Subsoil Loosening Research Articles

Short-term effects of subsoil management by strip-wise loosening and incorporation of organic material

Agricultural production in Central Europe increasingly suffers from extreme drought events. Improving root access to nutrient and water resources in the subsoil below the plow layer is a potential option to maintain productivity during dry summers. Here, we tested a strip-wise subsoil amelioration method that combines subsoil loosening with organic matter incorporation into the subsoil (biowaste or green waste compost) and compared it with a treatment of only subsoil loosening and a non-ameliorated control. A field experiment with randomized block design was conducted on a Luvisol with an argic horizon (Bt), with a rotation of spring barley and winter wheat. In the first two years after amelioration, we monitored soil physico-chemical parameters, microbial biomass, and shoot and root growth at anthesis as well as harvested grain yield and quality. Subsoil loosening with organic matter incorporation significantly decreased soil bulk density at the depth of compost incorporation when biowaste compost was used, but not when green waste compost had been incorporated. Nutrient stocks, nutrient availability and microbial biomass were not consistently affected by the subsoil amelioration. Nevertheless, the incorporation of organic material, especially biowaste compost, significantly increased root growth into the subsoil and subsequently significantly enhanced crop nutrient uptake, biomass and grain yield production. Green waste compost incorporation had less pronounced effects, with an increase in grain yield only in the second year after amelioration. Differences in crop development could not be explained by any single soil parameter, suggesting that it was rather a combined effect of loosened subsoil and better supply of subsoil resources that resulted in an increase in subsoil root length density and subsequently led to better crop performance.

Effects of loosening combined with straw incorporation into the upper subsoil on soil properties and crop yield in a three-year field experiment

Subsoil management needs to be integrated into the current tillage regimes in order to access additional resources of water and nutrients and sustain crop production. However, arable subsoil is often deficient in nutrients and carbon, and it is compacted, affecting root growth and yield. In this study, crop yield and soil responses to loosening of the upper subsoil, without and with straw injection below the plough layer (25–34 cm), were studied during three crop cycles (2016–2018) in a field experiment near Uppsala, Sweden. Responses to straw injection after loosening were studied after single and triple consecutive applications of 24–30 Mg ha−1 during 2015–2017 to spring-sown barley and oats. Subsoil loosening combined with one-time or repeated straw addition (LS treatments) significantly reduced soil bulk density (BD) and increased porosity, soil organic carbon (SOC) and total nitrogen (N) compared with loosening (L) alone (one-time or repeated annually) and the control. In treatment L, the soil re-compacted over time to a similar level as in the control.Field inspections indicated higher abundance of earthworms and biopores in and close to straw incorporation strips. Aggregates readily crumbled/fragmented by hand and casts (fine crumbs) were frequently observed in earthworm burrows. The treatment LS improved soil properties (SOC and porosity) and water holding capacity, but had no significant influence on crop yield compared with the control.Crop yield in all treatments was 6.5–6.8 Mg ha−1 in 2017 and 3.8–4.0 Mg ha−1 in 2018, and differences were non-significant. Absence of yield effect due to treatments could be possibly due to other confounding factors buffering expression of treatment effects on yield. Lower relative chlorophyll content in leaves in the loosening with straw treatment during early growth stages, did not affect final crop yield. Subsoil loosening performed three times gave no further improvement in soil properties and grain yield compared with one-time loosening. There was no difference in yield between repeated subsoil loosening + straw and one-time treatment. It will be interesting to study the long-term effects of deep straw injection and evaluate its impact under other soil and weather conditions.

Simulating Root Growth as a Function of Soil Strength and Yield With a Field-Scale Crop Model Coupled With a 3D Architectural Root Model.

