Nitrogen fertigation effect on photosynthesis, grain yield and water use efficiency of winter wheat

Abstract

Excessive fertilization is common in North China Plain. It is essential to determine the extent to which reduction of nitrogen application rates has little impact on yield and understand its physiological basis. Two seasons of field experiments were conducted in a winter wheat field with three nitrogen (N) fertilization treatments, i.e. N3, traditional N application rates (290kgN hm−2), N2, ∼65% N application rates of N3 (190kgN hm−2) and N1, ∼40% N application rates of N3 (110kgN hm−2). Yield (Y) and water use efficiency (WUE) of N2 did not reduce significantly in both seasons despite that the instantaneous net photosynthetic rates (An) and stomatal conductance (gs) of N2 were significantly lower than those of N3. Y and WUE of N1 treatment reduced significantly in the second season. The reduction of Y was better indicated by photosynthetic capacity (Amax) in the grain filling stage (around 48–50 days after the irrigation of reviving stage, Dari 48–50) because the decrease of Amax in this stage was proportional to Y. The Amax and apparent quantum efficiency (α) of N2 measured on Dari 48–50 were not significantly lower than those of N3, which could be the reason of no significant reduction of Y for N2. Thus, the fertilization amount of N2 (190kgN hm−2) can be applied in this area to keep Y steady for at least two years. Differences of the relationships between Amax and biological factors among treatments and non-stomatal limitation of photosynthesis were also discussed. These results are important for understanding the mechanisms of yield reduction by reducing N application and provide scientific basis for application of fertigation.