Farina Presentation

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GYPSUM

AND THE IMPROVEMENTOF SOIL PROPERTIES

IN SOUTH AFRICAMart Farina

Consultant - Omnia East Coast

[email protected]



INTRODUCTION

Intend to

– Set scene geographically

– Discuss Malcolm Sumner’s work on remediationof saline and sodic soils with gypsum

– Briefly highlight the start of acid-subsoil

amelioration research with gypsum

– Describe long-term effects of gypsum and deep

incorporation of lime on subsoil acidity in

KwaZulu-Natal







Schulze, R.E. and Lynch, S.D. 2007. Annual Precipitation. In: Schulze, R.E. (Ed). 2007. South African Atlas

of Climatology and Agrohydrology. Water Research Commission, Pretoria, RSA, WRC Report 1489/1/06,Section 6.2.



Mean Annual Precipitation



Median pHKCl Acid Saturation



Reclamation of Sodic Soils



Saline/Sodic Alfisol in Swaziland

• 80 ha field

– Split equally between Control and Gypsum

• Initial (with depth) EC 10-16 dS/m ESP 13-30

• Pipe drains installed @ 1.2 m in 1971

– Gypsum applied @ 20 t/ha in 1972

– Bunds built around area and flooded for 9 months

to leach salts – 2 crops of rice planted in 1972/73

• Sugarcane planted in 1974

– Plant and 6 ratoons



Effect of Gypsum on EC and ESPat End of Trial

0 0.5 1 1.5

15

105

Electrical conductivity (dS/m)

D e

p t h ( c m )

Control

Gypsum

0 5 10 15 20

15

105

Exchangeable sodium (ESP) (%)

D e

p t h ( c m )

Control

Gypsum



Effect of Gypsum on SugarcaneYield

60

70

80

90

100

110

120

130

140

1974 1975 1976 1977 1978 1979 1980 Mean

S u

g a r c a n e y i e l d ( T / h a )

Year

Control

Gypsum



Conclusions

• Gypsum

– Reduced EC and ESP down profile

– Soil reclaimed

– Increased yields particularly towardsthe end of trial

–Stable yields for last 5 years



Saline/Sodic Alfisol in kwaZulu-

Natal

• Pipe drains installed @ 0.85 m in 1970

• Gypsum @ 20 t/ha applied in 1971• Leaching by rainfall and irrigation

• Sugarcane planted in 1974

– Plant and 1 ratoon

Eff f G EC d



Effect of Gypsum on ECse andESP in Subsoil over Time

0

2

4

6

8

10

12

14

1970 1972 1974 1976 1978

E l e c

t r i c a l c o n d u c t i v i t y ( d S / m )

Year

Control

Gypsum

0

5

10

15

20

25

1970 1972 1974 1976 1978

E a x c a n g e a b l e S o d i u

m ( E

S P ) ( % )

Year

Control

Gypsum

Eff f G Di ibl



Effect of Gypsum on DispersibleSilt+Clay and Infiltration Rate

0 20 40 60

7.5

25

50

Dispersible silt+clay (%)

D

e p t h ( c m )

Control

Gypsum

0

2

4

6

8

10

12

14

16

I n f i l t r a t i o n r a t e ( m m / h

r )

Control

Gypsum



Effect of Gypsum on Cane andSucrose Yield

40

50

60

70

80

90

100

110

120

130

Plant 1st Ratoon

S u

g a r c a n e y i e l d ( T / h a )

Control

Gypsum

6

8

10

12

14

16

18

Plant 1st Ratoon

S u c r o s e y i e l d ( T / h a )

Control

Gypsum



Conclusions

• Leaching reduced EC – more pronouncedwith gypsum

• Gypsum reduced ESP to 10 –

insufficient• Gypsum reduced clay dispersion

• Gypsum increased infiltration rate

• Cane and sucrose yields not significant – Trended in right direction

– More time required for reclamation



The start of subsoil acidity

research in South Africa



Effect of Lime and Gypsum onSorghum on Acid Sandy Soil

0

10

20

30

40

50

60

70

80

90

100

R e l a

t i v e y i e l d ( % )

Control

Leachedwith satd.Gypsumsoln.

2 T Lime/ha

Treatment pH

Exch. Al

cmolc/kg

Control 4.4 0.46

Gypsum 4.7 0.10

Lime 6.4 0.00

Sumner (1970) Proc. S. Afr. Sug. Tech. 44:176-182.

Eff t f G Al d C



Effect of Gypsum on Al and Cawith Depth in Acid Sandy Soil

0

10

20

30

40

50

60

70

80

90

0 0.2 0.4 0.6 0.8

D e p t h ( c m

Exchangeable Al (cmolc/kg)

Control

1.6T Gypsum/ha

0

10

20

30

40

50

60

70

80

90

0 0.5 1

D e p t h ( c m )

Exchangeable Ca (cmolc/kg)

Control

1.6T Gypsum/ha

Sumner (1970) Proc. S. Afr. Sug. Tech. 44:176-182.



