Seaweed compost as an amendment for horticultural soils in Argentina


Courtesy of BioCycle Magazine

Seaweed (fresh, dry) or its products (extracts, composts, soil conditioners) have been long used in agriculture to enhance plant growth and productivity. In this study, we evaluated the effects that seaweed composts at different doses and degree of maturation had on the yield of tomatoes (Licopersicon esculentum Mill. cv. platense) grown on a horticultural soil in northeastern Patagonia. We used 10 tomato plants per treatment plot set in a randomized block design. Treatments were: 1) soil without amendment, control (S); 2) 5 kg m-2 of compost aged 9 months (C9-5); 3) 10 kg m-2 of compost aged 9 months (C9-10); 4) 5 kg m-2 of compost aged 20 months (C20-5); and 5) 10 kg m-2 of compost aged 20 months (C20-10).

Total weight and number of tomatoes, and aerial plant biomass (excluding fruits) were significantly higher for the compost treatments than those of the control. Also, compost treated plants bore mature fruits, in average, 9 days earlier and presented higher resistance to diseases than controls. The weight of tomatoes per plant grown in C20 was significantly higher than that of C9, differences that could be attributed to the lower salinity of compost C20 (C20 and C9 electrical conductivities were 1.5 and 15 dS m-1, respectively). The increased yield and resistance to diseases on tomato plants by addition of seaweed compost appear to be related to a complex number of factors not yet fully understood. It seems, however, that a combination of higher nutrient availability (mainly P) due to slight increases in pH of the soil amended, together with increases in readily available K and an improvement in soil physical conditions (increase in pore size and probably amelioration of hydric conditions), may have been responsible for the higher production of seaweed amended plots as compared to the control.

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