Lars J. Munkholm

Spatial and temporal effects of direct drilling on soil structure in the seedling environment

Despite more than 30 years of research and practical experience the interest in shallow tillage and especially direct drilling has remained low in Scandinavia. Excessive compaction of the topsoil layer is one of the major problems encountered when adapting shallow tillage and direct drilling in particular. The purpose of this study was to evaluate temporal and spatial effects of two different direct drilling techniques on bulk density and penetration resistance in the near seed environment. A sandy loam growing small grain cereals was followed during the first 3 years after conversion from conventional tillage to direct drilling to reveal short-term changes in soil structure. A field experiment with four blocks was conducted in 1999–2001 where a conventional mouldboard ploughing–harrowing system (PL) was compared with direct drilling performed by either a chisel coulter drill (DD-C) or a single disc drill (DD-D). Effects on density and penetration resistance were measured in the field after first, second and third year of crop establishment (T1, T2 and T3). Bulk density was determined at 0–100 mm depth using a dual probe gamma-ray transmission system. Penetration resistance was recorded in the field at 0–150 mm depth. At T2 column samples (diameter: 180 mm, height: 200 mm) were taken with the seed row through the centre. Penetration resistance was determined in these samples in a 10 mm×10 mm grid using a micropenetrometer (3 mm cone base diameter) at 0 to approximately 150 mm depth. Two samples from each treatment were analysed by a medical CT-scanner to determine spatial differences in bulk density. Irrespective of coulter type direct drilling gave a fast compaction of the arable layer below seeding depth when shifting from mouldboard ploughing to direct drilling. Soil strength was substantially higher already in the first year of direct drilling (i.e., maximum 0.4 and 1.2 MPa, for PL and DD-D/DD-C, respectively). Critical high penetration resistance (>2.0 MPa) and bulk density levels (>1.5 g cm-3) were reached at T2 and remained at the same level at T3. The DD-C direct drill produced a more favourable soil environment for crop establishment than the DD-D drill. A layer of approximately 40 mm loose granular soil above seeding depth and no indication of a direct compaction effect was found for the DD-C treatment. In contrast, the field as well as the laboratory results indicated a direct compacting effect for the DD-D drill. Despite the lack of direct compaction effect from the DD-C drill itself, evidence suggest that periodic non-inversion soil loosening of the lower part of the arable layer is needed on direct drilled sandy loam soil in a moist and cool climate.

Non-inversion tillage effects on soil mechanical properties of a humid sandy loam

Optimisation of soil tilth is of paramount importance in organic plant production in order to enhance crop growth. Non-inversion and reduced tillage systems are often claimed to be preferable for organic farming. The purpose of this study was to evaluate the early stage effects of converting a mouldboard-ploughed soil to a non-inversion tillage system. A multi-level experimental strategy including in situ, on-site and laboratory methods was followed in order to relate quantitative measures of soil physical properties directly to soil behaviour in the field. A non-inversion deep soil loosening (0¯35 cm) tillage system (NINV) was compared to a conventional mouldboard ploughing and harrowing tillage system (CONV). The experimental site was located on an organically managed sandy loam soil. The tillage treatments were applied to plots in two fields (B3 and B4) at the experimental site. Limited numbers of measurements were performed in the B3 field during the 1997¯1999 growing seasons. A more comprehensive programme was carried out in the B4 field in May and September 1998. A root-restricting plough pan was detected in the CONV treated soil. The NINV treatment effectively loosened the plough pan resulting in a visibly improved soil structure and a decrease in soil strength. The penetration resistance in the plough pan was reduced from about 1800 kPa in CONV to less than 1000 kPa in NINV when measured at field capacity. The loosening of the plough pan was still evident after 2 years without tillage operations in a perennial grass/clover crop. The topsoil of the CONV treatment had a more desirable tilth than that of the NINV treatment, which had higher soil strength at the 7¯14 cm depth. In accordance with this, the CONV treated topsoil fragmented more readily than the NINV soil in the field. The laboratory measurements on soil from the September sampling showed that the NINV treatment had lower friability index (i.e., friability index of 0.16 and 0.22 for NINV and CONV, respectively) and higher tensile strength of air-dry aggregates. The differences in topsoil tilth were not eliminated by natural soil meliorating processes during the growing season. This paper discusses the early stage effects of converting to non-inversion tillage. A number of years of continued treatment may be required before beneficial effects of non-inversion tillage are manifested in improved topsoil tilth.

