how to manage your soil: nitrogen and phosphorus•you need to apply nitrogen fertilizer every year...

Virginia Tech – Crop and Soil Environmental Sciences

How to Manage Your Soil:

Nitrogen and Phosphorus

Rory Maguire Associate Professor and Extension Specialist


Main Strategy

1.Soil test

2.Follow the soil test recommendations


So we can all go home and relax?

Virginia Tech – Crop and Soil Environmental Sciences Rory Maguire

Questions • Predict plant available P and K by soil testing,

but not reliably N – why? • Nutrient requirements are not the same for all

flower beds/ yards – why? • Nutrient management harder with organic

sources than chemical fertilizer? • If we know 55ppm P in soil is adequate for most

plants, why do soil tests range from 2-2000ppm? Where are they?

• Do urban areas contribute much P and N to the Chesapeake Bay? If so how?

• From what depth do you take a soil sample?


True or False • You need to apply phosphorus fertilizer

every year “for the roots” • You need to apply nitrogen fertilizer every

year “for the shoots” • 10-10-10 fertilizer - the last of these

numbers tells you how much lime it contains • You only need to soil test turf every 3 to 5

years • You can only soil test in the spring • Soil sample from established turf should be

taken from 2-4” depth


Natural (wildlife, forest) 3%

Fertilizer (non-agriculture) and legacy sediment from stream channels (urban/

suburban)30%

Chemical fertilizer (agriculture)

18%

Manure (agriculture)27%

Municipal and industrial wastewater

22%

Phosphorus contributions to the Chesapeake Bay

(Bay Model)


Nitrogen Transformations • Mineralization: Conversion of organic-N to ammonium-N

[Soil Organic Matter: 97 to 99% of total soil N]

• Nitrification: Conversion of ammonium-N to nitrite and to nitrate by soil bacteria [plant available]

• Losses of N from soil – Uptake – Leaching and runoff – Volatilization – Denitrification


Phosphorus Transformations

• Organic P (30-50%)

• Inorganic P fairly insoluble • Adsorbed Inorganic

• Precipitates +

+

+

+


Phosphorus Generally Limiting in Freshwater Systems

University of Manitoba Experimental Lakes Area Research Project

+ P+C+N

- P +C+N

Picture taken in 1974

- P+C+N

+ P+C+N


Poultry house

Fertilized turf

Fish farm

Non-Point Source Pollution Hard to Trace

Corn field

WWTP


N P K

Erosion of particulate P

Release of soil P

Outputs Inputs

Fertilizer Manure

In-channel processes

Stream bank and bed erosion /

deposition &

biological - chemical

uptake / release

Tile flow

Subsurface flow

P leaching is small

Pathways of Transport


Agronomic Soil Test P in Virginia for years 2004-2006. (% soils rated “Very High”)

92,303 Commercial Samples

≥10%-Yellow

≥20%-Orange

≥33%-Red Heckendorn and Maguire, 2007


Agronomic Soil Test P Data Base in Virginia for years 2004-2006. (% soils rated “Very High”)

32,172 Lawn & Garden Samples ≥10%-Yellow

≥20%-Orange

≥33%-Red Heckendorn and Maguire, 2007


Soil pH Data in Virginia for years 2004-2006

<5.0 5.0-5.4 5.5-5.9 6.0-6.4 6.5-6.9 ≥7.0

Com

TurfGardens0

5

10

15

20

25

30

35

ComTurfGardens

%

Soil pH

Turf Commercial

Heckendorn and Maguire, 2007


Is turf environmentally good or bad?

Virginia Tech – Crop and Soil Environmental Sciences How Important is Soil Erosion?


How important is soil erosion? How important is soil test P?

Virginia Tech – Crop and Soil Environmental Sciences Should we fertilize?


Livestock Farm

Nutrients In: •Fertilizer

•Feed

Nutrients Out •Crops

•Animal Products

“ A livestock farm is much more complex. We often cannot balance inputs of feed and fertilizers with outputs.

This results in excess nutrients that can be lost to air or water or build up in soils.

Nutrient Balance

Nutrient: •Losses to air, water

•Accumulations in soils


Figure 5.20

Urban landscape is easy to manage if you follow soil test

Nutrients In: Fertilizer

Nutrients Out:

Nutrient Balance …and follow nutrient recommendations

Turf or other


Frederick Series, Shenandoah Valley

Soil Test P, ppm0 50 100 150 200

Dis

solv

ed R

eact

ive

P, m

g/L

0.0

0.1

0.2

0.3

0.4

0.5

0.6

JC-RockCA-RockTG-AugustaGS-Augusta

r2 = 0.75 Y = 0.0117 + 0.003365X

Mullins (2001)


Typical disturbed urban soil

Extractable nutrient (lb/acre)

Rel

ativ

e Yi

eld

(%)

0

20

40

60

80

100

"Critical Level"

Critical ValueFor P Loss??

P Lo

ss in

Sur

face

Run

off

Critical ValueFor Yield

Turf

Qua

lity

Critical value for quality

Virginia Tech – Crop and Soil Environmental Sciences Years

0 5 10 15 20 25

Soil

Test

P L

evel

(ppm

)

0

20

40

60

80

100

120

Critical Level

North Carolina

McCollum (1991)


So how do we manage high phosphorus soils?

• Apply zero P fertilizers – No organic fertilizers such as compost

• Control erosion – “critical source areas”

• Remove clippings

• Soil test every 3-5 years


N Movement P Movement

Nitrate Leaches!! P Leaches Slowly

We know how nutrients move: Runoff versus Leaching


We know the importance of soil test P versus fertilizer

0

20

40

60

80

100

120

0-46-0 Poultry litter Alum-trt litter Control

1.2 10.8

20.8

103

Fertilizer Type

Fertilizer P rate = 170 lbs P2O5/acre Soil test P = 75 mg P/kg Runoff within 24 hours of application


General Recommendations 1. Apply soluble fertilizer at no more than 0.5 lb

N/1000 ft2 at one time 2. Do not apply fertilizer when heavy rains are

imminent 3. Fertilization may NOT be required:

1. If homeowners or clients are pleased with the appearance of their landscape plants;

2. If plants are established; 3. If plants are flowering or fruiting, since exposure

to high nitrogen at this stage may impede development;

4. For trees, unless nutrient deficiencies exist.


General Recommendations 1. Fertilizer applied should be the minimal

amount to achieve a defined objective 2. Slow-release fertilizer may be an

advantage when nutrients cannot be applied as frequently

3. Maintain turfgrass, as low-quality turfgrass areas are more likely to produce runoff and off-site contamination than healthy, well-maintained turfgrass areas

4. 3’ “Ring of responsibility” around water courses


Good or bad lawn?

High or low input?


Low input lawn up close


Some of my Recommendations 1. Stabilize disturbed soils ASAP 2. Define objective 3. Apply small amounts of nitrogen at a time or

use slow release N 4. Soil test and follow recommendations 5. Soil test and follow recommendations 6. Ring of responsibility 7. Easier to reach large acreage through lawn

service providers than individuals 8. We know what to do, implementation the main

issue


QUESTIONS?

Rory Maguire, VT [email protected] (540) 231-0472

how to manage your soil: nitrogen and phosphorus•you need to apply nitrogen fertilizer every year...

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