B. J. Chambers

Heavy metal contents of livestock feeds and animal manures in England and Wales

Abstract In this study, 183 livestock feeds and 85 animal manure samples were collected from commercial farms in England and Wales and analysed to determine their heavy metal (zinc, copper, nickel, lead, cadmium, arsenic, chromium and mercury) contents. Zinc and copper concentrations ranged from 150–2920 mg Zn/kg dm (dry matter) and 18–217 mg Cu/kg dm in pig feeds, depending on the age of the pigs. In poultry feeds, concentrations ranged from 28–4030 mg Zn/kg dm and 5–234 mg Cu/kg dm, with laying hen feeds generally having higher heavy metal contents than broiler feeds. Concentrations of Zn and Cu in dairy and beef cattle feeds were much lower than in pig and poultry feeds. Pig manures typically contained c.500 mg Zn/kg dm and c.360 mg Cu/kg dm, reflecting metal concentrations in the feeds. Typical concentrations in poultry manures were c.400 mg Zn/kg dm and c.80 mg Cu/kg dm, and in cattle manures c.180 mg Zn/kg dm and c.50 mg Cu/kg dm. The dry matter content of cattle and pig slurries was a useful indicator of heavy metal concentrations on a fresh weight basis.

Plant uptake of nitrogen from the organic nitrogen fraction of animal manures: a laboratory experiment.

Twenty slurries, 20 farmyard manures (FYM) and 10 poultry manures were chemically analysed to characterize their nitrogen (N) fractions and to assess their potential organic N supply. The organic N fraction varied between manure types and represented from 14% to 99% of the total N content. The readily mineralizable N fraction, measured by refluxing with KCl, was largest in the pig FYMs and broiler litters, but on average only represented 7–8% of the total N content. A pot experiment was undertaken to measure N mineralization from the organic N fraction of 17 of these manures. The ammonium-N content of the manures was removed and the remaining organic N mixed with a low mineral N status sandy soil, which was sown with perennial ryegrass ( Lolium perenne L.). N offtake was used as a measure of mineralization throughout the 199 day experiment. The greatest N mineralization was measured from a layer manure and a pig slurry, where N offtake represented 56% and 37% of the organic N added, respectively. Lowest (%) N mineralization was measured from a dairy cow slurry (< 2%) and a beef FYM (6%). The mineralization rate was negatively related to the C[ratio ]organic N ratio of the ammonium-N stripped manures ( P r = −0·63).

Effects of past sewage sludge additions on heavy metal availability in light textured soils: implications for crop yields and metal uptakes

The effect of heavy metal additions in past sewage sludge applications on soil metal availability and the growth and yield of crops was evaluated at two sites in the UK. At Gleadthorpe, sewage sludges enriched with salts of zinc (Zn), copper (Cu) and nickel (Ni) had been applied to a loamy sand in 1982 and additionally naturally contaminated Zn and Cu sludge cakes in 1986. At Rosemaund, sewage sludges naturally contaminated with Zn, Cu, Ni and chromium (Cr) had been applied in 1968-1971 to a sandy loam. From 1994 to 1997, the yields of both cereals and legumes at Gleadthorpe were up to 3 t/ha lower than the no-sludge control where total topsoil Zn and Cu concentrations exceeded 200 and 120 mg/kg, respectively, but only when topsoil ammonium nitrate extractable metal levels also exceeded 40 mg/kg Zn and 0.9 mg/kg Cu. At Rosemaund, yields were only decreased where total topsoil Cu concentrations exceeded 220 mg/kg or 0.7 mg/kg ammonium nitrate extractable Cu. These results demonstrate the importance of measuring extractable as well as total heavy metal concentrations in topsoils when assessing likely effects on plant yields and metal uptakes, and setting soil quality criteria.

A study of the impacts of Zn and Cu on two rhizobial species in soils of a long-term field experiment.

