Ground Cover Supplement : GC Supplement - Soil health
GROUND COVER HEALTHY SOILS 16 ROOTS Soil constraints ranked by region A study of variety trial results is helping to identify new sources of wheat germplasm better able to deal with subsoil constraints By Glenn McDonald TABLE 1 RELATIVE IMPORTANCE OF DIFFERENT SUBSOIL CONSTRAINTS BASED ON THE YIELDS OF 52 VARIETIES OF WHEAT GROWN AT 233 SITES BETWEEN 1994 AND 2006 Subsoil constraint Western Australia South Australia Victoria Rank* Mean yield advantage (%) Rank* Mean yield advantage (%) Rank* Mean yield advantage (%) Boron toxicity 3 8 2 11 4 7 High pH 6 3 4 5 3 2 Aluminium 2 7 3 4 2 1 Salinity 1 14 1 19 1 7 Zinc deficiency 4 2 =5 1 =5 0 Strong soils 5 0 =5 2 =5 6 * Ranking is based on the number of sites where tolerance to a particular constraint improved yields by at least 5 per cent over the intolerant varieties TABLE 2 THE TOLERANCE OF SOME COMMERCIAL VARIETIES TO A RANGE OF SUBSOIL CONSTRAINTS Variety Subsoil constraint Boron toxicity Tolerance to high pH Aluminium toxicity Salinity1 Zinc deficiency2 Pratylenchus resistance3 AGT ScytheA MT MT IT MT ME S AxeA MT MT IT MT ME S CorrellA T MT T MT ME S DrysdaleA IT MT T IT Ineff MS EllisonA MT MT IT T ME S Frame T T T IT Eff S GladiusA T T IT MT ME S Janz IT MT IT IT Ineff S Krichauff T T IT MT ME MR PugsleyA T IT T IT Eff S GBA RubyA IT IT T MT Eff S Tammarin RockA T MT T MT Ineff S Ventura IT MT T IT Eff S EGA WentworthA IT MT IT T Ineff MS Westonia T MT T T Eff S WyalkatchemA IT MT T T ME MR YitpiA T MT T T ME S YoungA IT IT T MT ME S 1. Salinity tolerance is based on the ability to exclude sodium from the leaf: T = tolerant, MT = moderately tolerant, IT = intolerant 2. Zinc deficiencies: Eff = efficient, ME = moderately efficient, Ineff = inefficient 3. Pratylenchus resistance: S = susceptible, MS = moderately susceptible, MR = moderately resistant GRDC-supported Research Fellow Dr Xinhua He, of the UWA School of Plant Biology, is assessing the hardpan-penetration ability of wheat roots using a thin wax layer to simulate a soil hardpan. This novel technique was pioneered in the US and further developed at UWA by Dr He's predecessor, Dr Tina Botwright-Acuna, who is now lecturer in crop science at the University of Tasmania. The laboratory research technique demonstrated that wheat plants growing above a hardpan layer were less able to access water and nutrients, leading to poor shoot growth and reduced grain yield. However, the converse was true for those wheat plants with roots able to penetrate the hardpan. Dr He has now assessed the 24 wheat varieties and breeding lines used in the laboratory trials in the field. The wheats were grown in two soil types: a sandy duplex soil with a hardpan at 20cm, and a red clay with no hardpan but which increased in soil strength with depth, especially as it dried out. The research team are pleased to report that the wheats that performed best in the screening trials with the wax hardpans also performed best in the field. This is an important result as it supports the original work, which showed that the wax layer technique was a good measure of a wheat line's ability to handle a soil physical constraint. The currently available commercial varieties EGA Bonnie RockA, CammA, CarnamahA, Halberd, Janz, Machete, Stiletto and Wilgoyne had superior root penetration ability in well- watered and drought-stressed conditions. The wheats Cranbrook, C18 and KarlgarinA did not penetrate the wax layer and died shortly after under drought conditions. Their inability to access additional soil water from deeper layers demonstrated the variation in root strength in current lines and varieties and the importance of root-penetration ability in drought conditions. While more work is required to understand the mechanisms that control root-penetration ability and the consistency of expression of the trait in different soils, the fact that there is considerable genetic variation suggests that breeders should be able to select for improved root-penetration ability. □ GRDC Research Code UWA00090 More information: Professor Len Wade, Charles Sturt University, EH Graham Centre for Agricultural Innovation, 02 6933 2523, firstname.lastname@example.org SOME WHEATS HAVE ROOTS CAPABLE OF PENETRATING THROUGH SOIL HARDPANS. A hardpan is a high-strength soil layer located beneath the soil surface that is formed by the subsoil being compacted by vehicle traffic, tillage, stock or the pressure of the overlying soil.
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