The development of a hydraulic seeding technique for unstable sand slopes. I. Effects of fertilizers, mulches and stabilizers

Summary

Hydraulic seeding (spraying a slurry of seed, fertilizer and limestone in water from a stationary or slowly moving tanker) is usually used to establish vegetation on bare ground on steep slopes but the technique may have poor outcomes. This experiment was undertaken to examine aspects of this sowing technique, including fertilizer application and adding mulch and chemical stabilizers, on the germination and establishment of grasses and legumes on sand waste left after china clay extraction, and from this suggest ways to modify and improve this seeding method.

Study site: A series of 10 experiments were carried out either within a temperate glasshouse or in the open at the University of Liverpool Botanic Gardens (northwest England).

General methods: Plastic seed trays were filled with a china clay sand waste and placed at an angle of 35º to simulate the angle of a waste tip slope in the field. Most were sown with a seed mix of 75% perennial rye-grass Lolium perenne (S23) and 25% white clover Trifolium repens (S184) at a rate equivalent to 80 kg/ha. Experiments were of randomized block design with three replicates and were carried out either within a temperate glasshouse or, where stated, in the open on an artificially created waste pile.

At the time of sowing, light watering was carried out to simulate hydraulic seeding. Experiments sited in the open were subsequently watered by natural rainfall. Glasshouse experiments received various controlled watering regimes.

Seedling establishment i.e. survival to the first post-cotyledon leaf stage, was recorded.

Treatments included: addition of fast- and slow-release fertilizers (with some comparisons of effects of application rate, of fine and coarse sand; and effect of application in relation to sowing time); addition of peat and straw mulches; and the effect of chemical stabilizers.

Experiment 1 Fast release complete fertilizer (ICI No. 5) slightly reduced L.perenne and T.repens establishment if applied at the rate of 85N:37P:60K kg/ha at the time of sowing, but the effects were not significant. Further application of slow release compounds (Enmag and Gold N) had no additional effect on L.perenne, but additional applications of Enmag impaired T.repens establishment further and additions of Gold N reduced establishment by 65%.

Experiment 2 Establishment of L. perenne declined with increasing application rates of a fast release compound fertilizer (ICI No 5, 17: 17: 17). The effect was greater on coarse sand than on fine and was greater for T.repens than for L.perenne.

Experiment 3 By delaying the time of fertilizer application (500 kg/ha of a compound fertilizer (ICI No 5, 17:17: 17) after sowing, the establishment of both clover and grass was progressively and markedly improved up to about 15 days after sowing..

Experiment 4 Heavy applications (50.4 kg/ha) of N, P and K, reduced establishment of both L.perenne and T.repens compared to the two lower rates tested (25.2 and 37.8 kg/ha); the effects of N and P were the most marked.

Experiment 5 Effects of sodium nitrate were generally greater than those of ammonium sulphate (both applied separately at rates of 20.2, 40.3, 60.5 and 80.6 kg/N/ha), although both were equally deleterious at the highest application rates. The effect of the fertilizers on establishment was less on loam soil than on sand, especially for L.perenne.

Experiment 6 The effect of sphagnum peat mulches (0% , 25% or 75% surface cover) on the seedling establishment on sand waste with four fertilizer treatments showed that mulching greatly reduced the deleterious effects of fertilizer treatments. A 75% mulch cover completely offset the deleterious effects of the fertilizer on L.perenne but not entirely so for T.repens.

Experiment 7. Establishment of both L.perenne and T.repens was greater on coarse than on fine sand, with the effect greatest for T.repens.

Experiment 8 When watered daily, large applications of both peat and straw mulches (75-100% cover) slightly increased L. perenne, but not T.repens, establishment. When watering was restricted to every fifth day, mulches had a greater effect on the establishment of T.repens than of L.perenne.

Experiment 9 Unisol91 and Essbinder X significantly reduced both L.perernne and T.repens germination. Heavy applications of Hiils 801 reduced the germination of T.repens. Erosion of seed and sand from the slopes by rain was reduced by mulching. Unisol increased sand and seed loss, although the small clover seed was less vulnerable. With most chemical stabilizers, a greater seed loss occurred at the higher application rate.

Experiment 10 The benefits of mulching slopes with peat was reduced when a chemical stabilizer was also applied. This was most marked on south facing slopes; T.repens germination was most effected.


In light of these results, the authors consider that hydro-seeding practice should be modified and flexible to suit the conditions prevalent at sowing and taking into account conditions at individual sites.

 

Note: The compilation and addition of this summary was funded by the Journal of Applied Ecology (BES). If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://links.jstor.org/sici?sici=0021-8901%28197712%2914%3A3%3C905%3ATDOAHS%3E2.0.CO%3B2-D