Accurate prediction of root growth and related resource uptake is crucial to accurately simulate crop growth especially under unfavorable environmental conditions. We coupled a 1D field-scale crop-soil model running in the SIMPLACE modeling framework with the 3D architectural root model CRootbox on a daily time step and implemented a stress function to simulate root elongation as a function of soil bulk density and matric potential. The model was tested with field data collected during two growing seasons of spring barley and winter wheat on Haplic Luvisol. In that experiment, mechanical strip-wise subsoil loosening (30–60 cm) (DL treatment) was tested, and effects on root and shoot growth at the melioration strip as well as in a control treatment were evaluated. At most soil depths, strip-wise deep loosening significantly enhanced observed root length densities (RLDs) of both crops as compared to the control. However, the enhanced root growth had a beneficial effect on crop productivity only in the very dry season in 2018 for spring barley where the observed grain yield at the strip was 18% higher as compared to the control. To understand the underlying processes that led to these yield effects, we simulated spring barley and winter wheat root and shoot growth using the described field data and the model. For comparison, we simulated the scenarios with the simpler 1D conceptual root model. The coupled model showed the ability to simulate the main effects of strip-wise subsoil loosening on root and shoot growth. It was able to simulate the adaptive plasticity of roots to local soil conditions (more and thinner roots in case of dry and loose soil). Additional scenario runs with varying weather conditions were simulated to evaluate the impact of deep loosening on yield under different conditions. The scenarios revealed that higher spring barley yields in DL than in the control occurred in about 50% of the growing seasons. This effect was more pronounced for spring barley than for winter wheat. Different virtual root phenotypes were tested to assess the potential of the coupled model to simulate the effect of varying root traits under different conditions.

Soil Use Legacy as Driving Factor for Soil Erosion under Conservation Agriculture

Water erosion can cause irreversible depletions in soil quality and crop productivity. The susceptibility of the soil to erosion is affected by current and historical management practices. Historical soil management practices like ploughing or subsoil loosening may lead to irreversible degradations of soils, which in turn increases soil erosion risk. Six “Wischmeier” plots under conservation agriculture, but with different historic treatments regarding soil use and management, were evaluated. These plots were installed in 1984 in Colonia del Sacramento, Uruguay on a Vertic Argiudoll. The objective of this study was to quantify how changes in soil quality, generated by different historical soil use and management over the last 35 years, contribute to current runoff and soil erosion in a cropping system under soil conservation practices using no-till, residue retention and cover crops. Considering differences in soil legacy effects of previous land use, plots were grouped in three treatments with contrasting historic index of agricultural intensification (IAI). The IAI was developed combining the duration of land use under agricultural production and the number and intensity of tillage activity resulting in the treatments: tillage with crop-pasture rotation (TIL_CP), no-tillage under several rotations (NT_Mix) and tillage with continuous cropping (TIL_CROP) with an increasing IAI of 3.5, 7.1 and 11.8, respectively. Rainfall events, runoff water and total, fixed and volatile solids were studied from 2017 to 2019. Soil physical (bulk density, penetration resistance, infiltration rate, aggregate stability), chemical (soil organic carbon (SOC), pH, phosphorous (P-Bray)) and biological properties (particulate organic matter (POM), potentially mineralizable nitrogen (PMN)) were assessed in 2019. Yearly average runoff amounted 209, 579 and 320 mm in 2017, 2018 and 2019, respectively. Yearly average soil losses were 233, 805 and 139 kg/ha with significant differences among years. The lowest soil losses were observed in TIL_CP (231, 615 and 146 kg/ha in 2017, 2018 and 2019, respectively) with lowest IAI of 3.5. Infiltration rate was the lowest in plots with highest IAI. Soil bulk density was highest (1.3 g/cm3) in plots with high IAI. SOC and PMN were lowest in TIL_CROP (3.0% SOC and 34 mg/kg PMN), holding the highest IAI of 11.8. Conservation agriculture minimized soil erosion losses in all plots and years, and erosion was much lower than the maximum tolerable threshold of 7,000 kg/ha for this particular soil. However, in historically intensively tilled and cropped soils, soil quality showed long-term adverse effects pointing towards a reduced resilience of the agricultural system.

