Interaction of plant genotype and management in the persistence of a perennial grass exposed to grazing and soil fertility stresses.

Increased stocking rates under typical pasture improvement practices in southern Australia have often been associated with low persistence by sown perennial grasses subjected to continuous stocking. Cultivars of the perennial grass phalaris ( Phalaris aquatica L.), which is widely used in southern Australia, vary in their phenology and growth habit. Winter-active cultivars have also been developed with improved stress tolerances, viz. heavy grazing pressure (Holdfast GT) and acid soils (Advanced AT). This study examined the persistence of phalaris genotypes over 4 years under five management treatments: high P-high stocking rate (18 sheep per hectare) rotationally stocked ( HPRS); high P-high stocking rate continuously stocked ( HPCS); high P-intermediate stocking rate (13·5 sheep per hectare) continuously stocked (HPCS13.5); low P-low stocking rate (9 sheep per hectare) rotationally stocked ( LPRS); and low P-low stocking rate continuously stocked ( LPCS). Basal frequency of phalaris declined rapidly under HPCS and LPCS in the first year of treatments when periods of low herbage mass occurred under low rainfall. Basal frequency in high P treatments stabilized and partially recovered but continued to decline in low P treatments. Holdfast GT survived the early decline in the HPCS treatment better than other winter-active cultivars and similar to a known grazing tolerant, semi-winter-dormant cultivar. Advanced AT and older winter-active cultivars were sensitive to continuous stocking but persisted better under rotational stocking or under a reduced rate of continuous stocking ( HPCS13.5). Rotational management clearly promoted persistence of winter-active phalaris, but long-term persistence will be better ensured by combining management with the use of genotypes with grazing tolerance traits. [ABSTRACT FROM AUTHOR]