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 2 Department of Life Sciences, University of Limerick, Limerick The Irish Fertiliser Manufacturers Association UNIVERSITY of LIMERICK O L L S C O I L L U I M N I G H

Outline of Presentation Background Background Introduction Introduction Results: Results: P balance P balance Soil-test P Soil-test P P recovery P recovery Summary and Conclusions Summary and Conclusions

Background agronomic importance agronomic importance environmental importance environmental importance trends in fertiliser P use and soil Morgan P values trends in fertiliser P use and soil Morgan P values

Fertiliser Use Courtesy of Soils Laboratory, Johnstown Castle

Introduction Long-term trend: fertiliser P vs. soil-test P Long-term trend: fertiliser P vs. soil-test P Trends in Morgan P: build-up or depletion Trends in Morgan P: build-up or depletion Soil-test P changes in relation to P balance Soil-test P changes in relation to P balance P balance = P inputs – P offtakes P balance = P inputs – P offtakes Potential for enrichment or depletion of soil-test P Potential for enrichment or depletion of soil-test P P recovery P recovery

P balance trial Component of larger trial: Fertiliser P requirements in relation to soil P status for grass production on representative soils 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 Objective: examine trends in P balance, soil-test P 32 sites (8 x 4); low and high index groups; 4 yrs 32 sites (8 x 4); low and high index groups; 4 yrs Fertiliser inputs: P 0, P 20, P 40, once-off P 60 kg ha -1 P Fertiliser inputs: P 0, P 20, P 40, once-off P 60 kg ha -1 P Herbage and soil samples Herbage and soil samples Paper: Irish Journal of Agricultural and Food Research Paper: Irish Journal of Agricultural and Food Research Focus: soils 14 and 30 Focus: soils 14 and 30

Location of soil series

Classification and characteristics of soil series Series / association Soil number Parent materialDrainagepH range Association-1313Sandstone-limestone diamicton Well drained5.0 – 6.4 Clonroche14Ordovician shale diamicton Well drained5.8 – 6.5 Association-1515Sandstone-shale diamicton Well drained5.7 – 6.6 Castlecomer22Upper Carboniferous (Silesian) shale diamicton Poorly drained5.2 – 6.0 Baggotstown30Calcareous fluvio-glacial gravel Well drained5.6 – 6.9 Kinvara33Limestone diamicton (shallow) Well drained5.6 – 7.3 Elton34Limestone diamictonWell drained4.8 – 6.5 Howardstown39Limestone diamictonPoorly drained4.9 – 6.3

Results: P balance

Effect of fertiliser P input on P balance Index P input Sum Sum Sum of 4 years (kg ha -1 ) Sum of 4 years (kg ha -1 )

Effects of soil series on P balance Sum SeriesIndex Index Sum of 4 years (kg ha -1 ) Sum of 4 years (kg ha -1 )

Cumulative P balance for soils 14 and 30 Index Soil no. P input kg ha -1 kg ha -1

Results: Morgan P Changes in P balance affect trends in soil-test P Changes in P balance affect trends in soil-test P

Effects of fertiliser P on Morgan P (a) low index group (Spring)

Effects of fertiliser P on Morgan P (b) high index group

Trends in Morgan P: low index group Soil 14 mg l -1 P Soil 30 mg l -1 P

Trends in Morgan P: high index group Soil 14 mg l -1 P Soil 30 mg l -1 P

Results: Morgan P Soil-test P decline esp. P 0 Soil-test P decline esp. P 0 Largest decline: higher index Largest decline: higher index Change on P 40 plots ns - annual fluctuations, inputs ~ offtakes Change on P 40 plots ns - annual fluctuations, inputs ~ offtakes P 20 and P 60 Morgan P comparable after 3 years P 20 and P 60 Morgan P comparable after 3 years Decline: 30 > 14 Decline: 30 > 14

Unit change ratio Change P balance : unit change Morgan P Change P balance : unit change Morgan P P 0 plots P 0 plots Low index: 79:1 (soil 14); 28:1 (soil 30) Low index: 79:1 (soil 14); 28:1 (soil 30) High: 29:1 (soil 14) and 12:1 (soil 30) High: 29:1 (soil 14) and 12:1 (soil 30) Variation with index and P input Variation with index and P input Effects of soil chemistry and texture Effects of soil chemistry and texture

% Recovery - P 60 (a) low index group % (b) high index group %

Results: P Recovery Highest on soil 30 Highest on soil 30 Highest in low index group Highest in low index group Increased with time … 4 years Increased with time … 4 years May underestimate recoveries attainable over a longer period May underestimate recoveries attainable over a longer period

Summary of results Changes in P balance and soil-test P affected by: Changes in P balance and soil-test P affected by: Soil series Soil series Fertiliser P input Fertiliser P input Initial soil-P status (index) Initial soil-P status (index) High offtakes reduced soil P rapidly: large decline in 4 yrs High offtakes reduced soil P rapidly: large decline in 4 yrs Depletion of soil P, fertiliser-P recovery varied widely between contrasting soils Depletion of soil P, fertiliser-P recovery varied widely between contrasting soils Clonroche loam 14 vs. light limestone Baggotstown 30 Clonroche loam 14 vs. light limestone Baggotstown 30

Conclusions Cannot assume direct relationships between inputs and offtakes in different soils 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 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 … Large reductions in soil-test P in 4 yrs with no fertiliser-P input … Cut vs. grazed swards: offtakes, duration Cut vs. grazed swards: offtakes, duration Regular soil testing essential Regular soil testing essential

Future Work Differences in soil-test P changes, recoveries between soils … causes? Differences in soil-test P changes, recoveries between soils … causes?

Acknowledgements IFMA IFMA Research Office, UL Research Office, UL Farmers Farmers The Irish Fertiliser Manufacturers Association UNIVERSITY of LIMERICK O L L S C O I L L U I M N I G H