Effects of NP Fertilizer Placement Depth by Year Interaction on the Number of Maize (Zea mays L.) Plants after Emergence Using the Additive Main Effects and Multiplicative Interaction Model

Field experiments were carried out at the Department of Agronomy of the Poznań University of Life Sciences to determine the effect of the depth of NP fertilization placement in maize cultivation on the number of plants after emergence. The adopted assumptions were verified based on a six-year field experiment involving four depths of NP fertilizer application (A1—0 cm (broadcast), A2—5 cm (in rows), A3—10 cm (in rows), A4—15 cm (in rows)). The objective of this study was to assess NP fertilizer placement depth, in conjunction with the year, on the number of maize (Zea mays L.) plants after emergence using the additive main effects and multiplicative interaction model. The number of plants after emergence decreased with the depth of NP fertilization in the soil profile, confirming the high dependence of maize on phosphorus and nitrogen availability, as well as greater subsoil loosening during placement. The number of plants after emergence for the experimental NP fertilizer placement depths varied from 7.237 to 8.201 plant m−2 during six years, with an average of 7.687 plant m−2. The 61.51% of variation in the total number of plants after emergence was explained by years differences, 23.21% by differences between NP fertilizer placement depths and 4.68% by NP fertilizer placement depths by years interaction. NP fertilizer placement depth 10 cm (A3) was the most stable (ASV = 1.361) in terms of the number of plants after emergence among the studied NP fertilizer placement depths. Assuming that the maize kernels are placed in the soil at a depth of approx. 5 cm, the fertilizer during starter fertilization should be placed 5 cm to the side and below the kernel. Deeper NP fertilizer application in maize cultivation is not recommended. The condition for the use of agriculture progress, represented by localized fertilization, is the simultaneous recognition of the aspects of yielding physiology of new maize varieties and the assessment of their reaction to deeper seed placement during sowing.

A rationale of broach-plow’s parameters of the ridge-stepped ploughing of slopes

The aim of this study was to develop an improved technology for ridge-stepped ploughing of slopes and plow, which protects the soil from water erosion, improves the accumulation and preservation of soil moisture. The paper proposes an effective method for ridge-stepped ploughing of slopes, including the alternation of layer’s incomplete rotation with its full rotation within its furrow by 1800 in combination with the band subsoil loosening. A technological model of a ridge-stepped ploughing with simultaneous subarable strip loosening was developed. The design of the developed plow for ridge-stepped ploughing is highlighted. During the study the followings were theoretically and experimentally established: with a longitudinal distance between the hulls of 50 cm, the required qualitative incomplete turnover of the layers with the lowest energy costs is provided with the following plow’s parameters of the odd hulls: plow length is 75 cm, plow width is 25 cm, stabilizing plate height is 15 cm, and the minimum distance from the ploughshare toe to the stabilizing plate is 25 cm.

Cereal Response to Deep Tillage and Incorporated Organic Fertilizer

This study examined the effect of stripwise subsoiling and subsoiling combined with the incorporation of organic material on crop development in a two-year field trial with typical weather in the first year and hot, dry weather in the second. Subsoiling and its combination with incorporated organic materials had strong effects on plant development and crop yield of spring barley (2017) and winter wheat (2018). The subsoil was loosened in 30 cm wide furrows down to a depth of up to 60 cm with a tine (DL) or a spader machine (SM) and was compared with the same methods of subsoil loosening combined with the incorporation of compost from biological household wastes (DLB and SMB). Furthermore, green waste compost (SMG), chopped straw (SMCS) and sawdust (SMS) were incorporated with the spader machine only. DL successfully reduced penetration resistance underneath the furrow and enhanced root growth underneath and near the furrow over the whole experimental period. Grain protein content above the furrow was enhanced compared with the untreated control (C) in the first year, but grain yield did not increase. DLB also reduced penetration resistance and increased root growth, but furthermore caused considerable increases in soil mineral nitrogen underneath the furrow throughout the vegetation period. Consequently, both yield and grain protein content above the furrow were tendentially increased as compared with the C. In SMB, grain yield increased even more than in DLB, compared to C, in 2017 (84% for SMB vs. 19% for DLB) and nearly equally in 2018 (65.4% vs. 65.2%) while all other treatments tendentially decreased grain yield above the furrow as compared with C. The results indicate that subsoiling with the introduction of organic material can reduce mechanical impedance and increase soil nitrogen and thereby ensure stable yields during dry periods, which become more frequent under climate change.

