Paper presented at the 52nd CFCS Annual Meeting, Guadeloupe, July 10-16, 2016 MANAGEMENT OF BIOLOGICAL PROCESSES IN AGRO ECOLOGICAL PERSPECTIVE
MULCHING EFFECTS OF FRESH SARGASSUM SEAWEED ON SOIL PROPERTIES AND PLANT GROWTH Kaeiron Saunders, Jabarry Belgrave and Francis Lopez Department of Biological and Chemical Sciences, The University of the West Indies, Cave Hill Campus, BB11000, Barbados
Keywords : SOLVITA, chlorophyll index, SPAD, plant height, number of leaves Abstract Mulch application of Sargassum seaweed (Sargassum spp.) to soil can help to reduce beach contamination in the Caribbean Region while providing beneficial horticultural effects. This study investigated the effects of fresh Sargassum mulch on soil properties and plant growth in a test crop of tomato (Solanum lycopersicum L. â HA 3019â ). Fresh Sargassum material (washed and unwashed) was applied as mulches (0, 5 and 8cm thick) to small field plots one week after transplanting of 3-week-old seedlings. The mulch material was raked away from the plots after three weeks exposure. Observations on soil moisture, electrical conductivity, pH and biological activity, and plant growth were made at 1 to 2-week intervals over a 6-week period with additional soil measurements after 10 weeks. Soil biological activity (respiration) was increased by the Sargassum mulch with values being similar for the 5cm and 8cm mulch layers. Soil moisture content, pH and electrical conductivity (EC) were increased as the mulch layer increased and EC values were only marginally reduced by Sargassum washing. An increase in plant growth compared to the control treatment was noted only in the washed Sargassum treatments. Potential benefits of Sargassum seaweed mulches on soil properties and plant growth can be nullified due to soil salinization effects. Materials and methods This study was established in a heavy clay soil at the Cave Hill Campus of the University of the West Indies. The soil was prepared to a fine tilth and beds (1m wide) were formed incorporating a pre-plant fertilizer (NPK+Mg 12:12:17:2, 200 kg ha-1). Two rows of tomato seedlings (3-week-old) were established on each bed with a spacing of 45cm between and 40 cm within rows. Fresh Sargassum seaweed was collected from Long Beach, Christ Church, Barbados, at high tide on the 9th November, 2015. It was removed from the shore line and placed into sacks for transport to the UWI Cave Hill campus for preparation and application. A split-plot design (5 replications) was used with mulch washing (washed, unwashed) as the main plots and mulch height (0, 5, 8 cm) as sub-plots. Washing of the Sargassum seaweed was done using a garden hose aimed at each sack for 15 minutes. Mulch treatments were applied 1 week after transplanting of seedlings and each sub-plot (0.72 m2) contained 4 plants. The fresh mulch material applied was estimated at 10 and 15 t ha-1 for the 5cm and 8cm mulch heights, respectively. The mulch material was raked away from the plots into the furrows after three weeks exposure. Observations were made at 1 to 2-week intervals over a 6-week period with additional soil measurements after 10 weeks. Plant growth was assessed by observing height and leaf number, and leaf greenness was determined for the first fully expanded leaf from the apex using a chlorophyll index meter (SPAD 502 Plus, Konica Minolta Sensing Inc., Japan). Soil moisture content was determined directly in field plots using a soil moisture probe (CS620, Campbell Scientific, USA). Soil samples (top 10cm) from each plot were dried for 24h at 40°C, ground and sieved using a 2 mm sieve. Soil pH and electrical conductivity were determined with probes (IQ170, IQ Scientific Instruments, USA) using a 1:2.5 soil/water ratio. Soil respiration was determined using the CO2-Burst method (SOLVITA, Woods End Laboratories Inc., USA). Main results At two weeks after treatment application, soil moisture content was significantly increased by the mulch treatments and was 1.5 and 2.5 times greater in plots with the 5cm and 8cm mulch treatments, respectively, compared to Control plots (Figure 1). Differences in soil moisture content between treatments were largely nullified by the removal of the mulch material after three weeks.
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