P & K Research---Soil & Plant Testing Issues Daniel Kaiser Assistant Professor Department of Soil, Water and Climate

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1 P & K Research---Soil & Plant Testing Issues Daniel Kaiser Assistant Professor Department of Soil, Water and Climate U of M Twin Cities dekaiser@umn.edu

2 Soil Testing for P and K Provides and index or estimate of crop sufficiency Not the total amount in the soil Tests can vary in the pool of a particular nutrient it estimates Sometimes tests may correlate to each other but they may not extract the same amounts

3 Pools of P in the Soil Canesteo Initial Sample Conc. HCL-Pi 12% Clarion Initial Sample Ca-P Conc. HCL-Pi 17% Dil. HCL 9% Dil. HCL 39% Conc. HCL-Po 34% Conc. HCL-Po 37% NaOH-Po 19% NaOH-Po 9% NaHCO3-Po 8% NaOH-Pi 6% Res. P % Water P 1% NaHCO3-Pi 2% NaHCO3-Po 2% NaOH-Pi 2% Res. P 1% Water P 1% NaHCO3-Pi 2% Fe/Al-P P chemistry can be complex but typically reacts with Ca, Fe, and Al to form compounds of varying solubility The amount of available P is low compared to total P

4 What Test Do You Use Phosphorus Bray-P1: acid soils with ph <7.5 Olsen: alkaline soils with ph >7.5 Mehlich-3: not recommended in MN, but generally results in values slightly higher than bray (~1-5 ppm) in acid soils Buffered extract that should work in high ph soils MN data has shown it may over extract P when carbonates are high Most labs will run this with ICP which results in higher values due to organic P being measured

5 Olsen Phosphorus (ppm) Olsen Phosphorus (ppm) Bray-P1 Phosphorus (ppm) Bray-P1 Phosphorus (ppm) Mehlich-3 vs Bray or Olsen Soil ph > 7.4 Soil ph < y =.1478x R² = y = 1.79x R² = Mehlich-3 Phosphorus (ppm) Mehlich-3 Phosphorus (ppm) y =.2921x R² = y =.4494x R² = Mehlich-3 Phosphorus (ppm) Mehlich-3 Phosphorus (ppm)

6 Soil Tests A good soil test correlates well to crop response Is reproducible Extract is generally irrelevant as long as it can be accurately related to crop response

7 Corn Correlation Data Critical Level = 12 Critical Level = 8 12 Bray-P1 12 Olsen P Relative Yield (%) 9 7 Relative Yield (%) Bray Phosphorus Test (ppm) I Have not added 213 data Likely no change in the soil test classes Olsen Phosphorus Test (ppm)

8 Soybean Relative Yield Data - P Critical Level = 14 Critical Level = 1 12 Bray-P1 12 Olsen P Relative Yield (%) 4 2 Relative Yield (%) Bray Phosphorus Test (ppm) Olsen Phosphorus Test (ppm)

9 Calibration If a soil test correlates to crop response it needs to then be calibrated Add in classifications Add in fertilizer recommendations A calibrated soil test will provide a probability of response to P or K This is what needs to be provided in order to make the data useful

10 Magnitudes of P Response - Corn N Bray-P1 Phosphorus Extraction Probability Magnitude of of Response Response Olsen Phosphorus Extraction n Probability of Response Magnitude of Response % % VL: L M H VH n= number of cells Probability of response = probability of a measurable yield response Magnitude of response = weighted average of grain yield for areas with no response to P and the average relative yield increase for responsive areas

11 Magnitudes of P Response Soybean Bray-P1 Phosphorus Extraction N Probability of Response Magnitude of Response n Olsen Phosphorus Extraction Probability of Response Magnitude of Response % % VL: L M H VH n= number of cells Probability of response = probability of a measurable yield response Magnitude of response = weighted average of grain yield for areas with no response to P and the average relative yield increase for responsive areas

