Ronald J Yates

The symbiotic performance between legumes and rhizobia relies on the plant-bacteria genetic compatibility and on the symbiotic partner’s capacity to overcome environmental stresses. Symbiosis contributes nitrogen to the plants, which, among other things, increases the number of chloroplasts, and the number and size of cells per leaf. Hyperspectral imagery can detect vegetation changes combining information stored in the image. The symbiotic performance ¡s affected by some abiotic stress factors such as low clay content and low soil water holding capacity. These soil features can be estimated using ground penetrating radar (GPR), a geophysics instrument based on energy pulses interacting with soil layers. The aim of this work was to investigate whether integrated remote sensing techniques are able to estimate the interaction of field pea inoculated separately with five strains of Rhizobium leguminosarum bv. viceae with different nitrogen fixation effectiveness levels. The experiment was carried out firstly in a glasshouse to assess the pure symbiotic performance and then in an agricultural area to assess the interaction with abiotic factors. Hyperspectral images and GPR measurements were captured to cover the glasshouse and field site experiments. The plant sample analyses consisted of plant dry weight, nitrogen content and nodulation score. The plant samples showed significant differences in nitrogen levels, nodule score and dry weight across strains. The analyses of the spectral band combinations confirmed the presence of outstanding indices sensitive to the differential symbiotic performance and were correlated with plant analyses. The GPR data also revealed a mixed composition of soil properties associated with variable water availability that affected root and plant growth. It is concluded that remote sensing can be a valuable tool for estimating legume nitrogen fixation in fields, and GPR for estimating below ground properties that affect plant growth in field experiments.

Exotic pasture legumes and their associated microsymbionts are important in providing biological nitrogen fixation in Australian agricultural systems. Southern African species of Lotononis from the Listia section can potentially provide sustainable agricultural productivity in systems affected by increasing dryland salinity and climate change. There are eight species in the Listia section: L. angolensis, L. bainesii, L. macrocarpa, L. marlothii, L. minima, L. subulata and L. solitudinis (Van Wyk, 1991). They are perennial, stoloniferous and collar-nodulated. The root-nodule bacteria (RNB) isolated from several of these species are pigmented and the symbiosis between these RNB and their hosts is highly specific (Yates et al., 2007). Pioneering work on L. angolensis, L. bainesii and L. listii isolates was performed in Africa in the 1950–60s by Botha (Kenya), Sandman (Zimbabwe) and Verboom (Zambia) and in Australia (Norris, 1958).