Addressing Soil Test Phosphorus Recommendations

Transcription

1 Addressing Soil Test hosphorus Recommendations Chad enn USDA Agricultural Research Service National Soil Erosion Research Laboratory

2 Improving Soil Testing and Recommendations recise recommendations Increase agronomic production efficiency Reduce non-point losses of

3 Traditional soil testing ? Y-Values??

4 Agronomic soil test extractants sorbed to OM Outer-sphere (AEC) Organic compounds in biomass Inner-sphere to Fe/Al oxides & 1:1s recipitated Fe/Al phosphates recipitated Ca phosphates Dissolve a subsection of various pools quantity Aims to dissolve what will become soluble over the growing season Correlated to plant uptake of and yield

5 Empirical vs. mechanistic soil testing and fertilizer recs The most commonly used tests, extract some portion of the labile soil pool. However, when different soils are used, solution concentration, buffer capacity, and diffusion rate may not be correlated, therefore any one of the values would not be correlated with predicted uptake and the simpler soil test would not be more reliable Stanley Barber: Soil Nutrient Bioavailability

6 Critical Soil Levels 9 lb/acre 18 lb/acre 27 lb/acre (lb/acre) Lins, Cox, and Nicholaides, Optimizing fertilization rates for soybeans grown on oxisols and associated entisols. SSSAJ

7 Strips on Low Soil: Highest yield Lowest yield Soybean: Fall 2017 Rye: Spring 2018

8 What about under-application? Don t assume recommendations are always on the side of over-application Higher yields means greater uptake which may require greater applications Or more frequent Long term tillage study by Karlen et al., 2013 Soil test and K measurements as well as calculated and K removal suggest that nutrient mining occurred

9 What about under-application? deficiency is usually not visible (i.e. purpling) 05/30/ /04/ /13/2018 This plant appeared perfectly healthy, even though it was deficient

10 Definition of effective bioavailability Nutrient must be in the: In solution roper chemical form for uptake lants do not uptake dissolved organic In the vicinity of the plant root at the time of uptake Location, location, location! lants take nutrients up from the solution, NOT directly from the soil

11 Soil-lant Nutrient Dynamics lant Uptake of Nutrient Solution WATER IN NO - 3 NH + 4 O 3-4 O 4 3- Labile Non-labile O 4 3- O 4 3- NO - 3 Soil-bound nutrients NH 4 + O 4 3- Soil-bound nutrients

12 Uptake of solution by plants Function of solution concentration Replenishment by soil solids (quantity) Three ways of obtaining solution All three depend on root architecture, solubility, and location of near roots Root interception Bulk flow J r = v o C l Diffusion: highly dependent on location of!

13 movement to roots: Diffusion Dominant mechanism, but SLOW and short range Gradient Higher Concentration Lower Concentration J r = D e b C l r Higher Concentration

14 Diffusion followed by root uptake: I N = I max (C l C m ) K m + C l C m lant uptake

15 Overall equation describing uptake with movement: D e b C l r + v oc l = I max (C l C m ) K m + C l C m Ion movement via diffusion Ion movement via mass flow Root uptake kinetics Solved transient-state equation using the Crank-Nicholson method by Dr. John Cushman in 1980

16 Different plants require different concentrations in solution in order to meet the required mass.. External Requirement

17 BUT, that requirement varies with soil buffer capacity and texture: tortuosity Diffusion coefficient: D e = D l ƒ l dc l dc s Buffer capacity (b) Visualization of diffusion in soils of varying properties Degryse and McLaughlin, SSSAJ, 2014

18 Soil Requirement Mass of solution uptake is universal across soil properties But that required mass of can be provided dynamically at different solution concentrations Example: 550 mg /corn plant over 120 days 19 times/day Soil bound- Solution- 0.8 mg /L *depends on root surface area 76 times/day Soil bound- Solution- 0.2 mg /L

19 Soil Requirement But we don t measure solution! (Intensity) We measure soil-bound (Quantity) So how much soil-bound do we need? It depends on the ability of the soil to supply the solution Quantity-Intensity relationship Soil properties: mineralogy, texture, OM, ph, etc. Total content and forms Also depends on physical location of and ability to move (diffusion)

20 Quantity/ Intensity

21 WS (mg /kg) enn et al., 2018; Agriculture M3- (mg/kg) Impact of soil ph 4.5 M3- is more efficient at low ph levels WS M3- Lower ph levels means less in solution = less uptake Soil ph 0

22 Fertilizer Requirements Function of: mass required Targeted soil quantity necessary under the specific conditions Fertilizer -Soil relationship Depends on current soil quantity and soil properties

23 Fertilizer- Soil Relationship A.N. Sharpley Dependence of runoff phosphorus on extractable soil phosphorus. JEQ

24 Soil extractable requirement Fertilizer rate recommendation Ideal rocess Soil properties mass requirement for max yield Crop type (cultivar?) Soil properties and management Fertilizer/soil- relationship Quantity/Intensity Buffered solution requirement location and movement

25 Outdated fertilizer recommendations Based on results from soil test 0 to 6 inches Not representative of No-till conditions i.e. location Based on calibrations conducted 30 to 50 years ago No consideration for soil type or conditions We have very different crop varieties now

26 Soil extractable requirement Fertilizer rate recommendation Empirical Soil properties mass requirement for max yield Crop type (cultivar?) Soil properties and management Fertilizer/soil- relationship Quantity/Intensity Buffered solution requirement location and movement

27 otential for Soil Quality Soil health can only improve accessibility, but that does not defeat the mass requirement i.e. thermodynamics Deeper roots or more roots Free-living rhizosphere microorganisms VA mycorrhizae Changes to Q/I relationship I don t need to fertilize with anymore This is temporary due to the buffered nature of Only changes in genetics can change the mass required by a plant

28 Current Recommendations Not bad Get us in the ballpark Not precise Lots of room for improvement Save $ Example: increase M3- by 10 ppm vs 20 ppm» 40 vs 70 dollars/acre for MA Improve production efficiency Reduce losses

29 Long Term Goal Utilize and improve the Barber-Cushman model for developing more precise and condition-specific fertility recommendations Required mass for various cultivars lant uptake kinetics curves Incorporate root modelling redict root solution concentrations and kinetics using easily obtained parameters At different depths Continue to use ST extractants, but vary the optimum level depending on soils, crop, and conditions

30 Required uptake mass and utilization efficiency: sand culture hydroponics

31 Questions?