Quantifying how winter wheat crops accumulate and use nitrogen reserves during growth

To reduce crop N requirements without reducing productivity it will be important to identify and quantify the inessential N in crop canopies. Field experiments established in October 2005 and October 2006 at ADAS Terrington, UK, and in June 2006 at Lincoln, New Zealand, tested wide-ranging N levels applied to one variety of feed winter wheat. Amounts of structural, photosynthetic and reserve N (SN, PN and RN, respectively) were defined and measured in components of the crop canopy (leaf lamina, leaf sheath, true stem and ear/chaff and grain) at anthesis and harvest, and the amounts of N remobilised from the PN and RN pools were calculated. At anthesis, RN accumulated for all N treatments in all experiments, and accounted for 44% of above-ground N (AGN) in optimally fertilised crops. This RN was principally located in the true stem, but was observed in all crop components at non-limiting fertiliser N treatments. Post-anthesis, RN appeared to be remobilised in preference to PN, thereby contributing to the maintenance of green area during the grain-filling phase and photo-assimilate production. The efficiency of post-anthesis N remobilisation of true stem RN was low (48%) compared to chaff (56%), leaf sheath (61%) and leaf laminae (76%), and in well fertilised crops significant quantities of ‘accumulation’ RN remained in true stem at harvest. The accumulation of significant quantities of RN at anthesis, even with deficient N supplies, suggests that it has a functional role during the grain-filling phase of growth. As ‘accumulation RN’ does not contribute to either the quantity or quality of grain, it reduces N-utilisation efficiency (UTE). Potential to improve UTE exists through increasing RN use during grain-filling and reducing ‘accumulation RN’ in non-photosynthetic organs.

► Amounts of structural, photosynthetic and reserve N were quantified in plant components at anthesis and harvest in wheat.
► Reserve N was demonstrated to be principally located in the true stem in high N conditions.
► Post anthesis N remobilisation of reserve N was 48% in true stem and 76% in the leaf lamina in high N conditions.
► Results suggest high N-use efficiency may be associated with increasing the use of reserve N in the true stem during grain-filling.