Anne Bhogal

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.

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.

Assessing the probability of carbon and greenhouse gas benefit from the management of peat soils.

This study proposes a method for assessing the probability that land management interventions will lead to an improvement in the carbon sink represented by peat soils. The method is able to: combine studies of different carbon uptake and release pathways in order to assess changes on the overall carbon or greenhouse gas budget; calculate the probability of the management or restoration leading to an improvement in the budget; calculate the uncertainty in that probability estimate; estimate the equivalent number of complete budgets available from the combination of the literature; test the difference in the outcome of different land management interventions; and provide a method for updating the predicted probabilities as new studies become available. Using this methodology, this study considered the impact of: afforestation, managed burning, drainage, drain-blocking, grazing removal; and revegetation, on the carbon budget of peat soils in the UK. The study showed that afforestation, drain-blocking, revegetation, grazing removal and cessation of managed burning would bring a carbon benefit, whereas deforestation, managed burning and drainage would bring a disbenefit. The predicted probabilities of a benefit are often equivocal as each management type or restoration often leads to increase in uptake in one pathway while increasing losses in another.

Net changes in soil and crop nitrogen in relation to the performance of winter wheat given wide-ranging annual nitrogen applications at Ropsley, UK

The effects of eight rates of nitrogen (N) application (0-245 kg/ha) on the performance of winter wheat over five seasons (1991-1995) on a long-term field experiment (established 1978) at Ropsley (UK) are described. In each of the five seasons, N was withdrawn from replicate plots in order to study the residual effect of fertilizer. N applications in excess of 140 kg/ha left significant residues as soil mineral N (SMN) in the autumn which, despite some loss over-winter, had a significant effect on the yield and N offtake of the subsequent crop. The amount of N carried over was equivalent to 8-20 % of the fertilizer N and was observed at N applications up to 40 kg/ha lower than the optimum rate (c. 200 kg/ha). Part of the unrecovered N was also considered to contribute to the long-term build-up of fertility at the site. The results suggest that restrictions on N use to below the optimum will reduce leachable N, but may have an impact on soil fertility and future crop productivity. In addition, the rate of N applied to preceding crops should be taken into account when formulating fertilizer advice on retentive soils.

The flux of dissolved nitrogen from the UK – Evaluating the role of soils and land use

Fluvial dissolved nitrogen (dissolved organic nitrogen [DON], nitrate and ammonium) fluxes from the terrestrial biosphere of the UK to surrounding oceans are explained on the basis of combined predictions of soil to water transfer and in-stream loss. The flux of different nitrogen species from land to surface waters is estimated using an export coefficient model employing catchment soil, land use and hydroclimatic characteristics, fitted to flux estimates derived from the Harmonised Monitoring Scheme between 2001 and 2007 for 169 UK catchments. In-stream losses of DON, nitrate and ammonium were estimated using a transit time filter in the fluvial network. Comparisons of modelled land to water N flux (2125 ktonnes N yr(-1)) with estimates of N fluxes to estuarine and ocean systems at the tidal limit (791 ktonnes N yr(-1)) suggest that significant in-channel N losses occur. These in transit losses are equivalent to up to 55 kg N ha(-1) yr(-1).

Dissolved organic nitrogen in agricultural soils : Effects of sample preparation on measured values

There is increasing interest in the soils dissolved organic nitrogen (DON) fraction. However, soil analytical procedures have to be such that the result is a true representation of the DON levels in the soil. Three separate studies investigated the effects of soil and extract preparation on measured soil mineral N (Nmin) and DON concentrations in agricultural soils, ranging in texture from sands to clays. In Study 1 (18 soils), storing soils fresh or freeze/thawing, extracting with 2 M KCl or distilled water and storing extracts fresh or frozen were all tested. Study 2 (60 soils) retested soil storage (fresh vs. frozen) and extractant (2 M KCl or distilled water). Study 3 compared water and 0.01 M CaCl2 as extractants. Average Nmin values (KCl) were 13.2 and 4.5 mg kg−1 dry soil in Studies 1 and 2. Average DON values (water) were 3.3 and 3.7 mg kg−1 dry soil, respectively. Both 2 M KCl or 0.01 M CaCl2 extracted more DON from soils than did water. We suggest water extracts give a more reliable estimate of true DON status. However, a practical difficulty was obtaining a clear extract due to deflocculation of clay in the water extract. Freezing soils or extracts before analysis affected measured DON values, with a statistically significant tendency for DON to decrease depending on the extractant used.

