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UNIVERSITY of LIMERICK O L L S C O I L L U I M N I G H. Temporal Trends in Soil-Test P and P Recovery in Grassland Soils. Dr Michael Herlihy 1 and Dr Juliet McCarthy 1,2 1 Teagasc, Johnstown Castle Research Centre, Wexford

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temporal trends in soil test p and p recovery in grassland soils

UNIVERSITY of LIMERICK

O L L S C O I L L U I M N I G H

Temporal 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

outline of presentation
Outline of Presentation
  • Background
  • Introduction
  • Results:
    • P balance
    • Soil-test P
    • P recovery
  • Summary and Conclusions
background
Background
  • agronomic importance
  • environmental importance
  • trends in fertiliser P use and soil Morgan P values
fertiliser use
Fertiliser Use

Courtesy of Soils Laboratory, Johnstown Castle

introduction
Introduction
  • 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
p balance trial
P 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
effects of soil series on p balance
Effects of soil series on P balance

†Sum of 4 years (kg ha-1)

results morgan p
Results: Morgan P
  • Changes in P balance affect trends in soil-test P
effects of fertiliser p on morgan p
Effects of fertiliser P on Morgan P

(a) low index group

(Spring)

results morgan p1
Results: 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 > 14
unit change ratio
Unit change ratio
  • Change P balance : unit change Morgan P
  • P0 plots
  • Low index: 79:1 (soil 14); 28:1 (soil 30)
  • High: 29:1 (soil 14) and 12:1 (soil 30)
  • Variation with index and P input
  • Effects of soil chemistry and texture
results p recovery
Results: P Recovery
  • Highest on soil 30
  • Highest in low index group
  • Increased with time … 4 years
  • May underestimate recoveries attainable over a longer period
summary of results
Summary 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
conclusions
Conclusions
  • 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
future work
Future Work
  • Differences in soil-test P changes, recoveries between soils … causes?
acknowledgements

UNIVERSITY of LIMERICK

O L L S C O I L L U I M N I G H

Acknowledgements
  • IFMA
  • Research Office, UL
  • Farmers

The Irish Fertiliser Manufacturers’ Association