“Self -liming Effect” (Reeve and Sumner, 1972)

Sesquioxide Gypsum

OH

OH-

Alkalinity

OH-

OH-

OH-

G l k b il idit t d



Depth (cm) Clay (%) Org C (%)0 – 15 41.2 1.5

15 – 30 41.2 1.2

30 –

45 46.1 0.845 – 60 48.7 0.5

60 – 75 46.8 0.4

75 – 90 46.4 0.3

Geluksburg soil acidity study area

16t/h l i h d id f i l



16t/ha calcium hydroxide four years previously



No gypsum

With gypsum



Initial objective – to compare deep

placement of lime with gypsum



Wye-double-digger



Deep limer

28 t/ha lime below

plough depth

15 t/ha lime ploughed in



Alubuster

Better access tosubsoil moisture



15 t/ha lime ploughed in. Note inability of roots to penetrate acid

band.



The effects of gypsum



15 t/ha lime to 50 cm.

15 t/ha lime + 10 t/ha

gypsum to 20 cm.

Eff t f G E h bl



Effect of Gypsum on ExchangeableCa with Depth

0

10

20

30

40

50

60

70

80

90

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

D e

p [ t h ( c m )

Exchangeable Ca (cmolc/L)

15 t/ha lime to 20 cm

25 t/ha lime to 50-60 cm

15 t/ha lime + 10 t/ha gypsum

Control

Eff t f G E h bl



Effect of Gypsum on ExchangeableMg with Depth

0

10

20

30

40

50

60

70

80

90

0.00 0.50 1.00 1.50 2.00 2.50

D

e p t h ( c m )

Exchangeable Mg (cmolc/L)




Control

Eff t f G E h bl



Effect of Gypsum on ExchangeableAl+H with Depth

0

10

20

30

40

50

60

70

80

90

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00

D e p t h ( c m )

Exchangeable Al+H (cmolc/L)




Control



Effect of Gypsum on Soil pH

0

10

20

30

40

50

60

70

80

90

4 4.5 5 5.5 6

D e p t h ( c m )

pH



15 t/ha lime + 10 t/ha gypsum to 20 cm

Control



Effect of Gypsum on Acid Saturation

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90

D

e p t h ( c m )

Acid saturation (%)




Control

Eff t f G E t t bl NO



Effect of Gypsum on Extractable NO3 with Depth

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60

D e p t h ( c m )

Extractable NO3 (mg/L)




Eff t f G E t t bl SO



Effect of Gypsum on Extractable SO4 with Depth

0

10

20

30

40

50

60

70

80

90

0 50 100 150 200 250 300

D e p t h ( c m )

Extractable SO4 (mg/L)






Gypsum effect on root development

Lime + gypsum Lime only



Effect of Gypsum on Root Length

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 2 4 6

D e p t h ( m )

Root length (m/L)

1986

15 t/ha lime

25 t/ha lime


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 2 4 6 8

D

e p t h ( m )

Root length (m/L)

1992

15 t/ha lime

25 t/ha lime




Effect of Lime and Gypsum onLeaf Nutrient Content

0

0.5

1

1.5

2

2.5

3

3.5

Ca Mg K P N

L e a f c o n t e n t ( % )

15 t/ha lime

25 t/ha lime




Longevity of Gypsum Effect

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000

C u m u l a t i v e y i e l d i n c r e a s e

o v e r c o n t r o l

( k g / h a )

Year

Lime + gypsum

Nardi plough

Wye-double-digger



Some management problems

Effect of Gypsum Rate on Acid



Effect of Gypsum Rate on AcidSaturation After 12 Years

0

10

20

30

40

50

60

70

80

90

20 30 40 50 60 70 80

D e p t h ( c m )

Acid saturation (%)

Zero

2 t/ha

4 t/ha

8 t/ha

16 t/ha



Soil heterogeneity



L 0 L 5 L 10

Effects of excess N

on subsoil acidity

Poor N management in sugarcane



Poor N management in sugarcane



Overall Summary and

Conclusions• Work conducted by Malcolm Sumner in the 1970’s

clearly demonstrated the benefits of gypsum inameliorating sodic and saline/sodic soils.

• Seminal research by Sumner (1970) and Reeve &Sumner (1972) also demonstrated the negative effectsof subsoil acidity on crop performance in the province

of KwaZulu-Natal and the benefits to be obtained fromgypsum. This resulted in the proposal of a “self -limingeffect”, whereby sulphate ions displace hydroxide ionsfrom sesquioxidic surfaces and the pH is elevated by aneutral salt.



• Long-term field trials initiated in 1979 have stronglysupported the validity of this mechanism.

• These trials have also unambiguously shown the benefitsof gypsum to be long lasting and far superior toalternative strategies of mechanically incorporating limeto depth.

• Considered particularly significant is the fact that over 15seasons, the cumulative maize grain yield benefit from 10t/ha of gypsum plus 15 t/ha of lime was almost 16 t/hagreater than that of treatments which received 15 t/ha of

lime only. Even treatments which received 25 t/ha of lime incorporated to 60 cm were surpassed by about 7.5t/ha. Since the cost of gypsum had been redeemed withinthree years, the magnitude of the economic benefit isclear.



• Soil and root samples collected to depth clearlyshowed the benefits of gypsum on soil properties.

However, there is unambiguous evidence toindicate that the quantities of gypsum required onacidic, heavy textured South African soils areappreciably greater than those considered adequateon similar soils in more highly weatheredenvironments.

• Anthropogenically induced subsoil acidity iswidespread in South Africa and, since the efficacy

of gypsum in eliminating subsoil acidity isdependent on the existence of sesquioxides,remains a problem. Good nitrogen management isimportant.



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