Spatial and temporal variability of nitrate in irrigated salad crops |
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Authors: | L Bruckler A M de Cockborne P Renault B Claudot |
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Institution: | (1) Unité de Science du Sol d'Avignon, INRA, Domaine St Paul, Site Agroparc, F-84914 Avignon, Cedex 9, France, FR |
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Abstract: | The objective of this study was to analyze the spatial and seasonal variations in NO3
–-N concentration in soil samples and solution samplers and the N leaching of an irrigated crop cultivated intensively in the
Mediterranean zone. Although much information is available from controlled field experiments concerning N concentration and
its spatial variability, quantitative estimates of nitrate fluxes under normal farming conditions and when the field is directly
managed by farmers are rare. This is particularly true for gardening crops in the Mediterranean zone, where high evapotranspiration
rates lead to intensive irrigation and may be responsible for N leaching. A field experiment was conducted in the Departement
du Gard under agricultural conditions. Salads (Cichorium endivia, Lactuca sativa) were planted in three consecutive periods. The field was irrigated with sprinklers. Local measurements with a neutron probe
were made at two sites (row, interrow), and an experimental plot (95 m×25 m) was surveyed at 36 points located on a 10 m×10
m equilateral grid to analyze the spatial variability of water and NO3
–-N balances. To analyze the basic statistical properties of our sampling scheme, random fields of soil concentration were
simulated with the turning-bands method. Sampling strategy simulations indicated that when a spatial structure exists, sampling
according to a regular grid was more efficient than a purely random sampling strategy. Global trends indicated high spatial
variability for nitrate leaching with differences between periods of different irrigation intensity (97 kg ha–1 NO3
–-N leaching during the spring and summer, and 199 kg ha–1 NO3
–-N leaching during autumn and winter). Leaching caused temporal variations in the spatial distributions of NO3
–-N. The origin of the spatial variability of N leaching was explained by first, the variability in NO3
–-N concentration in the soil profile, and second, by spatial variability in irrigation. Furthermore, the spatial distribution
of the NO3
–-N concentration was time dependent, and NO3
–-N spatial distributions became independent after approximately 2 or 3 months under our conditions. Our results show that
better management of irrigation and fertilizer in spring and summer may reduce N leaching and, thus, improve ground water
quality.
Received: 15 March 1996 |
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Keywords: | |
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