wAbstract
@In Terceira island (Azores, Portugal), 87 of the agricultural
land is used for permanent pasture under periodical grazing. The
edaphpclimatic conditions promote nitrate leaching into the groundwater
and runoff, which carries sediments and fertilizers into the surface
waters. Of particular interest is the fact that volcanic Andosols
are rarely study to analyze nitrogen dynamics. The soil capacity
to provide mineral N from its organic matter pool through mineralization
was estimated using two methods: in laboratory under controlled
moisture and temperature conditions; and in natural conditions
using in situ minilysileters. The direct N input through animal's
excreta was determined by a field mass balance. It was observed
that mineralization and animal excreta contributed respectively
with 160 and 65 kg mineral N ha-1 for the N budget.
N losses by leaching and runoff amount respectively for 89}18
kg ha-1 and 0.5}0.08 kg ha-1, representing
53 of the fertilizer inputs. To control such losses the fertilizer
amount should be recalculated considering the direct input through
the animal excreta and the mineral N input from the net mineralization
process. In addition, due to the random characteristics of the
rainfall events, the fertilization should be split into two or
more applications, hence reducing the amounts of mineral N available
for leaching. Further studies may be developed using a modeling
approach to allow the fertilizer management optimization.
keywords: Azores; Andosols; Grasslands; N mineralization rate;
Minilysimeters; Laboratory incubation; N lossesx
1. Introduction
2. Materials and methods
@2.1. Experimental site
@2.2. Experimental procedures to estimate the net mineralization
rate of the soil
@2.3. Analysis of N dynamics in natural conditions of the grazed
pasture
3. Results
@3.1. Laboratory incubation method
@3.2. In situ minilysimeters method
@3.3. Monitoring N dynamics in the permanent pasture with periodical
grazing
4. Discussion
@4.1. Net mineralization rates
@4.2. Ammonium (NH4-N) inputs through animal excreta
@4.3. Mineral N losses through leaching and runoff
5. Conclusions
References