P.C. Brookes

Rothamsted Research, Harpenden, England, United Kingdom

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Publications (108)375.98 Total impact

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    ABSTRACT: This study compares a traditional agricultural approach to minimise N pollution of groundwater (incorporation of crop residues) with applications of small amounts of biodiesel co-product (BCP) to arable soils. Loss of N from soil to the aqueous phase was shown to be greatly reduced in the laboratory, mainly by decreasing concentrations of dissolved nitrate-N. Increases in soil microbial biomass occurred within 4 days of BCP application-indicating rapid adaptation of the soil microbial community. Increases in biomass-N suggest that microbes were partly mechanistic in the immobilisation of N in soil. Straw, meadow-grass and BCP were subsequently incorporated into experimental soil mesocosms of depth equal to plough layer (23 cm), and placed in an exposed netted tunnel to simulate field conditions. Leachate was collected after rainfall between the autumn of 2009 and spring of 2010. Treatment with BCP resulted in less total-N transferred from soil to water over the entire period, with 32.1, 18.9, 13.2 and 4.2 mg N kg(-1) soil leached cumulatively from the control, grass, straw and BCP treatments, respectively. More than 99 % of nitrate leaching was prevented using BCP. Accordingly, soils provided with crop residues or BCP showed statistically significant increases in soil N and C compared to the control (no incorporation). Microbial biomass, indicated by soil ATP concentration, was also highest for soils given BCP (p < 0.05). These results indicate that field-scale incorporation of BCP may be an effective method to reduce nitrogen loss from agricultural soils, prevent nitrate pollution of groundwater and augment the soil microbial biomass.
    Water Air and Soil Pollution 01/2014; 225(2):1831. DOI:10.1007/s11270-013-1831-7 · 1.69 Impact Factor
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    ABSTRACT: Many soil microbes exist in biofilms. These biofilms are typified by variable quantities of extracellular polymeric substances (EPS: predominantly polysaccharides, glycoconjugates, and proteins) and the embedded microbial cells. A method to measure soil-EPS (the biofilm exclusive of microbial cells) has not yet been described. The present work investigates the potential of five extraction methods to estimate changes in soil-EPS content. A rationale for selection of appropriate EPS extraction and methodology is discussed, including the crucial consideration of both intracellular and extracellular contamination. EPS was developed in situ by provision of labile C (glycerol) to the microbial biomass of a moist soil and then applying desiccation stress. Only two out of the five extraction methods showed statistically significant increases in polysaccharide production responding to substrate addition. Humified organic matter, estimated by its humic acid equivalent (HAE) was used to indicate the degree of extracellular contamination, and/or creation of humic artefacts – both of which affect detection of changes in EPS. The HAE concentration was very high when applying original and modified methods designed to extract glomalin related soil protein (GRSP). Extraction methods involving heating with dilute sulphuric acid appeared to overestimate EPS-polysaccharide. Using microbial ATP as an indicator of cell-lysis, confidence could only be ascribed to EPS extraction with cation exchange resin. Using this method, the expected increases in EPS-polysaccharide were clearly apparent. The HAE/protein ratios of EPS extracts were also lowest with cation exchange – indicating this method did not cause excessive contamination from humified soil organic matter or create related artefacts. FULL ARTICLE AVAILABLE OPEN ACCESS: http://www.sciencedirect.com/science/article/pii/S0038071714000261
    Soil Biology and Biochemistry 01/2014; · 4.41 Impact Factor
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    ABSTRACT: Elevated CO2 respiration rates have been observed in soils treated with complex mixtures versus single low molecular weight (LMW) organic substrates, and it has been postulated that a more diverse range of soil microorganisms responds to increasingly complex mixtures of LMW organic substrates. To test this hypothesis, 13C-labelled substrates (glycine, an amino acid mixture and an extract of water soluble compounds from plant roots) were applied at 15 μg C g−1 soil to an arable top soil. The soils were incubated and destructively sampled after 8, 24, 48, 120 and 240 h, and the 13C content of biomarker PLFA for Gram negative bacteria, Gram positive bacteria, Actinobacteria and fungi was determined. There was no significant increase in the concentration of the biomarker PLFA, apart from Actinobacteria at the end of the incubation (120 and 240 h). However there were significant changes in total PLFA concentration due to increases in the 16:0 and 18:0 PLFA, which cannot be assigned to specific functional groups of microorganisms. 13C incorporation into the biomarker PLFA of all microbial groups was significant at every time point, but more 13C was determined in the biomarker PLFA of all microbial groups after the application of the amino acid mixture compared to glycine. Calculations of the proportion of the incorporated of 13C in the different biomarker PLFA suggested the routing of substrate 13C between the microbial groups over time. This was related to the broad functional ecology (‘r’ or ‘K’ strategy) of the different microbial groups. In conclusion, we observed that the response of all microbial groups (detected as 13C incorporation) was increased by the addition of more complex mixtures of LMW organic substrates, but that different microbial groups responded differently over time.
