Effects of nitrogen forms and amounts on nitrogen translocation, yield and quality of strong-gluten wheat

Objectives Nitrogen sources and application amount is not always reasonable in wheat production. This paper was to select the optimal nitrogen source and amount to increase of grain yield and quality of wheat, decrease field pollution, and at the same time found theoretical basis for reasonable and precise nitrogen application in forms and rates.

Methods A two-factor splitting plot experiment was conducted, with N form as the main factor (NO₃^–-N, NH₄⁺-N and CONH₂-N), and nitrogen levels of low (75 kg/hm²), medium (150 kg/hm²) and high (225 kg/hm²) as subplots. The N translocation, yield and quality of wheat were investigated.

Results 1) For all the three N supplying forms, the medium N rate of 150 kg/hm² showed the maximal nitrogen accumulation, the highest grain yield and harvest index at the wheat harvest stage. The medium N treatment also increased pre-anthesis N translocation and post-anthesis N accumulation. The biomass yields, all the grain protein fraction contents (except gliadin), protein contents, wet gluten contents, gluten indices, total starch, amylose, amylopectin, soluble sugar and sucrose contents were increased with the increase of nitrogen application rates. 2) Under the same N rate, the plant N content, biomass and grain yield of wheat with NO₃^–-N and CONH₂-N treatments were significantly higher than those with NH₄⁺-N treatment (P < 0.05), there were no significant differences between NO₃^–-N and CONH₂-N at medium and high N levels. As for quality of wheat, CONH₂-N was more benefit for increasing protein and gluten contents, and thus producing high grain quality; supplying of CONH₂-N was also promote N uptake and nitrogen production efficiencies, the NH₄⁺-N treatment, on the contrary, was the worst. 3) Nitrogen form affected spike number and nitrogen rate influenced the 1000-grain weight significantly. The highest yield was obtained with the medium N level (150 kg/hm²), and the best quality was obtained with the high nitrogen (225 kg/hm²). 4) Variance analysis showed that supplement of different forms and rates of nitrogen fertilizer significantly influenced N accumulation and its proportion at different growth stages of winter wheat (P < 0.01), and there was a highly significant interaction between N form and rate. Path analysis showed that the leaf N-translocation before anthesis directly affected yield with the direct path coefficient as 0.614.

Conclusions Amide nitrogen is found most suitable nitrogen form for wheat growth in the tested area. CONH₂-N in medium rate (150 kg/hm²) is suitable for increasing grain yield and nitrogen content, while in high rate (255 kg/hm²) is good for achieving high gluten grain. Therefore, nitrogen fertilization rate should be managed according to the yield and quality requirements in actual wheat production.