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EFFECT OF DIFFERENT INTENSITIES OF DROUGHT AND DEFOLIATION UPON THE MORTALITY OF PERENNIAL GRASSES

S.P. Boschma1, M.J. Hill2, J.M. Scott1, and G.G. Rapp2

1Department of Agronomy and Soil Science, University of New England, Armidale, NSW 2351
2
CSIRO, Division of Animal Production, PMB, Armidale, NSW 2350

Pastures often fail to recover following intense grazing during drought. With a greater understanding of the stress thresholds of pasture grass species, better management recommendations can be made which will increase the life expectancy of pastures and thereby increase production efficiency. This paper discusses some of the 1994-95 mortality data.

MATERIALS AND METHODS

The grasses used were: Lolium perenne (Lp) cv. Victorian; Phalaris aquatica (Pa) cv. Sirosa; Dactylis glomerata (Dg) cv. Porto, Festuca arundinacea (Fa) cv. Demeter, Microlaena stipoides (Ms) cv. Shannon and Danthonia richardsonii (Dr) cv. Taranna. Plots were cut at two intensities: moderate and severe. Three simulated rainfall regimes were applied: matching evaporation, 40-percentile and 10-percentile. Rain was excluded from the trial area using an automatic rain-out shelter. The grasses were assessed over spring-summer (S-S) and summer-autumn (S-A). Plant loss was defined as crowns which were dead or 10%-green.

RESULTS AND DISCUSSION

The species and moisture treatments and interactions were significant in S-S. The species-defoliation-moisture interaction is shown in Fig 1. There were generally more plant losses from the severe defoliation. Lp and Dg had the greatest losses. Fa had few and Ms no plant losses. There were significant species and moisture effects in S-A. The 10-percentile treatment had more deaths than the matching evaporation treatment (P<0.05).

Figure 1. Percentage of plants with dead or 10%-green crowns for 6 grasses at 2 defoliation intensities and 3 simulated rainfall regimes following spring-summer.

Grasses may be more sensitive to stress when flowering and replenishing reserves during spring. There was greater mortality/near mortality during S-S than S-A. The ranking of species is similar for both experimental seasons. The experiment continues for a second season in 1995-96.

ACKNOWLEDGMENTS

This project is funded jointly by Meat Research Corporation and the Land and Water Resources Research and Development Corporation.

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