Low input grasses useful in limiting environments (LIGULE)

This paper presents a case for the selection and development of a wider ran ge of perennial grasses for pastoral use in the higher rainfall (annual rai nfall >500 mm) zone of southern Australia, especially the southern sector o f the Murray-Darling Basin. There is also a need to reconsider the use of ` high-input' pastures on hill lands by developing more appropriate recommend ations for managing existing native grass pastures productively. Past experiments which compared native grass based pastures with sown pastu res promoted the view that indigenous grasses were inferior in most respect s to exotic improved species. Even though many of the findings were confoun ded with fertiliser, stocking rate, and other treatment erects, they reinfo rced the general direction of cultivar development programs which in the te mperate zone have been based mainly on the 4 exotic C-3 species Phalaris aq uatica L., Dactylis glomerata L., Lolium L. spp., and Festuca elatior var. arundinacea (Schreb.) Hackel (syn. Festuca arundinacea Schreb). This has le d to an imbalance in the adaptability and range of species available to be sown in pastures, particularly for sowing on less productive landscapes whe re stony, shallow, infertile, acid soils limit the persistence of current c ultivars. The pre-European vegetation of temperate Australia comprised species with a capacity for active growth and transpiration during summer. The water use pattern resulted in soil moisture being near capacity in late winter and sp ring, and exhausted by summer's end. Replacement of this vegetation with an nual-growing and summer-dormant C3 species has changed the water use patter n so that soils are drier in spring and wetter in autumn. This has reduced the pre-winter soil moisture deficit, which in turn has increased rates of deep drainage in winter. Land degradation in southern Australia is a consequence of this changed wat er use pattern. Deep drainage of water beyond the reach of plant roots has mobilised salts stored in the landscape and caused watertables to rise, whi ch has led to large areas becoming saline. Lack of growth in summer in past ures consisting of senescent annual-growing species and dormant C3 perennia l grasses limits utilisation of the products of nitrogen mineralisation, wh ich allows nitrate nitrogen to accumulate in summer and be readily leached by rainfall in autumn. This increases rates of soil acidification. Although there may be scope to reduce deep drainage by increasing pasture growth in spring in areas where there is little likelihood of summer rainfall, this is not the case in south-eastern Australia where significant falls of rain occur during summer and autumn. Catchment studies conducted in south-eastern Australia provide no evidence that pastures based on exotic species are superior to pastures containing n ative perennial grasses. Runoff and soil loss parameters were related to ca tchment condition rather than pasture type. Pastures which are heavily graz ed, and where ground cover is low during periods of high intensity rainfall , lose more water as runoff, and experience higher rates of soil erosion th an actively growing pastures which cover the ground. The water balance woul d predict that reducing runoff, either by direct species erects or by mecha nically increasing detention storage, if not balanced by equivalent increas es in evaporation, must lead to increases in deep drainage. It is concluded that, in the southern temperate zone, there is a need to ex plore management strategies which encourage adapted indigenous grasses to b ecome more prominent in upland pastures, as well as to develop a range of b etter adapted perennial grass varieties capable of reducing rates of land d egradation, specifically for sowing on the extensive recharge lands of the Murray-Darling Basin, and on acid soils, and soil types prone to accelerate d soil acidification.