Ararso Etana

Swedish experiments on the persistence of subsoil compaction caused by vehicles with high axle load

Abstract Final results from nine Swedish field experiments on soil and crop response to traffic by vehicles with an axle load of 10 Mg are reported. The traffic significantly compacted the soils to a depth of 50–60 cm. Eleven years later, virtually no alleviation of the compaction effects in the subsoil was observed, and crop yields were still affected in spite of normal annual freezing to a depth of 40–70 cm.

Effects of tillage depth on organic carbon content and physical properties in five Swedish soils

The soil tillage system affects incorporation of crop residues and may influence organic matter dynamics. A study was carried out in five 15‐20 year old tillage experiments on soils with a clay content ranging from 72 to 521 g kg ˇ1 . The main objective was to quantify the influence of tillage depth on total content of soil organic carbon and its distribution by depth. Some soil physical properties were also determined. The experiments were part of a series of field experiments all over Sweden with the objective of producing a basis to advise farmers on optimal depths and methods of primary tillage under various conditions. Before the experimental period, all sites had been mouldboard ploughed annually for many years to a depth of 23‐25 cm. Treatments included primary tillage to 24‐29 cm depth by mouldboard plough (deep tillage) and to 12‐ 15 cm by field cultivator or mouldboard plough (shallow tillage). Dry bulk density, degree of compactness and penetration resistance profiles clearly reflected the depth of primary tillage and substantially increased below that depth. Compared to deep tillage, shallow tillage increased the concentration of organic carbon in the surface layer but decreased it in deeper layers. Total quantity of soil organic carbon and carbon‐nitrogen ratio were unaffected by the tillage depth. Thus, a reduction of the tillage depth from about 25 cm to half of that depth would appear to have no significant effect on the global carbon cycle. # 1999 Elsevier Science B.V. All rights reserved.

Particulate-facilitated leaching of glyphosate and phosphorus from a marine clay soil via tile drains

Abstract Losses of commonly used chemical pesticides from agricultural land may cause serious problems in recipient waters in a similar way to phosphorus (P). Due to analytical challenges concerning determination of glyphosate (Gly), transport behaviour of this widely used herbicide is still not well known. The objective of the present study was to quantify and evaluate leaching of Gly in parallel with P. Leaching losses of autumn-applied Gly (1.06 kg ha−1) via drainage water were examined by flow-proportional sampling of discharge from 20 drained plots in a field experiment in eastern Sweden. Samples were analysed for Gly in particulate-bound (PGly) and dissolved (DGly) form. The first 10 mm water discharge contained no detectable Gly, but the following 70 mm had total Gly (TotGly) concentrations of up to 6 µg L−1, with 62% occurring as PGly. On average, 0.7 g TotGly ha−1 was leached from conventionally ploughed plots, compared with 1.7 g TotGly ha−1 from shallow-tilled plots (cultivator to 12 cm working depth). Higher Gly losses occurred in snowmelt periods in spring, but then with the majority (60%) as DGly. All autumn concentrations of PGly in drainage water were significantly correlated (p<0.001) to the concentrations of particulate-bound phosphorus (PP) lost from the different plots (Pearson correlation coefficient 0.84), while PP concentrations were in turn significantly correlated to water turbidity (Pearson correlation coefficient 0.81). Leaching losses of TotGly were significantly lower (by 1.3 g ha−1; p<0.01) from plots that had been structure-limed three years previously and ploughed thereafter than from shallow-tilled plots. Turbidity and PP concentration also tended to be lowest in discharge from structure-limed plots and highest from shallow-tilled plots. This difference in TotGly leaching between soil management regimes could not be explained by differences in measured pH in drainage water or amount of discharge. However, previously structure-limed plots had significantly better aggregate stability, measured as readily dispersed clay (RDC), than unlimited plots. The effects of building up good soil structure, with strong soil aggregates and an appropriate pore system in the topsoil, on mitigating Gly and P losses in particulate and dissolved form should be further investigated.