    Soil Biology and Biochemistry 09/2013; 34:57-64. DOI:10.1016/j.soilbio.2013.03.036 · 4.41 Impact Factor
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    ABSTRACT: Biochar has been widely proposed as a soil amendment, with reports of benefits to soil physical, chemical and biological properties. To quantify the changes in soil microbial biomass and to understand the mechanisms involved, two biochars were prepared at 350 °C (BC350) and 700 °C (BC700) from Miscanthus giganteus, a C4 plant, naturally enriched with 13C. The biochars were added to soils of about pH 4 and 8, which were both sampled from a soil pH gradient of the same soil type. Isotopic (13C) techniques were used to investigate biochar C availability to the biomass. Scanning Electron Microscopy (SEM) was used to observe the microbial colonization, and Attenuated Total Reflectance (ATR) to highlight structural changes at the surface of the biochars. After 90 days incubation, BC350 significantly increased the biomass C concentration relative to the controls in both the low (p < 0.05) and high pH soil (p < 0.01). It declined between day 90 and 180. The same trend occurred with soil microbial ATP. Overall, biomass C and ATP concentrations were closely correlated over all treatments (R2 = 0.87). This indicates that neither the biomass C, nor ATP analyses were affected by the biochars, unless, of course, they were both affected in the same way, which is highly unlikely. About 20% of microbial biomass 13C was derived from BC350 after 90 days of incubation in both low and high pH soils. However, less than 2% of biomass 13C was derived from BC700 in the high pH soil, showing very low biological availability of BC700. After 90 days of incubation, microbial colonization in the charsphere (defined here as the interface between soil and biochar) was more pronounced with the BC350 in the low pH soil. This was consistent with the biomass C and ATP results. The microbial colonization following biochar addition in our study was mainly attributed to biochar C availability and its large surface area. There was a close linear relationship between 13CO2 evolved and biomass 13C, suggesting that biochar mineralization is essentially a biological process. The interactions between non-living and living organic C forms, which are vital in terms of soil fertility and the global C cycle, may be favoured in the charsphere, which has unique properties, distinct from both the internal biochar and the bulk soil.
    Soil Biology and Biochemistry 02/2013; 57:513–523. DOI:10.1016/j.soilbio.2012.10.033 · 4.41 Impact Factor
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    Dataset: 90 knownsC
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    ABSTRACT: Soil contains approximately 2344 Gt (1 gigaton = 1 billion tonnes) of organic carbon globally and is the largest terrestrial pool of organic carbon. Small changes in the soil organic carbon stock could result in significant impacts on the atmospheric carbon concentration. The fluxes of soil organic carbon vary in response to a host of potential environmental and anthropogenic driving factors. Scientists world- wide are contemplating questions such as: ‘What is the average net change in soil organic carbon due to environmental conditions or management practices?’, ‘How can soil organic carbon sequestration be enhanced to achieve some mitigation of atmospheric carbon dioxide?’ and ‘Will this secure soil quality?’. These questions are far reaching, because maintaining and improving the world’s soil resource is imper- ative to providing sufficient food and fibre to a growing population. Additional challenges are expected through climate change and its potential to increase food shortages. This review highlights knowledge of the amount of carbon stored in soils globally, and the potential for carbon sequestration in soil. It also discusses successful methods and models used to determine and estimate carbon pools and fluxes. This knowledge and technology underpins decisions to protect the soil resource.