12 General thoughts on P Some work yet to do on the Olsen test but there is no evidence that high ph soils have a higher critical level If soil ph <7.4 use the Olsen P test Some evidence that direct application of P may benefit soybean Soils with high carbonates Two-year P applications may still work in high ph soils

13 Potassium Soil testing for potassium presents different problems K soil test levels are more dynamic over the growing season Soil tests available Ammonium acetate Mehlich-3 (same extract as for P)

14 17 1 Seasonal STK Variation SOIL TEST K (ppm) SOIL MOISTURE (%) 1 7 J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A MONTH OF THE YEAR Ebelhar, Varsa, and Peck. IL

15 Potassium Recycling to Soil Tissue K Content (lb K 2 O/acre) Vegetative tissue at physiological maturity Vegetative tissue at grain harvest time Soybean Crop residues K K Vegetative tissue at physiological maturity Corn Vegetative tissue at grain harvest time Crop residues K K1 Sep Oct Nov Dec Jan Feb Mar Apr May Sep Oct Nov Dec Jan Feb Mar Apr May Oltmans, Villavicencio, Clover, Mallarino. 211

16 K Recycling to Soil and Rainfall 1. Soybean 1. Corn.8.8 K Fraction Leached r² =.4, ns Y =.8 +.8X -.3X 2 R² =.73 P < Precipitation (inches) Precipitation (inches) From Physiological Maturity to Late Fall Oltmans and Mallarino. 211

17 Potassium in the Soil Soils have a vast difference in the potential to Hold K Mineralize/Release K K management is vastly different based on where you are at and what parent materials or clays are present Most soil clays in MN are a mixture of illite and smectite While K is relatively immobile in the soil it can move

18 What affects the K Availability Soil wetting/drying Freeze/thaw Oxidation state of Fe (i.e. degree of saturation with water) For smectite, as Fe 3+ Fe 2+, K is fixed For illite, as Fe 3+ Fe 2+, K is released

19 Corn Relative Yield (%) Corn Relative Yield (%) Corn Relative Yield (%) Corn Relative Yield (%) Moist and Dry K Field Correlation Canisteo, Nicollet, Webster All other soils 9 7 CL Loam SICL Dry K test (ppm) Dry K test (ppm) Canisteo, Nicollet, Webster All other soils 9 7 CL Loam SICL Moist K Test (ppm) Moist K Test (ppm) Barbagelata and Mallarino, 25

20 211 Dry vs. Slurry Test Ammonium Acetate K (ppm) Air Dry Slurry Slurry Test Lower Slurry Test Higher SiCL L SL LS SL SiL L SL SiL CL SiL L Spring 211 Fall 211

21 Looking Further: Red Wing, MN F211 Ammonium Acetate K (ppm) Air Dry Slurry lb K 2 O lb K 2 O 2 lb K 2 O 3 lb K 2 O Fall 211, treatments applied in spring No difference between tests for and lb rates 2 and 3 lb rates differed w/slurry higher Fixation upon drying

22 Thoughts on Potassium We still have some work to do Soybean may be resulting in a general lowering of soil test K in some areas of MN (NW in particular) May also be related to dry weather We are looking at moist/wet soil testing methods to see which soils are most affected I do not have enough data to support completely changing our K recs similar to Iowa Yes we do see responses to K in MN in contrast to what some people say

23 Plant Sampling: Is it Worth it Increasing emphasis from industry on detection of hidden hungers with plant tissue tests Ask yourself: am I better being proactive or reactive with my decisions? Also, how good is the data behind recommendations based on tissue testing?

