title: Effects of 15N application frequency on nitrogen uptake efficiency in citrus trees.
abstract: Two irrigation systems were used to compare nitrogen uptake efficiency in citrus trees and to evaluate the NO3- runoff in "Navelina" orange trees [Citrus sinensis (L.) Osbeck] on Carrizo citrange rootstock (Citrus sinensis x Poncirus trifoliata Raf.). These were fertilized with 125 g N as labelled K15NO3 and grown outdoors in containers filled with a sand-loamy soil. Two groups of 3 trees received this N dose either in five equally split applications by a flooding irrigation system or in 66 applications by drip. Trees were harvested at the end of the vegetative cycle (December) and the isotopic ratios of 15N/14N were measured in the soil-plant system. The N uptake efficiency of the whole tree was higher with drip irrigation (75%) than with flooding system (64%). In the 0-90 cm soil profile, the N immobilized in the organic fraction was similar for both irrigation methods (around 13 %), whereas the N retained as NO3- was 1% of the N applied under drip and 10% under flooding. In the last case, most of NO3- remained under root system and it could be lost to leaching either by heavy rainfalls or excessive water applications. These results showed that a drip irrigation system was more efficient for improving water use and N uptake from fertilizer, in addition to potentially reduced leaching losses.
authors.affiliation: Departamento de Citricultura y otros Frutales, Instituto Valenciano de Investigaciones Agrarias (I.V.I.A.), Carretera Moncada-Náquera, km 4.5. 46113, Moncada (Valencia), Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Quiñones
authors.forename: Josefina
authors.initials: J
authors.lastname: Bañuls
authors.forename: Eduardo Primo
authors.initials: EP
authors.lastname: Millo
authors.forename: Francisco
authors.initials: F
authors.lastname: Legaz
mesh_terms: D002957:Citrus / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D005308:Fertilizers / Q000032:analysis; D009566:Nitrates / Q000494:pharmacology*; D009584:Nitrogen / Q000378:metabolism* / Q000494:pharmacology; D009587:Nitrogen Isotopes; D018514:Plant Structures / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D017680:Potassium Compounds / Q000494:pharmacology*; D012987:Soil / Q000032:analysis; D014867:Water / Q000494:pharmacology; D014872:Water Movements
chemical_list: D005308:Fertilizers; D009566:Nitrates; D009587:Nitrogen Isotopes; D017680:Potassium Compounds; D012987:Soil; D014867:Water; D009584:Nitrogen; C023844:potassium nitrate