Tensile strength of soil cores in relation to aggregate strength, soil fragmentation and pore characteristics

Tensile failure of soil is desirable in tillage. Soil tensile strength estimates most often are obtained from compression tests of dry aggregates. As tillage is performed under moist conditions, it would be highly relevant to measure tensile strength at high water contents. Plough-layer soil was sampled in a compacted soil (PAC) and in a non-compacted reference soil (REF). Tensile strength was measured in a new direct tension test using undisturbed soil cores (4.45 cm in diameter and 5.00 cm in height) adjusted to either -50 or -100 hPa matric potential. The air-filled pore space, a, was determined from water retention measurements. Air permeability, Ka, was determined at -30, -100 and -300 hPa matric potentials and from these measurements an index of pore organization (PO=Ka/a) was calculated. Soil behaviour in the field was evaluated at approximately -300 hPa matric potential by measuring soil strength using the torsional shear box method and soil fragmentation using a simple soil drop test. The direct tensile strength results showed that the PAC soil had significantly higher tensile strength than the REF soil (e.g. 3.2 and 2.0 kPa, respectively at -100 hPa matric potential). This finding was in accordance with the aggregate tensile strength results and also agreed well with soil fragmentation in the field (i.e. geometric mean diameter (GMD) equal to 38.7 and 14.2 mm, respectively, for PAC and REF samples dropped from 75 cm height). The tensile strengths of the soil cores were close to the predicted values determined from the aggregate tensile strength results. The energy input in the soil drop test (i.e. approximately 8.9 J kg-1 dry soil) was low in comparison with the energy input in tillage but high compared with the specific rupture energy of soil aggregates (e.g. 0.4 and 0.3 J kg-1, respectively for PAC and REF aggregates adjusted to -100 hPa matric potential). The relatively poor fragmentation in the soil drop test indicated that a substantial amount of the energy input was stored as volumetric strain energy and/or lost to processes such as plastic deformation. The tensile strength of soil cores was negatively correlated to the macroporosity of the soil, whereas the ease of soil fragmentation was positively correlated to PO.

Nitrate leaching, yields and carbon sequestration after noninversion tillage, catch crops, and straw retention.

Crop management factors, such as tillage, rotation, and straw retention, need to be long-term to allow conclusions on effects on crop yields, nitrate leaching, and carbon sequestration. In 2002, two field experiments, each including four cash crop rotations, were established on soils with 9 and 15% clay, under temperate, coastal climate conditions. Direct drilling and harrowing to two different depths were compared to plowing with respect to yield, nitrate N leaching, and carbon sequestration. For comparison of yields across rotations, grain and seed dry matter yields for each crop were converted to grain equivalents (GE). Leaching was compared to yields by calculating yield-scaled leaching (YSL, g N kg GE), and N balances were calculated as the N input in manure minus the N output in products removed from the fields. Direct drilling reduced yields, but no effect on leaching was found. Straw retention did not significantly increase yields, nor did it reduce leaching, while fodder radish ( L.) as a catch crop was capable of reducing nitrate leaching to a low level. Thus, YSL of winter wheat ( L.) was higher than for spring barley ( L.) grown after fodder radish due to the efficient catch crop. Soil organic carbon (SOC) did not increase significantly after 7 yr of straw incorporation or noninversion tillage. There was no correlation between N balances calculated for each growing season and N leaching measured in the following percolation period.

Soil compaction limits root development, radiation-use efficiency and yield of three winter wheat (Triticum aestivum L.) cultivars

Abstract Soil compaction has increased during recent years due to the traffic with increasingly heavier machinery. We evaluated the effect of soil compaction on soil penetration resistance, rooting depth, light interception, radiation-use efficiency (RUE) and yield of three different cultivars of winter wheat (Triticum aestivum L.). On loamy sand two compaction treatments (PAC-1 and PAC-2) and a no compaction reference treatment (REF) were applied. PAC-1 was intended to affect primarily the subsoil whereas PAC-2 was intended to affect primarily the topsoil. PAC-2 showed the highest and REF the lowest penetration resistance in the topsoil, respectively. In the subsoil both compaction treatments showed higher penetration resistances than REF. In comparison with REF, the compaction treatments decreased the estimated effective rooting depth by ca. 10, 20 and 50 cm in the three winter wheat cultivars tested, equivalent to decreases in the available soil water in the root zone of up to ca. 90 mm. These differences indicate some genetic variation in the ability of cultivars to penetrate compacted soil, although the interaction between compaction treatment and cultivar was not significant. Due to almost sufficient precipitation, the impairment of root penetration resulted in a minor yield decrease of ca. 9% of grain yield in PAC-2 and ca. 8% of total dry matter (DM) in both compaction treatments. The latter was attributed to decreases in interception of light and to efficiency of light energy conversion into biomass. The RUE was positively correlated with an estimated effective rooting depth across cultivars, while DM yield was not. This correlation probably was a result of restrictions on stomatal opening mediated by drought stress and abscisic acid produced in the root system in response to occasional soil drying. Root-sourced signals, triggered in a direct response to soil compaction, may have contributed.

