leads to a higher persistence of pesticides in soils, though this persistence can be partially compensated for by a more intensive microbial activity under conservation tillage. (4) Despite strong changes in soil physical properties under conservation tillage, pesticide transfer is more influenced by initial soil conditions and climatic conditions than by tillage. Conservation tillage systems such as no-tillage improve macropore connectivity, which in turn increases pesticide leaching. We conclude that more knowledge is needed to fully understand the temporal and spatial dynamics of pesticide in soil, especially preferential flows, in order to improve the assessment of pesticide risks, and their relation to tillage management.

Effect of tillage intensity on population densities of Heterodera glycines in intensive soybean production systems

The effects of tillage on Heterodera glycines, the most important yield-reducing pathogen of soybean in the U.S., were examined in a long-term tillage and crop sequence study initiated in 1975 on a mollisol at Purdue University. Population densities of H. glycines were monitored under corn–soybean rotation and soybean monoculture in 2003 and 2004. Tillage treatments included: (A) fall moldboard plow + spring secondary tillage; (B) fall chisel plow + spring secondary tillage; (C) ridge tillage; and (D) no-tillage. In both years in the rotational plots, final population densities of H. glycines were proportional to tillage intensity. Under both soybean and corn rotation crops, highest population densities were observed with plowing + secondary tillage and lowest population densities were detected under no-tillage. In 2004, population densities in monoculture soybean soil declined with depth intervals in layers of 0–10, 10–20, and 20–30-cm depth under no-till, but not in plowed plots. Multiple regression analysis determined that the stratification of nematode population densities was strongly correlated to penetrometer resistance and potassium concentration of the soil. Tillage seemed to affect population densities of H. glycines by modification of the soil physical parameters in corn–soybean rotation plots. Reducing tillage intensity was beneficial in reducing population densities of H. glycines in rotational soils. Thus, the choice of tillage system can reduce the risk for damage by this widely distributed pathogen.

Crop Productivity and Economics during the Transition to Alternative Cropping Systems

Many environmental benefits accrue from reducing tillage and increasing crop diversity; however, economic factors often encourage the continued use of intensive tillage and specialized crop production. This study examined crop yields, input costs, and economic returns during the transition to a range of cropping system alternatives in the northern Corn Belt region, including different system (organic, conventional), tillage (conventional, strip‐tillage), rotation (corn–soybean, corn–soybean–wheat/alfalfa–alfalfa) [Zea mays L., Glycine max (L.) Merr., Triticum aestivum L., Medicago sativa L.], and fertility (no fertilizer/manure, fertilizer/manure applied at recommended rates) treatments. Increasing crop diversity and reducing tillage intensity reduced total costs by $24–102 ha−1 within conventional treatments, and $16–107 ha−1 within organic treatments. Yields of corn, soybean, and wheat were more than 15% lower when using organic vs. the highest yielding conventional practices. Treatments receiving fertilizer or manure had wheat yields more than 0.3 Mg ha−1 and alfalfa yields 2.7 Mg ha−1 higher than treatments that did not receive fertilizer or manure. Within conventional systems, no significant differences in the 4‐yr net present value of net returns were detected for tillage and rotation alternatives. Net present values for the organic systems without organic price premiums were at least $692 ha−1 lower than for the best conventional systems suggesting a barrier to the adoption of these systems should organic price premiums decline. However, when organic price premiums were included, most organic treatments had net present values comparable to or exceeding those from conventional treatments.

Some perspectives on carbon sequestration in agriculture

One of the main options for greenhouse gas (GHG) mitigation identified by the IPCC is the sequestration of carbon in soils. Since the breaking of agricultural land in most regions, the carbon stocks have been depleted to such an extent, that they now represent a potential sink for CO 2 removal from the atmosphere. Improved management will however, be required to increase the inputs of organic matter in the top soil and/or decrease decomposition rates. In this paper we use data from selected regions to explore the global potential for carbon sequestration in arable soils. While realising that C sequestration is not limited to the selected regions, we have, however, focussed our review on two regions: (i) Canadian Prairies and (ii) The Tropics. In temperate regions, management changes for an increase in C involve increase in cropping frequency (reducing bare fallow), increasing use of forages in crop rotations, reducing tillage intensity and frequency, better crop residue management, and adopting agroforestry. In the tropics, agroforestry remains the primary method by which sequestration rates may be significantly increased. Increases in soil C may be achieved through improved fertility of cropland/pasture; on extensive systems with shifting cultivation cropped fallows and cover crops may be beneficial, and adopting agro forestry or foresting marginal cropland is also an alternative. In addition, in the tropics it is imperative to reduce the clearing of forests for conversion to cropland. Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized North America where the majority of research pertaining to C sequestration has been carried out. More research is needed, especially for the Tropics, to more accurately capture the impact of region-specific interactions between climate, soil, and management of resources on C sequestration, which are lost in global level assessments. By itself, C sequestration in agricultural soils can make only modest contributions (3–6% of fossil fuel contributions) to mitigation of overall greenhouse gas emissions. However, effective mitigation policies will not be based on any single ‘magic bullet’ solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option.

