Overview – Nutrient Fate and Transport Mark B. David University of Illinois at Urbana-Champaign Presented at Building Science Assessments for State-Level Nutrient Reduction Strategies Nov. 13, 2012 What I will cover • what the problem is • N and P sources, balances, and river exports in the Mississippi River Basin (MRB) – Illinois as example – what is going to the Gulf • importance of modified hydrology (tile drainage) • timing of flow and nutrients; fate • myths; the challenge ahead What is the problem? • both local and downstream water quality problems from nitrate and total P – local: algal production due to P; drinking water for N – downstream: hypoxia in the Gulf of Mexico • USEPA requiring nutrient criteria in flowing waters Hypoxic zone, 2012 What was new (in 2007, now old) • reaffirmed previous assessment • importance of spring (April, May, June) nitrate • now phosphorus recognized as having role in Gulf • no one answer to fix problem – both agriculture and people (sewage effluent) • recommended 45% reduction in N and P going down Mississippi River Mississippi River Basin Nitrogen Mississippi River Basin Phosphorus Major Mississippi Subbasins Major Mississippi Subbasins Nutrient loads for 2001 to 2010 Nutrient yields for 2001 to 2010 Spring nitrate, upper Miss and Ohio Source of spring nitrate County Level Analysis of Mississippi River Basin • counties in MRB (all 1768) • 1997 to 2006 annual data on fertilizer, crops, animals, people, deposition • predictive model from watersheds applied to all MRB counties • both N and P From David et al. (2010) Nutrient Balances inputs + + - outputs - - Annual N Fertilizer Applications Fertilizer (kg N ha-1) 0.0 - 11.2 11.3 - 27.2 27.3 - 45.4 45.5 - 65.9 66.0 - 107.1 From David et al. (2010) Tile drainage is concentrated in the corn belt Fraction of county From David et al. (2010) Net N Inputs (NNI) kg N ha-1 Some counties negative, N from soil mineralization Illinois N budget through 2012 Linking N balances to N Export • hydrology overwhelming factor – channelization, tile drainage • can look at watershed N export as a fraction of net N inputs – most studies, about 25% – however in MRB we know it is larger in critical areas – can be > 100% in heavily tile drained watersheds Drainage by tiles and ditches Patterned tile systems Embarras River - Camargo Embarras River Embarras River Modeled January to June Nitrate Export Best model includes fertilizer, sewage effluent, and tile drainage Components of P Mass Balances • net P inputs = inputs – outputs inputs (fertilizer) outputs (grain harvest - human and animal consumption) • net indicates additions or removals from soil • little P (relative to N) is lost to streams, but it is biologically important • surface runoff and tile leaching • manure Fertilizer P Row Crop % Manure P Net P Inputs From Jacobson et al. (2011) Modeled January to June Total P From Jacobson et al. (2011) Illinois P budget through 2012 P from fields to rivers – Embarras River From Gentry et al. (2007) Particulate P from fields to rivers From Gentry et al. (2007) Importance of a Few Storm Events From Royer et al. (2006) Fate of N • limited in-stream losses of nitrate during high flow periods – Lake Shelbyville – Saylorville Reservoir • retention times too short • spring nitrate, headed to Gulf Fate of P • some sediment removal • problem of sediment already in streams/rivers – stream bank, bed erosion • algal biomass can move downstream • no way to easily get out of system (like nitrate) Source: Clay Soil and Water Conservation District, Minnesota What we know about nutrient sources • Upper Mississippi and Ohio subbasins are the major source of nitrate and total P – even more so in critical spring period • the tile drained cornbelt is clearly identified • mass balance of P has greatly decreased, but not N What can we do in agriculture? • given, – it is not typically over fertilization based on current rates and yields – may be zero or negative N & P balances in some areas of the tile drained Midwest • three types of conservation practices could help – nutrient-use efficiency – in-field management – off-site measures Potential Efficiencies -SAB report Perennial biofuels quickly reduce nitrate loss From Smith et al. (2013) Point sources in MRB? • sewage effluent and industrial (22% of annual N and 34% of P) • however, only 14% (N) and 20% (P) of spring load • not going to solve problem, but could help for P A few myths • no-till solves all problems • a few (bad) actors are the problem • over application of N (or P) is most of the problem • just targeting a few fields will solve most of the problem • edge of field denitrification can solve the problem • the response will take a long time (decades?) What’s making it difficult • more corn (and fertilizer) • more intensive tile drainage • warmer winters • more intense winter/spring precipitation • fall N in Illinois, Indiana, Ohio • the intensity of agriculture across the cornbelt • many (most?) practices to reduce nutrient loss don’t increase yield Conclusions • N and P balances don’t relate well to nitrate and P loss across the MRB (but could increase losses in a drought year) • counties with high fertilizer inputs have high crop fractions (& corn acres) and tile drainage – all lead to nitrate loss – corn & soybeans on tile drained land much more important than manure, deposition, or sewage effluent • P from both surface runoff and tiles – sewage effluent also important • high winter/spring flow and nutrient losses are a challenge, and seem to be getting worse Job ahead for us • 45% reductions in N and P will be quite difficult in upper MRB • we haven’t really started – not in any meaningful way • variety of methods and costs – many or most unrelated to yields • scale of problem is impressive • but, we do know how to do it!
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