The numeric visual evaluation of subsoil structure (SubVESS) under agricultural production

Subsoil degradation in agriculture is an increasing problem worldwide, particularly due to compaction caused by heavy machinery. Here, we describe a numeric assessment of subsoil structural quality in relation to soil as a crop growth medium and illustrate its utility with results from compaction experiments and from fields under minimum tillage. The scoring scheme resembles the topsoil visual evaluation of soil structure (VESS) (Guimarães et al., 2011) with more emphasis on examination of the profile wall and of soil fragments. The focus is on identification and evaluation of the anthropic ‘transition layer’ immediately below the topsoil, usually >30cm depth. Layers of contrasting hardness and colour were identified and the overall subsoil quality of each layer was scored from separate, sequential assessments of soil mottling, soil strength, visible soil porosity, the pattern and depth of root penetration and aggregate size and shape using a colour diagnostic flowchart. Use of the method enabled identification of extent and severity of compact transition layers in both well-drained and imperfectly drained soils. Porosity and strength assessments were particularly relevant. Reference soils under forest or long-term grassland helped to distinguish whether subsoil structural quality resulted from the natural soil composition or from degradation by land management. The derived scores may be used to judge the requirement for amelioration by subsoil loosening by mechanical inputs (e.g. deep tillage) and/or natural processes (e.g. shrinkage crack formation). The method was also used to identify differences in subsoil structural quality within fields associated with field traffic levels (Oxisol in Brazil) and with moisture status (Luvisol in France). The focus of SubVESS on structure rather than on texture may not permit recognition of effects such as low water holding capacity that influence agronomic potential. In such cases the more comprehensive evaluation of overall agronomic potential by methods such as the ‘profil cultural’ is required.

Subsoil loosening in a crop rotation for organic farming eliminated plough pan with mixed effects on crop yield

Compacted subsoil may reduce plant root growth with resulting effects on plant uptake of water and nutrients. In organic farming systems subsoil loosening may therefore be considered an option to increase nutrient use. We investigated the effect of subsoil loosening with a paraplow to ca. 35 cm depth within a four-crop rotation in an organic farming experiment at Foulum (loamy sand) and Flakkebjerg (sandy loam) in Denmark. In each of the years 2000–2003, half of four plots per site were loosened in the autumn bearing a young grass-clover crop (mixture of Lolium perenne L., Trifolium repens L. and Trifolium pratense L.) established by undersowing in spring barley ( Hordeum vulgare L.). The grass-clover was grown for another year as a green manure crop and was followed by winter wheat ( Triticum aestivum L.), lupin ( Lupinus angustifolius L.):barley and spring barley in the following 3 years. On-land ploughing was used for all cereal and pulse crops. Penetration resistance was recorded in all crops, and the results clearly showed that subsoil loosening had effectively reduced the plough pan and that the effect lasted at least for 3.5 years. Measurements of wheat root growth using minirhizotrons at Foulum in 2002/2003 did not show marked effects of subsoil loosening on root frequency in the subsoil. Subsoil loosening resulted in reduced growth and less N uptake of the grass-clover crop in which the subsoil loosening was carried out, probably due to a reduced biological nitrogen (N) fixation resulting from a smaller clover proportion. This had a marked effect on the growth of the succeeding winter wheat. Negative effect of subsoil loosening on yield of winter wheat and spring barley was observed without manure application, whereas small positive yield effect of subsoil loosening was observed in crops with a higher N supply from manure. Yield decrease in winter wheat was observed in years with high winter rainfall. There was no significant effect of subsoiling on grain yield of the lupin:barley crops, although subsoiling had a tendency to increase crop growth and yield during dry summers. Our results suggest that subsoil loosening should not be recommended in general under Danish conditions as a measure to ameliorate subsoil compaction.

