Impacts of Strategic Tillage in a No-Tillage Conservation Cropping System on Wild Oats Population

Abstract

Wild oats (Avena sterilis ssp. ludoviciana) is a major winter weed in no-tillage conservation agriculture (NTCA) systems of Australia’s Northern Grains Region. Many wild oat seeds shed before crop harvest and build a persistent seed bank in the 0-2 cm soil layer in a NTCA paddock. Reintroduction of tillage in a strategic way can be useful to manage this weed effectively. To understand the impact of strategic tillage (ST) on the soil seedbank dynamics and emergence pattern of wild oats, four tillage treatments were evaluated in a long-term NTCA paddock. The treatments were NT: no-tillage, ST1: ST applied in the first year of study only, ST2: ST applied in the second year of study only, and CT: conventional tillage. Soil samples were collected from 0-5, 5-10, and 10-15 cm depths to study the seedbank dynamics, and two 1 m2 permanent quadrats were established per plot to study the emergence pattern of wild oats. In NT, 95% of wild oat seeds were found at 0-5 cm depth, whereas 88% of seeds were distributed to a depth of 10 cm under ST1 or ST2, depending on when ST was applied. In CT, 75-85% of seeds were buried below 10 cm depth. In NT, 88% of seedlings emerged during the first 20 days after wheat planting (DAWP), but the rest continued to emerge until 45 DAWP, leading to a wide window of emergence. This produced multiple wild oat cohorts under NT with staggered phenology. In contrast, emergence of seedlings was completed within 20 DAWP from ST or CT and produced a single cohort of wild oat plants with matching phenology. Among the tillage plots, emergence was minimal in ST throughout the season. Strategic use of tillage was found to be effective to minimize wild oat infestation by burying seeds to a depth from where the seedlings could not emerge.