Primarily as a result of livestock grazing and early spring trampling, high-altitude (around 2,130 m) slopes near the Seven-Devils Mountains in northern Idaho (northwest USA) had become devoid of vegetation and subject to erosion. In 1957 trials were initiated to try and revegetated these slopes. The effects of various mulch and fertilizer treatments on emergence and establishment of grasses were studied.
In September 1957, 1.5 x 6 m replicated plots were broadcast with a non-indigenous grass seed mix (at approx. 25lb/acre) comprised equal portions of orchardgrass Dactylis glomerata, Primar slender wheatgrass Agropyron trachycaulum, mountain brome Bromus marginatus, smooth brome Bromus inermis, timothy Phleum pratense and Idaho fescue Festuca idahoensis. Mulch treatments were wood chip (1.3 cm and 2.5 cm deep), conifer tree boughs (50 or 100% soil cover); with combinations of lime and various rates of nitrogen, phosphorus, and potassium fertilizer (plus untreated controls). Vegetation was monitored until October 1958 (when established that all had failed).
In late August 1959, native hay (held down with chicken wire/boughs) containing native grass seed, and asphalt emulsion were tested as mulches, again overlaying plots broadcast with the non-native seed mix. These plots were monitored until autumn 1961.
Greenhouse trials using soil from the study area also investigated effects of lime or fertilizer addition on seedlings.
Except for native hay, all mulches were ultimately failures, although some initially enhanced seedling establishment for several months.
100% bough cover with fertilizer containing both N and P resulted in excellent establishment but summer drought led to high mortality, and in October 1958 there was no differences between treatments and most seedlings were dead.
Asphalt-emulsion initially resulted in better seedling survival of all species during 1960, but by July 1961 all were dead. The native hay mulch resulted in good establishment of native grasses but non-native species failed.
In the greenhouse studies, there was no increase in number of seedlings as a result of lime or fertilizer addition, but herbage production increased.