Soil Fertility Dynamics T. Scott Murrell Director, Northcentral U.S. National Alliance of Independent Crop Consultants, 2013 Annual Meeting, Jacksonville, FL. 22-26 Jan. 2013.
IPNI Nutrient Evaluation Efforts Soil Test Summaries Nutrient Use GIS
Median Bray P-1 equivalent soil test levels, 2010
Change in median Bray P equivalent soil test levels from 2005 to 2010
Soil test P distribution in 2010 compared to 2005 for the Corn Belt (12 states plus Ontario) 30% 25% 20% 15% 10% 5% 0% Corn Belt P 2005 2.0 million samples 2010 3.0 million samples Median (2010) 22 28 (2005) Bray P1 Equivalent, ppm
nugis.ipni.net 1987 P 2 O 5 Balance
nugis.ipni.net 1992 P 2 O 5 Balance
nugis.ipni.net 1997 P 2 O 5 Balance
nugis.ipni.net 2002 P 2 O 5 Balance
nugis.ipni.net 2007 P 2 O 5 Balance
Change in soil test level Expected changes in soil test levels based upon nutrient budgets + Application > removal ~ 0 Application removal Application < removal -
Annual change in median P, ppm Annual change in median soil P level for 12 Corn Belt states as related to state P balance, 2005-2009 0.5 0.0-0.5-1.0 y = 0.0897x - 0.063 r² = 0.62 IA NE IN OH MN KS SD MO KY -1.5 MI -2.0-2.5-3.0 IL 11 lb P 2 O 5 / ppm WI -25-20 -15-10 -5 0 5 NuGIS balance*, lb P 2 O 5 /A/yr *NuGIS is a GIS nutrient balance model (IPNI, 2010).
Median soil test K levels in 2010
Change in median soil K level from 2005 to 2010
Soil test K frequency distribution in 2001, 2005 and 2010
nugis.ipni.net 1987 K 2 O Balance
nugis.ipni.net 1992 K 2 O Balance
nugis.ipni.net 1997 K 2 O Balance
nugis.ipni.net 2002 K 2 O Balance
nugis.ipni.net 2007 K 2 O Balance
Soil Test Potassium: Difficulties with Identifying Trends Changes that occur are not consistently predictable What could be contributing to this variability?
P removal (lb P 2 O 5 /acre) Soil P decrease (ppm) Long-term crop removal and soil test P trends 0 100 200 300 400 500 Years of corn/soybean rotation 0 2 4 6 8 10 12 P Removal 43 lb P 2 O 5 / ppm Soil P decrease 0 1 2 3 4 5 6 7 8 9 10 Villavicencio and Mallarino, 2011. Personal communication
K removal (lb K 2 O/acre) Soil K decrease (ppm) Long-term crop removal and soil test K trends 0 Years of corn/soybean rotation 0 2 4 6 8 10 12 14 16 0 100 200 300 12 lb K 2 O / ppm 10 20 400 30 500 600 700 40 50 800 60 K Removal Soil K Decrease Villavicencio and Mallarino, 2011. Personal communication
Contributors to soil test K variability: Sampling variability
Short-range variability of soil test K: Across and down Nutrient stratification Banding 4 yr. ago Banding this year Banding 2 yr. ago
Depth (in.) Depth control: Important in reduced tillage systems No-till field with 10-yr history Tama silt loam 8 in. 160 580 ppm 4 in. 330 580 ppm 0 6 10 440 330 37 in. 160 440 580 440 160 37 in. 330 Robbins and Voss, 1991 (IA)
Frequency (50 total) Core number: Impact on variability 40 True average 35 30 25 20 17 20 5 cores per sample 15 10 5 0 0 2 7 3 1 40 35 30 25 20 15 10 5 0 34 8 8 0 0 0 0 10 20 30 40 50 60 70 Soil test P category upper limit (ppm) 20 cores per sample
Contributors to soil test K variability: Sampling frequency
Soil test level Sampling frequency: Affects ability to detect trends Sampled every 42 1 years Increasing or decreasing? 1 2 3 4 5 6 7 8 Crop year
Concept of a monitoring strip Area where intensive measurements are taken each season Soil tests Plant tissue tests Nutrient deficiency symptoms Grain nutrient content Diseases Insects Management practices etc.
K visual deficiency symptom index Visual symptoms of K deficiency are a useful diagnostic tool 2.0 170 1.5 1.0 Deficiency Symptom Index: 0 = None 1 = Moderate 2 = Severe 0.5 0.0 0 50 100 150 200 Soil test K (ppm) Wittry and Mallarino, Iowa State University
Example of K deficiency symptoms: soybean
Contributors to soil test K variability: Leaching of K from plant residue
Corn stover K content (lb K 2 O/acre) Changes in corn stover K content after physiological maturity 160 140 120 100 harvest 80 60 40 20 0-50 0 50 100 150 200 250 Days since physiological maturity Oltmans and Mallarino. 2011. Personal communication.
