Ni­tro­gen: A lim­it­ing fac­tor for crops that has im­pli­ca­tions for the en­vi­ron­ment

Prairie Post (East Edition) - - Farm News - COUR­TESY AAFC

Ni­tro­gen is es­sen­tial for crop growth, but in ex­cess, it can harm the en­vi­ron­ment. Ni­tro­gen is also the most lim­it­ing nutri­ent for crop pro­duc­tion in Canada and so is usu­ally ap­plied in the largest quan­ti­ties com­pared to other el­e­ments. There­fore, un­der­stand­ing how to man­age it is im­por­tant to both farm­ers and those con­cerned about the en­vi­ron­ment.

Re­searcher Dr. Mervin St. Luce of the Swift Cur­rent Re­search and De­vel­op­ment Cen­tre is ad­vanc­ing our knowl­edge of soil ni­tro­gen cy­cling and plant nutri­ent up­take mech­a­nisms in or­der to de­velop site- and crop­spe­cific ni­tro­gen man­age­ment guide­lines. With these science-based tools, farm­ers can make bet­ter-in­formed de­ci­sions on how best to man­age their ni­tro­gen fer­til­izer uti­liza­tion.

“My re­search aims to im­prove ni­tro­gen use ef­fi­ciency by match­ing crop ni­tro­gen de­mand with ni­tro­gen sup­ply from soil, from fer­til­izer added, from crop residue de­com­po­si­tion, and bi­o­log­i­cal fix­a­tion by legumes.” said Dr. Mervin St. Luce, Re­search Sci­en­tist, Agri­cul­ture and Agri-Food Canada.

Dif­fer­ent crops in­ter­act dif­fer­ently with ni­tro­gen

Dif­fer­ent plant species re­quire dif­fer­ent amounts of ni­tro­gen to ob­tain the great­est po­ten­tial yield. Dr. St. Luce, along with col­leagues from across Canada, has ob­tained re­search fund­ing through the Di­verse Field Crops and the Canola Agri-Science Clus­ters of the Cana­dian Agri­cul­tural Part­ner­ship for work on ad­vanc­ing our knowl­edge of ni­tro­gen use ef­fi­ciency in plants.

The ni­tro­gen re­quire­ment ver­sus yield re­la­tion­ship is de­ter­mined through re­search tri­als and pro­vided to pro­duc­ers as a ni­tro­gen re­sponse curve. As new high­yield­ing va­ri­eties of well-stud­ied crops are re­leased, such as wheat and canola, new re­sponse curves need to be de­ter­mined. How­ever, for less com­mon (di­verse) crops, in­clud­ing camelina and sun­flower, much less is known about the re­la­tion­ship be­tween ni­tro­gen re­quire­ments and peak yield po­ten­tial, so more re­search is needed to de­ter­mine the most ef­fi­cient use of ni­tro­gen fer­til­izer.

Team­ing up with Dr. Bao-Luo Ma of the Ot­tawa Re­search and De­vel­op­ment Cen­tre, Dr. St. Luce is colead­ing a project that will pro­vide canola pro­duc­ers with a com­plete in­for­ma­tion guide of site-spe­cific ni­tro­gen man­age­ment prac­tices for dif­fer­ent agri-eco­zones. This project will in­ves­ti­gate the crit­i­cal roles of root ar­chi­tec­ture in ni­tro­gen ab­sorp­tion, root an­chor­age strength (in­volved in lodg­ing re­sis­tance) and trait vari­a­tions. At the same time, Dr. St. Luce and Dr. Ma will be test­ing soil and plant di­ag­nos­tic tools used in as­sess­ing ni­tro­gen suf­fi­ciency. Stud­ies are also look­ing at how pulse crops, such as field peas, chick­peas, lentils and beans that are able to “fix” (add back) ni­tro­gen in the soil, play into the ni­tro­gen cy­cle.

Dif­fer­ent farm­ing prac­tices also im­pact ni­tro­gen use ef­fi­ciency

Per­haps even more im­por­tant than the type of crop grown is the in­flu­ence of agri­cul­tural man­age­ment and other hu­man ac­tiv­i­ties.

“From the way ni­tro­gen fer­til­izer is ap­plied, to the form and rate at which it is ap­plied, to the treat­ment of crop residue (such as straw and chaff left af­ter the crop is har­vested), to the choice of her­bi­cides or whether to use or­ganic crop­ping meth­ods, the farm­ing prac­tices cho­sen have a big im­pact on ni­tro­gen,” said Dr. St. Luce.

One way to study how ni­tro­gen moves through the crop and soil is by us­ing Ni­tro­gen-15 iso­topes as a tracer. In part­ner­ship with other AAFC sci­en­tists, Dr. St. Luce is us­ing this tech­nique to si­mul­ta­ne­ously trace and ac­cu­rately quan­tify ni­tro­gen de­rived from above-ground and be­low-ground crop residues left in the field, as well as from ni­tro­gen fer­til­izer ap­plied to crops. This will help to quan­tify the amount of ni­tro­gen a farmer should ex­pect in the soil af­ter grow­ing a pulse and how long it will be there, as well as a com­par­i­son of leav­ing – or not leav­ing - pulse crop residues on the ground. Ad­di­tion­ally, re­sults from this study will pro­vide a bet­ter un­der­stand­ing of the fate of ni­tro­gen fer­til­izer ap­plied to crops with re­spect to the crop­ping sys­tem and ap­pli­ca­tion rate.

Key Dis­cov­er­ies/Ben­e­fits:

• Ni­tro­gen is the most lim­it­ing nutri­ent for crop pro­duc­tion and is usu­ally ap­plied in the largest quan­ti­ties.

• Ni­tro­gen man­age­ment is very im­por­tant be­cause ni­tro­gen that is not taken up by crops is sus­cep­ti­ble to be lost from the soil plant sys­tem through var­i­ous path­ways, and can af­fect air and wa­ter qual­ity.

• AAFC re­search aims to im­prove ni­tro­gen use ef­fi­ciency by match­ing crop ni­tro­gen de­mand with ni­tro­gen sup­ply from soil, from fer­til­izer added, from crop residue de­com­po­si­tion, and bi­o­log­i­cal fix­a­tion by legumes.

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