Cumulative effects of nitrogen application to winter wheat at Ropsley, UK, from 1978 to 1990

In 1977, a four-course rotation was set up at Ropsley (UK) to study crop response to eight rates of nitrogen application (35-265 kg ha -1 ). This rotation continued until 1990 when continuous winter wheat was introduced. Results from 1978 to 1990 provide an opportunity to study the initial phase of cumulative effects from different rates of N fertilizer application on the recovery of N by cereals and the retention of N in the soil. From 1978 to 1990, considerable variation in the recovery of nitrogen by winter wheat was observed. Neither rainfall nor drainage, as indicators of possible denitrification or leaching losses, provided a useful explanation for this, possibly because of the relatively dry conditions prevailing after spring fertilizer application. There was no evidence of increased soil N fertility, beyond single year residues, as a result of large N applications over the 13-year period. In order to achieve the economic optimum grain yield, it was necessary to use N applications which produced inefficient recovery of N. Thus, greater return of N in crop residues and immobilization at relatively large N applications ( > 150 kg ha -1 ) contributed to an observed build-up in soil organic N over the period of study. Plots receiving, on average, 265 kg ha -1 appeared to gain c. 250 kg ha -1 N over control plots (35 kg ha -1 ) after 13 years of N application. Reducing the N application rate from the economic optimum to a more biologically efficient N rate (156 kg ha -1 ) was calculated to result in an average yield loss of 0.305 t ha -1 and cause an estimated £17 ha -1 loss in profit.

Effect of poultry manure on the leaching of carbon from a sandy soil as a potential substrate for denitrification in the subsoil

There is evidence from laboratory incubations that denitrifying bacteria occur in the deep subsoils of UK soils and that lack of available carbon (C) generally limits their activity. Animal manures can be a source of substantial carbon input to farming systems. This experiment measured the effect of broiler litter application on the movement of C in soil solution to depths below 1 m, which might be sufficient to allow denitrification of nitrate moving from the rooting zone towards ground water aquifers. Six broiler litter rates were applied each autumn from 1992-1994 to field plots on a loamy medium sand in Nottinghamshire, UK. Total loadings over the 3 years ranged from 0 to 125 t ha -1 broiler litter, supplying 0-32 t ha -1 total C. Teflon and ceramic water samplers, placed at 1.0 and 1.5 m, and monolith lysimeters (0.5 m 2 area, 1.5 m deep) were used to measure total organic carbon (TOC) concentrations in the drainage. Ceramic samplers indicated significantly (P < 0.05) larger concentrations than Teflon samplers; there were no differences between concentrations measured by Teflon samplers and the lysimeters. Water samples analysed for both dissolved and total C showed that nearly all was in a dissolved form. TOC concentrations on plots which received no manure were less than 20 mg litre -1 at 1 m for the duration of the experiment; concentrations peaked at 65 mg litre -1 with the largest manure loading. There was a linear relationship between C leached and C applied, with about 5% leached below 1 m by the end of the experiment. There was some evidence of movement of C to 1.5 m depth, but there were no large peaks corresponding to those at 1 m, because of either adsorption or microbial utilisation. The results provide evidence of movement of substantial C to depth in some circumstances, particularly on fields which regularly receive large dressings of organic manure. The availability of this as a substrate for denitrification needs further examination.

Regular applications of poultry litter to a sandy arable soil: effects on nitrate leaching and nitrogen balance

Intensive poultry units often have insufficient land for spreading manure at agronomically and environmentally acceptable rates. This experiment measured the effects of annual applications, at several rates, on nitrate-N leaching and the soil-crop N balance on a sandy soil. Poultry litter from a broiler unit was applied each autumn 1992-1995. Total loadings on the main experiment area (instrumented with ceramic and Teflon water samplers at 1.0 and 1.5 m, and monolith lysimeters, 1.5 m deep) were 0, 60 and 150 t ha -1 . Additional plots (not instrumented) received 30, 90 or 120 t ha -1 . There was good agreement in the nitrate-N concentrations measured by the Teflon and ceramic water samplers and the lysimeters; all three methods gave acceptable measurements of nitrate leaching on structureless sandy soils. Autumn applications of poultry manure should be avoided: leaching was much greater than when delayed into December. At rates of broiler litter which supplied more N than the crop required (generally above 10 t ha -1 each year), nitrate-N leaching losses were large; at the largest application rate (akin to a disposal, rather than a planned fertiliser strategy), concentrations peaked at c 500 mg litre -1 N. Despite the movement of dissolved organic carbon to 1 m depth, the N concentration profiles measured by the water samplers did not provide clear evidence of subsoil denitrification. A nitrogen balance sheet, based on available N applied (as either fertiliser or manure) with some adjustment for mineralisation of the manures organic fraction (10% annually) and for volatilisation (15%) was strongly correlated with soil mineral N each spring.

The Nutrient Content of Cattle Manures from Organic Holdings in England

ABSTRACT Generally, there is much available information about the nutrient composition of cattle manures produced by conventional farming systems. There is less information on manure composition from organic holdings. Therefore, the nutrient content of 14 cattle slurries and 43 cattle farmyard manures (FYM) from organic holdings in England and Wales was analysed. The mean values for nitrogen, ammonium, phosphorus, potassium. magnesium and sulphur all exhibited large standard deviations, indicating the wide variability in composition between holdings for both slurry and FYM. Differences in dry matter content explained much of the variation in the nutrient composition of slurries, but not FYM. Average values were in good agreement with means previously reported for cattle FYM and slurries from organic holdings in mainland Europe. The average composition of manures from organic holdings appeared to be of lower nutrient content than the average for conventionally produced manures. For total N. P and K, these differences were statistically significant (p < 0.05) for slurry. However, the variation was such that these differences were not statistically significant for FYM.