Agroecological Advantages of Early-Sown Winter Wheat in Semi-Arid Environments: A Comparative Case Study From Southern Australia and Pacific Northwest United States

Abstract

Wheat (Triticum aestivum L.) is the most widely-grown crop in the Mediterranean semi-arid (150-400 mm) cropping zones of both southern Australia and the inland Pacific Northwest (PNW) of the United States of America (United States). Low precipitation, low winter temperatures and heat and drought conditions during late spring and summer limit wheat yields in both regions. Due to rising temperatures, reduced autumn rainfall and increased frost risk in southern Australia since 1990, cropping conditions in these two environments have grown increasingly similar. This presents the opportunity for southern Australian growers to learn from the experiences of their PNW counterparts. Wheat cultivars with an obligate vernalization requirement (winter wheat), are an integral part of semi-arid PNW cropping systems, but in Australia are most frequently grown in cool or cold temperate cropping zones that receive high rainfall (>500 mm p.a.). It has recently been shown that early-sown winter wheat cultivars can increase water-limited potential yield in semi-arid southern Australia, in the face of decreasing autumn rainfall. Despite this research, there has to date been little breeding effort invested in winter wheat for growers in semi-arid southern Australia, and agronomic research into the management of early-sown winter wheat has only occurred in recent years. This paper explores the current and emerging environmental constraints of cropping in semi-arid southern Australia and, using the genotype × management strategies developed over 120 years of winter wheat agronomy in the PNW, highlights the potential advantages early-sown winter wheat offers growers in low-rainfall environments. The increased biomass, stable flowering time and late-summer establishment opportunities offered by winter wheat genotypes ensure they achieve higher yields in the PNW compared to later-sown spring wheat. Traits that make winter wheat advantageous in the PNW may also contribute to increased yield when grown in semi-arid southern Australia. This paper investigates which specific traits present in winter wheat genotypes give them an advantage in semi-arid cropping environments, which management practices best exploit this advantage, and what potential improvements can be made to cultivars for semi-arid southern Australia based on the history of winter wheat crop growth in the semi-arid Pacific Northwest.

Keywords: adaptation; climate change; deep sowing; drought; vernalization; winter wheat; yield gap.

FIGURE 1

Map showing the low (<300 mm annual precipitation), intermediate (300–450 mm) and high (>450 mm) precipitation zones of the inland PNW. Reprinted from Schillinger et al. (2006) with permission.

FIGURE 2

Comparison of seasonal temperatures and precipitation for Ouyen in southern Australia and Lind, WA in the PNW, and seasonal fit of winter wheat and spring wheat life cycles under current management.

FIGURE 3

Map of Australia showing semi-arid regions (200–400 mm annual precipitation; mid-gray) and dryland cropping sites in southern Australia (black).

FIGURE 4

A prototype deep-furrow drill fabricated at the Washington State University Lind Dryland Research Station. Commercially available deep-furrow drills cannot pass through heavy surface residue without plugging and are not sturdy enough for seed openers to penetrate through the hard, dry surface of no-till summer fallow. Growers and scientists seek a dual-purpose drill to sow winter wheat into heavy residue in both tilled and no-till fallow conditions. Hoe-type openers of the drill must be able to place seed as deep as 20 cm below the surface to reach adequate soil moisture for germination and emergence. The purpose of the deep furrow is to reduce the thickness of soil covering the seed to enhance seedling emergence. Photos by W. F. Schillinger.