2. Optimizing P Management for Multiple Benefits
Include
Michael Weintraub, Graham MacDonald, Laura Johnson, Phillip Haygarth, Tom Bruulsema, Tiequan Zhang, Jianbo Shen, Paul Withers, Douglas Smith, Andrew Sharpley, Katrina Macintosh, Donnacha Doody, Helen Jarvie, Lydie-Stella Koutika, Susanne Kraemer, Michael Miyittah, Richard McDowell, Stephen Powers

3. P can runoff in stormwater and cascade downstream
Once downstream,
P can have unintended impacts on the “goods and services” we receive from the natural environment – Ecosystem Services
This seems disconnected from the first part of the talk. Maybe start with MacDonald et al. for big picture and then go into specific examples of impacts are manifested
Adapted from MacDonald et al 2017

4. Inputs and Outputs of Excess P are often Disconnected
We do not see decreased outputs in response to decreased inputs yet
This is a complex issue because the impacts of excess P are separated in space and time – illustrated by Thames and/or Maumee input/output figure from Steve’s Nature paper. Gross P input includes fertilizer import, and for the Thames only, detergent import. Gross P output includes river export, food/feed exported from the basin via trade and, for the Thames only, disposal of food waste to landfill and disposal of sewage biosolids to landfill, sea or incinerator
Powers, S. M. et al. (2016). Long-term accumulation and transport of anthropogenic phosphorus in three river basins. Nature Geosciences DOI: /NGEO2693

5. 7.4mg/kg 20.7mg/kg Increased soil available P in China
Average soil available Olsen-P, 1980
7.4mg/kg
Soil Olsen-P <10 mg/kg accounting for 79.4%
Average soil available Olsen-P, 2006
20.7mg/kg
Soil Olsen-P <10 mg/kg accounts for 23.5%
(Li et al., 2011, Plant and Soil)

6. Not all P losses are from excess P applications (timing and placement)
Phosphorus loss associated with fertilizer application just prior to precipitation
Honey Creek in Ohio
Intense rainstorms following broadcast of P can generate high P concentrations in runoff but the direct agronomic or economic importance can be minimal.
As the time intervals increase between surface broadcast P applications and runoff-producing rainfall events, DRP concentrations spike less.

7. Managing for Crop Productivity is not Enough…
Soil test P within recommended levels
Yet losses of dissolved P have increased from most tributaries

8. Ecosystem Services Metrics
Can we manage agriculture to achieve benefits aside from just productivity?
Crop yield
We need cost/benefit research to make this a reality
Ecosystem Services Metrics
Biodiversity
Cost/ha
Phosphorus Losses
Hypothetical soil P

9. Ecosystem Services Impacts of P
Food-fiber-fuel
Nutrient cycling
C storage
Water retention
Landscape aesthetic
Impacts of P
Crop productivity
Biodiversity
Water quality
Fish
Recreation
Property value
link between P and water quality is simplest, but now we realize links to ES
Start with just watershed image at the bottom
Adapted from MacDonald et al 2017

10. Practices to Improve P Management
Reuse organic P waste
Draw down P in P saturated soils
Water management
Soil erosion control
Improved fertilizer efficiency
link between P and water quality is simplest, but now we realize links to ES
Start with just watershed image at the bottom
Adapted from MacDonald et al 2017

11. Changes at the Small Scale can Benefit the Entire System
link between P and water quality is simplest, but now we realize links to ES
Start with just watershed image at the bottom
Adapted from MacDonald et al 2017

12. Example: Soil P Drawdown
Soil P was sufficient to support crop P without added P for over 9 years
Soil P loss (tile) with P draw-down decreased by 35%, relative to continuous P addition
Tile drainage P loss accounts for ~85% of total soil P loss
These results suggest that P drawdown is slow; clay loam soil in ON CA

13. But, There can be Tradeoffs…
Key point: unintended consequences
One important interaction between tillage and phosphorus application needs to be considered. With less tillage, there is more stratification of the soil test. These long-term data from Indiana show that the top two inches in no-till increase to as much as three times the level of the top six inches. The top is what interacts with broadcast phosphates, and with surface runoff, and with the water running down macropores. In soils susceptible to either, stratification needs to be managed. Higher soil test P means less soil capacity to hold onto freshly applied P. And the high soil test P in itself is a chronic contributor – every runoff event is enriched, not by a lot, but higher than with a normal optimum level of soil test P.
Blended phosphorus and potassium fertilizers were broadcast applied before fall primary tillage; the last application before the present soil sampling occurred in November of 2002 at a rate of 224 kg/ha (0-46-0) and 336 kg/ha (0-0-60), respectively (West et al., 2002). Why did the no-till accumulate more total P? Note that corn yields were 5% and 15% less for no-till in rotation and continuous, respectively. But the lower removal of P in no-till may not be the full answer. The rich organic matter may also be keeping a greater fraction of the P in the available form, at least in a form extractable by the soil test.
Soil test P vs. depth in a long-term tillage experiment in poorly drained silty clay loam soil near West Lafayette, IN. Moldboard and chisel plots plowed annually to 20 cm. Data from Gál (2005) and Vyn (2000). P Fertilizer applied by broadcast. A

14. What does a holistic approach to P management look like?
We can implement all aspects of the 4R nutrient stewardship at the farm scale to maximize crop productivity and water quality
Right source: use recycled sources of P fertilizer such as struvite
Right rate: use soil tests that incorporate soil buffering capacity to ensure proper application of P
Right time: match applications to crop demand and low risk of runoff
Right place: apply fertilizer below the surface of the soil to prevent unintentional losses
Each point of stewardship comes with a cost
Major challenge what is the cost of maintaining water quality relative to benefit of high crop productivity?
End here
A holistic approach to P management will provide multiple benefits on a wide scale throughout the economy – this point requires specific examples – what does this actually mean in real life?

15. Possible Changes to Manage for Multiple Benefits (US)
Component
Agronomic
Agronomic + water quality
Soil P test
Mehlich 3
Mehlich 3 + buffering capacity
Soil sampling
Single depth only
Stratified or gridded sampling
Interpretation
Agronomic optimum
Economic optimum
Fertilizer sources
Standard fertilizer
Use struvite
Fertilizer application
Single rate application
Variable rate application
Crop system
Current varieties/rotations
Designer varieties/rotations to improve soil P acquisition efficiency
In order to manage for multiple environmental benefits, changes to ag. Practices required

16. Conclusions This is a complex issue
P sources and impacts are not connected in time and space
P loss occurs without excess P application
Managing P often gets more complicated and expensive the further you get from its source
But benefits of small scale solutions cascade to the large scale
Agricultural management should involve more than one ecosystem service (productivity), but this is limited by a lack of knowledge about cost/benefits of specific ecosystem services
A holistic approach to P management will provide multiple benefits on a wide scale throughout the economy
End here
A holistic approach to P management will provide multiple benefits on a wide scale throughout the economy – this point requires specific examples – what does this actually mean in real life?

17. Questions?