Hilton Experimental Site Research Articles

Critical Analysis of the van Bemmelen Conversion Factor used to Convert Soil Organic Matter Data to Soil Organic Carbon Data: Comparative Analyses in a UK Loamy Sand Soil

Converting soil organic matter (SOM) data to soil organic carbon (SOC) data usually uses the van Bemmelen factor of 0.58 (or in reverse its reciprocal of 1.724) as a universal conversion factor. The accuracy of this conversion factor has been questioned. Under the Kyoto Protocol (1997) dry combustion is recommended to provide reproducible analyses to measure soil carbon stocks. However, dry combustion equipment is expensive and entails high maintenance. For rapid and inexpensive measurements, loss-on-ignition (LOI) is often used. A total of 278 loamy sand topsoil (0-5 cm depth) samples were taken during three soil sampling sessions (9 January 2007, 22 January 2009 and 10 October 2011) from runoff plots, splash erosion plots and grassed/cultivated plots on the Hilton Experimental Site, Shropshire, UK. A total of 124 soil samples were collected from both runoff and splash plots in both 2007 and 2009 (Bhattacharyya et al., 2011a). Some 22 of the collected samples in 2011 were from grassland (Ah horizon) and eight from cultivated soils (Ap horizon). Homogenized soil samples were split and SOM was determined on oven-dried samples by LOI and total SOC was determined by dry combustion. A conversion factor of 0.845 was used to obtain SOC from total soil C, following Rawlins et al. (2011). Results showed strong associations (R² = 0.70, P 0.001, n = 278) between SOM and SOC data. For all data, SOM to SOC conversion factors varied between 0.36-0.98, with a mean value of 0.66 (SD = 0.105). The mean values of the conversion factor were 0.64, 0.69 and 0.56, respectively, for the samples collected in 2007, 2009 and 2011. Results indicate the van Bemmelen factor (0.58) is a reasonable predictor, but both temporal and spatial variations occur around it within a specific soil type. Thus, caution should be exercised in SOM/SOC data conversions using the van Bemmelen factor.

Temporal changes in soil temperature at the Hilton Experimental Site, Shropshire, UK (1982–2006): Evidence of a warming trend?

Soil temperature variations at different depths at a research site over a 25-year period (1982–2006) are discussed. Based on a database of 11,498 individual soil temperature measurements in loamy sand (Bridgnorth series) soils, soil temperature at the Hilton Experimental Site in Shropshire, UK, significantly increased between 1982 and 2006. The surface soil (0 cm) warmed twice as fast (∼0.1°C year−1) as soil at 100 cm depth (∼0.05°C year−1) and thus implies progressively steeper thermal gradients with soil depth through time. The trend of increase in soil temperatures at 0 cm was generally greater in winter. These observations contribute to the growing corpus of evidence of global warming.

Spatial variability in precipitation within the Hilton Experimental Site, Shropshire, UK (1982–2006)

AbstractAccurate precipitation measurements are essential for many hydrological and hydrogeological management strategies. Precipitation at the Hilton Experimental Site has been regularly measured since 1982. This paper summarises 157 rain gauge years of precipitation data, recorded between 1982 and 2006, using 11 rain gauges on the 0·5 hectare site. Precipitation varied markedly within the site. Precipitation totals were notably different between two adjacent rain gauges, the mean difference being 0·3% of the total. Variations in mean annual precipitation within the site were ⩽8%. Spatial variations in wind turbulence appeared to be the main factor influencing intra‐site variability. Precipitation totals varied with gauge exposure, with surface level gauges receiving ⩽5·9% more precipitation than standard rain gauges, the difference being less lower down the slope. On a steep (∼15° ) slope, basal sections had 2·5–7·9% more precipitation. Upper gauges received less, probably due to turbulence as increased exposure on the top of the slope resulted in precipitation being carried over the gauge orifice. Results confirm that due attention must be given to the inherent variability of precipitation amounts when calculating precipitation inputs. Copyright © 2008 John Wiley & Sons, Ltd.

