Regis Chikowo : Nitrogen cycling in agroforestry systems of sub-humid Zimbabwe

  News
  Newsroom
  Archive
  Calendar
  2012
  2011
  2010
  2009
  2008
  2007
  2006
  2005
  2004
  2003
  2002
  2001
  2000
  1999
  News
  RSS
  Calendar
  Open days
  Courses
  Congresses and symposia
  PhD-graduations and speeches

23 Mar 2004 16:00
Unit: Wageningen University
Location: Aula (gebouw 362), Gen. Foulkesweg 1, Wageningen
Promotor: prof.dr. K.E. Giller (Plant Production Systems)
Co Promotor: dr. P. Leffelaar

 This thesis focuses on nitrogen: its acquisition in cropping systems through biological N2-fixation and soil capture, its release by legume prunings and litter, its use by maize and its loss through leaching and as N2O gas. The context of the study is improved fallows using leguminous trees/shrubs on a sandy clay loam soil under sub-humid conditions in Zimbabwe. Sesbania Sesban, Acacia angustissima and Cajanus cajan improved N cycling significantly. On a sandy soil, these legumes adapted poorly. Nitrate leaching from the 0-0.4 m layer ranged from 29-40 kg ha-1 for Sesbania and Acacia plots within two weeks when 104 mm rainfall was received to an already fully recharged soil profile. Nitrous oxide emissions were small, with maximum of 0.3 kg ha-1 lost in 56 days. Fallows increased water infiltration rates, but the effect markedly decreased after one year of maize cropping in non-coppicing tree fallows. In a decomposition experiment, most of the senesced legume materials showed N immobilization up to 60 days. The reduction of nitrate- leaching is the single largest challenge to increased N recovery in the highly porous soils.
Print this activity