Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 129

The effect of residue type

The effect of residue type was investigated on the same soil type (Bridge-
north series) at a different location (Weston, Staffs). The above-ground
residues of a range of arable and horticultural crops (see Fig. 3.4.2) were
incorporated either with their own below-ground residues, or with the
below-ground residues left by a winter wheat crop (fertilized at 80 kg ha −1
N). In addition, plots were also included where only the below-ground
residues were incorporated for each of the harvested crops. Overall, the
trial was set out as three fully replicated randomized blocks, with crop type
and residue incorporation arranged on main and split plots, respectively.
Although crops were harvested at different times (as appropriate), residue
incorporation by ploughing for all treatments was carried out in a single
operation on 12 September 1995. Subsequently, a winter barley crop was
established and managed according to normal agronomic practice.

Results and Discussion

Effect of incorporation time

Time of residue incorporation is important for nitrate pollution. Delaying
cultivation decreased leaching only when a nitrogen-rich residue was
incorporated; there were no differences in mineralization/leaching between
different cultivation dates without residue incorporation (Table 3.4.2). The
implication of this is that time of residue incorporation might also affect
the fertilizer N requirement of the following crop. However, it was only
extreme differences in timing (June to January) and large inputs of residue
N (~180 kg ha −1 ) that showed measurable effects. In this experiment,
rainfall was such that NO 3 − -N was completely eluted from the soil profile;
with less rainfall, a proportion of the mineralized N would have been
available to the following crop, stressing the need to take account of winter
rainfall in recommendation systems.

Table 3.4.2. NO 3 -N (kg ha − 1 ) leached during the winter following incorporation of a green
residue. Standard error (n= 3) in parentheses.

Residue incorporation date

June August September October November January

With residue 204 (6.1) 164 (25.7) 181 (24.1) 133 (7.0) 139 (3.3) 129 (2.3)

No residue 135 (13.8) 147 (5.8) 133 (8.7) 114 (2.9) 139 (10.7) 125 (9.4)