Institute of Ag Professionals

Transcription

1 Institute of Ag Professionals Proceedings of the 2009 Crop Pest Management Shortcourse & Minnesota Crop Production Retailers Association Trade Show Do not reproduce or redistribute without the written consent of author(s).

2 Soil-Test Interpretations and Recommendations for P and K Breaking up Paradigms and Opening Possibilities Antonio P. Mallarino Iowa State University

3 Concepts for P and K Management Most relevant questions: - Soil-test levels for optimum yield - Application rates for deficient soils - Soil-test maintenance: Why, what level? - Recognize within-field soil-test and yield response variation, use VRT - Placement method: No issue for P in Iowa, but need deep-band K for ridge-till and maybe no-till. Use starter for corn for a few conditions

4 Volatile Grain and Fertilizer Prices Crop and fertilizer prices should affect - The most profitable P-K fertilizer rates in responsive low-testing soils - The pace or convenience of buildup - The soil-test level to maintain and the profitability of its maintenance - Return loss when fertilizer is applied to non-responsive high-testing soils

5 Water Quality Considerations Increased public perceptions about nutrient pollution from agriculture For sure tougher nutrient regulations or more strict enforcement No matter who is right or the cause, we are being watched and scrutinized Need to carefully consider economics, water quality, and practical issues

6 How Do We Manage P and K? Fertilizer costs money but yield pays the bills. Increased fixed production costs: land, seed, equipment Must use fertilizers efficiently but in a cost-effective and practical way High overall efficacy of crop production does not necessarily means maximum use efficiency of each input Practical issues: timing of operations, time dedication, business approach

7 Interpretation of Soil Test Results Soil testing is a useful tool but not perfect. Likely errors, uncertainty Field calibration gives a meaning to soil test values for different methods - critical value or range - interpretation classes - rates for the responsive range Soil-test values are related to crop yield response, not necessarily to absolute yield level!

8 What s a Critical Value or Range? Critical value/range separates responsive from non-responsive soils, but - Statistical, agronomic, or zero response? - Economic response? So the critical level changes every other week in response to wild price changes? - What probability of crop response? - Is there a single best way of determining a critical soil-test range?

9 Many Years of Calibrations for Bray 110 Relative Grain Yield (%) CORN SOYBEANS 40 VL L Op H VH Interpretation Classes VL L Op H VH Interpretation Classes Bray-1 Soil-Test P (ppm) Bray-1 Soil-Test P (ppm) Dodd & Mallarino, 2005

10 Calibrations for Four STP Methods calcareous soil RELATIVE YIELD OF CORN (%) No P recommended Bray P-1 Mehlich-3 Colorimetric No P recommended Olsen Mehlich-3 ICP 60 No P recommended No P recommended SOIL-TEST P (ppm) Mallarino, 2005

11 Soil Science Isn't an Exact Science Several ways for establishing critical ranges Not a single science-based best way Subjective judgment! Mallarino, 1995

12 Most Recent Iowa K Calibrations 110 Relative Corn Yield (%) ppm Soil-Test K (ppm) Mallarino and Barbagelata, 2005

13 Interpretation Classes for K 100 Relative Corn Yield (%) VL L Opt H VH Soil-Test K (ppm) Mallarino, 2006

14 Price Ratios Affect Net Returns and the Critical Soil-Test Level Returns To 46 lb P 2 O 5 ($/acre) 175 CORN CORN SOYBEAN SOYBEAN Historical Prices VL L O H VH Soil-Test Classes VL L O H VH Soil-Test Classes Soil-Test P (Bray-1, ppm) $4.00/bu corn $10.00/bu soyb $0.40/lb P 2 O 5 Mallarino, 2009

15 What Happens in the Real World? Soil testing is useful but NOT perfect. Sources of error and uncertainty: - temporal variation (soil, climate factors) - spatial variation and sampling error - sub-sampling and analytical error - laboratory bias - soil-test calibration uncertainty Uncertainty about magnitude of crop response and the optimum fertilizer rate

16 Uncertainty Due to Soil Sampling Error The Most Frequent, Important, and Undetected Source of Error in Soil Testing Wittry and Mallarino, 2004

17 Efficacy of Soil Sampling Methods Sawchik & Mallarino, 2008 Efficacy Index: Capacity to identify field areas with different crop response: - Dense acre grids: acre grids: 50% - Zone sampling: 39% - Sampling by soil type: 22% We must do better than just sampling by soil type!

