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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #146149

Title: NITROGEN MOBILIZATION, NITROGEN UPTAKE, AND GROWTH OF CUTTINGS OBTAINED FROM POPLAR STOCK PLANTS GROWN IN DIFFERENT N REGIMES AND SPRAYED WITH UREA IN AUTUMN

Author
item DONG, SHUFU
item CHENG, LAILIANG
item Scagel, Carolyn
item FUCHIGAMI, LESLIE

Submitted to: Tree Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2003
Publication Date: 1/2/2004
Citation: DONG, S., CHENG, L., SCAGEL, C.F., FUCHIGAMI, L. NITROGEN MOBILIZATION, NITROGEN UPTAKE, AND GROWTH OF CUTTINGS OBTAINED FROM POPLAR STOCK PLANTS GROWN IN DIFFERENT N REGIMES AND SPRAYED WITH UREA IN AUTUMN. TREE PHYSIOLOGY. 2004. 24: 355-359.

Interpretive Summary: Understanding how trees store nitrogen (N) in the fall and use it for new growth is important for determining the appropriate timing and rate of fertilizer application for optimizing plant growth and quality. The effects of foliar urea application in autumn on N storage and use for new growth in the following season were studied in poplar nursery trees grown at different N concentrations. Stock plants of young poplar trees from cuttings were fertigated at different N concentrations during the first growing season and a subset of trees from each N fertigation treatment was sprayed with 3% urea in the fall. The following year total tree biomass and reserve N levels were estimated for each treatment and cuttings were taken from trees and planted in pots containing N-free medium and fertigated with either nutrient solution without N, or nutrient solution with labelled N (15N). To determine the dependancy of new growth on stored and available N during regrowth rooted cuttings were harvested in July, and analyzed for total N and 15N content. Urea spray increased total N content and N reserves of young poplar stock trees. Cuttings from plants sprayed with urea spray used more N for new growth than plants from cuttings that did not receive urea sprays. Available N in the media during regrowth reduced the percentage N used for new growth. More of the N resulting from foliar applied urea was used for new growth than other stored N. The new growth of cuttings was closely related with N storage when grown in N-free media, and was more dependent on current applied N when grown in N-abundant conditions.Our results suggested that the new growth of poplar cuttings in spring was dependent on available N, and N from foliar applied urea N was easier remobilized than other stored N.

Technical Abstract: Effects of foliar urea application in autumn on nitrogen (N) reserves and remobilization for new growth following season were studied in poplar trees grown at different N concentrations. Stock plants of young poplar trees were fertigated at different N concentrations during the first growing season and a subset of trees from each N fertigation treatment was sprayed with 3% urea in the fall. The following year total tree biomass and reserve N levels were estimated for each treatment and cuttings were taken from the middle of each single-stem tree and planted in 2-gallon pots with N-free medium. Cuttings were grown outdoors and fertigated weekly with either Hoaglands nutrient solution without N, or Hoaglands nutrient solution with 15N. In mid-July rooted cuttings were harvested, and analyzed for total N and 15N content. Growth of stock plants was positively related to N supply in the previous growing season. Foliar urea application in autumn had no effect on growth of stock plants even though urea sprays increased both N concentration and amounts in stems. Regrowth of cuttings from stock plants was correlated to reserve N levels in cuttings when grown in N-free media regardless of previous treatments. When N was supplied in the growth media the strength of the relationship between regrowth performance and reserve N levels in cuttings was reduced. Cuttings from trees treated with foliar urea and grown in N-free media remobilized more N for new growth compared to cuttings from trees receiving no urea spray. Available N in the media during regrowth reduced the percentage of remobilized N. Our results suggested that the new growth of poplar cuttings in spring was dependent on current applied N, and autumn foliar applied urea N was easier remobilized than the stored N.