Root architecture alteration of narrow-leafed lupin and wheat in response to soil compaction

Root system architecture influences nutrient and water uptake efficiency and thus plant growth and productivity. Root architecture traits conferring efficiency in capturing resources from soil are considered a key factor in crop breeding for enhanced water and nutrient uptake. Mechanical impedance such as soil compaction is common in the Western Australian wheatbelt, limiting root growth and crop productivity. The present study investigated root responses to subsoil compaction in two field trials at Wongan Hills (central wheatbelt) and Buntine (northern wheatbelt) in Western Australia. Substantial alteration to rooting patterns was observed in the commercial wheat cultivar Wyalkatchem and in narrow-leafed lupin (Lupinus angustifolius) grown in sandy soils where compaction is common. The root systems of narrow-leafed lupin plants were dominated by a short and thickened taproot (10-26 cm depth, 7-14 mm root-collar diameter) and horizontally distributed primary lateral roots when compared to previous observations of the same genotypes under non-compacted soil conditions. Genotypic variability in root architecture traits among four wild genotypes and four commercial cultivars (Mandelup, Merrit, Quilinock and Tanjil) of narrow-leafed lupin was demonstrated. Taproot length, total root length, root surface area, root mass and root collar diameter were the most important root traits correlated to shoot yield (P < 0.001). Deep ripping resulted in significantly improved rooting depth (up to 100 mm) and root distribution in wheat in the soil profile compared to non-ripped soil, where roots were restrained mainly in the top 0-30 cm layer. Root number, root length, root length density, root mass and grain yield of plants grown in deep-ripped soil were increased by 38, 36, 27, 24 and 19%, respectively, compared to those of non-ripped treatment. The data from this study form the basis for future research leading to selection and breeding for suitable root traits for soil constraints and provides information for alleviating management of compacted soil in deep sandy soils.