Nitrogen Fertilization on Wheat Grain Protein Concentration in Argentina: A Meta-Analysis.

Wheat is a mayor crop in Argentina and over 60% is exported. However, Argentinean wheat is commercialized mainly without differential categories regarding milling quality. Improving milling quality through agronomical practices could make Argentinean wheat more competitive. Grain protein concentration (PC) is usually related to wheat’s milling quality and it is one of the easiest traits to modify through fertilization. The aim of this study was to summarize information available in Argentina on the effect of N fertilization on PC of wheat grain. A meta-analysis was conducted using data from 46 field trials (1995 to 2010) in the Argentine pampas, which included varieties from different quality groups. Trials included in the meta-analysis had standard experimental designs, contained at least one control and one N fertilization treatment, and presented yield and PC data. Treatments were divided into early N application (up to tillering stage) and late N application (after heading and close to anthesis). Treatments with both N and fungicide application were not included to avoid confounding effects. Results were pooled quantitatively using meta-analytic methods. Early season soil applied N fertilization increased yield but had no significant effect on PC, unless a very high N rate was applied, or growing conditions during grain filling were unusually dry and warm. Foliar fertilization close to crop anthesis increased PC 1.14% (95%CI: 0.93 - 1.36) over the control when enough N was applied (i.e. 20 to 40 N kg ha^-1).Therefore, early season N fertilization does not seem to be an economical sound way to increase grain PC. Late season foliar N fertilization increases PC, mainly when it is expected to be low (below 11%) due to growing conditions, genetics, or management. However, as PC depends significantly on growing conditions during grain filling, large variability can be expected on the response.