Title: Temporal Trends in Soil-Test P and P Recovery in Grassland Soils
1Temporal Trends in Soil-Test P and P Recovery in
Grassland Soils
- Dr Michael Herlihy1 and Dr Juliet McCarthy1,2
- 1 Teagasc, Johnstown Castle Research Centre,
Wexford - 2 Department of Life Sciences, University of
Limerick, Limerick
The Irish Fertiliser Manufacturers Association
2Outline of Presentation
- Background
- Introduction
- Results
- P balance
- Soil-test P
- P recovery
- Summary and Conclusions
3Background
- agronomic importance
- environmental importance
- trends in fertiliser P use and soil Morgan P
values
4Fertiliser Use
Courtesy of Soils Laboratory, Johnstown Castle
5Introduction
- Long-term trend fertiliser P vs. soil-test P
- Trends in Morgan P build-up or depletion
- Soil-test P changes in relation to P balance
- P balance P inputs P offtakes
- Potential for enrichment or depletion of
soil-test P - P recovery
6P balance trial
- Component of larger trial Fertiliser P
requirements in relation to soil P status for
grass production on representative soils - Objective examine trends in P balance, soil-test
P - 32 sites (8 x 4) low and high index groups 4
yrs - Fertiliser inputs P0, P20, P40, once-off P60 kg
ha-1 P - Herbage and soil samples
- Paper Irish Journal of Agricultural and Food
Research - Focus soils 14 and 30
7Location of soil series
8Classification and characteristics of soil series
Series / association Soil number Parent material Drainage pH range
Association-13 13 Sandstone-limestone diamicton Well drained 5.0 6.4
Clonroche 14 Ordovician shale diamicton Well drained 5.8 6.5
Association-15 15 Sandstone-shale diamicton Well drained 5.7 6.6
Castlecomer 22 Upper Carboniferous (Silesian) shale diamicton Poorly drained 5.2 6.0
Baggotstown 30 Calcareous fluvio-glacial gravel Well drained 5.6 6.9
Kinvara 33 Limestone diamicton (shallow) Well drained 5.6 7.3
Elton 34 Limestone diamicton Well drained 4.8 6.5
Howardstown 39 Limestone diamicton Poorly drained 4.9 6.3
9Results P balance
10Effect of fertiliser P input on P balance
Index P input Sum
12 0 -99.5
20 -48.1
40 12.5
60 -59.7
34 0 -143.5
20 -82.0
40 -10.7
60 -96.7
Sum of 4 years (kg ha-1)
11Effects of soil series on P balance
Sum 1997 - 2000 Sum 1997 - 2000
Series Index 1 2 Index 3 4
13 -54.8 -109.4
14 -48.9 -94.8
15 -65.8 -102.6
22 -7.6 -89.0
30 -38.3 -55.6
33 -79.9 -70.8
34 -45.7 -85.5
39 - -58.1
Sum of 4 years (kg ha-1)
12Cumulative P balance for soils 14 and 30
Index Soil no. P input 1999 2000
12 14 0 -87.7 -109.1
14 20 -38.4 -45.6
14 40 10.1 19.0
14 60 -36.8 -59.8
30 0 -66.3 -79.5
30 20 -36.2 -41.0
30 40 7.4 17.7
30 60 -34.4 -50.4
34 14 0 -125.2 -159.7
14 20 -71.2 -87.3
14 40 -19.8 -20.3
14 60 -76.1 -112.0
30 0 -90.2 -107.1
30 20 -54.6 -57.8
30 40 -3.2 9.5
30 60 -49.9 -67.0
kg ha-1
13Results Morgan P
- Changes in P balance affect trends in soil-test P
14Effects of fertiliser P on Morgan P
(a) low index group
(Spring)
15Effects of fertiliser P on Morgan P
(b) high index group
16Trends in Morgan P low index group
Soil 14
17Trends in Morgan P high index group
Soil 14
18Results Morgan P
- Soil-test P decline esp. P0
- Largest decline higher index
- Change on P40 plots ns - annual fluctuations,
inputs offtakes - P20 and P60 Morgan P comparable after 3 years
- Decline 30 gt 14
19Unit change ratio
- Change P balance unit change Morgan P
- P0 plots
- Low index 791 (soil 14) 281 (soil 30)
- High 291 (soil 14) and 121 (soil 30)
- Variation with index and P input
- Effects of soil chemistry and texture
20 Recovery - P60
(a) low index group
21Results P Recovery
- Highest on soil 30
- Highest in low index group
- Increased with time 4 years
- May underestimate recoveries attainable over a
longer period
22Summary of results
- Changes in P balance and soil-test P affected by
- Soil series
- Fertiliser P input
- Initial soil-P status (index)
- High offtakes reduced soil P rapidly large
decline in 4 yrs - Depletion of soil P, fertiliser-P recovery varied
widely between contrasting soils - Clonroche loam 14 vs. light limestone Baggotstown
30
23Conclusions
- Cannot assume direct relationships between inputs
and offtakes in different soils - Effects of soil series, fertiliser-P inputs, P
index on change in P balance, soil-test P and
recovery - Large reductions in soil-test P in 4 yrs with no
fertiliser-P input - Cut vs. grazed swards offtakes, duration
- Regular soil testing essential
24Future Work
- Differences in soil-test P changes, recoveries
between soils causes?
25Acknowledgements
- IFMA
- Research Office, UL
- Farmers
The Irish Fertiliser Manufacturers Association