Abstract:

Wheat grain falling number (GFN) is an important index that indicates the alpha_amylase activity and starch quality properties of wheat. The temporal dynamics of GFN and the effects of environmental conditions on GFN during grain filling have been scarcely reported systematically in the literature. In the present paper, field experiments were carried out in Harbin in 2002 to investigate temporal patterns in GFN, and how GFN was affected by N and P treatments and meteorological conditions during grain filling. Three genotypes of spring wheat with different qualities were used: a high protein_rich gluten genotype (`Wildcat'), a high protein_medium gluten genotype (`DN7742') and a low protein_poor gluten genotype (`NKH9'). The N and P applications included four treatments: 225 kg·hm^-2 N, 450 kg·hm^-2 P₂O₅ (F1); 300 kg·hm^-2 N, 300 kg·hm^-2 P₂O₅ (F2); 300 kg·hm^-2 N, 450 kg·hm^-2 P₂O₅ (F3) and 300 kg·hm^-2 N, 600 kg·hm^-2 P₂O₅ (F4). The results showed that temporal changes in GFN after anthesis could be fitted with a third_order convex curve (single peak curve), indicating that GFN rose in the initial stages and then fell during the middle and upper stages of grain filling. The effects of genotype and environmental factors on GFN formation were compared using this fitted curve. The temporal pattern in alpha_amylase activity fell to a greater extent during the initial stage and then rose weakly in the medium and upper stage. The results also indicated that from the 15th day after anthesis to maturity, with increasing nitrogen levels, medium phosphorus and high potassium levels (450 kg·hm^-2 P₂O₅, 600-630 kg·hm^-2 K₂O), GFN in the high protein_rich gluten genotype increased and the peak value rose but was delayed, and GFN decreased and the curve peak values fell but was ahead in both the high protein_medium gluten and low protein_poor gluten genotypes. GFN in the three genotypes all decreased with increasing phosphorus levels in the medium or low nitrogen treatments and at high potassium levels (300 kg·hm^-2 N, 600-610 kg·hm^-2 K₂O), and the curve differed among the three genotypes. The balance of nitrogen, phosphorus and potassium inputs was the key to forming higher GFN (lower alpha_amylase activity). Under conditions of moderate rainfall, the interaction of temperature and sunlight was the predominant influence on temporal formation patterns of GFN for different genotypes during grain filling, rainfall was the second, and PAR was the most sensitive among all the meteorological elements influencing the dynamic formation of GFN. Higher GFN was formed in all genotypes under conditions of high sunlight and high temperatures. Under conditions of high sunlight and temperature, the GFN in the high protein_rich gluten genotype increased with increasing PAR. The effects of meteorological conditions as well as differences among genotypes on GFN could be modeled by curve changes in the third_order equation. The variation of GFN in different genotypes under different environmental conditions (nitrogen and phosphorus fertilization and meteorological conditions) had significant affects on GFN.

Key words: Spring wheat, Grain falling number, Dynamic Change, Nitrogen and phosphorus level, Sowing date