Nutrient Management in
the Bay Watershed
Joshua McGrath
Assistant Professor
Soil Fertility and Nutrient Management Specialist
Laboratory for Agriculture and Environmental Studies
DEPARTMENT OF ENVIRONMENTAL
SCIENCE & TECHNOLOGY
Nutrient Management Basics
• There are 18 essential nutrients for plant
growth
• Two are a concern for water quality
– Nitrogen (N)
– Phosphorus (P)
• Nutrient use efficiency is generally the
percentage of nutrient applied that makes
it into the crop
Nutrient Management Basics
• A nutrient management plan guides application of
nutrients to maximize crop production, minimize losses,
and maintain or improve soil quality.
– Form, timing, placement, and amount
– Basically balances nutrient application with crop need
• How do we determine crop need?
– For phosphorus soil test is used to guide rate decisions
– For nitrogen no reliable soil test exists so a yield goal is typically
used (e.g. 150 bu/acre = 150 lbs-N/acre)
• A comprehensive plan includes conservation measures
to reduce losses
Nutrient Management Basics
• Sometimes nutrient inefficiencies can be economically efficient
• Climate and environmental conditions far outweigh management in
determining net nutrient use efficiency
• Environmentally significant nutrient losses are rarely economically
significant
• There will be nutrients lost to the environment (limit of technology)
with any farming operation
• N and P can be lost to the environment from fertilizer as easily if not
easier than from manure
– However, manure can be more difficult to handle and plan for
because it has very low and highly variable nutrient content
Modeled Nutrient Losses
Sources of Nitrogen
from Maryland
WWTP
25%
WWTP
20%
Agriculture
36%
Forest
10%
Sources of Phosphorus
From Maryland
Forest
Agriculture
39%
8%
Developed
Developed
29%
33%
How the Bay Model Works
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Riparian Forest Buffers and Wetland Restoration - Agriculture:
Coastal Plain Lowlands
Coastal Plain Dissected Uplands
Coastal Plain Uplands
Piedmont Crystalline
Blue Ridge
Mesozoic Lowlands
Piedmont Carbonate
Valley and Ridge Carbonate
Valley and Ridge Siliciclastic
Appalachian Plateau Siliciclastic
Riparian Grass Buffers - Agriculture:
Coastal Plain Lowlands
Coastal Plain Dissected Uplands
Coastal Plain Uplands
Piedmont Crystalline
Blue Ridge
Mesozoic Lowlands
Piedmont Carbonate
Valley and Ridge Carbonate
Valley and Ridge Siliciclastic
Appalachian Plateau Siliciclastic
Cereal Cover Crops on Conventional-Till:
Early-Planting - Up to 7 days prior to published first frost date
Late-Planting - Up to 7 after published first frost date
Cereal Cover Crops on Conservation-Till:
Early-Planting - Up to 7 days prior to published first frost date
Late-Planting - Up to 7 after published first frost date
Commodity Cereal Cover Crops / Small Grain Enhancement on
Conventional-Till:
Early-Planting - Up to 7 days prior to published first frost date
Late-Planting - Up to 7 after published first frost date
Commodity Cereal Cover Crops / Small Grain Enhancement on
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Conservation Plans - Agriculture1(Solely structural practices such as
installation of grass waterways in areas with concentrated flow, terraces,
diversions, drop structures, etc.):
Conservation Plans on Conventional-Till
Conservation Plans on Conservation-Till and Hay
Conservation Plans on Pasture Cover Crops1:
Conservation-Till:
Early-Planting - Up to 7 days prior to published first frost date
Late-Planting - Up to 7 after prior to published first frost date
Off-stream Watering with Stream Fencing (Pasture)2
Off-stream Watering with Stream Fencing and Rotational Grazing (Pasture) 3
Off-stream Watering without Fencing (Pasture)
Animal Waste Management Systems - Applied to model manure acre where
1 manure acre = runoff from 145 animal units:
Livestock Systems2
Poultry Systems2
Barnyard Runoff Control / Loafing Lot Management2
Conservation-Tillage1
Land Retirement - Agriculture
