Carbon content and bulk density of an irrigated Natrixeralf in relation to tree root growth and orchard management [Victoria]
1994
Emerson, W.W. | Foster, R.C. | Weissmann, D. (Commonwealth Scientific and Industrial Research Organisation, Glen Osmond (Australia). Div. of Soils) | Tisdall, J.M. (Victorian Dept. of Agriculture, Tatura (Australia). Inst. for Sustainable Irrigated Agriculture)
The reason for few feeder roots present in the surface of soil of irrigated orchards in the Goulburn Valley, Victoria was investigated as this may be reducing fruit yields. In each of 9 orchards, when the soil was near field capacity, root proliferation and earthworm activity were noted and a core taken. Where the C content of cores was 1 percent or less, few roots were present, the soil was severely compacted and inter-particle bonding was weak. Root proliferation, soil porosity and clay inter-particle bonding all reached a maximum at about 2.2 percent C. With 3-4 percent C present, few roots were seen, bonding remained strong, but the soil was again compacted. It is suggested that with increasing C content, carbohydrate gel progressively bonds portions of the mineral matrix together. Eventually, probably mainly as a result of earthworm activity, the mineral matrix becomes embedded in gel. Then, although the gel itself retains about 4.6 g H2O per g of C at 10 kPa suction, none is available for root growth, because of the high penetration resistance of the soil. Root growth is also inhibited at low C contents, because of the high bulk density. Maximum root proliferation occurred in permanent banks raised around mature trees, where the banks were wetted by capillarity every 2-3 weeks.
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