Suboptimal fertilisation compromises soil physical properties of a hard-setting sandy loam

Nutrient management affects not only crop productivity and environmental quality, but also soil physical properties related to soil tilth. Previous studies on soil physical properties have focussed on effects of fertiliser type, whereas the effect of fertiliser rate has been neglected. We examined the impact of no fertilisation (UNF) and different rates of mineral fertiliser (½NPK and 1NPK) and animal manure (1½AM) on an ensemble of soil physical characteristics, with the amount of fertiliser added at level 1 corresponding to the standard rate of plant nutrients for a given crop. Soil was from the Askov long-term field experiment, initiated in 1894 on a hard-setting sandy loam. We assessed clay dispersibility, wet-stability of aggregates, aggregate strength, bulk soil strength and soil pore characteristics. The soils receiving 1NPK and 1½AM had similar soil physical properties, the only differences being a wider range in the optimum water content for tillage and more plant-available water in the soil amended with 1½AM. Suboptimal fertiliser rates (UNF and ½NPK) increased clay dispersibility, soil cohesion and bulk density, and reduced aggregate stability. The physical properties of soils exposed to suboptimal fertilisation indicate that the level of soil organic matter, including active organic binding and bonding materials, has become critically low due to reduced inputs of crop residues. While long-term suboptimal fertilisation compromises soil physical properties, crop-yield-optimised rates of mineral fertilisers and animal manure appear to sustain several soil physical properties equally well.

Soil texture analysis revisited: Removal of organic matter matters more than ever

Exact estimates of soil clay (<2 μm) and silt (2–20 μm) contents are crucial as these size fractions impact key soil functions, and as pedotransfer concepts based on clay and silt contents are becoming increasingly abundant. We examined the effect of removing soil organic matter (SOM) by H2O2 before soil dispersion and determination of clay and silt. Soil samples with gradients in SOM were retrieved from three long-term field experiments each with uniform soil mineralogy and texture. For soils with less than 2 g C 100 g-1 minerals, clay estimates were little affected by SOM. Above this threshold, underestimation of clay increased dramatically with increasing SOM content. Silt contents were systematically overestimated when SOM was not removed; no lower SOM threshold was found for silt, but the overestimation was more pronounced for finer textured soils. When exact estimates of soil particles <20 μm are needed, SOM should always be removed before soil dispersion.

Visual soil evaluation: realizing potential crop production with minimum environmental impact.

1. Describing soil structures, rooting and biological activity and recognising tillage effects, damage and recovery from damage in clayey and sandy soilsAnne Weill and Lars J Munkholm 2. Assessing structural quality and crop performance for agronomy (VESS, VSA, SOILpak, Profil cultural, SubVESS)Tom Batey, Rachel M. L. Guimaraes, Josephine Peigne and Hubert Boizard3. Reduction of yield gaps and improvement of ecological function through local-to-global applications of visual soil assessmentDavid C. McKenzie, Mansonia A. Pulido Moncada and Bruce C. Ball4. Visual evaluation of grassland and arable management impacts on soil qualityLars J. Munkholm and Nicholas M. Holden5. Choosing and evaluating soil improvements by subsoiling and compaction controlRichard J. Godwin and Gordon Spoor6. Valuing the Neglected: lessons and methods from an organic, anthropic soil system in the Outer HebridesMary Norton Scherbatskoy, Anthony C. Edwards and Berwyn L. Williams 7. Evaluating land quality for carbon storage, greenhouse gas emissions and nutrient leachingJoanna M. Cloy, Bruce C. Ball and T. Graham Shepherd8. Soil structure under adverse weather/climate conditionsRachel M. L. Guimaraes, Owen Fenton, Brian W. Murphy and Cassio A. Tormena9. The expanding discipline and role of Visual Soil EvaluationBruce C. Ball and Lars J. Munkholm

Soil Surface Roughness Using Cumulated Gaussian Curvature

Optimal use of farming machinery is important for efficiency and sustainability. Continuous automated control of the machine settings throughout the tillage operation requires sensory feedback estimating the seedbed quality. In this paper we use a laser range scanner to capture high resolution maps of soil aggregates in a laboratory setting as well as full soil surface maps in a field test. Gaussian curvature is used to estimate the size of single aggregates under controlled circumstances. Additionally, a method is proposed, which cumulates the Gaussian curvature of full soil surface maps to estimate the degree of tillage.

Soil organic matter widens the range of water contents for tillage

Highlights • Soil organic carbon (SOC) affected the mechanical properties of soil aggregates.• Water contents for tillage is determined using water retention and consistency approaches.• There is a strong positive relation between SOC and range of water contents for tillage (ΔθRANGE).• ΔθRANGE determined based on the consistency approach is recommended over the water retention approach.