Effect of annual lupines growing on compacted sandy loam Stagnic Luvisol

The aim of the investigation presented in this paper was to identify the suitable and less energy-demanding methods to loose the subsoil compaction instead of mechanical subsoil loosening. The experiments with lupines (Lupinus luteus L. and Lupinus angustifolius L.) and spring barley (Hordeum vulgare L.) were made on the sandy loam Stagnic Luvisol. The field was compacted by tractors MTZ-82 (total weight 4.84 megagram Mg) characterized by multiple tyre-to-tyre passing. Parameters such as plants biomass (shoots and roots) and the changes in soil physical properties, the bulk density and penetration resistance, were measured. The best results showed yellow lupine on six times compacted soil where the penetration resistance was 1 MPa lower than on sites planted with barley or narrow-leafed lupine and decreased also soil bulk density on 3- and 6-times compacted soil by 0.1 and 0.05 Mg m−3, respectively. At the same time, lupine growth increased soil penetration resistance on uncompacted fields. As the positive effect of ameliorative plants growing occurs mostly in the following year, when roots are decayed and biopores are formed, further investigations with lupines are needed.

Mitigation of subsoil recompaction by light traffic and on-land ploughing: II. Root and yield response

Plough pans have been shown to severely hamper root development, limit rooting depth and reduce crop yields. We evaluated the effect of plough pan re-compaction on root and yield response for winter wheat in a field trial conducted in two neighbouring fields on a sandy loam. Plots were mechanically loosened by a subsoiler to a depth of 35 cm in 1997 and 1998. In 2 years following the loosening operation, perennial grass/clover was grown with limited traffic intensity. Subsequently oats were established and followed by winter wheat. On-land ploughing was compared with traditional mouldboard ploughing. In addition, the plots were either heavy-trafficked (10–18 Mg axle load and ∼200 kPa inflation pressure) or light-trafficked (<6 Mg axle load and <100 kPa inflation pressure). The loosened treatments were referenced by non-loosened soil. Root growth of winter wheat was followed applying the minirhizotron technique. In one of the fields, these measurements were supplemented with core sampling for root length determination approximately at anthesis. Soil water content was followed in one of the fields using time domain reflectometry (TDR). Grain yield and nitrogen content in grain were determined. The adjoining study showed that the combination of heavy traffic and traditional ploughing caused strong recompaction of loosened soil, whereas the combination of light traffic and on-land ploughing produced moderate recompaction. For the loosened plots in one field, the strongly recompacted soil produced 7% lower yield than moderately recompacted soil, whereas no clear difference was found for the other field. No clear difference between the loosened treatments on root growth was observed. Surprisingly, the non-loosened soil performed similar or even better than the loosened and moderately compacted soil. The non-loosened soil facilitated higher root intensity at depth and produced similar yield and N-uptake. Our results suggest that mechanical subsoil loosening of humid sandy loams only is recommendable in case of very severe subsoil compaction. Natural alleviation of subsoil structure induced by changes in soil management may comprise a favourable alternative to mechanical subsoil loosening.

