Soil Fertility 101?

Ray Weil

NutrientSmart - Guelph, Ontario January 2018

Guiding principles of soil fertility management

• Soils are complex, integrated systems.

• Soils are alive! C drives the food web.

• Soils are 3-D – use the whole profile.

• Each nutrient has its cycle – fertilizer can supplement, not supplant.

• Economic and environmental optima often allow a win – win.

• Lots of dollars still going down the drain.

Soil

Chemistry

Soil

Physics

Soil

Biology

Plant root

physiology

Soil types

formation

Landscape,

ecology

Soils are complex, integrated

systems.

.

Plant root

physiology

Rhizosphere

soil sheathsWashed roots

Mucigel

Root cap

cells

spilling C

Roothairs

Soils are alive –

roots are part of a

community

Crop rootsSoil Pests

Beneficial

nematodes

Beneficial

bacteria

Mycorrhizal

partners

Crop roots

Use the full

profile

Soils are three-dimensional

Which nutrient & water

reservoir do you want supporting your crops?

Calcium-

phosphates

Iron, Aluminum

-phosphates

Organic-

phosphorus

P in

Solution

2023

0.1

0.2

0.3

P fluxes

for 106

Ohio

fields, Kg

P/ha

Each

nutrient has

its soil cycle

Forms of water-soluble phosphorus

From Weil & Brady (20017) using means for 14 unfertilized pastures on alluvial Vermont Inceptisols in Young et al. (2013)]

News Flash! It’s not all orthophosphate

(H2PO4).

Six basic strategies that plant roots

may employ to enhance their uptake of

various forms of phosphorus from soils.

Increased root

absorptive

surface area

Chelate iron

or aluminum to

release P.

Dissolve Ca–P compounds

with acid exudates

Exude

phosphatase

enzymes to

release

P from organic

compounds

Exude substances

to stimulate

P-solubilizing

rhizobacteria.

Encourage

colonization by

mycorrhizal fungi that

help plants take up P

Six plant

strategies to

enhance P

availability

Root-Fungi alliance (Mycorrhizae) is a game changer for plants.

Sawyer, J.E., and A.P. Mallarino. 1999. Differentiating and understanding the Mehlich

3, Bray, and Olsen soil phosphorus tests. 19th Annual Crop Pest Management Short

Course, University of Minnesota.

Best case correlation data for two common P soil tests

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Dra

inag

e w

ate

r P, m

g / L

Total P Concentration

In Drainage WaterBroadbalk Experiment, England

0 10 20 30 40 50 60 70 80 90 100 110Olsen soil test P, mg/kg

From: Heckrath etal 1995

Agro

nom

icoptim

um

Nutrient Input-Output Balance on a Farm

Manure/Compost

Fertilizer

N fixation

Deposition

Feed: grain,

hay, salts

Bedding

Sales: crops,

animals, milk

Manure sales

Leaching

NOx losses

NH3 volatilization

Runoff

Erosion

Fast etal. 2009. Better Crops/Vol. 93 (No. 1)

Phosphorus buildup ‘sins’

of our grandfathers

Annual Total P Loading to Lake Erie

Lake Erie Algal Bloom,

Ohio soil photos:

Darrell Norton

Ca2+ & ionic Strength Reduce Dispersion

Gypsum

applied

to soil

surface

No

Gypsum

Before rain

Gypsum on surface

No tillGypsum Turbo-

tilled into soil

During rain

•Preferential

flow

•Bypass flow

•Macro-pore

flow

Hi -P

Lo -P

Water

Ca2+ precipitates soluble P

Cover crops can …

1. solubilize P

2. bring P to surface

P

J N Galloway et al. Science 2008;320:889-892

Internationally Traded

N(A) fertilizer (31 Tg N),

(B) grain (12 Tg N),

(C) meat (0.8 Tg N).

North America: ~ 6500 Tg N imported as fertilizer ~ 4500 Tg N exported as grain

Yield (kg N ha-1 yr-1)

N U

se E

ffic

ien

cy (

har

vest

ed /

app

lied

)

Zhang et al. 2015.

Goal: high NUE and YieldsWhere

we want to be.

Economists’ quadratic “model”:Y= a+bX+cX2

Interpretation of field responses to make nutrient application recommendations

Corn Crop Response to N Fertilizer

From Cerrato and Blackmer, 1990.