Grass ley set‐aside and soil organic matter dynamics on sandy soils in Shropshire, UK

AbstractErosion plot studies at the Hilton Experimental Site, Shropshire, UK, evaluated the effects of set‐aside on runoff, erosion and soil organic matter (SOM) dynamics. Ten runoff plots (slope angles 7–15°) were put to a grass ley in April 1991. Runoff and erosion rates during nine years were low, despite the occurrence of potentially erosive rains. Mean runoff was 0·24 per cent of precipitation (SD = 0·20, n = 89 plot years), compared with a 15‐year mean value of 0·13 per cent (SD = 0·04) on permanent (control) grassland. The mean plot erosion rate was 0·21 t ha−1 a−1 (SD = 0·14, n = 69 plot years). Mean SOM content increased consistently and sign fi a tly on the set‐aside plots, by a mean value of 1·07 per cent by weight (i.e. 1·07 g per 100 g of soil) in ten ye rs, from 2·04 per cent (1991) to 3·11 per cent (2001). Soil erodibility after six years of set‐aside (sampling date 24 April 1997) was determined using a drip‐screen rainfall simulator. Soil aggregate stability was higher on the grassed soils, compared with set‐aside and bare arable soils. Despite no significant (P > 0·05) differences be w en grassland and set‐asid oils, both these treatments were s gnificantly (P < 0·001) diff rent from bare soils. Contrary to the usually strong relationship between SOM and clay content, the percentage silt (r = 0·52, P < 0·001, n = 50) exhibited a stronger correlation with SOM than percentage clay content (r = 0·37, P < 0·01, n = 50). Furthermore, there were equally strong correlations between SOM and cumulative particle size fractions of both clay and silt contents (r = 0·51, P < 0·001, n = 50). In the absence of significant quantities of clay in these sandy soils, silts assist binding of SOM, which has significance for assessing soil carbon sequestration potential. Finally, future SOM and soil organic carbon benchmark work at the Hilton Site will improve harmonization of global SOM databases and enhance international estimates of rates and potential for soil carbon sequestration. Copyright © 2006 John Wiley & Sons, Ltd.

A pilot project on the potential contribution of palm‐mat geotextiles to soil conservation

AbstractGeotextiles constructed from Borassus aethiopum (black rhun palm) leaves are currently being investigated for their effectiveness in decreasing water erosion. The study aims to develop sustainable methods of soil conservation where the material meets selected criteria (readily available, simple and cost‐effective to manufacture, provides immediate erosion control and possibly increases soil fertility and organic matter content). Grid mats were manufactured in a cottage workshop in The Gambia, West Africa. They are currently under investigation at the Hilton Experimental Site in Shropshire, UK. Eight runoff plots (10 × 1 m on a 15° slope) are being used, with duplicate treatments: (i) bare soil; (ii) grassed; (iii) bare soil with 1 m palm‐mat buffer zones at the lower end of the plots; and (iv) completely covered with palm‐mats. Results from one year of field study (2002–03) indicate sediment yield is 36·8 per cent from replicated covered plots and 35·9 per cent from the replicated buffer zone plots, compared to the control bare plots. Sediment yield equated to 0·45 t ha−1 from bare soil, 0·09 t ha−1 from grassed plots and 0·17 t ha−1 from both the covered and buffer zone plots. The results suggest palm‐mat application as protective buffer strips is highly effective in temperate climates. Future work is intended to follow this pilot study and develop well‐researched guidelines for practical field applications in other global regions, namely Africa, Southeast Asia and South America. Copyright © 2006 John Wiley & Sons, Ltd.

Long-term effects of grass ley set-aside on erosion rates and soil organic matter on sandy soils in east Shropshire, UK

The contribution of ryegrass ( Lolium perenne) ley set-aside to soil conservation and soil organic matter (SOM) content was investigated. Ten runoff plots (7–15°, 12–27% slope) at the Hilton Experimental Site, Shropshire, UK, were put to a grass ley in April 1991. Runoff and erosion rates during 9 years were low, despite the occurrence of potentially erosive rains. Mean runoff was 0.24 ± 0.20% (±S.D.) of precipitation ( n = 89 plot-years), compared with a 15-year mean value of 0.13 ± 0.04% on permanent (control) grassland. Mean erosion rate was 0.21 ± 0.14 t ha −1 year −1 ( n = 69 plot-years). Erosion rate and slope were poorly correlated, suggesting leys are highly effective for soil conservation. Mean SOM content increased consistently and significantly on the set-aside plots from 20.4 g kg −1 in 1991 to 31.1 g kg −1 in 2001. Contrary to the usually strong relationship between SOM and clay content, the percentage silt exhibited a stronger correlation with SOM than percentage clay content. Furthermore, there were equally strong correlations between SOM and cumulative particle size fractions of both clay and silt contents. In the absence of significant quantities of clay in these sandy soils, silts assist binding of SOM, which has significance for assessing soil carbon sequestration potential.

