Effects of straw mulch on soil nitrate dynamics

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3.2. Soil nitrate dynamics
At emergence and immediately before harvest,
only small and non-significant differences in soil
nitrate between <strong>mulch</strong>ed and un<strong>mulch</strong>ed plots were
found (Table 4). Nitrogen mineralization after the
harvest process lead to a post-harvest increase <strong>of</strong>
nitrate in the soil (62 and 51 kg NO3–N ha 1 in the
un<strong>mulch</strong>ed soil, experiments 4 and 11, respectively).
The post-harvest amount <strong>of</strong> nitrate was greater in the
un<strong>mulch</strong>ed than in the <strong>mulch</strong>ed plots with a total
difference <strong>of</strong> 33.8 kg NO 3–N ha 1 in experiment 4
(not significant) and 17.6 kg NO3–N ha 1 in experiment
11 (significant at p = 0.035; Table 4).
The reason for this is seen in an immobilization <strong>of</strong>
nitrogen after incorporation <strong>of</strong> the (partially decayed)
<strong>straw</strong> into the soil due to the high C/N-ratio <strong>of</strong> <strong>straw</strong>
T.F. Döring et al. / Field Crops Research xxx (2005) xxx–xxx
Table 3
Effect <strong>of</strong> <strong>straw</strong> <strong>mulch</strong> in potatoes on soil moisture shortly before harvest (wt%): means S.E.
Soil moisture pre-harvest Experiment 1 (2001, n = 8) Experiment 4 (2002, n = 4) Experiment 11 (2003, n =4)
0–30 cm 30–60 cm 0–30 cm 30–60 cm 0–30 cm 30–60 cm
Un<strong>mulch</strong>ed 17.7 0.5 19.0 1.1 21.1 2.8 20.2 2.3 8.8 0.3 11.7 0.2
Mulched 18.9 0.8 18.0 0.6 21.1 2.3 20.6 3.1 9.3 0.3 11.8 0.2
L.S.D. 5% (untransformed) 1.6 ns 2.0 ns 2.6 ns 1.7 ns 1.6 ns 1.1 ns
ns: difference not significant (both for untransformed and angle-transformed data).
(Cheshire et al., 1999). The C/N-ratio <strong>of</strong> the <strong>straw</strong> in
experiment 4 was determined as 76.7; this value is
well below the long-time average C/N-ratio <strong>of</strong> 100 for
winter wheat <strong>straw</strong> presented by Boguslawski and
Debruck (1977). Per tonne <strong>straw</strong> applied, ca. 6.8 and
7.0 kg N (experiments 4 and 11, respectively) were
immobilized; this immobilization rate is at the upper
end <strong>of</strong> the range (1–7 kgNt 1 ) summarized by
Christensen and Olesen (1998).
3.3. Parameters <strong>of</strong> plant nutritional status and plant
growth
Hydro N-Tester values, as a measure <strong>of</strong> the
nutritional status <strong>of</strong> the plant, were significantly
reduced by <strong>straw</strong> <strong>mulch</strong> application in experiment 1
(Fig. 1). Plant height was slightly but significantly
Table 4
Effect <strong>of</strong> <strong>straw</strong> <strong>mulch</strong> applied to potatoes (var. Christa) on soil nitrate-N (kg ha 1 ) in two experiments a : means S.E., n =4
Soil nitrate a
Experiment 4 (2002) Experiment 11 (2003)
0–30 cm
At emergence (before <strong>mulch</strong>ing)
30–60 cm Sum (0–60 cm) 0–30 cm 30–60 cm Sum (0–60 cm)
b
Un<strong>mulch</strong>ed 70.2 12.5 40.4 11.4 110.6 23.6 40.1 4.1 14.3 2.7 54.4 6.7
Mulched 74.3 7.3 39.4 10.2 113.7 17.4 36.2 3.9 14.0 3.5 50.2 7.3
Pre-harvest (after haulm death) b
Un<strong>mulch</strong>ed 25.3 4.8 22.7 5.2 48.0 9.7 20.7 1.1 3.2 0.2 23.9 1.0
Mulched
Post-harvest
24.4 2.6 21.8 5.8 46.2 8.3 20.6 2.1 4.5 1.1 25.1 1.6
Un<strong>mulch</strong>ed 69.4 16.2 40.6 11.7 110.0 27.8 61.1 8.1 13.8 4.7 74.9 11.1
Mulched
Post-harvest difference
46.4 10.2 29.8 7.2 76.2 17.2 48.7 6.7 8.7 1.3 57.3 8.0
Un<strong>mulch</strong>ed-Mulched 23.0 11.7 10.8 7.2 33.8 18.8 12.5 2.6 5.1 4.1 17.6 4.8
LSD (5%) 37.1 ns 23.0 ns 59.8 ns 8.3 *
13.2 ns 15.2 *
ns: not significant.
a
For details <strong>of</strong> experimental conditions see Table 2; for sampling dates see text (Section 2.2).
b
There were no significant differences between <strong>mulch</strong>ed and un<strong>mulch</strong>ed treatments concerning soil nitrate at emergence and pre-harvest.
* p < 0.05.
UNCORRECTED PROOF
FIELD 4474 1–12
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