LONG-TERM BOTANICAL CHANGES IN CUT AND GRAZED GRASSLAND IN THE CONTINENTAL SUBARCTIC REGION OF NORWAY - M. Jorgensen^[11] and M. Pestalozzi^[12]

SUMMARY

The effects of cutting, grazing and fertilizer level on long-term botanical composition were examined in swards established in 1968 at Svanhovd (69°27'N 30°3'E). The grass swards were sown with a mixture of timothy, meadow fescue and smooth meadowgrass. The swards were either cut only, or cut in combination with grazing either with cattle or with sheep, and fertilized according to common practice in the region or with 150 percent of this amount. The botanical composition changed during the experimental period with large fluctuations in the amount of smooth meadow-grass and a notable decrease of timothy and meadow fescue. Both harvesting regime and level of fertilizer had significant effects on the botanical composition. Smooth meadow-grass dominated especially in swards which were ungrazed or grazed by cattle. In sheep grazed swards, tufted hair-grass dominated completely after some time, especially at the lower fertilizer level. Native grasses invaded the ungrazed swards to some extent, but were mainly couch grass at the higher fertilizer level and common bent and couch grass at the lower fertilizer level.

Keywords: botanical composition, fertilizer level, grassland, grazing, management.

INTRODUCTION

In northern Norway, permanent grassland dominated by indigenous species and ecotypes may be more favourable in terms of sustainable grass production than leys with high yielding but short lasting commercial species. The harsh climate combined with occasional winter damage make such leys very unpredictable in yield. The indigenous grasses such as smooth meadow-grass (Poa pratensis L.) dominating in permanent grassland in these areas, are generally more resistant towards these adverse conditions (Sveistrup and Ostergard, 1986).

One cut for silage combined with sheep or cattle grazing are common practices among farmers in northern Norway, but a proportion of the grassland area under cultivation is only cut. The species composition over time may be different in swards affected by grazing compared with those only cut for conservation, and this has implications for the amount and quality of herbage produced (Nesheim, 1994; Pestalozzi, 1987; Smith and Rushton, 1994).

Between 1968 and 1990 an experiment including permanent and temporary grassland in rotation was conducted at Svanhovd (69°27'N 30°3'E). The main purpose was to compare long-term effects of management on soil, botanical composition, yield and quality of yield of permanent grassland and short-term leys (ploughing and reseeding after three and six years). This paper reports on effects of harvesting regime and fertilizer level on botanical composition in swards with permanent grassland.

MATERIALS AND METHODS

Svanhovd has a continental climate with short summers (126 days with temperature >50°C), normal precipitation May-September is 219 mm, and cold winters where normal snow cover is 200 days. The experiment was situated on a peaty soil mixed with clay (pH 5.3). The soil was heterogeneous with silty clay/silty clay loam (20-30 percent organic matter) in some parts and up to 70 cm clay under a layer of peat on other parts. The permanent swards were established by sowing a mixture of equal amounts in terms of seed weight of timothy (Phleum pratense L. cv. 'Engmo'), meadow fescue (Festuca pratensis Huds. cv. 'Salten') and smooth meadow-grass (Poa pratensis L. cv. 'Holt'). Three different management regimes were used: (i) cut twice for silage and not grazed; (ii) cut once and grazed to c. 5 cm stubble height by heifers in the end of August (c. four days); or (iii) cut once and grazed to c. 5 cm stubble height by ewes with lambs at the beginning of June (c. five days) and September (c. ten days). The first cut was made approximately one week after heading of timothy in all three harvesting regimes. Therefore, the ungrazed plots were generally cut in mid July while plots grazed by sheep were cut on average 18 days later. Plots grazed by cattle fell in between for the cutting date. Two fertilizer levels were applied; 110 kg N, 36 kg P and 94 kg K ha^-l yr^-1 or 150 percent of this amount. Two thirds of the nitrogen was applied in spring and the rest after first cut.

The experiment was arranged in a strip split plot design with the rotations and permanent swards as vertical strips, management regimes as horizontal strips and the fertilizer levels as subplots. Botanical composition was estimated visually before the first cut each year and was classified as percentage of dry matter (DM) herbage of each of the sown species, native grasses and dicotyledonous species ('dicots'). No distinction was made between sown and invading 'wild' smooth meadow-grass plants. In 1991, the after-effects of the treatments were measured. The species composition was determined and species of dicots and native grasses contributing more than 5 percent of the DM yield were listed.

