Functional complementarity in diverse pastures : an agroecological approach for pasture-based dairy systems in temperate climates : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand

Abstract

The diversification of plant species within intensively managed pastures has been proposed as a potential solution to address climatic-driven issues of pasture-based livestock production. In New Zealand, pasture-based dairy systems are mostly composed of Lolium perenne L. with a smaller proportion of Trifolium repens L. Bromus valdivianus Phil. and Dactylis glomerata L. are grass species which have attributes of interest for pasture-based dairy systems, such as great productivity, quality and persistence. Previous studies have shown that these four species present distinct functional traits, such as deep- or shallow-root system and cool- or warm-season activity, among others. This thesis hypothesises their distinct functional traits to be complementary to each other when these four species comprise a diverse pasture. The leaf regrowth stage, plant-based grazing management, is adopted as the defoliation criteria management. Three studies were developed in the thesis. The first study assessed and validated the hydraulic lift, a new functional trait occurring in the root system C3 grass species. The second study investigated agronomical parameters and ecological features of a diverse pasture comprising L. perenne, B. valdivianus, D. glomerata and T. repens. When grown as a diverse pasture, these four species presented complementary functional traits, including growth asynchrony (seasonal growth activity) and development synchrony (temporal overlapping of their individual optimal LS intervals). Therefore, termed during the thesis as a diverse pasture of complementary species (DPCS). In relation to binary pastures (one grass and one legume component), DPCS presented lowered seasonality of production, annual and seasonal overyielding and a decrease in the ingression of volunteer species. The third study investigated the suitability of DPCS for dairy animals by measuring their nutritional quality, grazing behaviour, and dietary preferences of dairy cows. The animals displayed no preference when offered binary and DPCS simultaneously. Overall, this thesis provides enough evidence to support the advising of diverse pastures comprising L. perenne, T. repens, B. valdivianus, and D. glomerata defoliated according to the leaf regrowth stage as an alternative for pasture-based dairy systems in temperate humid climates.