The development of a hydraulic seeding technique for unstable sand slopes. II. Field evaluation.
Hydraulic sowing 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 stabilizer to reduce seed loss by erosion. Hydraulic sowing techniques in a series of field trials on sand wastes produced by the china clay industry at St. Austell were examined using a seed mixture containing Trifolium repens cv. S100, Festuca rubra, F. ovina and Agrostis tenuis [A. capillaris]. Conventional hydraulic sowing techniques resulted in establishment of approx. 2-25 grass seedlings/100 cm2 and 1-13 T. repens seedlings, whereas establishment by traditional agricultural methods was 30 and 14 seedlings, resp. Toxicity of fertilizer to germinating seeds and inhibition of germination by stabilizers were primarily responsible for this poor establishment. Acceptable establishment was obtained by applying seed alone, but where natural seed burial was limited or the soil was dry, establishment was markedly improved by the addition of a mulch. Fertilizer toxicity varied with site and climatic conditions, but could be reduced by mulching. However, effective establishment was obtained in some experiments by delaying fertilizer application until germination had occurred. Of the chemical stabilizers tested, none gave a significant improvement in establishment. Effective mulching and stabilization was obtained by using long-fibre flexible materials rather than the mulches typically used in conventional hydraulic treatments. In general, T. repens establishment was more sensitive than grass to site conditions and hydraulic treatment, and sometimes failed completely. It is concluded that the requirements of legumes must be considered as many commercial hydraulic operations fail not through failure of grass establishment, but through subsequent N deficiency.