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

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

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: 10.1038/NGEO2693

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)

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.

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

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

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

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

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

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

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

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?

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

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?

Questions?