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sur le développement des zones arides et semi-arides

Titre : Agronomic and physiological performance of four perennial grasses under summer dry conditions in New Zealand

Auteur : Sharifiamina Shirin

Université de soutenance : Lincoln University

Grade : Doctor of Philosophy in Plant Science 2018

Résumé
Agronomic and physiological performance of four perennial grasses under summer dry conditions in New Zealand The main aim of this research was to quantify the effects of different levels of moisture and nitrogen (N) supply on dryland brome, cocksfoot, perennial ryegrass and tall fescue pastures grown under summer dry conditions. This was assessed from establishment (2014/15) to the end of the second year (2015/16) in two field experiments. Moisture and temperature are the major factors that affect germination. To quantify their combined effects, a laboratory experiment was used to calculate hydrothermal time requirements. Increasing temperature from 25 to 30 and 35 °C caused a rapid decline in germination rate of cocksfoot and tall fescue even when moisture was not limited (0 MPa). Applying moisture stress, especially when temperature was higher than 20 °C resulted in a more rapid decline in cocksfoot germination rate and final germination percentage than in perennial ryegrass, tall fescue and brome. To explore the effects of different soil moisture levels on pasture production in the field, two experiments were established in October 2014 at Ladbrooks and Ashley Dene, which differed in plant available water content (PAWC). The Wakanui soil at Ladbrooks has a 41-55% higher PAWC than the stony Lismore silt soil at Ashley Dene. A Latin square design was established at both sites with four grass species and four replicates. During establishment period, from October 2014 to June 2015, total dry matter (DM) production at Ladbrooks was 4.34 t ha-1 compared with 1.93 t ha-1 at Ashley Dene, with no differences among species. In the second year from July 2015 to July 2016, the experiments included a nitrogen (N) treatment. At Ladbrooks 900 kg N ha-1 and at Ashley Dene 500 kg N ha-1 were applied. In 2015/16, mean annual DM production was 19.8 t ha-1 for +N and 9.20 t ha-1 for −N treatments at Ladbrooks. At this location, there were no differences for DM production among the species. In 2015/16 at Ashley Dene, the +N cocksfoot treatment DM was 6.0 t ha-1 higher than the average of 3.2 t ha-1 for the other ±N species. This difference at Ashley Dene was explained by the interaction between species and N after 85 mm of rainfall in mid-January of 2016, when only the cocksfoot responded to the applied N.

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