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    ABSTRACT: Export Date: 2 January 2013, Source: Scopus, Article in Press
    Agriculture, Ecosystems and Environment; 01/2012
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    ABSTRACT: The aim of this work was to determine the magnitude of the priming effect, i.e. short-term changes in the rate (negative or positive) of mineralisation of native soil organic carbon (C), following addition of biochars. The biochars were made from Miscanthus giganteus, a C4 plant, naturally enriched with 13C. The biochars were produced at 350 °C (biochar350) and 700 °C (biochar700) and applied with and without ryegrass as a substrate to a clay-loam soil at pH 3.7 and 7.6. A secondary aim was to determine the effect of ryegrass addition on the mineralisation of the two biochars.After 87 days, biochar350 addition caused priming effects equivalent to 250 and 319 μg CO2–C g−1 soil, in the low and high pH soil, respectively. The largest priming effects occurred at the start of the incubations. The size of the priming effect was decreased at higher biochar pyrolysis temperatures, which may be a way of controlling priming effects following biochar incorporation to soil, if desired. The priming effect was probably induced by the water soluble components of the biochar. At 87 days of incubation, 0.14% and 0.18% of biochar700 and 0.61% and 0.84% of biochar350 were mineralized in the low and high pH soil, respectively. Ryegrass addition gave an increased biochar350 mineralisation of 33% and 40%, and increased biochar700 at 137% and 70%, in the low and high pH soils, respectively. Certainly, on the basis of our results, if biochar is used to sequester carbon a priming effect may occur, increasing CO2–C evolved from soil and decreasing soil organic C. However, this will be more than compensated for by the increased soil C caused by biochar incorporation. A similar conclusion holds for accelerated mineralisation of biochar due to incorporation of fresh labile substrates. We consider that our results are the first to unequivocally demonstrate the initiation, progress and termination of a true positive priming effect by biochar on native soil organic C.
    Soil Biology and Biochemistry 11/2011; 43(11):2304-2314. DOI:10.1016/j.soilbio.2011.07.020 · 4.41 Impact Factor
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    M. Redmile-Gordon, R. P. White, P. C. Brookes
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    ABSTRACT: The trichloroacetic acid (TCA) based reagent proposed by Jenkinson and Oades (1979) fits all the criteria required to measure soil microbial biomass ATP (biomass ATP). Amongst other components it contains paraquat (0.1 M 1,1′ dimethyl-4,4′ bipyridylium dichloride), usually extracted from the herbicide Gramoxone. Paraquat is added as an analogue of ATP. It is tightly fixed to soil and so decreases ATP fixation. However, Gramoxone is now banned as an agricultural chemical in both Europe and North America. Our aim was to find an effective replacement for paraquat to measure biomass ATP. The best replacement was 0.6 M imidazole in 1.10 M TCA containing 0.25 M P (termed the TIP reagent). Biomass ATP concentrations were not significantly different in five soils extracted by either reagent 10.37 and 11.17 μmol ATP g−1 biomass C, respectively; standard error of differences of means = 0.36; p = 0.091.
    Soil Biology and Biochemistry 05/2011; 43(5):1098-1100. DOI:10.1016/j.soilbio.2011.01.007 · 4.41 Impact Factor
  • European Journal of Soil Science 01/2011; 62(1):1 - 4. DOI:10.1111/j.1365-2389.2010.01338.x · 2.39 Impact Factor
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    ABSTRACT: The advantages of no-tillage (NT) over conventional tillage (CT) systems in improving soil quality are generally accepted, resulting from benefits in soil physical, chemical and biological properties. However, most evaluations have only considered surface soil layers (maximum 0–30 cm depth), and values have not been corrected to account for changes in soil bulk density. The objective of this study was to estimate a more realistic contribution of the NT to soil fertility, by evaluating C- and N-related soil parameters at the 0–60 cm depth in a 20-year experiment established on an oxisol in southern Brazil, with a soybean (summer)/wheat (winter) crop succession under NT and CT. At full flowering of the soybean crop, soil samples were collected at depths of 0–5, 5–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm. For the overall 0–60 cm layer, correcting the values for soil bulk density, NT significantly increased the stocks of C (18%) and N (16%) and microbial biomass C (35%) and N (23%) (MB-C and -N) in comparison to CT. Microbial basal respiration and microbial quotient (qMic) were also significantly increased under NT. When compared with CT, NT resulted in gains of 0.8 Mg C ha−1 yr−1 (67% of which was in the 0–30 cm layer) and 70 kg N ha−1 yr−1 (73% in the 0–30 cm layer). In the 0–5-cm layer, MB-C was 82% higher with NT than with CT; in addition, the 0–30 cm layer accumulated 70% of the MB-C with NT, and 58% with CT. In comparison to CT, the NT system resulted in total inputs of microbial C and N estimated at 38 kg C ha−1 yr−1 and 1.5 kg N ha−1 yr−1, respectively. Apparently, N was the key nutrient limiting C and N stocks, and since adoption of NT resulted in a significant increase of N in soils which were deficient in N, efforts should be focused on increasing N inputs on NT systems.