RESULTS AND DISCUSSION

In 1969 the swards were dominated by smooth meadow-grass which was significantly more prevalent in the lower fertilizer treatment (Table 1). Meadow fescue constituted 20-30 percent of the botanical composition, whereas timothy made up less than 5 percent of the DM yield. In 1968/1969 the snow cover was stable from October till late spring. This may have caused ideal conditions for low temperature fungi and explain the low proportion of timothy. Timothy is less resistant towards infection by such fungi than meadow fescue and smooth meadow-grass (Arsvoll, 1977; Vestman, 1978).

Smooth meadow-grass dominated all swards in the initial years, but after a few years dicots, mainly creeping buttercup (Ranunculus repens L.), increased on the swards (Figure 1). Especially in the winter season of 1972, but also in 1973 there were periods with rain and mild weather that may have caused ice accumulation and thereby damages in the swards. The proportion of sown grasses may have decreased due to these adverse conditions, and eased the invasion of creeping buttercup, a common species of poorly drained, peaty soils in this region (Nesheim, 1986). In 1975 the proportion of creeping buttercup was particularly high and the swards were sprayed with a herbicide to control the species. This resulted in an invasion of native grass particularly in swards affected by grazing.

In ungrazed swards and swards grazed by cattle, the proportion of smooth meadow-grass fluctuated greatly during the experimental period (Figure 1). In sheep grazed swards, the proportion of smooth meadow-grass decreased and thereafter remained low.

The main native grass species invading these swards was tufted hair-grass (Deschampsia cespitosa L.) and dominated especially at the lower fertilizer level (Figure 1). This is in agreement with results of Nesheim (1994) who also found larger proportions of tufted hair-grass on sheep grazed swards compared to swards cut only or grazed by cattle. Tufted hair-grass is a common species on poorly drained, slightly acidic soils and was observed to be avoided by the sheep in this study. The early grazing in spring may also have been hard on the sown grasses causing damage in the sward where tufted hair-grass and creeping buttercup could be established. The plots were sprayed again in 1980, but there were no major effects due to this treatment.

Figure 1. Botanical composition as percentage of DM yield of permanent grassland plots under different harvesting regimes during 22 years. Results are average of three replicates and two fertiliser levels.

Table 1. Botanical composition as percentage of DM yield at first cut of permanent grassland plots under different harvesting regimes. f1=110 kg N, 36 kg P and 94 kg K ha^-1 yr^-1, f2=150 % of this amount. Results are average of three replicates.

Table 2. Dominating native grasses and dicots as percentage of DM yield at first cut of permanent grassland plots in 1991. f1=110 kg N, 36 kg P and 94 kg K ha^-1 yr^-1, f2=150 % of this amount. Results are average of three replicates.

In ungrazed swards meadow fescue amounted to 10-20 percent in some years, but generally remained fairly low in proportion. In grazed swards it almost vanished four years after sowing. Timothy increased in proportion five years after sowing especially on swards cut only and swards cut and grazed by cattle, but it never contributed more than 10-15 percent of the proportion. Furthermore, in other studies sheep grazing had negative effects on the content of meadow fescue and timothy, but it has been observed that timothy may be enhanced by cutting combined with light cattle grazing late in autumn compared to cut only (Nesheim, 1994; Pestalozzi, 1987).

The inventory made in 1991 showed that the native grasses on ungrazed swards were mainly couch grass (Elytrigia repens L.) and common bent (Agrostis capillaris L.) which had replaced smooth meadow-grass completely on some replicates (Table 2). Common bent was only found at the lower fertilizer level. One of the replicates of the high fertilizer level plots grazed by sheep contained 72 percent creeping buttercup, but otherwise this species occupied only a few percent of the herbage matter.

REFERENCES

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Smith, R.S. & Rushton, S.P. 1994. The effects of grazing management on the vegetation of mesotrophic (meadow) grassland in Northern England. Journal of Applied Ecology, (31),13-24.

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