Agriculture Reference
In-Depth Information
Fig. 4.2.2.
Leached N (solid lines) measured with porous cups (KL) or lysimeters (KZ) and
simulated by the LIXIM model in fallow soil, after grass destruction, for six treatments.
Table 4.2.1.
Nitrate N (kg ha
−
1
) leached under bare soil during the two winters following grass
destruction. The 'measured' values are derived from lysimeters in the KZ site or porous cups in the
KL site: mean (
SD
). The 'calculated' values are LIXIM outputs.
1997/98
1998/99
Calculated
Measured
Calculated
Measured
KL PG-0N
348
355 (64)
154
155 (54)
KL PG-200N
522
380 (1)
200
162 (13)
KL PG-400N
439
405 (48)
192
180 (60)
KL GC-50N
539
420 (51)
190
150 (70)
KZ PG-250N
209
181 (23)
115
151 (17)
KZ GC
310
191 (31)
135
172 (15)
N mineralization rates in situand under controlled conditions
The kinetics of N mineralization calculated by the model are shown at
Fig. 4.2.4. N mineralization rates ranged from 1.1 (KZ) to 2.4 (KL) kg N
ha
−1
nday
−1
during the period 0-100 (KZ) or 0-200 (KL) normalized days
(1 nday = 1 day at 15
C and optimal water content; Mary
et al
., 1999). In
laboratory incubations, initial nitrogen mineralization rates were 1.8-2.0 kg
Nha
−1
day
−1
; lower rates of 1.4 kg N ha
−1
day
−1
were measured for the 0N
treatment (KL site). N mineralization in control soils (data not shown) was
85% of the mineralization rate observed in treated soils. This suggests that
soils which were not treated with fresh organic residues contained large
amounts of easily mineralizable OM. Net N immobilization did not occur,
°
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