    Soil Biology and Biochemistry 12/2010; DOI:10.1016/j.soilbio.2010.08.013 · 4.41 Impact Factor
  • M. Durenkamp, Y. Luo, P.C. Brookes
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    ABSTRACT: The efficiency of the fumigation extraction method on the determination of soil microbial biomass carbon and ninhydrin-N was tested in three different soils (UK grassland, UK arable, Chinese arable) amended with black carbon (biochar or activated charcoal). Addition of activated charcoal to soil resulted in a significant decrease in K2SO4 extractable carbon and ninhydrin-N in all three soils, whereas the addition of biochar generally did not. A lower concentration of the extraction reagent (0.05 M vs. 0.5 M K2SO4) resulted in a significantly lower extraction efficiency in the grassland soil. The extraction efficiency of organic carbon was more affected by black carbon than that of ninhydrin-N, which resulted in a decreased biomass C/ninhydrin-N ratio. The impact of black carbon on the extraction efficiency of soil microbial biomass depended on the type of black carbon, on the concentration of the extraction medium and on soil type.
    Soil Biology and Biochemistry 11/2010; DOI:10.1016/j.soilbio.2010.07.016 · 4.41 Impact Factor
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    ABSTRACT: The preparation of soil for measurement of properties such as microbial biomass P involves the removal of plant roots. Any soil attached to the roots (root-attached soil) is also removed. In a very poorly drained silty clay loam under grassland we found that the root-attached soil contained more than twice the quantity of bicarbonate extractable P than the bulk soil. Discarding this root-attached soil could potentially result in underestimation of bicarbonate extractable P. We also showed that preferential inclusion of deeper soil due to variability of root density with depth is likely to result in underestimation of soil bicarbonate extractable P in fumigated and unfumigated soil samples. Additionally we investigated a conventional and alternative (rapid) sod preparation technique that might affect the accuracy of measurement of sod bicarbonate extractable P as part of a microbial biomass P measurement. Preparation technique made no significant difference to the quantity of P recovered.
    Soil Science Society of America Journal 11/2009; 73(6-6):1861-1863. DOI:10.2136/sssaj2009.0021N · 2.00 Impact Factor
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    ABSTRACT: The drying and re-wetting of soils can result in the modification of the amounts and forms of nutrients which can transfer, via leachate, from the soil to surface waters. We tested, under laboratory conditions, the hypothesis that the rate of re-wetting of a dried soil affects the solubilisation and concentrations of different forms of phosphorus (P) in leachate. A portion of grassland pelostagnogley soil (sieved moist <2mm) was dried at 35°C and another portion maintained at approximately 40% water-holding capacity. Water (25ml) was added at ten regularly spaced time intervals in 2.5-ml aliquots to the surfaces of both soils over periods of 0, 2, 4, 24 and 48h, resulting in different rates of application. The leachate was collected and analysed for dissolved (<0.45μm) and particulate total P and molybdate reactive and unreactive P. The rate of re-wetting significantly changed the concentrations of P, especially dissolved forms, in the leachate. Dissolved P concentrations were highest in leachate from the 2-h treatment, while particulate P concentrations were highest in the 0-h treatment leachate. In all cases, most P was unreactive and, therefore, likely to be in an organic form. Soil drying decreased microbial biomass, but this could not be directly linked to an increase of P in leachate. These results suggest that changes in patterns of rainfall frequency and intensity predicted by climate change scenarios could significantly affect the quantities of P leached from soils.
