Assessment of the rate of weed seed decay in chaff-lining systems of South Australia

Failure to control annual weed species that persist through cropping phases facilitates replenishment/establishment of weed seedbanks. Consequently, this maintains weed interference in subsequent years of crop production. Harvest weed seed control (HWSC) has been widely adopted in Australia since its inception over three decades ago to prevent redistribution of weed seeds across cropping fields during commercial harvesting operations (Walsh et al. 2017). Implementation of HWSC obstructs fresh seedbank inputs by subjecting the weed seed bearing chaff fraction to a treatment, such as combustion (narrow windrow burning), mechanical pulverisation (impact mills), decomposition (chaff-lining) and removal (chaff cart). Chaff-lining has been readily adopted by growers because of the low cost of modifying a harvester to confine the chaff fraction into a narrow row between stubble, or onto dedicated wheel tracks in controlled traffic farming systems (chaff-tramlining). There is a paucity of literature examining seedbank decline of important Australian weed species in chaff-lines, however a common conjecture is that a mulching effect is created by a combination of physical and chemical influences (Walsh et al. 2018). Field observations suggest that in the absence of seed decay, control failures of annual weed species and volunteer crop plants may be exacerbated. Therefore, growers urgently need information that substantiates the implications of chaff-lining to weed seedbanks.

若无法防控在作物种植季持续存活的一年生杂草种群，将促使杂草种子库（weed seedbanks）得到补充与建立，进而在后续作物生产周期中持续引发杂草竞争危害。收获期杂草种子防控（Harvest weed seed control, HWSC）自三十余年前问世以来，已在澳大利亚得到广泛推广应用，其核心目的是避免商业收获作业过程中杂草种子在农田地块间发生重新扩散（Walsh等，2017）。HWSC通过对携带杂草种子的谷壳组分实施针对性处理，阻断新鲜杂草种子向种子库的输入，常见处理方式包括焚烧（窄条谷壳焚烧，narrow windrow burning）、机械粉碎（冲击式粉碎机，impact mills）、降解处理（谷壳垄置，chaff-lining）以及谷壳移除收集（谷壳转运车，chaff cart）。谷壳垄置（chaff-lining）因改造联合收割机以将谷壳组分归集至秸秆间窄行，或归集至控制耕作系统（controlled traffic farming, CTF）专用轮迹（谷壳轮迹铺设，chaff-tramlining）的成本低廉，已被广大种植户普遍采用。目前针对澳大利亚重要杂草种群在谷壳垄置带中的种子库衰减情况的研究文献较为匮乏，但学界普遍推测，该处理会通过物理与化学因素的综合作用形成覆盖效应（Walsh等，2018）。田间观测结果显示，若缺乏种子降解过程，一年生杂草种群与自生作物植株的防控失败风险可能会进一步加剧。因此，种植户亟需可验证谷壳垄置处理对杂草种子库影响的相关科学依据。