The role of agroforestry trees in intercepting leached nitrogen in the agricultural systems of the central highlands of Kenya.
Loading...
Date
2003
Authors
Mugwe, J. N.
Wamicha, W.
Mugendi, D.N.
Kung'u, J.B.
Kanyi, M.
Journal Title
Journal ISSN
Volume Title
Publisher
East African Agricultural and Forestry Journal
Abstract
Application of N-rich tree biomass to crop
fields in agroforestry associations can cause a
build-up of mineral-N in the top soil in excess
of crop demand during early stages of crop
growth. It is therefore important to monitor
movement of such mineral-N in the soil, so
that management options to minimise its
potential loss via leaching can be designed. A
randomised complete block experiment to
investigate mineral-N movement down a soil
profile in an agroforestry system was
conducted in an Ultisol in the central
highlands of Kenya during the Long and
Short Rains of 1998 cropping seasons. The
trial consisted of 10 treatments repricated 3
times. Maize was used as the test crop, and
was grown alone or in hedge row
intercropping with or without fertiliser/
prunings applications. The hedge row tree
species were Leucaena leucocephala and
Calliandra calothyrsus. The results indicated
that the bulk of mineral-N in these soils was
in the form of nitrate-N with ammonium-
nitrate comprising less than 10%. During the
first season which had plenty of rain, mineral-
N progressively moved (was leached) down
the soil profile as the season progressed,
accumulating in the deeper soil horizons in
stark contrast with the second dry season
where mineral-N accumulated in the top soil
layers. Treatments that received tree leafy-
biomass but had no trees ± fertiliser recorded
higher amounts of mineral-N in the 100-to-
300 cm depth averaging 15 to 30 mg N/kg.
On the other hand, soils in treatments with
Leucaena leucocephala and Calliandra
calothyrsus tree hedges recorded an average
I
of 1 to 3 mg N/kg in the same depth,
indicating that trees are capable of
intercepting and recapturing the crop-
inaccessible nutrients, below the roots of the
annual crops by the action of their deep roots.
Indeed, results on the total root length
indicated that less than 5% of all the maize
roots were located below the 90 cm soil depth
while 75% leucaena and 40% calliandra roots
were found below the same depth.
Description
http://dx.doi.org/10.4314/eaafj.v69i1.1807
Keywords
Agriculture, Agronomy, Forestry, Agroforestry, Soil fertility, Cultivation systems, Nitrogen
Citation
East African Agricultural and Forestry Journal volume 69 issue 1-2 69-79