Field studies of the effects of jute geotextiles on runoff and erosion in Shropshire, UK

Abstract. Jute geotextiles are widely used to stabilize steep banks and road cuttings. Jute protects bare surfaces until seeded grass becomes established, then after several years, the jute decays. To evaluate two types of jute geotextiles, eight erosion plots were established in July 1994 at the Hilton Experimental Site, Shropshire, UK. On 10 April 1995, the plots were treated as follows: jute geotextile net; jute mat; perennial rye grass (Lolium perenne); and bare soil, with duplicates of each treatment. Over one year, sediment yields from jute net and jute mat were 1.1% and 1.2%, respectively, of the yield from the bare control. Although both had similar soil protection qualities, runoff was very different. The runoff from the jute net was 35% and the jute mat 247% of the control. Results demonstrate the effectiveness of jute net for erosion and runoff control, while the jute mat may both conserve soil and ‘harvest’ rain or redirect runoff.

A comparison of the texture of grassland and eroded sandy soils from Shropshire, UK

In previous studies, periodic sampling of topsoils on runoff plots on sandy soils at the Hilton experimental site, Shropshire, UK, suggested erosion decreased the topsoil clay content and increased the coarse fraction. However, a comparison of soil and sediment properties suggested erosion selectively removed sand. Therefore, to cross-check the effects of erosion on soil properties, topsoil samples were collected from bare, eroded runoff plots and compared with samples from adjacent non-eroded grassland. Bare, eroded soil was stonier and particularly deficient in sand compared with grassed soil. Textural differences were very marked in the medium and coarse sands, especially the 0.5–1.0 mm fraction. On the basis of mean properties, the grassed soil was a very slightly stony loamy sand and the bare soil a slightly stony sandy loam. Soil organic matter was significantly less in the bare soils than the grassed soils and thus may have contributed to the higher erodibility of sands in bare soils.

Effects of grass ley set-aside on runoff, erosion and organic matter levels in sandy soils in East Shropshire, UK

Investigations were conducted to assess the potential contribution of grass ley set-aside to soil conservation. Ten runoff plots at the Hilton experimental site, Shropshire, UK, were put to a temporary grass ley in April 1991, to simulate one specific set-aside land use. Plot slope angles varied between 7 and 15°. Runoff and erosion rates over 5 years were low, despite the occurrence of potentially erosive rains. Mean runoff was 0.22% of precipitation (S.D. 0.16, n = 49 plot years), compared with an 11-year mean value of 0.14% on permanent grassland. Erosion rates decreased to tolerable levels once ∼ 30% vegetation cover had established, then rates remained low, despite the occurrence of potentially erosive rains. Under developed ley cover, plot erosion rates were ∼ 0.1−0.5 t ha −1 year −1, with a mean value of 0.23 t ha −1 year −1 (S.D. 0.14) for 49 plot years. Results suggest erosion rates progressively decrease through time, as the ley cover matures. Erosion rate and slope angle were poorly correlated, suggesting leys are highly effective for soil conservation, even on steep slopes. Physical processes of slope wash became inefficient in transporting soil, while plot observations suggest that biological processes became more important, particularly exposure and subsequent erosion of soil from mole hills and worm casts. Mean soil organic matter content increased consistently and significantly on the set-aside plots, by a mean value of 0.39% in 2 years and 0.78% in 4 years. Soil erodibility significantly decreased. Results suggest that using grass leys for set-aside could prove a viable soil conservation technique. Grassland could also be used as ‘soakaways’ in arable systems; braking, filtering and infiltrating runoff, thus decreasing net sediment transfer downslope.

Comparison of soil and sediment properties of a loamy sand soil

Ten 25 m 2 runoff plots at the Hilton experimental site, east Shropshire, UK, have been used to compare the physicochemical properties of loamy sand plot soils and sediment eroded from the plots over one year. Sediment contained more sand (2 mm–60 μm) and less clay (< 2 μm), silt (2–60 μm) and coarse fraction (> 2 mm) than soil. Erosion rates increased with slope and proportionally more silt and particularly clay were eroded on steeper slopes. Selective clay depletion has serious implications for soil structure and fertility. Correlations existed between the organic matter contents and particle size distributions of soil and sediment, but the sediment had less organic matter and lower pH values than soil. Sediment also contained lower concentrations of calcium, iron, potassium, magnesium, manganese and phosphorus than soil. Relationships between erosion and soil textural change appear to be partly technique-dependent, which suggests more uniformity in approach would be beneficial in studies on the effects of erosion on soil fertility.

