Field Evaluation of Approaches for Reducing Reliance on P and K Fertilizers

1. Field Evaluation of Approaches for Reducing Reliance on P and K Fertilizers Gregory Porter and Paul Ocaya Department of Plant, Soil & Environmental Sciences University of Maine, Orono Aroostook Research Farm, Presque Isle, ME

2. Updated Potash Recommendations • Data from MPB funded experiments has been used to update soil test recommendations for potato • Peter Sexton, Bruce Hoskins, and Greg Porter • “Sufficiency” versus a “Build and Maintain” approach • Soil K plus fertilizer K20 to maximize crop value (yield, quality) • Lower potash recommendations on most soils, especially higher pH and CEC soils • Average savings of 50-60 lbs/A over current method

3. Progress Report • 2011 Grant Received: • $18,000 Maine Potato Board • Potassium Management Experiments • Three experiments were conducted as planned evaluating “sufficiency-level” versus “build and maintain” approaches • Also included a treatment with reduced at-planting rates and foliar KTS treatments • Russet Burbank and Atlantic varieties, RCBD experiments with six replications per treatment • Three sites with a range of soil-test K levels

4. 2011 Potassium Fertilization Experiments “Build & Maintain” versus “Sufficiency Approach”. Build&Maintain: 150 to 280 lbs/A K20 Sufficiency: 60 to 190 lbs/A K20 Foliar Program (total rate=sufficiency trt.): 15 to 145 lbs/A K20 at planting 45 lbs/A K20 as KTS (5 GPA follow by weekly 1 GPA) 2011 K experiment, site #1 2011 K experiment, site #3

5. 2011 Potassium Experiment (Atl), Site #3 Applied rates were close to soil-test recommendations on this site. KTS program was 145 lbs/A K2O at planting, KCL followed by 45 lbs/A K2O as KTS (5 GPA in June followed by weekly 1 GPA applications).

6. 2011 Potassium Experiment (RB), Site #2 Applied rates were above soil-test recommendations on this site. KTS program was 145 lbs/A K2O at planting, KCL followed by 45 lbs/A K2O as KTS (5 GPA in June followed by weekly 1 GPA applications).

7. 2011 Potassium Experiments - Summary • Foliar Program with KTS • No evidence of yield or quality advantages. • Reduced Potash Rate: • Sufficiency-Level Recommendation showed promise for reducing K fertilizer costs, however: • More data needed given crop value implications, 3 sites isn’t enough information • Minimum K2O rate may need to be increased (to > 60 lbs/A) • NS, but yield trended down in 2 of 3 RB tests • Blackspot increased in 2 of 3 ATL tests; 1 of 3 RB tests Above: K exp #1. Below: K exp #3.

8. Soil Test P Calibration • 2007-2009 Studies: • Weak response on 2 of 5 sites (40%) testing MH in Available P • No response on 3 sites • Fitzgerald, 1998: • 11 sites on commercial farms testing soils H in Available P (23 to 43 lbs/A based on Modified Morgan). • 1 of 11 sites (9%) had a significant yield response to P2O5 • 10 of 11 sites had no significant response Response of Atlantic Potatoes to P2O5 Fertilizer on Soils with High Available P:C. Fitzgerald, University of Maine, 1998

9. Can P Fertilizer Rates Be Reduced? • YES • ME Soil Testing Service recommendations could save ~40-80 lbs/A P2O5 • P fertilizer rates might be further reduced following hay or green manures • Follow calibrated soil test guidelines • A minimum of 60-80 lbs per acre of banded P2O5 is recommended • Due to Al and Fe fixation • Exception: Long-term manure amended soils with VH Avail P Nutrient Management Plots, 2010

10. 2011 Phosphorus Experiments • Experiment #1 • Russet Burbank • 0, 60, 120, 180, 240, and 300 lbs/A P2O5 • Short-term crop rotation treatments • potatoes oats • potatoes brassica green manure • potatoes oats/timothy/clover • Split-plot RCBD, 4 replications per treatment 2011 P Rate x Green Manure Experiment

11. 2011 Phosphorus Experiments • Experiment #2 • Shepody • 60 versus 150 lbs/A P2O5 • Long-term crop rotation treatments • Potatoes-oats • Potatoes-brassica green manure • Potatoes-peas/clover • Potatoes-canola • Split-plot RCBD, 4 replications per treatment 2011 Long-term GM P and N Response Study, Shepody

12. Summary – Phosphorus Studies • Two experiments were completed as planned: • No significant yield or quality benefits from the green manure crops versus the standard oat rotation • The results are consistent with recent studies suggesting that P2O5 rates can be reduced by 40 to 80 lbs/A • Green manure effects on P availability • No indication of increased availability based on yield response data • Crop uptake data will provide more conclusive evidence

13. GM x N Experiment • Rotation crops compared: oats, canola, Caliente mustard, pea w/white clover • Pea w/white clover reduced N fertilizer requirement by 80-100 lbs/A after several rotation cycles • Caliente mustard reduced the amount of N fertilizer needed for potatoes (~40-60 lbs/A) compared to oats • Canola N benefit was inconsistent • Except at low N fertilization rates, yields were not consistently affected by rotation crop

14. Outcomes … Information leading to: • P and K recommendations which will help maintain yield and quality • Potential P and K fertilizer savings in the range of 40-80 lbs/A or more P2O5 and K2O.

15. Questions? • Comments? Paul Cyr Photo U.S Potato Board