Modeling Wheat Growth, Nitrogen Accumulation, Partitioning and Remobilization with Pyg Model.

Wheat grain yield has increased constantly over time due to management and genetic improvement accompanied in some cases with high risk of reductions in grain protein content (GPC) and baking quality. This reduction in GPC may result from the imbalance between carbon assimilation and, nitrogen assimilation and remobilization during grain growth. The relationship among all the components of the carbon and nitrogen balance in the crop were analyzed and simulated with the model PYG. The results were contrasted with field data from experiments conducted during 2012, 2013, and 2014 with 11, 15 and 7 cultivars and three contrasting treatments, low nitrogen availability (lowN-lowN), high nitrogen availability (highN-highN), and low nitrogen availability until anthesis and high nitrogen availability thereafter (lowN-highN). The experimental setup allowed us to observe all the range of low-high grain yield and low-high GPC. The model was able to capture the variability in yield and GPC as well as the dynamics of growth. It contributed also to determine the relevance of pre and post anthesis nitrogen uptake and the relevance of nitrogen remobilization in grain nitrogen balance and protein formation. The proportion of nitrogen assimilated before anthesis was greater than after anthesis, however in the lowN-highN treatment and some cultivars of highN-highN, the amount of nitrogen assimilated in post anthesis was significant. The capacity to assimilate nitrogen in post anthesis was significantly related to leaf senescence in the field and in simulations, and contributed (as indicated by simulations) to a larger capacity to assimilate carbon during grain fill.