Programa e Resumos - I Congresso Ibérico de Ciência do Solo 2004

I Congresso Ibérico da Ciência do Solo – 15 a 18 de Junho de 2004, Bragança, Portugal
Influence of tephra mulch thickness and grain-size on soil temperature.
Francisco Díaz, Guacimara Mejías, Marisa Tejedor & Concepción Jiménez
Dept. Edafología y Geología, Universidad de La Laguna, Facultad de Biología, Avda.
Astrofísico Francisco Sánchez s/n, 38204, La Laguna, Tenerife, Islas Canarias, España – Tel:
(+34) 922318368 – Fax (+34) 922318311 – E-mail: martesa@ull.es
Abstract
Comunicación: Poster
In the present work, we examine the effect of tephra mulching (basaltic pyroclast) -in
particular, grain size and mulch thickness- on soil temperature in an arid region of the
Canary Islands (Spain).
The study was carried out in seven experimental plots measuring 5.5 x 4.5 m 2 , each 1.5
m apart and all in the same landscape position (slope < 1%). In each plot 40 cm of a soil
typical of the area was placed (Haplocalcids,. with 694.5 g kg -1 clay, 252.2 g kg -1 silt,
53.3 g kg -1 sand, 2.5 g kg -1 organic carbon, 1.8 dS m -1 CEs. The soils in all the plots
were covered on the same day (August 1999) with a layer of basaltic tephra. The plots
differed as regards the thickness of the covering and the mulch grain size. Three were
covered with 10-cm basaltic pyroclasts of three different grain sizes (fine, medium and
coarse). In a further three, layers of 5, 10 and 15-cm of medium-grain size mulch were
used. One plot was left uncovered as a control. Temperature sensors were placed at 3-
cm depth in the soil in the centre of each plot. The PT100 sensors were connected
throughout the experimental period to a microprocessor via a UTI signal conditioner in
Wheatstone bridge mode. Measurements were taken every half hour for an entire year
(1 June 2000-30 May 2001). A full meteorological station installed in the zone took air
temperature readings every 15 minutes at a height of 2 metres above ground. Total
rainfall during the year was 34 mm and the average annual temperature 20.3ºC.
All the mulches studied considerably reduced both diurnal and seasonal temperature
fluctuations, although the effect on soil temperature differed according to the
characteristics of the mulch. Thicknesses of 10 to15 cm of medium-grain tephra were
found to be the most effective in maintaining adequate temperatures for plant
development. Lower thicknesses as well as fine and coarse grain sizes had lower
temperature attenuation capacity. These results are of practical interest in that they
permit optimisation of farming systems based on the use of volcanic mulch.
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