18 Number of Cores per Soil Sample 14 CONFIDENCE INTERVAL (+- ppm P) About 1 acre 19 ppm Median STP (Optimum Class) Ouch!! +- 4ppm!! NUMBER OF CORES PER SAMPLE Mallarino, 1994

19 Laboratory Testing Issues Precision of the measurement Uncertainty Accuracy of the measurement Bias Good precision but bias Good testing Bad precision and bias Bad precision no bias Adapted from Robert Miller

20 Users Must Consider Probabilities! Soil-test interpretations must provide a probability of crop response to the user! Category Iowa Wisconsin Very Low 80% >90% Low 65% 60-90% Opt/Medium 25% 30-60% High 5% 5-30% Very High <1% <5%

21 Strict Response-Based Management Emphasizes short-term returns, not long-term returns or maximum yield Requires good accuracy and precision of testing, calibrations, and optimum economic fertilizer rates each year Requires frequent soil sampling and careful fertilizer application methods Reasonable for "really" fixing soils, where buildup/maintain isn't practical

22 Buildup & Maintenance Management Emphasizes long-term productivity and returns, and reduced risk of yield loss Less sensitive to errors in soil testing, calibrations, and recommendations Does not require frequent soil testing Reasonable in soils with moderate or little "fixation" and with secure land tenure for at least 2-3 years

23 P and K ARE NOT Like Nitrogen Excess N for one crop is money wasted and polluted water: No carryover But NOT necessarily for P and K in Iowa and most soils of the Corn Belt - can bank P-K to a large extent, retention by soil IS NOT fixation - additions and removal are responsible for long-term soil-test trends Concept: Can manage both fertilizer and soil-test values over time

24 Strong Long-Term Trends Database Soil-Test P (ppm) OPTIMUM INITIAL P ANNUAL P 2 O 5 /acre = 0 = 23 = 46 = 69 Annual P stopped VERY HIGH INITIAL P Annual P stopped Years of Corn-Soybean Rotation Mallarino, 2005

25 Cumulative P Applied & Soil P Cumulative P Applied (lb P 2 O 5 /acre) Bray-1 Soil P 2.2 ppm/year increase Cumulative P Applied 56 lb P 2 O 5 /year increase Year of Cropping with 56 lb P 2 O 5 /acre/year Bray-1 Soil P Change (ppm) Prater & Mallarino, 2007

26 Cumulative P Removal & Soil P 0 0 Cumulative P Removal (lb P 2 O 5 /acre) Bray-1 Soil P 0.78 ppm/year avg. decrease r 2 = 0.83 Cumulative P Removal 37 lb P 2 O 5 /year avg. decrease r 2 = Bray-1 Soil P Decrease (ppm) Year of Cropping without P Application Prater & Mallarino,

27 What Are Recommended Rates For? What is the objective of fertilizer rates we or crop consultants recommend? Target maximum net return each year? Be sure that fertility doesn't limit yield? Short-term or long-term productivity? Iowa philosophy for P and K rates: - There is high probability of a large response in the low-testing classes - Long-term profitability of the system - Can manage soil-test values over time

28 Iowa P Interpretations and Recs Adapted from PM 1688 Soil Test P Categories* Soil Test Method Very Low Low Optimum High Very High Bray-1 or Mehlich Mehlich-3 ICP Olsen Crop Corn Soybean Corn-Soybean (50) 0 * Soils with Low Subsoil P ppm Slow build up Fertilizer Recommendations P 2 O 5 /acre Maintain adjusting for yield/removal No need or doesn't pay Yield levels affects removal, NOT the Optimum soil-test P level