Soybean tissue K content (lb K 2 O/acre) Changes in soybean tissue K content after physiological maturity 160 140 120 100 80 60 40 harvest 20 0-50 0 50 100 150 200 250 Days since physiological maturity Oltmans and Mallarino. 2011. Personal communication.
Percent of initial K remaining Amount of water affecting K leaching from residue 100 90 80 70 60 50 40 30 20 10 0 Non-irrigated Irrigated by overland flow (2 in. every 7-21 days) 0 10 20 30 40 50 Water, inches Schomberg, H.H. and J.L. Steiner. 1999. Soil Sci. Soc. Am. J. 63:607-613
Contributors to soil test K variability: Soil moisture
Potassium fixation Dehydrated K ion Hydrated K ion Planar positions Clay mineral layer Interlayer positions Edge positions Havlin et al., 1999
Wetting/drying cycles impact variability Sample Treatment Fixed K Exchangeable K --------- meq/100g ---------- Drummer (Dekalb) Dry 72.8 29.6 Wet 66.6 38.6 Drummer (Urbana) Dry 71.6 33.7 Wet 65.7 39.6 Cisne (Brownstone) Dry 43.9 30.9 Wet 39.2 42.9 Stucki, 1996 (IL)
Soil test K (ppm) Soil moisture (%) Seasonal variation in soil test K 170 160 150 140 130 120 110 100 90 80 70 60 Soil test K Soil moisture 1994 1995 1996 1997 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 50 45 40 35 30 25 20 15 10 5 0 Ebelhar et al. 1997. Personal communication. Soil test values are ammonium acetate extractable.
How the scientific community is responding to variability in soil test K Two primary efforts have been underway to address K variability: Conduct new crop response trials Re-examine the effect of drying soils prior to analysis
Scientific response to soil test K variability: Updated crop response trials
Corn grain relative yield (%) Very low Low Optimum High Very high Changes in soil test K critical levels: Categories used previously Iowa, U.S. 110 100 90 80 70 60 50 40 0 50 100 150 200 250 300 350 Soil test K (ppm) Mallarino, A.P. 2003.
Corn grain relative yield (%) Very low Low Optimum High Very high Changes in soil test K critical levels: Categories used previously Iowa, U.S. 110 100 90 80 70 60 Many other soils Canisteo, Colo, Ely, Nicollet, Tama, Webster 50 40 0 50 100 150 200 250 300 350 Soil test K (ppm) Mallarino, A.P. 2003.
Corn grain relative yield (%) Very low Low Optimum High Very high Changes in soil test K critical levels: Categories currently used Iowa, U.S. 110 100 90 80 70 60 Many other soils Canisteo, Colo, Ely, Nicollet, Tama, Webster 50 40 0 50 100 150 200 250 300 350 Soil test K (ppm) Mallarino, A.P. 2003.
Scientific response to soil test K variability: Re-examining the effect of drying soils prior to analysis
Soil test K (ppm) Monitoring soil test K over time: Effects of drying the soil sample 250 200 0 lb K2O/acre 108 lb K2O/acre K applications discontinued 150 100 50 0 Field moist Air-dried 0 10 20 30 40 Years of corn/soybean rotation Mallarino, A.P. Personal communication. Soil test values are ammonium acetate extractable.
Soil test K (ppm) Effect of sample drying on soil test K 120 100 80 y = 161.23x -0.543 R² = 0.9527 Harpster silty clay loam Clarion loam 60 40 20 y = 84.336x -0.278 R² = 0.88 0 0 5 10 15 20 25 30 Soil moisture (%) Luebs, R.E. et al. 1956. Soil Sci. Soc. Am. Proc 20:45-50. Note: curve fitting and statistics not performed by the authors.
Soil test K (ppm) Dowdy, R.J. and T.B. Hutcheson, Jr. 1963. Soil Sci. Soc. Am. Proc. 27:31-34. Initial soil test K levels affect changes as soils are dried 400 350 300 250 200 150 Bedford: no K added Bedford: K enriched 100 50 0 0 5 10 15 20 25 30 Soil moisture (%)
Corn relative yield (%) Keeping samples moist may improve the relationship of soil test K to yield response 110 Dried 100 90 80 70 60 Clay loam Loam Silty clay loam 0 100 200 300 400 500 Soil test K (ppm) Barbagelata and Mallarino. 2005. Personal communication.
Corn relative yield (%) Keeping samples moist may improve the relationship of soil test K to yield response 110 Moist 100 90 80 Clay loam 70 Loam Silty clay loam 60-50 50 150 250 350 450 Soil test K (ppm) Barbagelata and Mallarino. 2005. Personal communication.
Summary Soil test P levels are declining in the Midwest, and these declines can be explained by mass balance Soil test K levels are declining in many states in the Midwest, but declines are not explained by mass balance perhaps because of high variability Causes of soil test K variability: Sampling variability Sampling frequency Leaching of K from crop residues Soil moisture Drying of soil samples prior to analysis Scientific response: Update crop response data Investigate drying of soils prior to analysis