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| Titel |
Soil water repellency patterns following long-term irrigation with waste water in a sandy calcareous soil, SE Spain |
| VerfasserIn |
J. Mataix-Solera, L. García-Irles, A. Morugán, S. H. Doerr, F. García-Orenes, I. Atanassova, M. A. Navarro, H. Ayguadé |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030279
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| Zusammenfassung |
| One of the consequences of long-term irrigation with waste water can be the development of
soil water repellency (WR). Its emergence can affect soil-water balance, irrigation
efficiency and crop yield. Water repellency development has been suggested to be
controlled by parameters such as organic matter quantity and type present in the
waste water, soil properties (particularly the texture), and the overall time period of
irrigation. Here we examine the effect of long-term (~20 years) irrigation with
low quality waste-water on soil wettability under a Populus alba tree stand used
as a “green filter”. The plot exhibited considerable micro-topography (ridges and
furrows) and consisted of sandy calcareous soil (Xerofluvent). Water repellency
and organic carbon content (OC) were studied in 160 samples taken from the plot
and from an adjacent area used as control (no irrigated). From the control area 40
samples were taken from the first 5 cm of mineral soil (C samples). From the irrigated
plot a total of 120 samples were collected. To account for the micro-topography of
the terrain, 40 samples each were taken from ridges (R samples; 0-5 cm depth),
furrows (F samples; 0-5 cm depth), and from furrows at depth (FD samples, 5-10 cm
depth).
Soil WR was assessed in the laboratory for all air dry samples using the water drop
penetration time test (WDPT Test). Samples with WDPT -¤ 5 seconds were classified as
non-repellent. Organic carbon content (OC) was analyzed in all samples by potassium
dichromate oxidation method. We also carried out a detailed chemical characterisation of the
organic matter in two furrow samples that exhibited contrasting wettability, but no major
difference in OC content (F10: WDPT 9960s, OC 6.7%; F31: WDPT 10s, OC 7.5%).
Following accelerated solvent extraction with Dichloro-methane/MeOH (95:5), the extract
was analysed by GC-MS.
All samples from the control area (C) were wettable (mean WDPT=1s). In the irrigated
plot, water repellency was present for 48% of R samples (mean WDPT=135s), 95% of F
samples (mean WDPT=802s), and 93% of FD samples (mean WDPT=267s). A good
correlation between WR and OC was found by pooling all groups of samples (r=0.830***),
and in some cases separately per group: R samples (r=0.885***), FD samples (r=0.651***).
However, the correlation within group of F samples was low (r=0.269ns). This sample group
had the highest frequency occurrence and the highest mean values of WR, indicating that not
only quantity of OC is controlling the development of WR. This notion is supported by the
results from samples F10 and F31. Despite their exposure to the same waste water, the
organic material extracted from the highly repellent sample F10 exhibited more than twice
the content of n-alkanols (~C26) and alkanoic acids (C18-24) compared to sample
F31.
Based on these results we speculate that for the study plot, the combination of the
following factors allowed high levels of water repellency to develop: (1) sandy soil texture,
(2) long-term use of waste water, (3) low quality of waste water treatments, and (4)
potentially also organic matter inputs from the vegetation have. The results suggest that rather
than total OC content, a specific fraction of the organic matter pool controls repellency
development, with n-alkanols and alkanoic acids playing a key role. It is conceivable that
water repellency-induced preferential flow has led to an increased accumulation of these
compounds at the flow path margins, leading to a self-enhancement of water repellency in
sample F10. |
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