Farming systems impact on key weed species of the northern dryland cropping region

Abstract

Farming systems that reduce the reliance on herbicide use and are less susceptible to weed incursions are required into the future. A 8-year long farming system experiment, comparing diverse farming system strategies, was initiated in March 2015 at Pampas on the Eastern Darling Downs. A baseline farming system, representative of current local best management practice, and various modified farming strategies that differ in the diversity of crops grown, intensity of cropping (i.e. proportion of time in-crop), nutrient input and/or soil restoration approaches were compared. This diverse range of farming systems assessed has provided a unique platform to monitor weed population dynamics and see if the farming strategy used can influence the weed load over time. Thirty-four weed species have been identified at the site, with sowthistle (Sonchus oleraceus) recorded the most frequently. Over the course of the experiment, compared to the baseline system there has been an increase in the diversity of weeds observed in systems with lower cropping intensity, greater crop diversity, and increased nutrition. In contrast, farming systems with a higher cropping intensity saw a significant decrease in the diversity of weeds present (68% less species than the baseline), and a significantly lower weed density compared to the baseline; the average weed population density in higher intensity cropping systems was only 22.5% of the baseline. This data demonstrates that increasing the frequency of crops sown in a farming system will have a dramatic effect on the resulting weed load in the farming system. A higher intensity farming system involving a diversity of crops can provide both resilience to weed incursions (indicated by lower weed diversity) as well as suppressing weed population growth. Alternatively, farming systems with lower cropping intensity, higher nutrient availability or higher crop diversity can facilitate conditions which favour spikes in weed incursions.