Property changes by erosion of loamy sand soils in east Shropshire, UK

Erosion affects the physical and chemical properties of soils. A study was conducted to determine changes in the textural and chemical composition of a loamy sand (psammept) in east Shropshire, UK, over a 6-year period from 19 December 1985 until 20 May 1991. Soil properties were measured using an array of ten 25-m 2 runoff plots at the Hilton experimental site. Fifty plot soil samples were taken on 19/12/85 and 22/4/91 and field readings of runoff and erosion collected regularly. Over the total period, average cumulative erosion on these bare arable loamy sand soils was equivalent to 47.2 t/ha. The mean coarse fraction (>2 mm) of the plot soil samples significantly increased, from 9.74 to 12.18%. Mean sand (2 mm–60 μm) content increased from 57.55 to 64.69%. Both mean silt (60-2 μm) and clay (<2 μm) contents decreased, from 27.76 to 19.57% and 4.95 to 3.56%, respectively. There were positive associations between erosion rate and soil textural change, which were especially evident on plots which experienced cumulative erosion rates >30 t/ha. Soil organic matter decreased from a mean of 2.54% on 19/12/85 to 2.04% on 22/4/91. Both soil macronutrient (K, Ca and P) and micronutrient (Fe and Cu) concentrations decreased during this period, the loss of K and Ca being statistically significant. Exposure of bare soil allowed mean soil pH to fall from 5.55 to 5.05. Measurements suggest that erosion rates which regularly recur on arable soils in northern Europe have serious long-term implications for soil fertility.

Effects of ‘Agri‐SC’ soil conditioner on the erodibility of loamy sand soils in East Shropshire, UK: preliminary results

Abstract. The effect of Agri‐SC’ soil conditioner on the erodibility of loamy sand soils has been investigated at the Hilton experimental site, Shropshire, since March 1988. Factors measured have included runoff and erosion, soil structure, crust strength, splash susceptibility, aggregate stability, soil micromorphological properties, response to compaction and penetrometer resistance.Treatment decreased runoff and erosion rates, bulk density, splash erosion, crust strength and penetrometer resistance, and increased pore space and aggregate stability. The effects on crust strength, aggregate stability and bulk density were statistically significant. The results suggest that applications of ‘Agri‐SC’ could have beneficial effects for soil conservation.

Erosion rates on bare loamy sand soils in east Shropshire, UK

Abstract. Results from over seven years of monitoring of erosion rates on bare arable loamy sand soils at the Hilton experimental site, Shropshire, UK, are reported. On bare plots, rates are very variable; erosion during one summer convectional storm exceeded that recorded during six individual years of plot measurement. Exposure of erodible arable soils to convectional storms puts them at risk of excessive erosion. Plot erosion rates were frequently high, with rates up to 67.4 t/ha occurring during an individual storm. Rates were influenced by rainfall erosivity, slope steepness and soil organic content. Mean soil organic content on the bare plots decreased over five years by 0.08%/yr.

A comparison of runoff and erosion rates on bare and grassed loamy sand soils

Abstract. Runoff and erosion rates on loamy sand soils were measured at the Hilton experimental site, Shropshire. Little runoff and no erosion occurred on a steep runoff plot inserted into permanent grassland. Most precipitation infiltrated into the soil and was transmitted down slope as interflow within the Ah horizon. In contrast, considerable amounts of runoff and erosion occurred on the bare arable plots. These results suggest that incorporation of strips of permanent grassland into arable systems could assist soil and water conservation. Considering the high erosion rates on bare steep plots, conversion of slopes &gt; 12° to permanent grassland seems appropriate.

Soil organic matter and erosion processes on arable loamy sand soils in the west midlands of England

Plot studies at the Hilton experimental site, Shropshire (U.K.) show that small reductions in soil organic content markedly increase erodibility and erosion rates. Soil organic material varies vertically within crusting topsoils, with more organic-rich material ingressing to a ‘filtration pavement’ beneath the surface crust. Consequently, the organic content of soils eroded from plots is less than in situ plot soil. Soil organic content decreased through time on bare soils.