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

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

Soil carbon and nitrogen changes as influenced by tillage and cropping systems in some Iowa soils

Soil organic C (SOC) and total N (TN) contents play a crucial role in sustaining agricultural production systems. Short-term (≤10-year) management effects on SOC and TN dynamics are often complex and variable. Three experiments were conducted to evaluate short-term tillage and cropping system effects on SOC and TN within the 0–30 cm soil depth across Iowa. The first experiment with no-tillage and chisel plowing treatments was established in 1994 on Clarion-Nicollet-Webster (CNW), Galva-Primghar-Sac (GPS), Kenyon-Floyd-Clyde (KFC), Marshall (M), and Otley-Mahaska-Taintor (OMT) soil associations under a corn (Zea mays L.)–soybean (Glycine max (L.) Merr.) rotation. The second experiment with no-tillage, strip-tillage, chisel plowing, deep ripping, and moldboard plowing treatments was initiated in 1998 on the CNW soil association in a corn–soybean rotation. The third experiment consisting of smooth bromegrass (Bromus inermis Leyss.), switchgrass (Panicum virgatum L.) and corn–soybean–alfalfa (Medicago sativa L.) treatments was established in 1991 on Monona-Ida-Hamburg (MIH) soil association under no-tillage management. Short-term tillage effects on SOC and TN occurred primarily at the 0–15 cm soil depth. Tillage effects did not vary significantly with soil association. No-tillage resulted in greater SOC and TN contents than chisel plowing at the end of 7 years of tillage practices averaged over the CNW, GPS, KFC, M, and OMT soil associations. The increase in SOC and TN with no-tillage was not related to SOC and TN stratification in the soil profile or annual C and N inputs from crop residue, but most likely due to decreased mineralization rate of soil organic matter. However, tillage effects on SOC and TN were negligible at the end of only 3 years of tillage practices on the CNW soil association. Smooth bromegrass and switchgrass systems resulted in greater SOC and TN contents at both 0–15 cm and 15–30 cm soil depths than a corn–soybean–alfalfa rotation after 10 years of management on the MIH soil association. Smooth bromegrass and switchgrass systems increased SOC by 2.3 and 1.2 Mg ha−1 yr−1 at the 0–15 cm soil depth, respectively. We conclude from these short-term experiments that reducing tillage intensity and increasing crop diversity to include perennial grasses could be effective in improving C and N sequestration in Midwest soils.

The effect of tillage intensity and time of herbicide application on weed communities and populations in maize in central Europe

Soil-conserving cropping systems aim at reducing tillage intensity to decrease soil erosion, leaching of nitrate and pesticides, and production costs. They are, therefore, likely to change the efficiency of weed control and hence weed populations. There is a lack of information on how reduced tillage systems, especially no-tillage (NT), affect the development of weed populations and the efficiency of weed control of maize crops under the humid, temperate climate of large parts of Europe. An experiment was conducted at two sites of the Swiss midlands to investigate the impact of the time of chemical weed control on weed populations in different tillage systems. Pre- and post-emergence herbicides were applied in a conventional tillage (CT) system with a moldboard plough, in a minimum tillage (MT) system with a chisel plough, and in a NT system in a winter wheat ( Triticum aestivum L.)–oilseed rape ( Brassica napus L.)–winter wheat–maize ( Zea mays L.) crop rotation. Crop residues were left on the field and stubble tillage was not carried out. The density of weeds in treatments without herbicide tended to be lower in NT than in MT and CT. An analysis of variance and canonical discriminant analysis (CDA) showed that perennial weeds such as Epilobium spp. L. and Sonchus arvensis L. were related to NT, and annual broad-leaved species were associated with MT and CT. In general, post-emergence weed control was more efficient than pre-emergence weed control regardless of the tillage system. However, NT systems may be adopted successfully when weed control measures are adapted to changing weed populations.

