Effects of Algal Fibre and Perlite on Physical Properties of Various Soils and on Potato Nutrition and Quality on a Gravelly Loam Soil in Southern Norway

Abstract

Large quantities of seaweed are harvested world-wide for industrial processing, but significant amounts of by-product remain unused and may cause environmental pollution if returned to the sea. Its potential for use in agriculture is therefore of interest. Algal fibre waste from a large alginate extraction plant in Norway was studied with respect to its potential both for soil physical amelioration and as a nutrient source for potatoes. The material contained perlite, itself a wellknown growth substrate, as this was used to filter the fibre in the factory. The effects on soil moisture retention and aeration properties of incorporating up to 80% fibre waste or pure perlite were studied on five widely contrasting soil types. The algal fibre waste had similar effects to pure perlite on soil aeration and on the proportion of water held at low soil moisture tension. It had, however, a far greater effect on moisture retention at higher tension levels. Plant-available water increased by 3.6 vol.% when 10% by volume of fibre was incorporated, as against 1.2 vol.% with the same volume of pure perlite. The effects were similar in all soils. The effect on potato growth and quality of spreading 20 or 40 Mg ha -1 of algal fibre was studied by comparison with the use of various amounts of compound nitrogen- phosphorus-potassium (NPK) fertilizer. The algal fibre contained large amounts of plant nutrients. In the absence of fertilizer, potato yield increased by 30% and 70% with the use of 20 and 40 Mg ha -1 , respectively. These increases declined to 7% and 17% at the highest rate of fertilizer application (120 kg N, 55 kg P and 187 kg K ha -1 ). The effect of 10 Mg ha -1 algal fibre was equivalent to that of 20-25 kg N in compound fertilizer. Algal fibre had little effect on soil contents of available P, K, calcium and magnesium, but the level of sodium rose sharply. Electrical conductivity did not, however, rise excessively. A considerable amount of mineral N remained in the soil after harvest, but most was lost to leaching before the following year's ryegrass crop could make use of it.