title: Soil temperature, nitrogen concentration, and residence time affect nitrogen uptake efficiency in citrus.
abstract: We try to elucidate which environmental and soil factors control nitrogen uptake efficiency in citrus. Effects of residence time and nitrogen (N) concentration (three 500-mL applications of 7 mg N L(-1), representative of reclaimed water used for citrus irrigation in central Florida, or one 150-mL application of 70 mg N L(-1)) on nitrogen uptake efficiency (NUE) of young citrus seedlings were studied. Increasing residence times from 2 to 8 h increased NUE from 36 to 82% and from 17 to 34% for high and low application frequencies, respectively. We developed a model to predict N uptake based on root density, N concentration, and soil temperature (Ts). Assuming a base temperature (Tb) of 10 degrees C, N uptake temperature sum (UTS) = sigma(Ts - Tb)/24 (degrees CdN, degree day units of N uptake). To eliminate the risk of N leaching for young seedlings, minimum uptake periods of 5 and 16 degrees CdN were required at initial soil N concentrations of 0.9 and 2.5 mg N L(-1), respectively. After correcting for differences in root length, this information was then used to predict the effect of irrigation practices on N uptake from reclaimed water for mature trees. Applying 2500 mm yr(-1) vs. 400 mm yr(-1) reclaimed water reduced the NUE of N in this water from 100 to 63% during the summer and from 100 to 28% during the winter. Reductions in NUE at higher irrigation rates appeared to be related to N displacement below the root zone prior to complete N uptake.
authors.affiliation: Agronomy Dep., Univ. of Florida, Gainesville 32611, USA. jmscholberg@mail.ifas.ufl.edu
authors.forename: J M S
authors.initials: JM
authors.lastname: Scholberg
authors.forename: L R
authors.initials: LR
authors.lastname: Parsons
authors.forename: T A
authors.initials: TA
authors.lastname: Wheaton
authors.forename: B L
authors.initials: BL
authors.lastname: McNeal
authors.forename: K T
authors.initials: KT
authors.lastname: Morgan
mesh_terms: D002957:Citrus / Q000254:growth & development / Q000502:physiology*; D003247:Conservation of Natural Resources; D005308:Fertilizers; D006801:Humans; D009584:Nitrogen / Q000008:administration & dosage / Q000378:metabolism*; D018517:Plant Roots / Q000502:physiology; D036226:Seedlings / Q000254:growth & development / Q000502:physiology; D012987:Soil; D013696:Temperature; D013997:Time Factors; D014881:Water Supply
chemical_list: D005308:Fertilizers; D012987:Soil; D009584:Nitrogen