Tillage Intensity, Mycorrhizal and Nonmycorrhizal Fungi, and Nutrient Concentrations in Maize, Wheat, and Canola

Reduced tillage can change numerous physico‐chemical properties of soil and the activity of various microorganisms including mycorrhizal and pathogenic soil fungi, and thus influence nutrient uptake by plant roots. We studied the colonization of roots by mycorrhizal and nonmycorrhizal fungi and nutrient concentrations in plant tops grown during a 3‐yr rotation of maize (Zea mays L.), winter wheat (Triticum aestivum L.), and canola (Brassica napus L.) in two sites in Switzerland where fields have been under three tillage treatments (conventional, CT; chisel plow, CP; and no‐tillage, NT) since 1987. Maize roots were colonized to a greater extent by mycorrhizal fungi with NT than with CP or CT treatments. Wheat roots were equally and weakly colonized by mycorrhizal fungi in all treatments but were relatively heavily (up to 35% of the root length) colonized by several nonmycorrhizal fungi such as Olpidium, Polymyxa, and Gaeumannomyces–Phialophora complex. Canola roots, as expected, were not colonized by any mycorrhizal fungi but were colonized by O. brassicae Reduced tillage intensity altered the concentration of some nutrients in the leaves of mycorrhizal host plants (maize and wheat) but did not change those in nonhost canola. Changes in nutrient concentrations in maize and wheat leaves were likely due to the combined effects of colonization of their roots by various mycorrhizal and nonmycorrhizal fungi and not to some changes in the physical or chemical properties of soils. Cluster analysis showed that Mn concentration in wheat leaves was closely related to the Gaeumannomyces–Phialophora complex and concentrations of Ca, K, and Zn were related to tillage intensity and to the Polymyxa colonization of roots. We conclude that the colonization of roots by nonmycorrhizal root parasites, and especially by nonfilamentous obligate fungi, need to be taken into account in mycorrhizal studies conducted under field conditions.

Soil microbial biomass and mineralization of carbon and nitrogen in ecological, integrated and conventional forage and arable cropping systems

In a cropping systems experiment in southeastern Norway, ecological (ECO), integrated (INT) and conventional (CON) forage (FORAGE) and arable (ARABLE) model farms were compared. After 5 experimental years, topsoil was sampled in spring from spring grain plots and incubated for 449 days at controlled temperature (15 °C) and moisture content (50% water-holding capacity). There were no detectable differences between model farms in terms of total soil C or N. For INT and CON, however, values of microbial biomass C and N, microbial quotient (Cmic/Corg), and C and N mineralization were, or tended to be, higher for FORAGE than for ARABLE. For the ECO treatment, values were similar for FORAGE and ARABLE and did not differ significantly from that of CON-FORAGE. For INT and CON, the metabolic quotient (qCO2) was lower for FORAGE than for ARABLE. Again, for the ECO treatment, values were similar for FORAGE and ARABLE and did not differ significantly from that of CON-FORAGE. We estimated the sizes of conceptual soil organic matter pools by fitting a decomposition model to biomass and mineralization data. This resulted in a 48% larger estimate for CON-FORAGE than for CON-ARABLE of physically protected biomass C. For physically protected organic C the difference was 42%. Moreover, the stability of soil aggregates against artificial rainfall was substantially greater for CON-FORAGE than for CON-ARABLE. On this basis, we hypothesized that the lower qCO2 values in the FORAGE soils were mainly caused by a smaller proportion of active biomass due to enclosure of microorganisms within aggregates. Altogether, our results indicated a poorer inherent soil fertility in ARABLE than in FORAGE rotations, but the difference was small or absent in the ECO system, probably owing to the use of animal and green manures and reduced tillage intensity in the ECO-ARABLE rotation.