Two agriculturally important species of rhizobia, Rhizobium leguminosarum biovar viciae (pea rhizobia) and R. leguminosarum bv. trifolii (white clover rhizobia), were enumerated in soils of a long-term field experiment to which sewage sludges contaminated predominantly with Zn or Cu, or Zn plus Cu, were added in the past. In addition to total soil Zn and Cu concentrations, soil pore water soluble Zn and free Zn2+, and soluble Cu concentrations are reported. Pea and white clover rhizobia were greatly reduced in soils containing ≥200 mg Zn kg-1, and soil pore water soluble Zn and free Zn2+ concentrations ≥7 and ≥3 mg l-1, respectively, in soils of pH 5.9–6. Copper also reduced rhizobial numbers, but only at high total soil concentrations (>250 mg kg-1) and not to the same extent as Zn. Yields of field grown peas decreased significantly as total soil Zn, soil pore water soluble Zn and free Zn+2 increased (R2 = 0.79, 0.75 and 0.75, respectively; P < 0.001). A 50% reduction in seed yield occurred at a total soil Zn concentration of about 290 mg kg-1, in soils of pH 5.9–6. The corresponding soil pore water soluble Zn and free Zn2+ concentrations were about 9 and 4 mg l-1, respectively. Pea seed yields were not significantly correlated with total soil Cu (R2 = 0.33) or soil pore water soluble Cu (R2 = 0.39). Yield reductions were due to a combination of greatly reduced numbers of free-living rhizobia in the soil due to Zn toxicity, thus indirectly affecting N2-fixation, and Zn phytotoxicity. These effects were exacerbated in slightly acidic soils due to increased solubility of Zn, and to some extent Cu, and an increase in the free Zn2+ fraction in soil pore water. The current United Kingdom, German and United States limits for Zn and Cu in soils are discussed in view of the current study. None of these limits are based on toxicity thresholds in soil pore water, which may have wider validity for different soil types and at different pH values than total soil concentrations.

Nutrient composition of poultry manures in England and Wales

Abstract In this study, 121 poultry manure samples were collected from commercial holdings in England and Wales. The nutrient contents of the individual manure samples varied widely. In general, broiler/turkey litters had a higher dry matter content (c.60%) than layer manures (c.35%), although all manure types had similar concentrations of nutrients (N, P, K, Mg, S) on a dry weight basis. Typically N:P:K ratios were 6:2:2 for layer manures and 6:2:3 for broiler/turkey litters. The readily plant available N content (ammonium-N+uric acid-N) of the poultry manures was 30–50% of the total N. The dry matter content of poultry manures is suggested as a useful indicator of total fresh weight nutrient concentrations.

An assessment of nitrification inhibitors to reduce nitrous oxide emissions from UK agriculture

A trial was conducted consisting of 14 experiments across sites in England of contrasting soil type and annual rainfall to assess the effectiveness of nitrification inhibitors (predominantly dicyandiamide (DCD) but limited assessment also of 3, 4-dimethylpyrazole phosphate (DMPP) and a commercial product containing two pyrazole derivatives) in reducing direct nitrous oxide (N2O) emissions from fertilizer nitrogen (N), cattle urine and cattle slurry applications to land. Measurements were also made of the impact on ammonia (NH3) volatilization, nitrate (NO3−) leaching, crop yield and crop N offtake. DCD proved to be very effective in reducing direct N2O emissions following fertilizer and cattle urine applications, with mean reduction efficiencies of 39, 69 and 70% for ammonium nitrate, urea and cattle urine, respectively. When included with cattle slurry a mean, non-significant reduction of 56% was observed. There were no N2O emission reductions observed from the limited assessments of the other nitrification inhibitors. Generally, there were no impacts of the nitrification inhibitors on NH3 volatilization, NO3− leaching, crop yield or crop N offtake. Use of DCD could give up to 20% reduction in N2O emissions from UK agriculture, but cost-effective delivery mechanisms are required to encourage adoption by the sector. Direct N2O emissions from the studied sources were substantially lower than IPCC default values and development of UK country-specific emission factors for use in inventory compilation is warranted.

The importance of former land use in determining successful re-creation of lowland heath in southern England

In order to reverse losses of lowland heathland substantial areas of former agricultural and forestry land are currently being targeted for restoration. In this study we assessed the success of heathland re-creation on 37 former arable, improved grassland and conifer plantation sites in southern England, UK. The similarity between the vegetation and seed banks of the re-creation sites and undisturbed heathland controls were examined in relation to former land use, soil properties and re-creation management. Former land use was found to be the most important determinant of re-creation success. On former arable, and to a lesser extent improved grassland, antecedent management had caused significant changes to seed bank and soil properties. As a result, regeneration of Calluna heath had been minimal, even on sites where appropriate management (e.g. cropping, addition of pH amendments) had been undertaken and heathland species introduced. In contrast, former plantation seed banks and soils were similar to heathland controls, and, as a result, rapid regeneration of Calluna heath had taken place. It was concluded that conifer removal provides the most practical and cost-effective means of re-creating Calluna heath on former heathland, although further research is required to assess the effect of litter removal and the rate at which heather seed banks decline following conversion to forestry. In contrast, re-creation on former agricultural sites will require effective management to reduce soil pH, fertility and the abundance of competitive species as well as the introduction of heathland propagules. Given limited resources a more realistic objective for these sites is likely to be reversion to an acid grassland or grass-heath.

