Effects of Nitrogen Reduction Combined with Chitosan Oligosaccharides on the Root Growth and Rhizosphere Soil Enzyme Activity of Cottons
Improving the rhizosphere soil environment and promoting the development of cotton roots are of great significance for the healthy growth,yield,and quality of cotton.To explore the effect of reduced nitrogen fertilizer application combined with chitosan oligosaccharide on promoting cotton root growth and regulating soil enzyme activity,a pot experiment and field plot experiment were conducted.Five treatments were set,i.e.,no fertilizer,conventional fertilization(N 400 kg/ha,P2O5 140 kg/ha,K2O 130 kg/ha),20%nitrogen reduction fertilization,20%nitrogen reduction fertilization+450 g/ha chitosan oligosaccharide with a degree of polymerization of 2 to 6,and 20%nitrogen reduction fertilization+450 g/ha chitosan oligosaccharide with a degree of polymerization of 2 to 20.The effects of nitrogen fertilizer reduction combined with chitosan oligosaccharide with different degree of polymerization on cotton root growth and rhizosphere soil enzyme activity were studied.The results showed that,except for soil catalase,the two chitosan oligosaccharide treatments reduced soil urease,sucrase,and phosphatase activities to varying degrees.The largest decrease was observed in soil phosphatase activity,with reductions of 10.6%and 5.5%compared to the 20%nitrogen reduction treatment,for the 2 to 6 and 2 to 20 degree polymerization chitosan oligosaccharide treatments,respectively.The 2 to 6 degreepoly merization chitosan oligosaccharide treatment increased soil nitrate nitrogen content by 38.1%compared to the 20%nitrogen reduction treatment,while the 2 to 20 degree polymerization chitosan oligosaccharide treatment decreased soil nitrate nitrogen content by 43.4%.Additionally,the 2 to 6 and 2 to 20 degreepoly merization chitosan oligosaccharide treatments increased cotton root length by 64.2%and 40.1%,root surface area by 74.8%and 54.4%,and root volume by 106.2%and 73.2%,respectively,compared to those in the 20%nitrogen reduction treatment.These findings indicate that chitosan oligosaccharide with a degree of polymerization of 2 to 6 is more effective in promoting cotton root growth than that with a polymerization degree of 2 to 20.
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