Dynamics of biomass and N accumulation of alfalfa under three N fertilization rates

• Published in: Plant and soil Vol. 219; no. 1/2; pp. 177 - 185
• Main Authors: Belanger, G, Richards, J.E
• Format: Journal Article
• Language: English
• Published: Dordrecht Kluwer Academic Publishers 01-01-2000; Springer; Springer Nature B.V
• Subjects: Aboveground biomass; Accumulation; Agronomy. Soil science and plant productions; Alfalfa; ammonium nitrate; application rate; Biological and medical sciences; Biomass; Biomass production; Defoliation; dry matter partitioning; Fertilization; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; growth; leaves; Medicago sativa; Nitrogen; nitrogen content; Nitrogen fertilization; Nitrogen fixation; Nitrogen, phosphorus, potassium fertilizations; nutrient uptake; Plants; Regrowth; Rhizobium; roots; seed inoculation; Seeding; shoots; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Soils; New Brunswick; Nitrogen fertilization; Medicago sativa; Regrowth; Biomass; Nitrogen; Forecast model; Inorganic element; Field experiment; Dose activity relation; Absorption; Leguminosae; Dicotyledones; Angiospermae; Nutrient; Spermatophyta; Fodder crop; Biological accumulation
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1023/a:1004749828745

The dynamics of biomass and N accumulation following defoliation of alfalfa and the application of N fertilization has rarely been studied under field conditions, particularly in the seeding year. Our objectives were to determine the effect of N fertilization on the dynamics of biomass and N accumulation during the first regrowth of alfalfa in the seeding year, and to determine if a model describing critical N concentration developed for established stands could be used in the seeding year. In two separate experiments conducted in 1992 and 1993, the biomass and N accumulation of alfalfa grown with three N rates (0, 40 and 80 kg N ha⁻¹) were determined weekly. Maximum shoot growth was reached with 40 kg N ha⁻¹ in 1992, and maximum shoot growth was not reached with the highest N fertilization rate in 1993. Nitrogen fixation, root N reserves and soil inorganic N uptake when no N was applied were, therefore, not sufficient to ensure non-limiting N conditions, particularly when growth rates were the highest between 14 to 21 d after defoliation. Nitrogen fertilization increased shoot biomass accumulation in the first 21 d of regrowth, biomass partitioning to the shoots and shoot and taproot N concentrations. The model parameters of critical N concentration developed by Lemaire et al. (1985) for established stands of alfalfa were not adequate in the seeding year. The N requirements per unit of shoot biomass produced are greater in the seeding year than on established stands, and this was attributed to a greater proportion of leaves in the seeding year.