Effects of uniaxial stress on the physical properties of four Swedish soils

The effects of uniaxial stress and soil water content at the time of compression on the degree of compactness (D), defined as the bulk density expressed as a percent of a reference bulk density, and on other soil physical properties were investigated. Stresses of 25, 50, 100, 200 and 400 kPa were applied to large, loose soil samples of light, heavy and humus-rich clays as well as loamy sand in a laboratory experiment. D increased approximately with the log of applied stress over the range of gravimetric water contents normally encountered during field work. Thus, a modified version of the compression model proposed by [Larson, W.E., Gupta, S.C., Useche, R.A., 1980. Compression of agricultural soils from eight soil orders. Soil Sci. Soc. Am. J., 44: 450–457] could be used to compute the stress that gives the optimal degree of compactness for crop growth. The soil compression index, which shows the susceptibility of a soil to compaction, was greatest for the heavy clay and about 30% less for the humus-rich clay, even though they had almost the same clay content. For the loamy sand, D was greatest in the driest sample (water content = 0.01 kg kg−1). In clayey soils, samples at a water content of < 0.20 kg kg−1 were not tested, and the maximum value of D was reached when the soils were compressed at or slightly below field capacity but, as the uniaxial stress increased, the soil water content at which maximum D was reached decreased. In wet clayey soils, soil matric tension was influenced by compaction. Stresses of 200 kPa and above caused the air permeability to fall below a value that is regarded to be critical with respect to crop growth.

Phosphorus leaching from clay soils can be counteracted by structure liming

Two field experiments with drained plots on clay soils (60% and 25% clay) demonstrated a significant reduction in leaching of total phosphorus after application of structure lime. Aggregate stability was significantly improved. Phosphorus leaching in particulate form was significantly reduced following structure liming at the site with a very high clay content. Sites representing low (50 mg kg−1) and high (140 mg kg−1) levels of phosphorus extractable with acid ammonium lactate in topsoil displayed differing effects on leaching of dissolved reactive P (DRP). This form of phosphorus was only significantly reduced compared with the control at one site with high topsoil phosphorus status and relatively high (17–18%) degree of phosphorus saturation in the subsoil. Laboratory experiments with simulated rain events applied to topsoil lysimeters from the same site also demonstrated a significant reduction in leaching of DRP. These findings indicate that structure liming is an appropriate leaching mitigation measure on soils with both a high clay content and high soil phosphorus status.

Effects of aluminium water treatment residuals, used as a soil amendment to control phosphorus mobility in agricultural soils.

Phosphorus (P) leaching from agricultural soils is a serious environmental concern. Application of aluminium water treatment residuals (Al-WTRs) at a rate of 20 Mg ha(-1) to clay soils from central Sweden significantly increased mean topsoil P sorption index (PSI) from 4.6 to 5.5 μmol kg(-1) soil. Mean degree of P saturation in ammonium lactate extract (DPS-AL) significantly decreased from 17 to 13%, as did plant-available P (P-AL). Concentrations of dissolved reactive P (DRP) decreased by 10-85% in leaching water with Al-WTR treatments after exposure of topsoil lysimeters to simulated rain. Soil aggregate stability (AgS) for 15 test soils rarely improved. Three soils (clay loam, silty loam and loam sand) were tested in greenhouse pot experiments. Aluminium-WTR application of 15 or 30 ton ha(-1) to loam sand and a clay loam with P-AL values of 80-100 mg kg(-1) soil significantly increased growth of Italian ryegrass when fertilised with P but did not significantly affect growth of spring barley on any soil. Al-WTR should only be applied to soils with high P fertility where improved crop production is not required.

Effect of mouldboard ploughing and shallow tillage on sub-soil physical properties and crop performance

Abstract This study was conducted in spring 2011 in a long-term field experiment with the objective of assessing the effect of shallow tillage (ST) and mouldboard ploughing (MP) on important soil physical properties and crop performance. Undisturbed soil samples were taken before sowing from depths of 15–20, 25–30 and 35–40 cm for the determination of saturated hydraulic conductivity (Ks), bulk density (Bd), and water retention capacity in laboratory conditions. Penetrometer resistance (PR) was measured in the field after 1 month of sowing. Plant density of barley (Hordeum vulgare) was also counted after 1 month of sowing. Field water content was significantly higher for MP than ST at 15–20 cm (MP = 27%, ST = 22.5%) and 25–30 cm depth (MP = 29.3%, ST = 24.8). Water retention at 1 m suction was also significantly higher in the treatment with MP at the depth of 25–30 cm (31%) than in the ST treatment (27.7%). Significantly higher Ks value was found for ST at depths of 15–20 (13.09 cm h−1) and 25–30 cm (5.10 cm h−1) than for MP (11.15 and 3.52 cm h−1, respectively). Soil Bd was significantly lower in MP treatments for the first two investigated depths (1.43 and 1.44 g cm−3, respectively) than in the ST (1.54 and 1.53 g cm−3). Significant higher PR value was found for ST, especially at the depth of 5–35 cm, but the result was not so high as to reduce the root growth. Water content determined parallel with PR measurement was not significantly different for the two treatments. Plant density as well as crop yield in the ST treatment was higher (3840 kg ha−1) than in the MP treatment (2490 kg ha−1). Therefore, we concluded that long-term ST treatment markedly influenced crop performance and yield by facilitating soil physical properties.

