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 semiarid (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

Time‐lapse mapping of crop and tillage interactions with soil water using electromagnetic induction

“…Looking at Figure 4, during the wet stage until about the end of June, there is no significant difference between SB and SP, whereas the EC a in WW, which started higher than that in SB and SP, rapidly fell to significantly below that of SB and SP, indicating a higher degree of water uptake at a time when spring rains continued to replenish water contents at the soil surface. This finding is consistent with an earlier root development of WW resulting in a greater root length for WW early in the season (Entz, Gross, & Fowler, 1992) and a significantly higher water uptake from the top 50–100 cm of the soil profile compared to SB and SP (Cann, Schillinger, Hunt, Porker, & Harris, 2020). For WW, it has been suggested that the root mass increases exponentially until the start of rapid aboveground growth and then increases linearly until anthesis (Gregory, McGowan, Biscoe, & Hunter, 1978).…”

“…For WW, it has been suggested that the root mass increases exponentially until the start of rapid aboveground growth and then increases linearly until anthesis (Gregory, McGowan, Biscoe, & Hunter, 1978). Over time, WW and SB both develop deep roots of 0.8–1.8 m (Cann et al., 2020; Gregory et al., 1978; Kirkegaard & Lilley, 2007) with similar root architectures. However, the highest rooting depths are associated with WW (Thorup‐Kristensen, Salmerón Cortasa, & Loges, 2009), whereas peas have the shallowest rooting profile of annual crops, with 90% of all roots contained in the top 60 cm (Gregory, 1988; Liu, Gan, Bueckert, & Van Rees, 2011) with a similar trend in root length densities.…”

Optimal Agronomics Increase Grain Yield and Grain Yield Stability of Ultra-Early Wheat Seeding Systems

“…This impact may be more prominent when abiotic or biotic stresses result in increased mortality during the growing season. This recommendation differs from that of Cann et al [45] primarily due to the availability of soil moisture after spring snow melt on the northern Great Plains.…”

“…Similar avoidance strategies have been studied in the Mediterranean climates of Australia and the United States Pacific Northwest where wheat grain yield is limited due to heat and soil moisture availability [43,45]. Adoption of winter growth habit wheat cultivars and adjusting seeding to earlier dates in both regions was associated with significant grain yield benefit attributed to longer vegetative growth phases, increased root development and depth, increased transpiration efficiency, subsoil moisture availability and avoidance of heat stress at grain fill [45,46]. The implementation of a similar ultra-early seeding system for spring wheat on the northern Great Plains in response to increases in growing season temperature and reductions in growing season precipitation can serve as a mechanism to reduce future yield loss.…”

Selection for Yield Over Five Decades Favored an Isohydric and Phenological Adaptations to Early-Season Drought in Australian Wheat

“…Climate change in the Mediterranean-climate region of Australia is increasing maximum temperature, reducing minimum temperature and growing season rainfall, and delaying rst autumn rain or the onset of 'autumn break' (Pook et al, 2009;Hochman et al, 2017;Cann et al, 2020). In response to the delayed in autumn break, many Australian wheat growers are sowing their entire cropping land before the autumn break, further increasing the risk of early season drought (Fletcher et al, 2015(Fletcher et al, , 2016.…”