Mitigation of subsoil recompaction by light traffic and on-land ploughingII. Root and yield response

Plough pans have been shown to severely hamper root development, limit rooting depth and reduce crop yields. We evaluated the effect of plough pan re-compaction on root and yield response for winter wheat in a field trial conducted in two neighbouring fields on a sandy loam. Plots were mechanically loosened by a subsoiler to a depth of 35 cm in 1997 and 1998. In 2 years following the loosening operation, perennial grass/clover was grown with limited traffic intensity. Subsequently oats were established and followed by winter wheat. On-land ploughing was compared with traditional mouldboard ploughing. In addition, the plots were either heavy-trafficked (10–18 Mg axle load and ∼200 kPa inflation pressure) or light-trafficked (<6 Mg axle load and <100 kPa inflation pressure). The loosened treatments were referenced by non-loosened soil. Root growth of winter wheat was followed applying the minirhizotron technique. In one of the fields, these measurements were supplemented with core sampling for root length determination approximately at anthesis. Soil water content was followed in one of the fields using time domain reflectometry (TDR). Grain yield and nitrogen content in grain were determined. The adjoining study showed that the combination of heavy traffic and traditional ploughing caused strong recompaction of loosened soil, whereas the combination of light traffic and on-land ploughing produced moderate recompaction. For the loosened plots in one field, the strongly recompacted soil produced 7% lower yield than moderately recompacted soil, whereas no clear difference was found for the other field. No clear difference between the loosened treatments on root growth was observed. Surprisingly, the non-loosened soil performed similar or even better than the loosened and moderately compacted soil. The non-loosened soil facilitated higher root intensity at depth and produced similar yield and N-uptake. Our results suggest that mechanical subsoil loosening of humid sandy loams only is recommendable in case of very severe subsoil compaction. Natural alleviation of subsoil structure induced by changes in soil management may comprise a favourable alternative to mechanical subsoil loosening.

Subsoil loosening does little to enhance the transition to no-tillage on a structurally degraded soil

Long-term cropping with conventional cultivation on New Zealand’s easily compacted soil causes soil structure degradation. The objective of this study was to ascertain if soil physical properties, and crop establishment and yield could be improved by subsoil loosening in the first year of conversion from conventional tillage to no-tillage. Plots on a Milson silt loam (Argillic Perch-Gley Pallic Soil, Typic Ochraqualf) were Paraplowed (PP), straight-legged subsoiler (SL), mole ploughed (M), or left as non-loosened controls (C) in the autumn of 1997. Forage brassica was sown with a Cross-Slot™ no-tillage drill. Wheat was established on the plots in the spring of 1997. Subsoil loosening resulted in some transient improvements in measured soil physical properties. Initially, subsoil loosening significantly reduced soil strength. Shortly after subsoil loosening, cone indices showed disruption to 300 mm with PP, 350 mm with SL and 100 mm with M. About 80% of profile cone indices from the PP and SL treatments were less than the critical value of 2 MPa compared to 48% for C and M. At 267 days after subsoil loosening, PP continued to have significantly lower cone index values than C and M. In May, the bulk density of PP plots was significantly lower than SL, M and C although reconsolidation in all plots was observed 9 months later after the wheat was harvested. Air permeability for PP, SL and M was significantly greater than C in June. Subsoil loosening did not increase plant populations or yield of the brassica or wheat crops. Vertical rooting depth was greater in the PP treatment. Few significant differences in wheat rooting patterns were found at depth.

Properties, degradation risks and rehabilitation possibilities of heavy soils in Bulgaria

The objective of this study was to determine soil properties, limiting site deficiencies for agricultural production and degradation risks of some major soil groups of Bulgaria. Vertisols, Planosols, Chernozems and Luvisols were characterised based on soil analyses. Temporal waterlogging in combination with water erosion, soil compaction and chemical degradation limit the fertility of Vertisols and Planosols. Chernozems and Luvisols are partly compacted. To ensure soil productivity for coining generations and to protect soil and water resources, the evident soil degradation must be halted. Long‐term field studies of soil rehabilitation variants were conducted. Soil parameters and crop yield were the main indicators used to estimate soil quality. Pipe drainage in combination with subsoiling and the application of gypsum and limestone, respectively, are effective measures for site rehabilitation of degraded Vertisols and Planosols. Degraded Luvisols and Chernozems characterised by distinct and persistent subsoil compaction can be regenerated by subsoil loosening and following site‐adapted soil management practices.