Structure liming enhances aggregate stability and gives varying crop responses on clayey soils

ABSTRACT It has been suggested that liming can improve soil structure and thereby decrease losses of particles and associated nutrients. In this study, two types of structure lime, slaked lime (Ca(OH)2) and a mixed product of calcium carbonate (CaCO3) and slaked lime (Ca(OH)2), were applied at three different rates in field trials on clayey soils (23%–40% clay). A combination of primary tillage and structure liming was also studied, in a split-plot trial on a clayey soil (25% clay). Aggregate (2–5 mm) stability, measured as reduction in turbidity (which is strongly correlated with losses of particulate phosphorus), was significantly increased with the highest application rates of both structure lime products. Aggregate size distribution was also improved with structure lime, creating a finer tilth in the seedbed. Yield response to structure lime was not consistent, with both negative and positive responses over the four-year study period. Positive yield responses can possibly be attributed to the finer tilth preventing evaporation in two dry growing seasons. Negative yield responses were probably an effect of impaired phosphorus availability associated with limited precipitation in May-July in 2011 and 2013. Two years after liming, soil pH levels were significantly elevated in plots with the highest application rate of structure lime, whereas no significant increases were found three years after liming. However, a lingering effect of liming was still detectable, as manganese concentration in barley grain was significantly lower in plots with the highest application rates of both structure lime products in the fourth study year. These results indicate that structure liming can be used as a measure to mitigate phosphorus losses from clayey soils, thereby preventing eutrophication of nearby waters. However, the yield response was varying and unpredictable and thus further investigations are needed to determine the circumstances in which field liming can act efficiently not only to prevent phosphorus losses, but also to ensure consistent yield increases.

Effects of seedbed properties on crop emergence. 6. Requirements of crops with small seeds

The effects of seedbed properties on emergence of various crops were studied in a series of experiments. Results for crops with seeds weighing <7 mg are reported here. The experiments were carried out in shallow plastic boxes placed directly on the ground in the field. Small seeds require shallow sowing, which is a great disadvantage in the event of dry weather after sowing, particularly on clay and clay loam soils, where the upper 3-cm soil layer quickly dries to wilting point. Nevertheless, good emergence of crops with seeds weighing 2–7 mg (white mustard, Sinapis alba L., oilseed rape, Brassica rapa L., Metzg., sugar beet, Beta vulgaris L. and red clover, Trifolium pratense L.) was often obtained when the seed was placed at about 3-cm depth directly on a firm basal layer with >6% plant-available water and covered by soil dominated by aggregates <5 mm. Cruciferous crops germinated most rapidly, which facilitated emergence from shallow depth. Sowing could be slightly shallower in coarse-textured than in fine-textured soils, since the former soils dry less rapidly to below wilting point. For timothy (Phleum pratense L.) with seeds weighing about 0.5 mg and requiring a sowing depth <2.5 cm, it was impossible to design a seedbed that eliminated the risk of poor emergence in dry weather. Firming of the seedbed after sowing favoured emergence only in initially dry seedbeds. The risk of poor emergence because of surface layer hardening was minimised by placing seeds at a depth and in seedbed conditions that promoted the fastest possible emergence.

Surface Runoff of Pesticides from a Clay Loam Field in Sweden

Pesticides stored at or close to the soil surface after field application can be mobilized and transported off the field when surface runoff occurs. The objective of our study was to quantify the potential pesticide losses in surface runoff from a conventionally managed agricultural field in a Swedish climate. This was achieved by measuring surface runoff volumes and concentrations in runoff of six spring-applied pesticides and autumn-applied glyphosate and its metabolite aminomethylphosphonic acid (AMPA). Measurements were performed for 3 yr both during the growing seasons and during intervening winter snowmelt periods on a clay loam field close to Uppsala. During growing seasons, surface runoff was generated on only five occasions during one 25-d period in 2012 when the infiltration capacity of the soil may have been reduced by structural degradation due to large cumulative rainfall amounts after harrowing. Concentrations in surface runoff exceeded Swedish water quality standards in all samples during this growing season for diflufenican and pirimicarb. Surface runoff was generated during three snowmelt periods during the winter of 2012-2013. All of the applied pesticides were found in snowmelt samples despite incorporation of residues by autumn plowing, degradation, and leaching into the soil profile during the period between spraying and sampling. Concentrations of glyphosate ranged from 0.12 to 7.4 μg L, and concentrations of AMPA ranged from 0 to 2.7 μg L. Our results indicate that temporal changes in hydraulic properties during the growing season and when the soil freezes during winter affect pesticide losses through surface runoff.