Effects of irrigation and nitrogen fertilizer rates on oilseed flax stem lodging resistance and yield

Although market demands for oilseed flax (Linum usitatissimum L.) gradually expanded in recent years, low yields restricted the development of oilseed flax. Lodging is a common problem in oilseed flax production which causes yield loss and quality deterioration. Effective water and fertilizer management is an important measure for improving oilseed flax yields. In order to investigate the effects of irrigation and nitrogen fertilizer application on lodging resistance and yield of oilseed flax, a field experiment was conducted in 2012-2013 with hybrid variety of "Longyaza1" oilseed flax in Yuzhong County, Gansu Province. In the experiment, the main plots were irrigated at 2 700 m³·hm^-2 (W₁) and 3 300 m³·hm^-2 (W₂), while the subplots were fertilized with nitrogen (N) at 0 kg·hm^-2 (N₀ or CK), 37.5 kg·hm ^-2 (N₁), 112.5 kg·hm^-2 (N₂) and 225 kg·hm^-2 (N₃). Water meter was used to strictly control irrigation amount, urea was used as N fertilizer, two-thirds as base fertilizer and one-third as top-dresser before budding stage. Then the effects of irrigation and nitrogen fertilization rates on lodging resistance traits (i.e., lodging resistance index, stem strength, stem chemicals contents) and yield of oilseed flax were determined. The results showed that with increasing irrigation, stem strength and lodging resistance index of oilseed flax declined. Then the plant height and gravity center height increased while stem diameter and culm wall thickness decreased. Also while above-ground dry weight increased, below-ground dry weight and the root-shoot ratio decreased with increasing irrigation. The contents of cellulose, lignin, soluble sugars and starch of oilseed flax stem decreased. Also with increasing nitrogen input, oil flax stem strength and lodging resistance index initially increased and then decreased. The height and gravity center height of the plant increased while stem diameter, culm wall thickness, root dry weight and root-shoot ratio initially increased and later decreased. Furthermore, above-ground dry weight increased and stem contents of various biochemical components and yield initially increased and then decreased. Further analysis showed that lodging resistance index of oilseed flax was positively correlated with stem strength, stem diameter, culm wall thickness, root dry weight, root-shoot ratio and then cellulose, lignin, soluble sugar and starch contents. Lodging resistance index of oilseed flax was also negatively correlated with plant height, gravity center height and above-ground dry weight. Compared with high irrigation, low irrigation increased stem strength, lodging resistance index and yield respectively by 30.55%, 41.06% and 0.53%. Thus excessive irrigation was did not enhance lodging resistance of oilseed flax. The highest stem strength and yield occurred under N₂ treatment. Compared with CK, N₂ treatment increased stem strength and yield respectively by 36.8% and 15.9%. Compared to high nitrogen treatment (N₃), N₂ treatment increased stem strength and yield respectively by 3.95% and 0.8%. Thus, neither too high nor too low nitrogen fertilization was necessary in oilseed flax cultivation. The appropriate amounts of irrigation and nitrogen fertilizer was very important for preventing lodging, ensuring high production and increasing productivity of oilseed flax. Under the experimental condition in this study, W1N2 treatment (of 2 700 m³·hm^-2 irrigation and 112.5 kg·hm^-2 pure N) was the proper combination of irrigation and nitrogen fertilizer for high oilseed flax yield.