Reducing tillage intensity — a review of results from a long-term study in Germany

This paper reviews research performed at the Justus-Liebig-University of Giessen, Germany into the impact of different tillage systems on soil properties and quality. The impact of intensive soil tillage treatments on several soil properties was described by means of selected data obtained through long-term interdisciplinary research. The experiments were based on comparative application (long-term, up to 18 years investigations) of the respective tillage options on different soils (e.g. Eutric Cambisol, Eutric Fluvisol) ranging in texture from sand to a silt loam. These soils are located at five field sites with different crop rotations in the central German state of Hesse. Tillage intensity of the systems was considered to decrease in the following sequence: Conventional plough tillage (CT), reduced tillage (RT), and no-tillage (NT). For elucidating the impact of tillage intensity, the tillage extremes CT and NT were compared. Physical conditions of soil as influenced by the application of RT were considered to be intermediate between CT and NT. In general, bulk density in the upper layer of NT soils was increased, resulting in a decrease in the amount of coarse pores, and a lower saturated hydraulic conductivity when compared with the CT and RT soils. Surface cover by crop residues and higher aggregate stability under NT protected soil fertility by avoiding surface sealing and erosion. Lateral losses of herbicides were also reduced under NT conditions, whereas the susceptibility for preferential vertical transport of herbicides needs further evaluation. Accumulation of organic matter and nutrients near the soil surface under NT and RT were favorable consequences of not inverting the soil and by maintaining a mulch layer on the surface. Those improvements were associated with enhanced biological activities in NT and RT topsoils. Increased earthworm activity in NT treatments was associated with a system of continuous macropores which improved water infiltration rates. Earthworms support decomposition and incorporation of straw. Soils which have not been tilled for many years were more resistant to vehicle passage; consequently, the compaction by traffic was lower. Penetration resistance curves indicate that a uniformly stable structure had developed over the years in NT soils. Overall, the results show that RT and NT were beneficial to the investigated soil properties. If crop rotation, machinery, and plant protection are well adapted for the introduction of conservation tillage, these systems may replace conventional ploughing systems in many cases in German agriculture.

Aggregation and organic matter fractions of three Nigerian soils as affected by soil disturbance and incorporation of plant material

Soil management involving organic matter incorporation and reduced tillage intensity has often been reported to improve soil structure. However, the mechanisms and roles of soil organic matter (SOM) fractions in the process of soil structural stabilisation are not well documented. Furthermore, documentation of their positive effects on soils in the tropics is scarce. This study examined the changes in soil structure in response to SOM fractions dynamics in an incubation experiment. Three Nigerian soils: Iwo series (Oxic Tropudalf), Itagunmodi series (Tropeptic Euthrothox) and Owode series (Oxisol) were incubated with ground barley straw ( Hordeum vulgare L.) or green ryegrass ( Lolium perenne L.) with and without disturbance of the soil during incubation. The incorporation of plant material significantly increased the light fraction organic matter (LFOM) with density <1.7 g cm −3 but had no effects on the heavy fraction polysaccharides (HFPS), i.e. polysaccharides attached to heavy fraction soil minerals with density >1.7 g cm −3. A significant decline of LFOM was recorded with time of incubation (0–41 days: 21%, 30% and 36% decrease for the no plant material treatment, the barley straw treatment, and the green ryegrass treatment, respectively). This was associated with a significant rise of HFPS. Furthermore, the added plant material clearly decreased the soils' fraction of dispersible clay even before incubation, which was interpreted as a direct effect of the LFOM on the clay. Therefore, the use of dispersible clay as an indicator of macro-aggregate stability is questioned. After 41 days of incubation the concentration of water-stable aggregates was on an average 9% higher for soils with added plant material relative to soils not receiving plant material. When packing the post-incubation soil in metal cores, the volume of pores with equivalent neck diameter >10 μm was from 0.024 to 0.033 m 3 m −3 higher and the saturated hydraulic conductivity 18–24% higher for soils with added plant material than for soils without. Disturbance of the soil during incubation reduced the concentration of water-stable aggregates by 7% relative to undisturbed. Also the volume of pores with a neck diameter >10 μm and the saturated hydraulic conductivity were significantly reduced (by 6% and 19% relative, respectively) when the soil was disturbed during incubation. The results demonstrate that rapid changes of SOM fractions can occur over a short incubation period and that these changes have a pronounced positive effect on the structure of these tropical soils. It also suggests that incorporated plant material may correct tillage induced degradation of soil physical properties over a relatively short time.

