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Flores P.,Instituto Murciano Of Investigacion Y Desarrollo Agrario Y Alimentario La Alberca | Hellin P.,Instituto Murciano Of Investigacion Y Desarrollo Agrario Y Alimentario La Alberca | Fenoll J.,Instituto Murciano Of Investigacion Y Desarrollo Agrario Y Alimentario La Alberca | Murray P.J.,Cross Institute Programme for Sustainable Soil Function
Acta Horticulturae | Year: 2012

The impacts of increasing nitrogen (N) supply and various N sources (NO3 - vs NH4 + and organic-N vs. inorganic-N) on plant growth and the natural abundance of 13C (σ13C) were studied in pepper (Capsicum annuum L. 'Quito') seedlings grown in 1 L pots filled with peat in a growth chamber. In a first experiment, plants were irrigated at four different N levels (0, 1, 3 and 7 mM NO3 -). In a second experiment, treatment consisted of three different NO3 -/NH4 + ratios (100/0, 50/50 and 0/100) at a constant N concentration of 3 mM. In a third experiment, plants were irrigated with different organic-N/inorganic-N ratios (100/0, 98/2, 96/4, 92/8 and 88/12) by using NO3 - as inorganic N source, and a liquid fertilizer derived from sheep manure (LSM) as organic N source. Increasing N levels (applied as NO3 -) significantly increased plant growth and plant N concentration. At the highest N level, the C/N ratio increased, which, together with the increase in the σ13C values, indicates a decrease in stomatal conductance. On the other hand, the N form (NO3 - vs. NH4 +) significantly affected growth and carbon isotope composition. NO3 --grown plants showed the lowest σ13C values, which can be attributed to the fact that these plants presented higher leaf stomatal conductance than NH4 +-grown plants. Finally, changes in growth and carbon discrimination in plants grown under combined organic and inorganic fertilization were related with the plant response to NO3 - application and osmotic stress following liquid manure application. Source


Paterson E.,James Hutton Institute | Sim A.,James Hutton Institute | Osborne S.M.,James Hutton Institute | Murray P.J.,Cross Institute Programme for Sustainable Soil Function
Soil Biology and Biochemistry | Year: 2011

Microbial communities in soil are highly species-rich, recognition of which has led to the view that functional redundancy within communities may buffer many impacts of altered community structure on soil functions. In this study we investigated the impact of long-term (>50 years) exclusion of plant-inputs (bare-fallow treatment) on soil microbial community structure and on the ability of the microbial biomass to mineralise tracer additions of 13C-labelled plant-derived C-substrates. Exclusion of plant-inputs resulted in depletion of soil organic matter (SOM) and a reduction in microbial biomass size. The microbial community structure was also strongly affected, as indicated by the distinct phospholipid fatty acid (PLFA) profiles in bare-fallow and grassland soils. Mineralisation of labile plant-derived substrates was not perturbed by the bare-fallow treatment. The incorporation of labile plant-derived C into PLFA biomarkers was found to differ between soils, reflecting the distinct community structures of the soils and indicating that these substrates were utilised by a broad range of microbial groups. In contrast, the mineralisation of recalcitrant plant-derived substrates was reduced in bare-fallow soil and the fate of substrate-derived C within PLFA biomarkers was, initially, similar between the soils. These results indicate that utilisation of these recalcitrant substrates was a function restricted to specific groups, and that exclusion of plant-derived inputs to soil had reduced the capacity of bare-fallow microbial communities to utilise this substrate type. Therefore, the study suggests that long-term selective pressure on microbial communities, resulting in altered community structure, may also result in altered functional attributes. This structure-function relationship was apparent for utilisation of recalcitrant plant-derived substrates, but not for the more widely distributed attribute of labile C-substrate utilisation. © 2011 Elsevier Ltd. Source


Gregory A.S.,Rothamsted Research | Webster C.R.,Rothamsted Research | Watts C.W.,Rothamsted Research | Whalley W.R.,Rothamsted Research | And 9 more authors.
Soil Science Society of America Journal | Year: 2010

In this study, we explored the effect of the roots of different forage grasses on soil hydraulic properties at the plot scale. To achieve this, we set up a field experiment in which six different grass cultivars were grown on replicated field plots at North Wyke, UK. We used tension infiltration measurements to assess soil hydraulic properties and structure. These measurements were made over two consecutive seasons. Measurements of shrinkage, water repellence, and the water release characteristic on soil samples taken from the North Wyke site were also made. We also wanted to compare the effects of different grasses on soil structure with the effects of differences in soil management; we therefore made tension infiltration measurements on fallow soil, permanent grassland, and arable land on a longterm experiment at Rothamsted, Harpenden, UK. Our data showed that the saturated hydraulic conductivity of the capillary matrix of the soil sown with grass depended on the grass species. Grass species affected the characteristic pore size estimated from tension infiltration data, At the Rothamsted site, we were able to infer that the development of macropore structure can be ranked grassland > arable > fallow (from the greatest to the least amount of macropores). In the North Wyke site, all the grass plots showed evidence of a macropore structure, consistent with the grassland site at Rothamsted, but there did not appear to be any variation between grass species. We concluded that changes to soil structure were probably due to physical rearrangement of soil particles by shrinkage. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. Source

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