Persistence of deep loosening of naturally compacted subsoils in Nova Scotia

Naturally compacted subsoils, as a result of geogenic and/or pedogenic processes, are a common phenomenon in soils formed on medium textured basal tills in the Maritimes. This study was conducted to determine whether soil loosening following tile drainage could improve the long-term physical condition of naturally compacted subsoils and consequently improve soil permeability and crop productivity. The effects of subsoiling at various soil depths (35 to 70 cm) perpendicular to tile lines on soil structural form, and crop biomass yield and root growth were investigated over a 4-yr period (1989–1993) on sandy loam to loam Luvisolic, Gleysolic, and Brunisolic soils, at three sites in Nova Scotia. For two of the sites, soil bulk density measured using gamma ray attenuation showed a significant decrease immediately after subsoiling, and soil hydraulic conductivity determined using a constant head well Guelph permeameter was increased, relative to the non-subsoiled control. At one of the sites, subsoil loosening increased crop winter survival and productivity. Subsoiling did not appear to significantly improve the long-term permeability or environment for root growth below the 45-cm soil depth. Evidence of subsoil reconsolidation was found at each site within the three year period. Key words: Subsoiling; drainage; Luvisolic, Gleysolic and Brunisolic soil; soil physical properties

Effects of subsoil loosening on soil physical properties, plant root growth, and pasture yield

Abstract Subsoil loosening of an 8‐year‐old dryland pasture soil (Templeton silt loam) at either of two depths (27 or 47 cm) resulted in a significant (P 10%) in soil bulk density and a concomitant increase in soil porosity compared with undisturbed soil. The hydraulic conductivity of the loosened soil was significantly (P < 0.05) greater than that of the undisturbed soil, reflecting the increased pore continuity within the depth of loosening. These more rapid drainage rates resulted in a drier soil profile at the start of spring, 10 months after subsoil loosening. These improved soil physical conditions permitted more rapid root growth and the development of a more extensive pasture root system with a significantly (P < 0.1) greater (36%) root length below 30 cm depth. Subsoil loosening resulted in significant increases in pasture production over the first 3 months of spring (August‐October).

Persistence of Loosened Horizons and Soybean Yield Increases in Bolivia

AbstractSoil compaction is a major factor limiting soybean [Glycine max (L.) Merr.] production in tropical eastern Bolivia. An experiment was conducted from 1985 through 1989 on a fine‐loamy, siliceous, isohyperthermic Aquic Ustropept with a compacted horizon (0.12–0.33 m) to determine the persistence of subsoil loosening by deep tillage and its effect on soybean yield responses. Four tillage treatments were investigated: conventional tillage consisting of disk harrowing to 0.12‐m depth (CN), subsoiling in 1985 only to 0.40‐m depth (SS/85), disk plowing in 1985 only to 0.30‐m depth (DP/85), and annual subsoiling (SS/YR). All three deep tillage treatments completely loosened the compacted horizon, reducing penetrometer resistance (PR) from a maximum of 3.05 to 2.01 MPa. From December 1987 onward, which coincided with an exceptionally wet period, subsoil reconsolidation occurred, and by June 1989 the PR of CN, DP/85, and SS/85 exceeded 3 MPa. Reconsolidation was attributed to a close‐packing rearrangement of soil particles under wet conditions. Coupled with increasing subsoil strength, a relatively greater reconsolidation occurred in SS/85 and DP/85, resulting in reduced “loosened” zones of 0.07‐m and 0.04‐m thickness, respectively. The pattern of relative reconsolidation suggests it occurred from above downward and from below upward, the latter perhaps being related to a high water table. In contrast SS/YR maintained a much thicker “loosened” horizon. overall subsoil reconsolidation, soybean yield responses continued for 3 yr with SS/85, and for 4 yr with DP/85 and SS/YR. Although substantial differences in relative reconsolidation existed between DP/85, SS/85, and SS/YR, few significant differences in yield were found when soil water was limiting.

