Responses to drought stress and water logging of 12 diverse pastoral lines in pakihi podzol soil : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Science with Honours at Lincoln University

Abstract

New Zealand's farm systems rely on grazed pasture and fodder crops as the critical feed for livestock. 40% of New Zealand's agricultural land is in pastures which support livestock industries, generating an annual export revenue of NZ$33.8 billion. Due to climate change and tightening environmental regulations such as the 190 N application limit, the status quo perennial ryegrass white clover pasture is becoming less suitable for production in many regions of New Zealand, where water stress and waterlogging stress are increasing in frequency. Diverse pastures are a potential means to improve intra-annual yield stability and increase nitrogen fixation. To determine which species could be suitable for use in a diverse pasture mix for a farm conversion in Golden Bay, a randomised block experiment was set up to test 12 lines of perennial forages. The species included white clover, red clover, Alsike clover, Lotus pedunculatus, perennial ryegrass, cocksfoot, prairie grass, tall fescue and chicory. The species received treatments of waterlogging and drought stress. Drought plants were maintained just above PWP for 42 days, while waterlogging plants were submerged for 15 days, then removed and replaced in 3-day cycles according to stress levels. Under drought stress, all species had significantly reduced total biomass yields, ranging from a 55 % reduction in Alsike clover to a 25 % reduction in Caucasian clover. Under waterlogging, only white clover and red clover showed significant decreases in aboveground dry matter, but most species had at least an 80 % increase in senescence. Other traits measured included plant dry matter, photosynthesis, stomatal conductance, water potential, leaf senescence, leaf damage, SPAD and soil moisture. It was found that, on average, all other grass species were more tolerant in most traits than perennial ryegrass under drought, and all fescue lines were more tolerant than ryegrass under waterlogging. Compared with white clover, red clover and L. pedunculatus were more tolerant to drought and waterlogging, and Alsike clover performed similarly. The findings suggest suggest merit for examining diverse pastures based on L. pedunculatus, white cover, red clover, Alsike clover, chicory, cocksfoot, Continental and mediterranean fescues in the Golden Bay climate on Pakihi podzol. Among the legumes, L. pedunculatus was the best performing species for environments that experience drought as well as waterlogging. Despite similar biomass to white clover and red clover under drought and higher productivity under waterlogging, lotus had lower levels of senescence under both stresses, retaining greater root biomass under waterlogging. In grasses, hybrid tall fescue had the lowest levels of senescence under both stresses. Among the grass lines there were similar productivity levels and stress-induced changes. However, under both stresses, the fescue lines maintained the lowest levels of senescence among the grasses. Therefore, they could be tested as a suitable base to replace the traditional perennial ryegrass-based pasture used on Pakihi podzol in high rainfall environments. Future work under field conditions is needed to substantiate the findings from this research and progress the understanding of how the species interact with each other in response to the environment and grazing.