Spring applied organic manures as a source of nitrogen for cereal crops: experiments using field scale equipment

The effects of spring top-dressed applications of broiler litter, pig slurry and cattle slurry on winter wheat and winter barley yield and quality were investigated on a field scale at three UK sites between 1992 and 1994, using commercially available application equipment. Broiler litter was applied at rates ranging from 5.3 to 8.8 t/ha, and slurries from 54 to 89 m 3 /ha. Few practical problems were encountered when spreading broiler litter, but when spreading cattle slurry there was some crop damage and soil compaction from the tanker wheelings adjacent to tramlines. Coefficients of variation for manure spreading using commercial spreaders ranged from 20 to 32%. Spring applied manures increased yields of winter wheat and winter barley, and lowered optimum inorganic fertilizer nitrogen (N) rates. When the N efficiency of the manures was compared to that of inorganic fertilizer N, broiler litter N efficiencies ranged from 10 to 49 %, cattle slurry was c. 30% and pig slurry c. 50%. The experiments demonstrated that poultry litters and slurries can be applied successfully to growing cereal crops in spring as part of an integrated policy for N supply.

The impact of modern farming practices on soil fertility and quality in England and Wales

Data are presented on the effects of modern farming practices on soil as an agricultural resource in England and Wales (E&W), namely: nutrient status, pH, soil organic carbon (SOC), heavy metal concentrations, and on soil erosion risk. Fertilizer-N inputs to tillage (arable) and grassland soils increased from 84 and 65 kg/ha N in 1969 to 151 and 120 kg/ha N, respectively, in 1997. The estimated N surplus (inputs less outputs) increased from 84 and 96 kg/ha N to 102 and 154 kg/ha N, respectively, over the same time. Phosphorus inputs to tillage (mean 37 kg/ha P) and grassland (mean 21 kg/ha P) changed little over the period. However, P surpluses decreased from 25 kg/ha P in 1969 to 15 kg/ha P in 1997 on tillage land (largely as a result of greater P offtakes), and from 20 to 17 kg/ha P in 1997 on grassland (largely because of a small decrease in fertilizer P). The cumulative tillage land soil P surplus was c . 580 kg/ha P, and was estimated to increase topsoil total P concentrations by c . 170 mg/kg P and Olsen-extractable soil P by c . 26 mg/l P. The mean annual P surplus for grassland was 18 kg/ha P which, over the study period, added c . 427 kg/ha P to the soil, an increase in topsoil total P of c . 214 mg/kg P, and in Olsen-extractable P of 19 mg/l P. Concentrations of SOC in some soils have decreased between 1980 and 1995, especially where soils have been ploughed out of grassland and on lowland organic and peaty soils in tillage. The mean SOC of soils in arable/ley cultivation in 1980 was 3·4% and 2·8% in 1995. The proportion of arable soils with pH Although there were statistically significant changes in the mean soil concentrations of Cd, Cu, Ni, Pb and Zn between 1980 and 1995, many of the changes were small in absolute terms. Hence, there was little evidence of marked or systematic changes in topsoil total heavy metal concentrations that could not be explained by factors other than increased pollutant loadings. Over the next 50 years or so, the threat from soil erosion to crop productivity will be greatest on shallow soils ([les ] c . 0·3 m depth), mostly over chalk and sandstone as further removal of soil will lead to increased drought stress. Provided that nutrient supplies are maintained, the evidence is that losses in arable crops on eroded soils would range between 2% and 8% of current yields. Thus, within the limitations of the data available, both in time and space, we found little evidence that most soils in E&W cannot continue to support modern farming practices, and the associated crop and animal outputs, given appropriate inputs of nutrients and an adequate degree of crop protection.

Nitrogen value of poultry litter applications to root crops and following cereal crops

The efficiency of poultry litter nitrogen (N) utilization was studied in seven field experiments in eastern England during harvest years 1991 to 1994. Poultry litter was applied at different application rates in winter or spring, prior to sugar beet or potatoes. The mean manure N efficiency based on crop yields was 33% (range 25–43%) for sugar beet and 36% (range 13–66%) for potatoes. For potatoes, the manure N efficiency was greater from spring (mean 43%) than from winter application timings (mean 30%). The manure readily available N applied (i.e. ammonium-N+uric acid-N) and fertilizer N replacement values were well related ( P P 600 kg/ha total N to sugar beet, root sugar concentrations were depressed ( P P 600 kg/ha total N. Yield increases were also recorded in cereal crops grown the following season, but only where high rates of manure N (>600 kg/ha) had been applied. The current work has shown that the fertilizer N replacement value of poultry litter can be predicted based on the amounts of total and readily available N applied, providing guidance to farmers on appropriate reductions in inorganic fertilizer N applications to make allowance for poultry litter N supply.