Effects of soil physical conditions on root growth and water use of barley grown in containers

The results of an experiment to study the effects of subsoil loosening on root growth and water use of barley plants grown in 1.0-m-deep, 65-mm-diameter plastic tubes are reported. Changes in the dry bulk density (1280–1530 kg m −3) of the 0.2-m-deep soil layer immediately below the plough layer hand disproportionate effects on rates of root growth, and following this on crop water use and dry matter yield. Increasing the number of large pores in the sieved sandy loam soil at a depth of between 0.2 and 0.4 m allowed roots to proliferate easily and at the same time to extract the water held at relatively low suctions. When no extra water was added, these plants came under water stress sooner than those grown in containers with relatively compacteds ubsoil. Reduced rates of root growth meant that water was made available over a longer period of time. The variable and unpredictable yield responses of crops to subsoil loosening reported in the literature must be owing in part to the patterns of rainfall distribution during the season in relation to root growth and the development stage of the crop. Under certain conditions subsoil loosening will increase crop water stress and reduce yield. The validity of the techniques used for observing root growth was supported by the linear ( β=1.09) relationship obtained at the end of the experiment between the length of root at the soil/plastic interface and the corresponding number of root ends observed at the centre of the soil core ( r 2=70%, n=216), although there was still a considerable degree of scatter in the position of individual points.

Effects of subsoil loosening and irrigation on soil physical properties, root distribution and water uptake of potatoes ( Solanum tuberosum)

The effects of irrigation and subsoil loosening to 0.45-m depth on potato (cv. ‘Record’) root growth and water uptake in a sandy loam soil are reported. Root length was measured by destructive core sampling, and the penetration of roots into the subsoil monitored using glass minirhizotrons. Subsoil loosening resulted in an increased root length below ploughd depth, but only in irrigated plots. Despite large reductions in soil penetration resistance, the maximum depth of rooting was little affected by the loosening operation. In the summer of 1984, soil drying occurred to 1.2-m depth, with the depth of water extraction consistently 0.3–0.4 m below the observed rooting depth. It was inferred that up to 13% of the total water uptake was supplied by capillary rise to the root zone. Root water uptake in unirrigated treatments was limited by soil water deficits in excess of 50 mm, resulting in significant reductions in tuber yield. However, no differences in water uptake and yield were observed between loosened and unloosened plots. Evidence from several sources suggested that soil shrinkage on drying allowed sufficient roots to penetrate the compact, unloosened subsoil. This may have been sufficient to maintain water uptake rates similar to those found in loosened treatments.

Crop and soil response to subsoil loosening, deep incorporation of phosphorus and potassium fertilizer and subsequent soil management on a range of soil types.: Part 2: Soil structural conditions

Abstract. In a series of experiments on 16 sites both a power‐driven rotary‐tine Wye Double Digger and a rigid tine winged subsoiler produced significant subsoil loosening and fissuring. The Double Digger consistently produced the greatest clod breakdown together with the least soil bulk densities and cone penetration resistances. Management strategies after loosening had an important influence on the longevity of the loosening effect. The rate of recompaction was least with controlled traffic and bed systems and increased with random traffic and with the growing of root crops. No significant differences in crop response were monitored between the two loosening treatments, yield response depending largely on the extent of moisture stress experienced by the crop. Loosening on silty soils reduced yields in wet seasons and this was associated with soil structural instability. Visual soil profile examination is necessary to support bulk density and cone penetration resistance measurements when assessing soil compaction.