Lucerne taproot biomass
affected early-spring canopy
expansion
Edmar I. Teixeira
Derrick J. Moot
Andrew L. Fletcher
Agriculture and Life Sciences Division
Lincoln University, P.O. Box 84,
Canterbury, New Zealand
Email: teixeie2@lincoln.ac.nz
Crops with limited taproot biomass produced smaller leaves in early-spring.
Smaller leaves reduced radiation interception and consequently shoot yield.
Results
140
42-day crop
28-day crop
120
• Crops had similar shoot RUE of 1.64 g DM/MJ PAR (Figure 1).
Shoot yield (g DM/m2)
th
PAR i on 14 Sep 03
100
• Accumulated radiation was ~40% lower in crops grazed at 28-day intervals
(Figure 1).
80
• Lower radiation interception was caused by smaller primary and axillary leaves
(Figure 2).
60
40
• Compared with the 42-day crop, the area of the largest leaf (Y0, mm2/node) of
the 28-day crop was reduced to 62% in primary nodes and 25% in axillary nodes
(Figure 2).
y=1.64x
R 2 =0.96
20
0
0
10
20
30
40
50
60
70
80
1000
2
Accumulated intercepted PAR (MJ/m )
2
Y0 =927 mm
2
Primary leaves 42-day crop (R =0.99)
2
Primary leaves 28-day crop (R =0.98)
Figure 1. Shoot yield against intercepted PAR of lucerne crops.
800
Leaf area (mm2/node)
Background
• Shoot yield is linearly related to
radiation interception which is a
function of canopy expansion.
• Low levels of taproot biomass
reduce lucerne yield.
2
Axillary leaves 42-day crop (R =0.99)
2
Axillary leaves 28-day crop (R =0.62)
Y0 =576 mm
600
Bell-shaped function:
2
3
Y=Y0 *exp(-a*(X-X 0 ) +b*(X-X 0 ) )
400
Y0 =360 mm
200
• How do root reserve levels affect
lucerne shoot yield in early spring?
2
Y0 =93 mm
2
2
0
0
42-day crop
28-day crop
Materials and methods
• Lucerne crops were grazed frequently (28-day cycle) or infrequently (42-day
cycle).
• Taproot biomass was 3t/ha in the 42-day crop but reduced by 30% in the 28-day
crop.
• Shoot yield and light interception were measured weekly in each crop at
Canterbury, New Zealand.
• The area of fully expanded leaves at each individual node position was measured
from node 1 (base) to the most recent node (top).
CHRISTCHURCH
NEW ZEALAND
www.lincoln.ac.nz
1
2
3
4
5
6
7
8
9
10
Node position on main-stem
Figure 2. Total leaf area at each main-stem node position on 1 Oct 03.
Conclusions
• Limited root reserves reduced crop canopy expansion in earlyspring.
• Crop yield reduction was caused by smaller individual leaves at each
node position.