    Biology and Fertility of Soils 07/2009; 45(6):635-643. DOI:10.1007/s00374-009-0375-x · 3.40 Impact Factor
  • J. C. Aciego Pietri, P. C. Brookes
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    ABSTRACT: Our aim was to determine whether the smaller biomasses generally found in low pH compared to high pH arable soils under similar management are due principally to the decreased inputs of substrate or whether some factor(s) associated with pH are also important. This was tested in a soil incubation experiment using wheat straw as substrate and soils of different pHs (8.09, 6.61, 4.65 and 4.17). Microbial biomass ninhydrin-N, and microbial community structure evaluated by phospholipid fatty acids (PLFAs), were measured at 0 (control soil only), 5, 25 and 50 days and CO2 evolution up to 100 days. Straw addition increased biomass ninhydrin-N, CO2 evolution and total PLFA concentrations at all soil pH values. The positive effect of straw addition on biomass ninhydrin-N was less in soils of pH 4.17 and 4.65. Similarly total PLFA concentrations were smallest at the lowest pH. This indicated that there is a direct pH effect as well as effects related to different substrate availabilities on microbial biomass and community structure. In the control soils, the fatty acids 16:1ω5, 16:1ω7c, 18:1ω7c&9t and i17:0 had significant and positive linear relationships with soil pH. In contrast, the fatty acids i15:0, a15:0, i16:0 and br17:0, 16:02OH, 18:2ω6,9, 17:0, 19:0, 17:0c9,10 and 19:0c9,10 were greatest in control soils at the lowest pHs. In soils given straw, the fatty acids 16:1ω5, 16:1ω7c, 15:0 and 18:0 had significant and positive linear relationships with pH, but the concentration of the monounsaturated 18:1ω9 PLFA decreased at the highest pHs. The PLFA profiles indicative of Gram-positive bacteria were more abundant than Gram-negative ones at the lowest pH in control soils, but in soils given straw these trends were reversed. In contrast, straw addition changed the microbial community structures least at pH 6.61. The ratio: [fungal PLFA 18:2w6,9]/[total PLFAs indicative of bacteria] indicated that fungal PLFAs were more dominant in the microbial communities of the lowest pH soil. In summary, this work shows that soil pH has marked effects on microbial biomass, community structure, and response to substrate addition.
    Soil Biology and Biochemistry 07/2009; 41(7):1396-1405. DOI:10.1016/j.soilbio.2009.03.017 · 4.41 Impact Factor
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    ABSTRACT: Soil biological processes contribute stability against physical disruption. We present an approach of step-wise fragmentation to assess the role that microbes and organic matter have on soil aggregate stabilisation. Compared to slaking and ultrasound procedures, the approach has a low impact on the microbial biomass. It also does not impose a severe drying stress. Grassland soil was found to be more stable than arable soil. Further examination of the arable soil revealed that increased disruption by shaking caused unstable microaggregates 53–250 μm in size to fragment, leaving a higher proportion of stable microaggregates in this size range. Carbohydrates, C:N, and basal respiration were found to be higher in the stable microaggregates than the other size fractions. Our results indicate that a distinct size range of soil aggregates exists in which microbial stabilisation dominates. This contradicts other research and questions the usefulness of measuring the biological properties of aggregate size fractions without understanding the physical effects of the fractionation procedure.
