nutrient management in the bay watershed · underlying issue …understanding, and quantifying, the...
TRANSCRIPT
DEPARTMENT OF ENVIRONMENTAL
SCIENCE & TECHNOLOGY
Laboratory for Agriculture and Environmental Studies
Nutrient Management in
the Bay Watershed
Joshua McGrath
Assistant Professor
Soil Fertility and Nutrient Management Specialist
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 Phosphorus
From Maryland
Agriculture
39%
WWTP
20%
Forest
8%
Developed
33%
Sources of Nitrogen
from Maryland
Agriculture
36%
WWTP
25%
Forest
10%
Developed
29%
How the Bay Model Works
• 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
• 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
versus
Process Based Model
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
Crops
Local
Manure
Animals Soil
¼
¾
Ag P Cycle Has Become Fragmented
Animals Soil
Crops
Manure
? ? ?
Feed mill
Global
¼
¾
Delaware N Balance
0
10
20
30
40
50
60
70
80
90
100
1994 1996 1998 2000 2002 2004 2006
lbs/a
cre
/year
N-Management Based N-In/Out
Uses total N from manure
Does not account for various credits
Climatic Variation
Delaware P Balance
-5
0
5
10
15
20
25
30
1994 1996 1998 2000 2002 2004 2006
lbs/a
cre
/year
P-Management P-In/Out
Accounts for legacy P in soils
Education, Nutrient Management
Planning, and Poultry Diet Changes
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
Varies N rate according to yield
potential and N responsiveness
0
10
20
30
40
50
60
70
80
90
0.30
0.33
0.34
0.38
0.40
0.42
0.45
0.47
0.50
0.52
0.55
0.57
0.60
0.62
0.65
0.67
0.70
0.72
0.75
0.77
0.80
0.82
0.85
0.87
0.90
NDVI
Pre
sc
rib
ed
N R
ate
, lb
/ac
Poorest Crop Best Crop
Flat Rate
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.
http://www.enst.umd.edu/laes
Lab for Ag & Environmental Studies