Humate application alters microbiota–mineral interactions and assists in pasture dieback recovery

Pasture dieback is a rapidly expanding decaying pasture syndrome that affects millions of hectares of agricultural land in Queensland, Australia, making it useless for the cattle industry and decimating farmers’ income and welfare. Since the syndrome was first identified in the early 1990s, farmers and agronomists have tried various methods for pasture recovery, including slashing, burning, ploughing and resowing grass, fertilising, destocking, and overstocking. In most cases, after a minimal initial improvement, the grass reverts to dieback within a few weeks. Here, we present an application of potassium humate, a well-known plant growth stimulator, as a possible long-term recovery option. Humate was applied once at the rate of 12 ml per m2. Humate application did not alter the alpha or beta diversity of soil bacterial communities, nor did it change the mineral profile in the soil. However, humate application altered soil microbiota–mineral temporal interactions and introduced subtle changes in the microbial community that could assist pasture recovery. A single humate application increased paddock plant biomass significantly up to 20 weeks post-application. Eleven months after the single application, the paddock was grazed to the ground by the cattle just before the rainfall season. After pasture regrowth, the humate-treated plots significantly improved root morphometric indicators for both grass and dicots and increased the ratio of grass/weeds by 27.6% compared to the water-treated control. While this treatment will not resolve the dieback syndrome, our results invite more research to optimise the use of humate for maximum economic benefit in paddock use under pasture dieback syndrome conditions.