Where has all the phosphorous gone? Long term effects of alternative phosphorus sources on soil...
-
Upload
jodie-baldwin -
Category
Documents
-
view
225 -
download
3
Transcript of Where has all the phosphorous gone? Long term effects of alternative phosphorus sources on soil...
Where has all the phosphorous gone?Long term effects of alternative phosphorus sources
on soil fertility
Bill Bowden, WMG Craig Scanlan, DAFWA, Northam
February 2015
Background to the talk• Rediscovering the site• What the old trial was all about:
– Sources– Peak P– P budgets and residual value
• What current measurements can we show:– Chemical fertility: P, OC%, CEC, N– Physical: Wetting, compaction, bio-ploughs, water use– Biology: disease, weeds
Location
• Insert Text here
• Insert Text here
Location
• Insert Text here
Location
What the old trial was about?
– Alternative sources of P to orthophosphates (Super, DAP etc)• Water soluble phosphates
– The commercial fertilisers
• Less soluble phosphates– The raw minerals – A, B and C grade rock Ps– Calcined rock P– Reactive rock P – Lime super and partially acidulated super
– Peak P – how real is it?• Christmas Island story• Duchess, Mt Weld etc
– P budgets and residual value• Where does the P go• Changes in P availability• Changes in soil fertility
80Ba6 – Sources of P on pale grey sand• History of site
– Pre trial – not well documented• Semi-cleared 1973 and super and sub-clover spread into regenerating
scrub• Occasional grazing by sheep• Site cleared (200 metres by 100 metres) in 1980
– Trial (Bolland et al, 1987, AJEA, 27:647-56)• P treatments top-dressed in May 1980 and incorporated with tines• 1980-1986 crop sequence:- Illyarrie lupin, Seaton Park sub-clover, Pitman
serradella, Illyarrie lupin, volunteer pasture, volunteer pasture, cross plot Jacup wheat, Mortlock oats, Forrest barley
• Basal muriate of potash and gypsum applied at 100 kg/ha in sowing years (1980-83 and 1986) and 30 kg/ha MnSO4 in lupin years.
80Ba6 treatment detailssuper C500 C-ore
kgP/ha t fert/ha drill runs kgP/ha t fert/ha drill runs kgP/ha t fert/ha drill runs0 0 0
47 0.5 1 237 1.8 4 189 1.7 395 1.0 2 396 2.9 6 378 3.4 7210 2.2 4 792 5.9 12 693 6.2 12420 4.4 9 1188 8.8 18 1386 12.5 25
Phosphorus source details super C500 Core
component percent compositiontotal P 9.6 13.5 11.1
water soluble P 7.4 0.1 0.1citrate soluble P 1.2 6.8 0.1
calcium 23.2 17.4 9.2aluminium 0.4 11.2 11.9
iron 0.5 6.8 7.9sulphur 11.2 0.2 0.2
Residual effects of fertilisers
Change soil fertility:– Carry forward of nutrient– Build up of soil organic matter– Build up of soil nitrogen pools– Induced deficiencies– Non-wetting soils– Weeds and diseases
Table 1. Processes which reduce nutrient availability in farming systemsfixation transport
organic net increase in soil organic pools loss in productsseed pools and OC% redistribution to camps and windrows
erosion of organic matter
inorganic reactions with soil minerals erosionreversion in fertiliser granules leachinginduced deficiencies gaseous losses
• Insert Text here
0 5 10 15 20 25 30 35 400.00
0.20
0.40
0.60
0.80
1.00
1.20
Dissolution of homogeneous "slow release" fertilisers
0.1
2
4
8
16
32
64
time
cu
mu
late
d d
iss
olu
tio
n
0 5 10 15 20 25 30 35 400.00
0.20
0.40
0.60
0.80
1.00
1.20
Nutrient run down [a/(t+a)]soil type (reversion) effect
2
4
16
64
256
1024
time
res
idu
al n
utr
ien
t
Insert Heading here• Insert Text here
0 5 10 15 20 25 30 35 400.00
0.20
0.40
0.60
0.80
1.00
P availability of low solubility sources = dissolution rate (see key) by residual
This assumes no level effects or feedbacks of soil on dissolution
0.1
2
4
8
16
32
64
time
P a
va
ilab
ility
I
2014 response to 1980 treatmentsleft: 1188 kg P/ha (C500), nil, right 792 kg
P/ha (C500)
2014 response to 1980 treatmentsextreme left: 420 kg P/ha (super), centre 1388
kg P/ha (Core), extreme right 792 kg P/ha (C500)
2015 - Watch this space• Take soil profile samples to complete the P budget• Bioassay with a wheat crop
– Responses to N, P, NP and deep cultivation– Test strip diagnostics– Risks with management of residues, weeds and non-wetting
• Investigate soil compaction and bio-plough effects• Use soil bank and current samples to follow changes
in soil fertility
Three key messages• Poorly soluble P sources can have long term
residual effects• Poor, long term volunteer pasture lets soil OC
levels build up• Watch this space for interesting long term soil
fertility effects
Acknowledgements
Thanks go to the 1980 instigators of the trial: Mike Baker and Mike Bolland.To the landowners, David Frankland, Geoff Pearson.To the funders, NACC, and to the sponsors, the West Midlands Group and DAFWA
Questions?