Tree Planting - Agriculture
Carbon Sequestration / Alternative Crops
Nutrient Management Plan Implementation - Agriculture
Enhanced Nutrient Management Plan Implementation – Agriculture1
Alternative Uses of Manure / Manure Transport
Poultry Phytase
Dairy Precision Feeding / and Forage Management1
Swine Phytase
Continuous No-Till:
Below Fall Line
Above Fall Line
Water Control Structures
Export Coefficient Model
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versus
Process Based Model
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There is tremendous debate
over the accuracy of all
these models
Underlying Issue
…understanding, and quantifying, the nutrient balance on a
farm, and at larger scales such as watersheds, represents the
first step in strategic nutrient management planning. This is
the highest level of planning for any operation and focuses on
the development of long-term goals and the broader
strategies needed to achieve these goals. (Sims et al. 2008)
We are importing nitrogen and phosphorus in
grain to the Chesapeake Bay Watershed
Traditional Ag P Cycle
¼
Crop
s
Soil
Local
Animals
Manure
¾
Ag P Cycle Has Become Fragmented
¼
Feed mill
Crops
Soil
Animals
¾
Global
Manure
???
Delaware N Balance
lbs/acre/year
N-Management Based
100
90
80
70
60
50
40
30
20
10
0
N-In/Out
Climatic Variation
Uses total N from manure
Does not account for various credits
1994
1996
1998
2000
2002
2004
2006
Delaware P Balance
P-Management
30
P-In/Out
Accounts for legacy P in soils
lbs/acre/year
25
20
15
10
5
0
1994
-5
Education, Nutrient Management
Planning, and Poultry Diet Changes
1996
1998
2000
2002
2004
2006
What we learned from the budgets
• Nutrient management has had an impact on a
statewide basis
• Phosphorus surpluses exist at the farm-gate due to
soil P accumulation not at the regional level
– BMP’s should address site specific concerns and be targeted
using a transport – source tool such as the P index
• Nitrogen surpluses exist as a result of how we make
recommendations
– NUE must be priority
– BMPs such as cover crops do not markedly improve NUE
Nitrogen Requirement is Complex
• Nitrogen requirement to achieve maximum yield for
cereal grains is determined by N responsiveness, N
availability, and potential yield.
– All three factors vary spatially and temporally
– All three factors are independent of each other and independent
of time.
• Soil type, climate, and previous management vary in
space and time and influence yield potential, N
availability, and N responsiveness independently.
• N surpluses exist due to our recommendations and
seasonal and spatial variability
• Example: A process based approach emphasizes cover
crops – which generally do not address the N surplus
Technology example:
Active Optical Sensors
• Emit light in the red
and near infrared
wavelength (60/sec)
• Average reflectance
measurements
calculated every
second
• Calculates simple
ratio or NDVI
– NDVI = (NIR –
Red)/(NIR + Red)
• Correlate sensor
reading to crop vigor
and N need
• Not affected by:
– Light conditions
– Atmospheric
conditions
– Variety
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90
Prescribed N Rate, lb/ac
Varies N rate according to yield
potential and N responsiveness
90
80
10
Flat Rate
70
60
50
40
30
20
Poorest Crop
Best Crop
0
NDVI
Thoughts on Phosphorus
• The P surplus – as it is commonly
portrayed – is a myth
– Incinerating poultry litter does not address the
issue and is morally questionable
• Proper manure management can help
address the N issue – slowly available N
source with higher nutrient use efficiency
Closing Remarks
• First we must address underlying issues
– Regional N surpluses
– Local P hotspots
• We don’t know everything yet
– New technologies
– System approach
• Keep global issues in mind when making local
decisions
– Ultimately global issues related to energy
consumption, food demand, and fertilizer supply will
surpass local issues of water quality.
Lab for Ag &
Environmental Studies
http://www.enst.umd.edu/laes
[email protected]