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Research article2010Peer reviewed

Spatial variation of N-2-fixation in field pea (Pisum sativum L.) at the field scale determined by the N-15 natural abundance method

Haugaard-Nielsen, Henrik; Holdensen, L.; Wulfson, D.; Jensen, Erik Steen


Grain legumes such as field pea are known to have high variability of yield and dinitrogen (N-2) fixation between seasons, but less is known about the yearly spatial variability within a field. The objective of this study was to improve the understanding of spatial field scale variability of field pea dry matter (DM) yield and nitrogen (N) acquisition from fixation and soil within a 10 ha farmer's field. A 42 m systematic random grid providing 56 plant sampling locations across 10 ha supplemented by soil data provided from an existing database were used to determine whether the observed spatial variability could be explained by the variability in selected abiotic soil properties. All measured soil variables showed substantial variability across the field and the pea dry matter production ranged between 4.9 and 13.8 Mg ha(-1) at maturity. The percent of total N derived from the atmosphere (%Ndfa) at flowering, estimated using the N-15 natural abundance method, ranged from 65% to 92% with quantitative N-2-fixation estimates from 93 kg to 202 kg N ha(-1). At maturity %Ndfa ranged from 26% to 81% with quantitative N-2-fixation estimates from 48 kg to 167 kg N ha(-1). Significant correlations were found between pea dry matter production and humus content, potassium content (collinear with humus) and total N in the 0-25 cm topsoil. No correlation was found between any individual soil property and %Ndfa or kg N fixed ha(-1). It was not possible to create a satisfactory global multi-regression model for the field dry matter production and N-2-fixation. A number of other models were tested, but the best was only able to explain less than 40% of the variance in %Ndfa using seven soil properties. Together with the use of interpolated soil data, high spatial variation of soil N-15 natural abundance, a mean increase in pea N-15 natural abundance of 1 delta unit between flowering and maturity and a reference crop decline of 1.3 delta N-15 unit over the same period increased noise of derived variables, making modeling of N-2-fixation difficult. Furthermore, complex interactions with other soil variables and biotic stresses not measured in this study may have contributed significantly to the variability of fixation and yield of pea within the field. Pea N-2-fixation obtained from two additional 10 ha farmer fields was in agreement with the other findings highlighting that N-2-fixation takes place under a range of physical and chemical soil properties and is controlled by local site specific conditions. In future studies addressing field scale variability we recommend that soil variables wherever possible should be measured in the same plots as the sampled crop. Sampling designs that optimize the use of a priori information about the field soil and landscape properties for positioning plots and that facilitate estimates of local variances should be considered.


Field scale; Natural N-15 abundance; Nitrogen fixation; Pisum sativum; Spatial variability

Published in

Plant and Soil
2010, Volume: 327, number: 1-2, pages: 167-184
Publisher: SPRINGER

    UKÄ Subject classification

    Agricultural Science

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