    Soil and Tillage Research 03/2009; DOI:10.1016/j.still.2008.07.005 · 2.58 Impact Factor
  • Soil Biology and Biochemistry 02/2009; 41(2):440-443. DOI:10.1016/j.soilbio.2008.09.002 · 4.41 Impact Factor
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    J.C. Aciego Pietri, P.C. Brookes
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    ABSTRACT: Effects of changing pH along a natural continuous gradient of a UK silty-loam soil were investigated. The site was a 200 m soil transect of the Hoosfield acid strip (Rothamsted Research, UK) which has grown continuous barley for more than 100 years. This experiment provides a remarkably uniform soil pH gradient, ranging from about pH 8.3 to 3.7. Soil total and organic C and the ratio: (soil organic C)/(soil total N) decreased due to decreasing plant C inputs as the soil pH declined. As expected, the CaCO3 concentration was greatest at very high pH values (pH > 7.5). In contrast, extractable Al concentrations increased linearly (R2 = 0.94, p < 0.001) from below about pH 5.4, while extractable Mn concentrations were largest at pH 4.4 and decreased at lower pHs. Biomass C and biomass ninhydrin-N were greatest above pH 7. There were statistically significant relationships between soil pH and biomass C (R2 = 0.80, p < 0.001), biomass ninhydrin-N (R2 = 0.90, p < 0.001), organic C (R2 = 0.83, p < 0.001) and total N (R2 = 0.83, p < 0.001), confirming the importance of soil organic matter and pH in stimulating microbial biomass growth. Soil CO2 evolution increased as pH increased (R2 = 0.97, p < 0.001). In contrast, the respiratory quotient (qCO2) had the greatest values at either end of the pH range. This is almost certainly a response to stress caused by the low p. At the highest pH, both abiotic (from CaCO3) and biotic Co2 will be involved so the effects of high pH on biomass activity are confounded. Microbial biomass and microbial activity tended to stabilise at pH values between about 5 and 7 because the differences in organic C, total N and Al concentrations within this pH range were small. This work has established clear relationships between microbial biomass and microbial activity over an extremely wide soil pH range and within a single soil type. In contrast, most other studies have used soils of both different pH and soil type to make similar comparisons. In the latter case, the effects of soil pH on microbial properties are confounded with effects of different soil types, vegetation cover and local climatic conditions.
    Soil Biology and Biochemistry 04/2008; DOI:10.1016/j.soilbio.2008.03.020 · 4.41 Impact Factor
  • J. C. Aciego Pietri, P. C. Brookes
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    ABSTRACT: Most investigations into the effects of changing soil pH on microbial activity use, from necessity, soils taken from different sites so that soil physical and chemical properties are confounded. Studies along continuous gradients of soil pH within a single soil type are rare, simply because so few exist, in UK or even worldwide. Here we report measurements of mineralisation of native organic matter and added arginine along a continuous soil pH gradient (range about pH 3.7–8.3) of a UK silty clay loam soil (Chromic Luvisol or Typic Paleudalf). The soil has been maintained under constant management for more than 100 years, with winter wheat sown annually. The soil NH4+-N concentration was maximal at the lowest pH (pH 3.7), declining exponentially until pH 5.5 and remaining negligible thereafter. However, unexpectedly, soil NO3−-N concentration was also maximal at pH 3.7 and was significantly negatively correlated with increasing pH thereafter. To investigate these unexpected NO3−-N results, arginine was added as a labile source of organic N and its extent of ammonification and nitrification measured at soil pHs 3.79, 4.42, 6.08 and 7.82. While arginine ammonification was apparently greatest at pHs 3.79 and 4.42, similar to mineralisation of soil organic N, nitrification of this added N was greatest at soil pH 7.82 and least at pH 3.79, the reverse of the situation with soil organic N, but much more in line with what was expected. It was concluded that the decline in soil NO3−-N with increasing pH in the unamended soils was an artefact, caused by increasing plant uptake of NO3−-N as yield increased, rather than a true effect of low pH increasing nitrification of soil organic N. Our results differ from most previous studies, which showed poor correlations between soil pH and arginine mineralisation. This was attributed to our use of much longer incubation times (up to 50 days) than usually employed. Under our conditions, arginine was therefore shown to be a useful model for mineralisation of labile soil organic N.
    Soil Biology and Biochemistry 03/2008; 40(3):797-802. DOI:10.1016/j.soilbio.2007.10.014 · 4.41 Impact Factor

Publication Stats

13k Citations
375.98 Total Impact Points

Institutions

  • 2004–2014
    • Rothamsted Research
      • Department of Sustainable Soils and Grassland Systems
      Harpenden, England, United Kingdom
  • 2006
    • Kenya Agricultural Research Institute
      Nairoba, Nairobi Area, Kenya
    • China Agriculture University-East
      Peping, Beijing, China