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

Spatial and Temporal Variability

Mean 1.79

SD 0.39

CV 21.5%

Mean 0.91

SD 0.31

CV 34.5%

Mean 1.29

SD 0.40

CV 31.2%

Mean 18.9

SD 10.7

CV 56.6

Variation between seasons >

Variation within a season

PM should consider both spatial

and temporal aspects

a. Grower’s Knowledge & Experience

Measuring Variability

Heavy black soil, brigalow softwood

High yielding

Open black soil, plain, no tree

Medium yielding

Light soil, box, scattered brigalow

Poor yielding

b. Continuously (on the go yield monitoring)

Measuring Variability

b. Continuously (proximal sensing)

Measuring Variability

ECa (mS/m)

0 50 100 150 200 250

Avera

ge w

heat yie

ld (

t/h

a)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Y=3.95 - 0.02 ECa_LL, r2=0.97

NS; ECa_UL

c. Remotely (Satellite imagery, Landsat)

Measuring Variability

near-IR – red

near-IR + red

NDVI_2007

0.2 0.4 0.6

Wh

ea

t g

rain

yie

ld_

20

07

(t/

ha

)

0

1

2

3

4

5Y = 6.48 - 0.35 NDVI, r2=0.79

d. Discretely (point sampling of soil)

Measuring Variability

Potential management classes

Ground-truthing

Cl (mg/kg)

0 500 1000

So

il d

ep

th (

m)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Low

Medium

High

EMgP (%)

30 60

NO3-N (mg/kg)

0 20 40

VMCLL

(cm3/cm3)

0.2 0.3 0.4

Site-specific soil management:

Amelioration

Gypsum responses

Cumulative gross margin for surface applied gypsum $143/ha over 3-4 years

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Wheat 2005 Chickpea 2007 Wheat 2008

Gra

in y

ield

(t/

ha

)Gypsum 0

Gypsum 2.5 t/ha (2005)

a a

a

a

b

b

Gypsum reduces Cl concentration

0

20

40

60

80

100

120

140

160

0 500 1000 1500

Cl (mg/kg)

So

il d

ep

th (

cm

)

Control

Gypsum spread

115 t

NaCl

98

7

4

56

3

2

1

16

15

13

14

121110

0 2 5 0 5 0 0 7 5 0 1 ,0 0 01 2 5M e te rs

Low

Medium

High

N46N23N0

N46N0N23

N0N23N46

Applied nitrogen (kg N/ha)

0 10 20 30 40 50

Wheat

gra

in y

ield

(t/

ha)

1

2

3

4

5High

Medium

Low

Site-specific nutrients management:

Matching inputs

Matching Inputs to Realistic Yield Potential

• Determine realistic yield potential

in presence of soil constraints

Realistic Yield Potential = Ymax

Soil constraints Soil Nutrition

Ymax = (Starting Soil Water + In Crop Rain) * Water Use Efficiency

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

Soil

de

pth

(m

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Low

Medium

High

Matching Nitrogen Fertilizer: EconomicsZone 1

(20 ha)

Low

Zone 2

(28 ha)

Medium

Zone 3

(16 ha)

High

Field average

(64 ha)

Realistic yield potential

(t/ha)

Nitrogen requirement

(kg N/ha)

Average available N in

the soil (kg N/ha)

Farmer’s rate (kg N/ha)

Actual N required (kg

N/ha)

Consequence of uniform

N application

3.36

150

3.9 t urea

required

114

46

36

1.29

59

2.0 t urea

waste

0

46

119

2.22

100

0.06 t urea

wasted

45

46

55

2.21

101

2.0 t urea

waste

31

46

70

Matching Nitrogen Fertilizer: Environmental

Applied nitrogen (kg N/ha)

0 25 50

N-leachin

g (

kg/h

a)

0

5

10 High

Medium

Low

Applied nitrogen (kg N/ha)

0 25 50N

-de

nitrifica

tio

n (

kg/h

a)

0

7

14 High

Medium

Low

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

Thanks to number of colleagues who have

worked on the project over the years

And many more……

Thanks!