A presentation at the WCCA 2011 event in Brisbane.

1. Spatial variation of soil constraints and its
implications for site-specific soil and nutrient
management in conservation agriculture
Yash Dang, Lindsay Bell and Ram Dalal

2. Spatial and Temporal Variability
Mean 18.9
Mean 1.79 Mean 0.91 Mean 1.29
SD 10.7
SD 0.39 SD 0.31 SD 0.40
CV 56.6
CV 21.5% CV 34.5% CV 31.2%
Variation between seasons >
Variation within a season
PM should consider both spatial
and temporal aspects

3. Measuring Variability
a. Grower’s Knowledge & Experience
Heavy black soil, brigalow softwood
Open black soil, plain, no tree
Light soil, box, scattered brigalow
High yielding
Medium yielding
Poor yielding

4. Measuring Variability
b. Continuously (on the go yield monitoring)

5. Measuring Variability
b. Continuously (proximal sensing)
4.0
2
Y=3.95 - 0.02 ECa_LL, r =0.97
Average wheat yield (t/ha)
3.5 NS; ECa_UL
3.0
2.5
2.0
1.5
1.0
0 50 100 150 200 250
ECa (mS/m)

6. Measuring Variability
c. Remotely (Satellite imagery, Landsat)
near-IR – red
near-IR + red
5
Y = 6.48 - 0.35 NDVI, r2=0.79
Wheat grain yield_2007 (t/ha)
4
3
2
1
0
0.2 0.4 0.6
NDVI_2007

7. Measuring Variability
d. Discretely (point sampling of soil)

8. Potential management classes

9. Ground-truthing
Cl (mg/kg) EMgP (%) NO3-N (mg/kg) VMCLL (cm3/cm3)
0 500 1000 30 60 0 20 40 0.2 0.3 0.4
0.0
Low
0.2 Medium
High
0.4
Soil depth (m)
0.6
0.8
1.0
1.2
1.4

10. Site-specific soil management:
Amelioration

11. Gypsum responses
3.5
Gypsum 0 b
3.0
Gypsum 2.5 t/ha (2005)
a
2.5
a a
Grain yield (t/ha)
2.0
b
1.5
a
1.0
0.5
0.0
Wheat 2005 Chickpea 2007 Wheat 2008
Cumulative gross margin for surface
applied gypsum $143/ha over 3-4 years

12. Gypsum reduces Cl concentration
Cl (mg/kg)
0 500 1000 1500
0
20
Control
Gypsum spread
40
Soil depth (cm)
60
80
100 115 t
NaCl
120
140
160

13. Site-specific nutrients management:
Matching inputs
Low
16
Medium
15
High 13
14
10 11
12
5
7 High
8
9
Medium
6 N46 Low
Wheat grain yield (t/ha)
5 N23
1 4
N0 4
N46
2 N0
N23
3
N0
N23
N46 3
M e te rs
0 12 5 2 50 50 0 7 50 1 ,0 0 0
2
1
0 10 20 30 40 50
Applied nitrogen (kg N/ha)

14. Matching Inputs to Realistic Yield Potential
• Determine realistic yield potential
in presence of soil constraints
Ymax = (Starting Soil
Water + In Crop Rain) *
Water Use Efficiency
Realistic Yield
Potential = Ymax
Soil constraints Soil
Nutrition

15. Nitrogen Requirement
N required (kg/ha) = (RYP x protein goal x 1.75 x 2)- Av. NO3-N to 0.9 m
NO3-N (mg/kg)
0 20 40
0.0
Low
0.2
Medium
High
0.4
Soil depth (m)
0.6
0.8
1.0
1.2
1.4

16. Matching Nitrogen Fertilizer: Economics
Zone 1 Zone 2 Zone 3 Field average
(20 ha) (28 ha) (16 ha) (64 ha)
Low Medium High
Realistic yield potential 3.36 2.21
(t/ha) 1.29 2.22
Nitrogen requirement 59 100 150 101
(kg N/ha)
Average available N in 119 55 36 70
the soil (kg N/ha)
Farmer’s rate (kg N/ha) 46 46 46 46
Actual N required (kg 114 31
N/ha) 0 45
Consequence of uniform 2.0 t urea 0.06 t urea 3.9 t urea 2.0 t urea
N application required waste
waste wasted

17. Matching Nitrogen Fertilizer: Environmental
10 High 14 High
N-denitrification (kg/ha)
Medium Medium
N-leaching (kg/ha)
Low Low
5 7
0
0
0 25 50
0 25 50
Applied nitrogen (kg N/ha)
Applied nitrogen (kg N/ha)

18. In Summary
 Integrate spatial data with grower’s
knowledge and ground-truthing to
identify spatial variability of constraints
to crop production
 Evaluate sustainable development
goals (economic, environmental and
social) for site-specific soil and nutrient
management

19. Thanks to number of colleagues who have
worked on the project over the years
Thanks!
And many more……