The grazing environment (i.e. the quantity and quality of pasture available) drives sheep production in Australia. The long-term viability of the sheep industry is dependent on the sustainable use of pasture, which requires monitoring. Remotely sensed data have the potential to monitor changes in pasture resources within and between seasons. Remotely sensed data have the potential to; map pasture resources within a paddock, differentiate paddocks within a farm, differentiate farms within a region and differentiate grazing environments across the country. This thesis examines the application of remotely sensed data in the sheep industry at three scales (within a paddock, at the paddock/farm scale and at a continental scale). Data from a hand-held active sensor (Crop Circle™) were used to estimate green dry matter (GDM) within a paddock and produce a map that highlighted the variability within the paddock. The normalised difference vegetation index (NDVI) and soil adjusted vegetation index (SAVI) were used to estimate GDM in mixed annual and perennial swards over three years at two sites. Comparisons between NDVI, SAVI, pasture height and GDM indicated that producers should continue to use pasture height to estimate GDM but the Crop Circle™ could be used to map GDM variability within a paddock.

Grasses have always been and will continue to be the most important resources for humans and their domestic animals. This study focused on one species of grass, Napier ('Pennisetum purpureum' Schumach.), that is valuable for fodder in both tropical and sub-tropical regions of the world. Napier grass cultivation is likely to increase, especially in east Africa, associated with the increase in human population coupled with a growing demand for livestock products. However, because the present arable land is fully committed, cultivation is expanding into marginal areas. These areas are usually characterised by high temperatures and reduced precipitation, likely to be adversely impacted by global warming associated with increased atmospheric CO₂ levels. This study was designed to increase understanding about how different Napier grass provenances respond to reduced water supply through rainfall and rising temperatures and their impacts on herbage productivity and quality. Such understanding would guide recommendations for farmers in these marginal areas to improve Napier grass management. Techiniques in tissue water status and gas exchange were applied to assess if they could be effective predictors of herbage yield and quality in Napier grass when subjected to water-stress and high temperature stress. The project was implemented in three phases: (1) a glasshouse study that tested the physiological techniques on two Australian cultivars, (2) field trials that tested the techniques on 10 acessions of Napier grass in two contrasting environments in Kenya, and (3) glasshouse study comparing Napier grass (C₄) with a common reed (C₃) subjected to water and heats tress and exposed to high atmospheric CO₂ concentrations.