Recommended

optimum = 220

kg/ha

Y= a+bX=cX2

200 lbs N/ 158 bu~ 1.25 lbs N/ bu of yield

Recommended

optimum =

110 kg/ha

Corn Crop Response to N Fertilizer

105 lbs N/ 158 bu~ 0.65 lbs N/ bu of yield

On average, Maryland farmers are ahead of

other regions in nitrogen management

• Using less fertilizer with manadatory nutrient

management plans (1.2 0.8-0.9 lb N/bu

expected yield)

• Split applications of N

• Soil N tests (PSNT)

• Adapt-N and other

computer models to

predict N needs.

https://plantsciences.missouri.edu/nutrientmanagement/nitrogen/images/practices_figure2.jpg

Nitrogen Use and Corn Yield Trends in Maryland

https://stock-clip.com/video-footage/hand+squeeze+orange+juice+in+a+glass

Good

start…

https://www.pinterest.com/pin/549017010801557308/

Next

level…

5 ft2 corn rows

apart

Barley cover crop responding at Thanksgivingto UAN side-dressed to corn previous June

?

But Maryland, too, still has a “leaky” N system

Leftover N from June side-dressing being used by rye cover crop in Nov.

1

2 3

4

Veihmeyer, F.J. 1929. An improved soil sampling tube. Soil Science 27:147-152.

1 ft

2 ft

2 ft

2 ft

1 ft

2 ft

2 ft

2 ft

Transect of 8-10 cores per farm

0-15

15-30

30-45

45-60

60-75

75-90

90-105

105-120

120-135

135-150

150-165

165-180

180-195

195-210

Depth

, cm

0 5 10 15 20 25 30 35 40 45 50

Ammonium-N, kg/ha

SoybeanCorn

Crop

0-15

15-30

30-45

45-60

60-75

75-90

90-105

105-120

120-135

135-150

150-165

165-180

180-195

195-210

Depth

, cm

0 5 10 15 20 25 30 35 40 45 50

Nitrate-N, kg/ha

SoybeanCorn

Crop

*

*

*

*

*

*

*

*

*

NO3--NNH4

+-N

Means of 20 profiles. Paired side-by-side soybean & cornfields on 4 farms in PG, Howard and Kent Counties. Fall 2016.

Kg N /ha in each 15 cm layer

EARLY planting is essential for fall

cover crop activityAugust

1m

2m

0m

Nov 2015

Soil nitrate

NO3-N (kg/ha)

Dep

th (

cm)

Dep

th (

cm)

Apr 2016

ab

ab

ab

ab

ab

ab

ab

ab ab

ab ab

ab ab

ab a

ab ab

NO3-N (kg/ha)

Letter indicates sig different NO3-N in layer (p < 0.05, unless noted)

(0.08)

(0.09)

Field Suction Lysimeters Sample Soil Pore Water 4 ft Deep

• Data collected from February -April

• 3 replications 60’ x 300’ plots• Covers planted 15 Sept.1. No cover2. Sole rye3. Sole radish4. Triticale, radish, & clover

mixture5. Triticale, radish, & clover

mixture, planted two weeks later

Even cover crop frost-killed in December impacted pore-water nitrate at 100 cm deep in February-March-April

Nitrate in sandy soil pore water, 90 cm deep on 22 Feb. 2017

Triticale-clover-radish mix planted 15 Aug – 30 Sept

EPA Std

Down the drain? Changes (1960 to 2010) in pH & potassium concentrations in rivers across the US.

PotassiumIn rivers

Kaushal, et al. 2018. Freshwater salinization syndrome on a continental scale. Proc. Natl Acad. of Sciences.

KFertilizer

?

https://www.no-tillfarmer.com/articles/4664-reasons-to-no-till-plant-into-green-cover-crops

Keys to effective nutrient mgtwith cover crops:

• Plant early—get deep roots in Fall

• Include brassica + legume + grass

• Kill late—let covers work for you in Spring

• Soils are integrated systems.

• Soils are alive!

• Soils are deep.

• Each nutrient has its cycle

• Fertilizer can supplement, not supplant.

• Economic and environmental win-win.

• Lots of dollars still going down the drain.

Lots to think about…

Thanks for your attention.

And remember:• Start where you are. • Use what you have. • Do what you can.

- Arthur Ashe