Issues in P management for water quality protection

1
Issues in P management for water quality
protection

• Charles Wortmann
• cwortmann2_at_unl.edu

2
Factors affecting P loss

• Site/management factors
• Soil P levels 
• P application practices time, rate and method of
  application
• Management practices such as tillage, cover
  crops, conservation practices, etc.

• Transport factors
• Runoff
• Erosion rainfall, snowmelt and irrigation  
• Distance from center of field to a stream,
  water body, etc.
• Also, sub-surface drainage, percolation and
  under-ground movement of P to seepage areas

3
Main factors affecting P loss

• Previous weighting erosionsoil test P manure
  P application gt runoff distance fertilizer P
  application
• Current weighting erosion gtgt runoff soil test
  P gt distance to water body if within 300 ft gt P
  application (rate, time and method of application
  are somewhat important but P source is not of
  much importance.)

4
Much better information available today

• Most available information on P loss is from the
  last 10 years
• Much information is now available from medium to
  long term studies conducted in the field under
  natural precipitation as compared to information
  from micro-plot studies with simulated rainfall.

5
Medium to long term field studies 4 phases since
1998

• Effects of manure application on water, sediment
  and nutrient loss during year of application.
• Residual effect of previous applications for up
  to 6 yr
• Effect of deep plowing to invert excessively high
  P surface layer.
• Effect of vegetative filters at outlets.

6
Erosion and P loss

• Total P loss is proportionally related to erosion
• Dissolved P loss is less related

7
Sediment-P vs. dissolved P

• How important is sediment-P relative to dissolved
  P entering water bodies?
• Dissolved P is immediately available.
• How much sediment P will eventually be available
  to aquatic vegetation?
• Water P concentration
• How much re-suspension of sediments occurs?
• 70 eventually becomes available??

8
Soil test P and runoff P
Dissolved P concentration in runoff significant
at very low STP. The increase in concentration
from Bray-P1 20 to 400 ppm is a 7 fold increase.
9
Soil test P and runoff P
Sediment bound-P is the larger fraction. Total P
concentration in runoff is significant at very
low STP. The increase in Bray-P1 from 20 to 400
ppm caused a 3.2 fold increase in total P.
10
Manure P application and runoff P concentration

• P runoff risk decreases quickly with time after
  application.

11
Manure P application and runoff P concentration

• Similar event of time but less dramatic.

12
Manure application and sediment/ runoff loss

• Runoff and sediment greatly reduced by compost
  application.
• Residual benefit continued for several years.

13
Years 4 5 since last application
14
(No Transcript)
15
Manure application and runoff

• Both erosion and runoff decreased by about 2 for
  every ton/ac dry matter applied annually

16
(No Transcript)
17
(No Transcript)
18
Fertilizer vs. manure P

• For similar amounts applied, similar risk

19
P based application annual vs. once in 3-5 years

• P based is when P applied P removed
• P runoff risk is similar if P is applied annually
  as compared to at 4x rate once in 4 years (page
  10).
• Applying once in 4 years at 4x rate will
• Save time
• Reduce compaction
• Allow application of enough manure to fully meet
  N need for one year

20
(No Transcript)
21
Method of application

• Incorporation/injection vs. surface applied
• Surface application
• Increased risk during days after application
• Increased surface soil P, an on-going risk
• N loss and odors
• Incorporation effect on erosion risk?

22
Deep plowing to reduce P at the soil surface

• Soil with very stratified P levels plowed in 2004
• Mean P loss for 0405 was 54 less with plowing

23
P application to grazing lands

• Results in excessively high STP at the soil
  surface (page 11)
• Greatest runoff potential during the late spring
• Infiltration rates are slow due to high soil
  water content.
• A large proportion of the lost P is dissolved P

24
Cover crops

• Reduce P loss by reducing runoff and erosion

25
Erosion control

• Reduced sediment-P movement
• Increased sediment-P trapping for reduced total P
  loss
• Many conservation practices for sediment control
  may not have much effect on volume of runoff and
  dissolved P loss