Abstract
This paper investigates why there are usually very few feeder roots present in the surface soil of irrigated orchards in the Goulburn Valley, as this may be reducing fruit yields. Nine orchards were selected to cover the range of soil and water management. In each orchard, 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% 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% C. With 3-4% 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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Claims 6
Claim · model-written summary
At 1% carbon or less, few orchard roots occurred and soil was severely compacted with weak bonding.
Not reportedSetting
Verbatim
e0“Where the C content of cores was 1% or less, few roots were present, the soil was severely compacted and inter-particle bonding was weak.”
t0“tree root growth”
Claim · model-written summary
Root proliferation, porosity and clay bonding peaked near 2.2% carbon.
Verbatim
e0“Root proliferation, soil porosity and clay inter-particle bonding all reached a maximum at about 2.2% C.”
t0“tree root growth”
Claim · model-written summary
At 3–4% carbon, few roots occurred despite strong bonding, and soil was compacted.
Verbatim
e0“With 3-4% C present, few roots were seen, bonding remained strong, but the soil was again compacted.”
t0“tree root growth”
Claim · model-written summary
High soil carbon was interpreted to embed mineral matrix in gel and restrict root water access through penetration resistance.
Verbatim
e0“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.”
t0“tree root growth”
Claim · model-written summary
Low carbon inhibited root growth through high bulk density.
Verbatim
e0“Root growth is also inhibited at low C contents, because of the high bulk density.”
t0“tree root growth”
Claim · model-written summary
Permanent banks around mature trees wetted every 2–3 weeks had maximum root proliferation.
Verbatim
e0“Maximum root proliferation occurred in permanent banks raised around mature trees, where the banks were wetted by capillarity every 2-3 weeks.”