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In 2003/04, heavy rain fell after the late-drilled treatments were established, again
causing capping of the soil surface on the sandy soil at Pewsey with rill erosion down
the tramlines. This rain also caused gushing of run-off down the tramlines on some
traps on the L-RC treatment at Wilton, and increased run-off from the headland area
at East Knoyle (Table 1). Consequently, run-off volumes were up to c. fivefold greater
on the late-drilled treatments than on the early-drilled treatments. As in the first year,
the increased run-off mobilised significantly more sediment and P on the ploughed
soil compared with the reduced cultivated soil at Pewsey (Table 1). At Wilton, flowweighted
SS and TP concentrations were increased on the L-RC treatment but not
significantly so. However at East Knoyle, flow-weighted SS and P concentrations
were significantly lower in the run-off on the headland area, perhaps reflecting a more
consolidated surface that was more resistant to sediment entrainment. Sufficient
crop cover had developed on the early drilled treatments at all sites in 2003/04 to
prevent accelerated sediment and P mobilisation, and there were no significant soil
cultivation treatment effects. Mean cumulative sediment and TP export ranged up
to 0.8 t/ha and 0.6 kg/ha in 2003/04, with the majority (60-97%) of the TP export in
particulate (> 0.45 mm) form at all three sites (Table 1).
Table 1:
Treatment effects on cumulative run-off volume, and loads of SS, TP
and DP at each site in 2003/04. Flow-weighted concentrations (g/L
for SS and mg/L for TP and DP) are given in brackets
Site Run-off SS TP DP
Treatment (mm) (kg/ha) (g/ha) (g/ha)
Pewsey
E-TC 3.2 77 (2.3) 48 (1.5) 3 (0.08)
E-RC 3.2 57 (1.8) 38 (1.1) 4 (0.12)
L-TC 15.8 650 (4.3) 548 (3.6) 31 (0.18)
L-RC 14.1 184 (1.3) 183 (1.3) 23 (0.16)
Significance *** *** *** **
l.s.d. 129 107 17
East Knoyle
E-TC 1.5 49 (3.2) 47 (3.0) 5 (0.32)
E-RC 2.5 75 (3.3) 72 (3.2) 9 (0.39)
Headland 9.7 70 (0.7) 148 (1.4) 19 (0.22)
L-RC 1.8 32 (1.7) 30 (1.6) 5 (0.28)
Significance NS NS *
l.s.d. 9
Wilton
E-TC 2.0 63 (2.8) 51 (2.3) 3 (0.12)
E-RC 2.4 43 (1. 8) 39 (1.6) 2 (0.07)
L-TC 5.0 150 (3.0) 97 (2.0) 12 (0.06)
L-RC 13.2 787 (4.6) 583 (3.4) 3 (0.10)
Significance NS NS NS NS
*, ** and *** denotes significance at the 5%, 1% and 0.1% level, respectively. NS, not
significant; l.s.d., least significant difference.
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