Managing Agricultural Phosphorus for Environmental Protection

J. Thomas SimsPeter J.A. Kleinman

Nature of nonpoint P• Wide array of processes

transport P from ag fields to surface and shallow groundwater– Erosion– Interflow– Overland flow– Matrix flow– Preferential flow

• P controls eutrophication in most freshwater systems

Eutrophication• P pollution became

apparent in the 70’s and 80’s

• Reduction in point sources helped in some places

• Still the most pervasive surface water impairment in the US

• Ag is now the major source of P

Controlling non-point

• Much more difficult than point source– Need cooperation from growers

• Some voluntary measures have become mandatory.

• Many new BMP’s in place now, and also being reasearched.

Definitions“A practical affordable

approach to conserving a farm’s soil and water resources without sacrificing productivity”

-Ontario Federation of agriculture, 2004

“Management practices used to control the generation or delivery of pollutants from agricultural activities to water resources and to prevent impacts to the physical and biological integrity of surface and groundwater”

-Osmond et al. 1995

Questions

• Conserving resources and improving agricultural productivity

Or

• Practices implemented, sometimes involuntarily, to reduce non-point source pollution.

2 key principles• Control of soil erosion

– Riparian buffers– Grass filter strips– Terraces– Strip cropping– Constructed wetlands

• Nutrient management– Prudent application – Recommended

practices to minimize P loss

Tillage

• Reducing tillage decreases particulate P losses

• But…• Conservation tillage

can increase dissolved P losses over time

Tillage

Manure

• Highly over fertilized soils in regions dominated by animal production

• P has accumulated in these soils, well above the amount for optimum for crop growth

• Can be significant sources of soluble and bioavailable particulate P losses

• Would take many years to remediate• Comprehensive nutrient management plans

need to be adopted

Scale?

• Look at the cause of the problem

• Alternatives to land application of manure

Nutrient management

• “Managing the amount, source, placement, form and timing of the application of nutrients and soil amendments.”– Budget and supply nutrients for plant

production– Properly use manure or organic byproducts– Minimize ag nonpoint pollution– Maintain or improve the physical, chemical,

and biological condition of the soil

NMP’s need to address:

• To effectively scale up NMP’s, some considerations need to be taken into account.

• The watershed• County/state• The region• Nation/international region

Farm scale BMP’s

• Balance inputs and outputs– Inputs: animal feeds,

fertilizers, biosolids, uptake from subsoil and natural additions

– Outputs: harvested portions of crops, animal products, losses to air, soil, or water.

Fertilizer management• Excessive import of

mineral fertilizers, not seen as a problem

• Regular soil testing is key

• Prescriptive application of mineral fertilizer using methods that maximize the availability of P

Feed Management

• Amount of P in feed for CAFO’s

• Import more P in feed than is exported in crops and animal products

• 50% or more of the imported P stays on the farm

Reductions in CAFO P• In swine and poultry,

alternative feeding strategies can reduce output

• Phytase enzyme• Dairy cattle typically

overfed P• Grass based grazing

systems better, up to 80%

Manure Export

• Reduce nutrient surpluses by re-locating animal manure to farms deficient in P

• High costs relating to the transport of the manure

• Pelletizing poultry litter• In DE, ~1440 Mg of P were moved to

different farms, out of ~6800 Mg produced that year.

Manure storage

• Provides flexibility for manure management

• Allows land application for when crops are growing

• 3-month storage resulted in the most cost-effective control of non-point P

Barnyard and feedlot• Combination of impervious surfaces and high

concentrations of animals causes these areas to be point source polluters

• Improved barnyard management resulted in the largest reduction in watershed P, and was the most cost-effective BMP studied

• A vegetative filter removed 90% of total P from milk house waste on a dairy farm

• Constructed wetlands slow runoff, and let particulate matter settle.

Soil testing• Should be an integral part

of any NMP• Helps save money, and

gauges the effectiveness of your current practices

• NRCS recommends 3 year minimum testing

• 15-30 cm deep• Traditional P tests

correlate well with runoff and subsurface flow

Manure testing

• Concerns: obtaining a representative sample, and rapid application of manure after testing

• Primarily concerned with Nitrate• P testing is now becoming mandatory• Difficult to estimate how much will be plant

available

Timing and methods

• Methods of application greatly influence P loss in runoff

• Often broadcast, maybe tillage

• Incorporation is best, also methods to reduce erosion help

Methods

• Effective depth of interaction is 1.3 -37.4 mm

• Cultivating reduces soluble P losses, but increases particulate P loss

• Injection and knifing are good solutions

Application Rate

• Has a direct impact on dissolved P losses from broadcast manures

• A strong relationship exists between dry matter application rate of various manures and the fraction of P in dissolved form (graph on previous slide)

• Starter fertilizer is often added even if it is not needed to boost yields

Timing

• Immediately after application, risk for loss is highest

• Declines over time as P is bound in the soil

Management of Runoff, Erosion, and subsurface flow in Ag fields

Transport oriented:– Improve infiltration– Reduce slope length– Increase soil cover– Intercepting runoff

water

Cultivation Practices

• Conservation tillage– Leaves at least 30% of soil covered with

residue• Over time, can increase the amount of

dissolved P losses• Best solution?

Cover Crops

• Grasses, legumes, or other crops that protect the soil, and scavenge excess nutrients

• Improve soil structure, and SOM• Where dissolved P is the greatest

concern, cover crops aren’t as effective

Artificial Drainage

• Improve soil productivity

• Decrease runoff and soil erosion

• May dump directly into water bodies, reducing the impact of other BMP’s

Buffers

Grassed Waterways

• Prevent channel erosion

• Can intercept runoff and break up slope length

• Up to 20x erosion prevention

• Contour cultivating is similar

Irrigation Management / Stream bank Protection

• Irrigation can greatly increase erosion, exacerbating particulate P losses

• Application timing can greatly reduce this• Exclude livestock from near streams• Up to 76% reduction in P loads• Funding for bank protection is available

from the NRCS

BMP Systems

• While one BMP can be effective at reducing P pollution, combinations of BMP’s are the most effective.

• Varies from region to region• 75% of critical areas in a watershed must

be treated with appropriate BMP’s to achieve water quality standards

Watershed Scale• Impacted by many

farmers and point sources

• Prioritize the watersheds in an area

• In the bay, 25% of agland used BMP’s, after 10 years, only 9% reduction in non point pollution

• Even if P applications stop, could take 20 years to decline

Delmarva Peninsula• In 96’ environmental

groups filed a lawsuit against USEPA

• EPA made 10 yr timetable

• Public got involved after fish kills

• MD and DE passed Nutrient management laws

Research on BMP’s / PSI

• Develop improved animal feeding strategies

• Stabilize P in less soluble forms

• Improve PSI to provide more quantitative estimates of P loss.

• Phosphorus Site Index

• Site specific evaluations of P transport factors

• Required for areas where the M-3 test value is >150 mg/kg

Lake Erie• In the 60’s and 70’s suffered from severe

eutrophication from excessive P loading• Impacts on aquatic species were so extreme the

lake was considered “dead”• Since then, major improvements have been

made• An average of $7000 per farm was spent in the

river watersheds.• Education is credited with reducing fertilizer

sales by 37% and 25%

Future directions

• Since not all farms or fields contribute equally, there is no silver bullet

• Finding critical areas is important• A more rapid means to conduct P loss

assessments is needed, particularly at larger scales.

• Many BMP’s are limited to single fields or farms

Cost effective and flexible• Best way to encourage

growers is to reduce costs

• Worries over point source• Many local governments

have adopted some policies

• Ability to change as new research is done