24 Limitations on the Use of Plant Tissue Tests Reliability of interpretive data Utilization of ratio and balance concepts Hybrid/Varietal influences Changing physiological processes that occur at varying elemental concentrations Source: 1959 Plant Analysis and Fertilizer Problems Colloquium --Cited from Jones Jr., 212

25 Values for Making Interpretations Critical value Tissue concentration value at 9% of maximum yield Standard value General mean for crops normal in appearance under well-managed conditions Sufficiency range Range between deficiency and toxicity --Cited from Jones Jr., 212

26 Relative Corn Yield (% of Maximum) n=485 Deficient Excessive Mean = 2.6% When Ear Leaf N < 2.47 RelYLD= (Leaf P) (Leaf N) Ear Leaf N Concentration (%) at R2 R 2 =.48 P<.1

27 Ear Leaf Nitrogen Ear Leaf Phosphorus Relative Corn Yield (% of Maximum) Relative Corn Yield (% of Maximum) 12 4 n=485 2 When Ear Leaf N < 2.47 RelYLD= (Leaf P) (Leaf N) 2 R 2 =.48 P< Ear Leaf N Concentration (%) at R2 Ear Leaf Potassium 12 4 n=435 2 When Ear Leaf K < 1.43 RelYLD= (Leaf K) (Leaf K) 2 R 2 =.13 P< Ear Leaf K Concentration (%) at R2 Relative Corn Yield (% of Maximum) Relative Corn Yield (% of Maximum) When Ear Leaf P <.38 RelYLD= (Leaf P) (Leaf P) 2 R 2 =.45 P< Ear Leaf Sulfur 12 n=385 Ear Leaf P Concentration (%) at R Ear Leaf S Concentration (%) R2=.4

28 Sufficiency Ranges Calculated Response Trial Data Crop Stage Nutrient Low High Plant Analysis Handbook Corn R2 N V5 P* R2 P V5 K* R2 K* R2 S Soybean V5 P* na na R2 P* V5 K* na na R2 K* R2 S *Analysis indicated that a model was significant but R 2 was less than.2

29 Soybean Trifoliate P at R2 Relative Soybean Yield (% of Maximum) 12 4 n=99 2 When Tri P <.45 RelYLD= (Tri P) (Tri P) 2 R 2 =.32 P< Trifoliate P Concentration (%) at R2 R 2 =.47 Data shows two sets of response Similar data for K exists Do critical levels differ by site or some other factor Effect of luxury consumption

30 Corn V5 %P Soybean V5 %P Relative Corn Yield (% of Maximum) 12 4 n=125 2 When Plant P <.38 RelYLD= (%P) (%P) 2 R 2 =.3 P< Whole Plant P Concentration (%) at V5 Corn V5 %K Soybean V5 %K Relative Soybean Yield (% of Maximum) 12 4 n= When Plant P <.23 RelYLD= (%P) (%P) 2 R 2 =.8 P< Whole Plant P Concentration (%) at V5 Relative Corn Yield (% of Maximum) n=151 When Plant K < 3.6 RelYLD= (%K) (%K) 2 R 2 =.3 P< Whole Plant K Concentration (%) at V5 Relative Soybean Yield (% of Maximum) n=1124 When Plant K < 3.12 RelYLD= (%K) - 1.9(%K) Whole Plant K Concentration (%) at V5 R 2 =.3 P<.1

31 Relative Corn Grain Yield (%) Relative Corn Grain Yield (%) Phosphorus and Potassium Example Early Plant Concentration Limited locations Long Term P Study 29 2 Locations (Lamberton & Morris) Long Term K Study 21 2 Locations (Delavan & Morris) V5 Phosphorus Concentration (%) V5 Potassium Concentration (%) R 2 =.14 R 2 = %

32 Summary Tissue data coming from labs is reliable, interpretations are the questionable aspect of this system I would be more proactive in my management than reactive Tissue testing opens a whole new can of worms Data with P is slightly better, don t waste your time trying to manage K with a tissue test Soil tests are not affected by as many outside factors as plant tissue tests

33 Remember In a tissue test you are seeing an interaction of A particular hybrid/variety Grown in a particular location Sampled at a particular stage in growth Sampled under a particular environmental conditions (time of day variation) Ideal values for a tissue test represent more of a moving target

34 Thank You Questions? SW&C Field Crew Jeff Vetsch Cooperators and Consultants Daniel Kaiser University of Minnesota