Flohr Bonnie M, Hunt James R, Kirkegaard John A, Rheinheimer Brad, Swan Tony, Goward Laura, Evans John R, Bullock Melanie
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) Agriculture and Food, Adelaide, SA, Australia.
Department of Animal, Plant and Soil Sciences, La Trobe University, Melbourne, VIC, Australia.
Front Plant Sci. 2020 May 15;11:548. doi: 10.3389/fpls.2020.00548. eCollection 2020.
Wheat production in southern Australia is reliant on autumn (April-May) rainfall to germinate seeds and allow timely establishment. Reliance on autumn rainfall can be removed by sowing earlier than currently practiced and using late summer and early autumn rainfall to establish crops, but this requires slower developing cultivars to match life-cycle to seasonal conditions. While slow-developing wheat cultivars sown early in the sowing window (long-cycle), have in some cases increased yield in comparison to the more commonly grown fast-developing cultivars sown later (short-cycle), the yield response is variable between environments. In irrigated wheat in the sub-tropics, the variable response has been linked to ability to withstand water stress, but the mechanism behind this is unknown. We compared short- vs. long-cycle cultivars × time of sowing combinations over four seasons (2011, 2012, 2015, and 2016) at Temora, NSW, Australia. Two seasons (2011 and 2012) had above average summer fallow (December-March) rain, and two seasons had below average summer fallow rain (2015 and 2016). Initial plant available water in each season was 104, 91, 28, and 27 mm, respectively. Rainfall in the 30 days prior to flowering (approximating the critical period for yield determination) in each year was 8, 6, 14, and 190 mm, respectively. We only observed a yield benefit in long-cycle treatments in 2011 and 2012 seasons where there was (i) soil water stored at depth (ii) little rain during the critical period. The higher yield of long-cycle treatments could be attributed to greater deep soil water extraction (<1.0 m), dry-matter production and grain number. In 2015, there was little rain during the critical period, no water stored at depth and no difference between treatments. In 2016, high in-crop rainfall filled the soil profile, but high rainfall during the critical period removed crop reliance on deep water, and yields were equivalent. A simulation study extended our findings to demonstrate a median yield benefit in long-cycle treatments when the volume of starting soil water was increased. This work reveals environmental conditions that can be used to quantify the frequency of circumstances where long-cycle wheat will provide a yield advantage over current practice.
澳大利亚南部的小麦生产依赖秋季（4月至5月）降雨来使种子发芽并确保适时播种。通过比目前更早播种并利用夏末和初秋降雨来种植作物，可以减少对秋季降雨的依赖，但这需要生育期较慢的品种来使生命周期与季节条件相匹配。虽然在播种窗口早期播种的生育期慢的小麦品种（长周期），在某些情况下与后期播种的更常见的生育期快的品种（短周期）相比产量有所增加，但产量反应在不同环境中存在差异。在亚热带的灌溉小麦中，这种差异反应与耐水分胁迫的能力有关，但其背后的机制尚不清楚。我们在澳大利亚新南威尔士州的特莫拉对短周期和长周期品种×播种时间组合进行了四个季节（2011年、2012年、2015年和2016年）的比较。其中两个季节（2011年和2012年）夏季休耕期（12月至3月）降雨高于平均水平，另外两个季节夏季休耕期降雨低于平均水平（2015年和2016年）。每个季节初始植物可利用水量分别为104、91、28和27毫米。每年开花前30天（近似产量决定关键期）的降雨量分别为8、6、14和190毫米。我们仅在2011年和2012年的季节中观察到长周期处理有产量优势，当时（i）深层土壤储存有水分，（ii）关键期降雨较少。长周期处理的较高产量可归因于从深层土壤中提取更多水分（<1.0米）、干物质生产和籽粒数量。2015年，关键期降雨很少，深层没有储存水分，各处理间没有差异。2016年，作物生长期间降雨量高，使土壤剖面充满水分，但关键期的高降雨量消除了作物对深层水分的依赖，产量相当。一项模拟研究扩展了我们的发现，表明当起始土壤水量增加时，长周期处理的产量中位数有优势。这项工作揭示了一些环境条件，可用于量化长周期小麦比当前种植方式具有产量优势的情况出现的频率。
