The legacy of pasture drill rows on soil chemical characteristics and subsequent wheat production

Aims: To examine the legacy of pasture drill rows sown to various configurations of subterranean clover (Trifolium subterraneum L.), lucerne (Medicago sativa L.) and phalaris (Phalaris aquatica L.), on soil chemical characteristics and wheat (Triticum aestivum L.) production in the year following pasture removal.

Methods: A field experiment comparing 10 pasture species combination treatments conducted on a Red Kandosol soil in a semi-arid environment in south-eastern Australia was monitored from the end of the pasture phase until harvest of the first wheat crop. Quadrats were fixed to the soil surface to mark previous pasture drill rows. Soil within and between rows was sampled to 0.6 m at three times and analysed for mineral nitrogen (N), pH, total carbon (C) and available macro-nutrients, and related to wheat growth rate and yield.

Results: Significantly higher total C, mineral N and plant-available potassium (K), and lower sulphur (S) concentrations, were still evident in the original pasture drill row after grain harvest compared to the inter-row area, four years after pastures were sown. Grain yield was 11% greater in wheat growing on the original pasture drill row compared to between rows. Pure lucerne swards had less mineralised N than mixed lucerne swards associated with reduced water in the soil profile.

Conclusions: This study establishes the enduring legacy of pasture drill rows observed up to 14 months post-removal and highlights the opportunity to improve soil fertility through manipulation of pasture sowing configurations in a cropping field in south-eastern Australia.