The Nitrogen Cycle options for interventions. Rob Norton Regional Director, ANZ International Plant Nutrition Institute. @IPNIANZ Fertcare Sugarcane Workshops Brandon, Queensland Tuesday 11 April 2017.
Not another talk about N cycles? There is no shortage of N in bio-geological systems. There is a shortage of reactive-n in biological systems.
What does it tell us? Most of the N is in the atmosphere non-reactive N There are several sources of reactive-n (N R ) Fertilizers, N fixation, Combustion, Atmosphere. There are several pools or types of N. Organic, Mineral, Gaseous. N flows through these pools in reasonably predictable ways. There are some key pools of N R Plants/Water Nitrate, Ammonium Soil Organic N Air Nitrous/Nitric Oxides, Ammonia
Nitrogen Cascade deviations in the N Cycle Current view of the N flows through systems European Nitrogen Assessment - INI
Key processes in the N cycle/cascade Transformations are controlled biologically controlled Microbes. Oxygen Temperature Substrates Losses driven by Environment X Management
Key Transformations Formation of nitrate Ammonification is the formation of ammonia/ammonium from organic matter, Rapid, not often the rate limiting step Nitrification is a two step process Oxidation so requires oxygen Water (<70% WFPS) Temperature (>10 o C) Substrate (OC%/OM% 6ES Mineralisation Index Immobilization mineralisation Depends on C:N ratio of the organic material If there is relatively more C than N (>30:1) N is withdrawn from the mineral N pool.
Each % Organic carbon mineralizes ~ 25 kg N/ha. One t/ha legume DM fixes 35-45 kg N/ha (less removal)
The Ideal Fertilizer : nutrient release is synchronized with the crops nutrient requirements.
The problem with nitrate - NO 3 - Nitrate Nitrate is the major form in which N is taken up by plants It is an anion (negative charge) the plant cell inside is negatively charged so uptake is active requiring energy to assimilate it and then reduce nitrate to ammonium (biologically active form) Nitrate Reductase Energy cost to assimilate nitrate. Sugarcane can take up ammonium (and some amino compounds). Especially where nitrate is abundant Nitrate is mobile. Ammonium is adsorbed. Robinson et al. (2011) PLOS ONE 6(4): e19045. doi:10.1371/journal.pone.0019045
Enhanced Efficiency Fertilizers (EEF) Delays the nutrient availability for plant uptake for some period of time after application Stabilized Fertilizers products treated with inhibitors Low Solubility Fertilizers - slow release products Coated Fertilizers controlled release products
Stabilized Fertilizers: Nitrification Inhibitors Inhibit the process of nitrification (ammonium oxidisers) 64 selected chemicals tested as nitrification inhibitors Some examples (from Chen et al. 2009): Mostly operate by depressing Nitrosomonas activity (AOB) But do not affect ammonium oxidizing archea (AOA). Duration of activity Nitropyrin(<30 d), DMPP(25-70 d), DCD(25-55 d) High temperatures reduce duration.
Stabilized Fertilizers: Nitrification Inhibitors Much interest has been in reducing nitrous/nitric oxides Consequence of denitrification Gaseous loss No oxygen Mineral Nitrogen Ammonium Nitrate deep drainage Denitrification High OM Anaerobic High nitrate Warm
Effect of temperature and soil water Ammonium Chen et al. 2010. SBB 42, 660-664 Nitrate
Stabilized Fertilizers: Urease Inhibitors Used with urea inhibit the first step in converting urea to ammonia and carbon-dioxide hydrolysis Urea + Water ---------> Carbon dioxide + ammonia Urease is common in plant material so is rarely missing. Abundance does vary with plant material Rapid evolution of ammonia Lost to the atmosphere. NBTP - N-(n-Butyl) phosphoric triamide Two formulations Others but not commercialized.
Stabilized Fertilizers: Urease Inhibitors i% to 25% of N lost as ammonia Worst case scenarios for ammonia loss: GTB is rich in urease so needs high NBPT rates Cantaerella et al. 2008
Stabilized Fertilizers: Other Products Organic acids Humates Oils Neem oil Tars Biostimulants Seaweed Extracts
Low Solubility Fertilizers: Slow release Low solubility compounds Urea-formaldehyde reaction products (polymers) 1930 s. Commercialised 1940 s; Solid & Liquid products Several products not used widely if at all now Isobutyldiene urea (IDBU) No free urea, N released by slow hydrolysis, 8-12 weeks.
Coated Fertilizers: Controlled Release Products Provide a barrier between the urea and the soil and control the rate of hydrolysis. Many types of coats Sulfur coating Breaks down over time Allows water in Hydrolysis commences Integrity of the coat
Coated Fertilizers: Controlled Release Products Polymer/Resin - coating/encapsulation Polymers Rapidly growing area dual layering eg Polymer over S Incorporate inhibitors multi-coating
Water Release Profiles at Constant Temperature (ESN) % N Released 100 80 60 40 20 0 5 C 10 C 23 C 0 7 14 21 28 35 42 49 56 63 70 77 84 Time (days)
Coated Products for N a sample
What could EEF s do? Increase yield by ensuring more N get into the crop. Reduce leaching losses of nitrate by preserving it as ammonium or keeping it locked away. Reduce losses of volatile ammonia. Reduce the denitrification of nitrate by keeping it as ammonium or keeping it locked away Focus has been on N 2 O but losses as N 2 are agronomically significant
What does the evidence say? Variable response for use of inhibitors (grains). Leaching Nitrification inhibitors Light soils, wet. Denitrification High C, wet soils Volatilization Surface ammonium sources. Polymer coated Urease inhibitors
Assessing benefits of EEF s Is the loss process operating within the period of activity of the EEF? Did leaching /denitrification/volatilization conditions occur. Will the control of nitrate release be long enough? Duration of control period Match nitrate demand of the developing crop. Will the N saved provide a yield benefit to the crop? Problem of comparing at one rate. Example 1-100 kg normal Urea compared to 100 kg EEF Urea Example 2 100 kg normal Urea compared to 80 kg EEF urea» (Was N limiting?)
What to look for in the evidence for EEF s Y i e l d EEF Urea Normal Urea A. Reduced N for same yield B Higher yield with the same N rate N Rate Full rate range of both evidence at the lower values for the control
Summary EEF s are one part of achieving improved outcomes if you know where the losses are occurring. The Right Rate, The Right Time and The Right Place are also important
IPNI Documents.
Other references on EEF s Chein et al, 2009 Recent developments of fertilizer production and use to improve nutrient efficiency and minimize environmental impacts. Advances in Agronomy, 102, 267-321. Chen et al. 2008. Prospects of improving efficiency of fertilizer nitrogen in Australian agriculture, a review of enhanced efficiency fertilizers. Australian Journal of Soil Research, 46, 289-301. Trenkel 2010. Slow- and controlled-release and stabilized fertilizers. An option for enhancing nutrient use efficiency in Agriculture. IFA document library (download) Verberg et al. 2015. Ch. 7. Use of enhanced efficiency fertilizers to increase fertrilizer nitrogen use efficiency in sugarcane. In. A review of Nitrogen Use efficiency in sugarcane. SRA (download) Snyder 2016. Enhanced nitrogen fertilizer technologies support the 4R concept to optimize crop production and minimize environmental losses. International Nitrogen Conference, http://www.ini.com.au
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