The Development of a Hydraulic Seeding Technique for Unstable Sand Slopes. II. Field Evaluation

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Abstract
(1) Hydraulic seeding is used to establish vegetation in areas inaccessible to traditional agricultural machinery. This paper examines hydraulic seeding techniques in a series of field trials on sand wastes produced by the china clay industry using a clover and grass seed mixture containing Trifolium repens L., Festuca rubra L., F. ovina L. and Agrostis Tenuis sibth. (capillaris L.). (2) Hydraulic seeding, as currently practised in Britain, involves application of fertilizer and/or seed to steep slopes as a water-based slurry. Mulches are typically added to bury the seed and chemical stablizer to reduce seed loss by erosion. In trial plots under field conditions, conventional hydraulic seeding techniques produced limited establishment of grasses and legumes. Toxicity of fertilizer to germinating seeds and inhibition of germination by stablizers were primarily responsible for this poor establishment. (3) In some circumstances, acceptable establishment was obtained by applying seed alone. However, in other situations, particularly where natural seed burial was limited or dry soil conditions prevailed, establishment was markedly improved by the addition of a mulch. Fertilizer toxicity was found to vary in intensity with site and climatic conditions, but could be reduced by mulching. However, effective establishment was obtained in some experiments by omitting the fertilizer and delaying its application until germination has occurred. Of the chemical stablizers tested, none gave a significant improvement in establishment while some made it worse. In all experiments, effective mulching and stablization was obtained by the use of long-fibre flexible materials rather than the mulches typically used in conventional hydraulic treatments. (4) The success of hydraulic seeding is discussed in relation to the effects of mulching, substrate characteristic and climatic conditions on the availability of favourable microsites and natural seed burial processes. In general, clover establishment was more sensitive to site conditions and hydraulic treatment, and sometimes failed completely. It is suggested that current hydraulic seeding techniques should be modified. Some components should be omitted completely and greater emphasis be placed on the effects of site and climatic conditions. More attention must be paid to the requirements of legumes since many commercial hydraulic operations fail not through failure of grass establishment, but through subsequent nitrogen deficiency.