Changes in total, mineralizable and light fraction soil organic matter with cropping and tillage intensities in semiarid southern Alberta, Canada

There has been a trend toward increased cropping intensity and decreased tillage intensity in the semiarid region of the Canadian prairies. The impact of these changes on sequestration of atmospheric CO 2 in soil organic carbon (C) is uncertain. Our objective was to quantify the changes in total, mineralizable and light fraction organic C and nitrogen (N) due to the adoption of continuous cropping and conservation tillage practices. We sampled three individual long-term experiments at Lethbridge, Alberta, in September 1992: a spring wheat ( Triticum aestivum L.)-fallow tillage study, a continuous spring wheat tillage study and a winter wheat rotation-tillage study. Treatments had been in place for 3–16 years. In the spring wheat-fallow study, different intensities (one-way disc > heavy-duty cultivator > blade cultivator) of conventional tillage (CT) were compared with minimum tillage (MT) and zero tillage (ZT). After 16 years, total organic C was 2.2 Mg ha −1 lower in more intensively worked CT treatments (one-way disc, heavy-duty cultivator) than in the least-intensive CT treatment (blade cultivator). The CT with the blade cultivator and ZT treatments had similar levels of organic C. The CT treatments with the one-way disc and heavy-duty cultivator had light fraction C and N and mineralizable N amounts that were about 13–18% lower than the CT with the blade cultivator, MT or ZT treatments. In the continuous spring wheat study, 8 years of ZT increased total organic C by 2 Mg ha −1, and increased mineralizable and light fraction C and N by 15–27%, compared with CT with a heavy-duty cultivator prior to planting. In the winter wheat rotation-tillage study, total organic C was 2 Mg ha −1 higher in a continuous winter wheat (WW) rotation compared with that in a winter wheat-fallow rotation. The lack of an organic C response to ZT on the WW rotation may have been due to moldboard plowing of the ZT treatment in 1989 (6 years after establishment and 3 years before soil sampling), in an effort to control a severe infestation of downy brome ( Bromus tectorum L.). Our results suggest that although relative increases in soil organic matter were small, increases due to adoption of ZT were greater and occurred much faster in continuously cropped than in fallow-based rotations. Hence intensification of cropping practices, by elimination of fallow and moving toward continuous cropping, is the first step toward increased C sequestration. Reducing tillage intensity, by the adoption of ZT, enhances the cropping intensity effect.

Tillage intensity effects on soil properties and crop yields in a long-term trial on morainic loam soil in southeast Norway

Many tillage studies focus primarily on grain crops, whereas other important agricultural crops receive little attention. This paper presents yield results for various crops grown in the tenth to sixteenth year of a long-term tillage trial on loam soil in southeast Norway. Traditional plough tillage was compared with deep and shallow tine cultivation and with minimum tillage, and the residual effects of tillage were measured in the seventeenth and eighteenth years. Soil bulk density, air permeability and other soil conditions were found to be favourable for crop growth on all treatments in the tenth year. The yield levels of cereals ( Hordeum vulgare L., Triticum aestivum L. and Avena sativa L.) and potatoes ( Solanum tuberosum L.) showed consistent increases of 2–8% with declining tillage intensity, whereas yields of fodder beet ( Beta vulgaris L.) were highest after plough tillage. The latter result was thought to be due to lower soil temperatures under reduced tillage. Yields of brassica crops were greatly affected by tillage intensity, owing to a marked reduction of clubroot ( Plasmodiophora brassicae Wor.) infection with reduced tillage. Average yields for these crops were 23%, 52% and 59% higher with deep tine cultivation, shallow tine cultivation and minimum tillage, respectively, than with plough tillage. The effects were particularly dramatic in the case of fodder rape ( Brassica napus L. ssp. oleifera Sinsk. f. biennis Reichb.) and cabbage ( Brassica oleracea L. var. capita L.). Liming raised the yields of some brassica crops but did not influence the effect of tillage. Soil acidity was measured twice during the trial period and again in the second residual year, and showed values which were 0.1–0.3 pH units lower with reduced tillage than with plough tillage. This rules out the conclusion that the effect of tillage on clubroot was associated directly with acidity. Positive residual effects of reduced tillage systems were found on the yields of both brassicaceous and gramineous crops. Reduced tillage intensity may thus be recommended for all crops studied, with the exception of fodder beet, on morainic loam soils of southeast Norway.