29 Yield Response, P Rate, & Classes 25 Corn 43 Sites Yield Increase (bu/acre) lb P 2 O 5 /acre 100 lb P 2 O 5 /acre 0 VL L Opt H VH Mallarino, 2009

30 Net Returns, P Rates, & Classes 60 Corn 43 Sites Net Return ($/acre) lb P 2 O 5 /acre 50 lb P 2 O 5 /acre -20 VL L Opt H VH Mallarino, 2009

31 What Economic Return Are We After? 220 Grain Yield Total Net Return Return per Pound Corn Grain Yield (bu/acre) lb P 2 O 5 /acre Total Return ($/acre) lb P 2 O 5 /acre Return/lb P 2 O 5 ($) lb P 2 O 5 /acre Mallarino, 2009

32 Iowa K Interpretations and Recs Adapted from PM 1688 Soil Test K Categories* Soil Test Method Very Low Low Optimum High Very High Ammonium Acetate or Mehlich ppm Crop Corn Soybean Corn-Soybean (60) 0 * Soils with Low Subsoil K Fertilizer Recommendations K 2 O/acre Slow build up Maintain adjusting for yield/removal No need or doesn't pay Yield levels affect removal, NOT the Optimum soil test level

33 With Likely Large Crop Response GRAIN YIELD (bu/acre) Soil K Very Low, Large 70 bu/acre Response K FERTILIZER (lb K 2 O/acre) Mallarino, 2007

34 Price Ratios and Returns to K 600 Very Low Soil Test, High Probability of a Large Crop Response $7.5/bu CORN $0.30/lb K 2 O $5/bu CORN $0.45/lb K 2 O $2.5/bu CORN $0.60/lb K 2 O Net Return to K ($/acre) Fertilizer Application Rate (lb K 2 O/acre) Mallarino, 2008

35 With Small Crop Response Likely 190 Optimum Soil K, Small 7 bu/acre Response GRAIN YIELD (bu/acre) K FERTILIZER RATE (lb K2O/acre) Mallarino, 2007

36 Price Ratios and Returns to K Optimum Soil Test, Small Probability of a Small Crop Response 60 $7.5/bu CORN $0.30/lb K 2 O 40 $5/bu CORN $0.45/lb K 2 O $2.5/bu CORN $0.60/lb K 2 O Net Return to K ($/acre) Fertilizer Application Rate (lb K 2 O/acre) Mallarino, 2008

37 Risk, Land Tenure, and Maintenance The probability of a crop response for the Optimum class is 25% or less Removal-based rates are designed to maintain an Optimum test value. They maximize crop yield but may NOT maximize net return for one crop A farmer in economic trouble or with uncertain land tenure may not need to, or should not, apply maintenance rates

38 Very Important Considerations Land tenure, farmer's management philosophy, and practical issues that should be considered by users - Short-term or long-term philosophy? - Rates for low-testing soils to attain maximum yield, maximum net return for one crop, or a large return per lb of fertilizer even risking lower yield? - Apply to maintain a soil-test level? Which one? With what probability?

39 Recognize Uncertainty and Options 110 Uncertainty! Uncertainty! Relative Grain Yield (%) No doubts CORN No doubts No doubts SOYBEANS 40 VL L Op H VH Interpretation Classes VL L Op H VH Interpretation Classes Bray-1 Soil-Test P (ppm) Bray-1 Soil-Test P (ppm) Dodd & Mallarino, 2005

40 Philosophies and Risk Assumed High Risk High Risk Low Risk Type 1 Risk: the net return to the last few input units is negative and reduce the maximum return Type 2 Risk: Insufficient input limits yield and longterm returns to the production system Low Risk Soil Nutrient Level or Fertilization Rate Adapted from Dale Leikam

41 Philosophy for P-K Recommendations There is uncertainty in assessing crop P and K needs and optimum fertilizer rates With P and K can implement short-term or long-term management philosophies Practical issues and farmers' business management style are very important The philosophy for recommendations and options should be explained so users can make informed decisions

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