IS DUAL CROPPING UNDER CENTRE PIVOTS A JUSTIFIABLE IRRIGATION PRACTICE?

Leon Van Rensburg, JH Barnard, JB Sparrow, ATP Bennie and CC Du Preez

Department of Soil, Crop and Climate Sciences

BACKGROUND

• WRC (Report No K5/1647, 2012): MANAGING SALINITY ASSOCIATED WITH IRRIGATION AT ORANGE-RIET AND VAALHARTS IRRIGATION SCHEMES

* Calibration and validation of the SWAMP model

* Crop selection

* Soils

* Crop production

* Irrigation scheduling

*Best management practice

R

U

Northern Cape

Eastern Cape

Free State

North West

Western Cape

Northern Province

KwaZulu-Natal

Mpumalanga

Lesotho

Gauteng

Vaal

Orange

Riet

Harts

32°0'0"E

32°0'0"E

28°0'0"E

28°0'0"E

24°0'0"E

24°0'0"E

20°0'0"E

20°0'0"E

21°0'0"S 21°0'0"S

24°0'0"S 24°0'0"S

27°0'0"S 27°0'0"S

30°0'0"S 30°0'0"S

33°0'0"S 33°0'0"S

36°0'0"S 36°0'0"S

Ü0 160 320 480 64080

Kilometers

Legend

R Orange-Riet Irrigation Scheme

U Vaalharts Irrigation Scheme

Rivers

Lower Vaal WMA

Upper Orange WMA

BACKGROUND

ORANGE-RIET

VAALHARTS

VAALHARTS

VAALHARTS

CASE STUDY: VAALHARTS (V6 & V7)

VAALHARTS

IS DUAL CROPPING UNDER CENTRE PIVOTS A JUSTIFIABLE IRRIGATION PRACTICE?

Soil properties

Soil depth

0- 0.3 0.3-0.6 0.6-.9 0.9-1.21.2-1.5

1.5-1.8 Mean

Clay content (%) 5 6.5 8 9 9 10.5 8

Bulk den (kg m-3) 1605 1653 1626 1627 1654 1656 1636

Ksat (mm h-1) 39.8 34.5 - - - 24.3 32.9

pH (H2O) 7 7.5 7.8 8.1 8.1 8 7.7

CEC (cmolc kg-1) 2.9 3 2.5 2.5 2.8 3 2.8

ECe (mS m-1) 73 83.3 77.1 84.4 79.7 88.5 81

SAR 1.25 1.74 1.71 1.81 1.88 2.08 1.74

MATERIAL AND METHODS: Soil information

Agronomic practices (East)

Season 1 2 3 4

Crop rotation Wheat Maize Fallow Groundnuts

Cultivar Duzzie Pannar 6126 Aqua

Planting date 12 June 2007 15 Dec 2007 5 Nov 2008

Harvesting date 29 Nov 2007 12 June 2008 25 July 2009

Planting density

150 kg ha-1 80 000 plants ha-1 114 kg ha-1

Total kg N ha-1 222 225 104

Total kg P ha-1 40 33 33

Total kg K ha-1 50 50 52

Pest management

- Eptam

TreflinTemikHarnas

Hammer

Cultivation practices

Plough, tiller & plant

Bale, plough, disc, till & plant

Disc, plough, till, & plant

Agronomic practices (v6, west)

Season 1 2 3 4

Crop rotation Peas Groundnuts Wheat Cotton

Cultivar Solara Aqua Duzie -

Planting date July 2007 Dec 2007 June 2008 Dec 2008

Harvesting date 14 Nov 2007 May 2008 1 Dec 2008 25 July 2009

Planting density

120 kg ha-1 120 kg ha-1 150 kg ha-1 18 kg ha-1

Total kg N ha-1 93 168 209 247

Total kg P ha-1 17 30 38 33

Total kg K ha-1 50 40 50 52

Pest management

Galliant -BuctrilMCPA

TreflinTemik

RoundupMetamidofos

Cultivation practices

Burn, plough, wonder till & plant

Bale, burn, rip & plant

Burn, wonder till & plant

Bale, burn, rip & plant

Gain of water:Rainfall and Irrigation

Evaporation and transpiration

Salts will accumulate

Leaching

Drainage effluent(Degrading ground and surface waters)

MATERIAL AND METHODS: Water balance

MATERIAL AND METHODS: Measurements

Rainfall

Irrigation

Soil water

Water table depth

East

Rainfall

Irrigation

Soil water

Water table depth

West

RESULTS ON SWB: EAST (V7)

Crop ∆W R I E T D

Wheat 61 204 441 66 497 -21

Maize 11 350 266 41 417 -147

Fallow 21 121 0 46 0 -54

Groundnuts 36 260 402 43 281 -302

RESULTS ON SWB: WEST (V6)

Crop ∆W R I E T D

Peas 13 202 344 41 496 4

Groundnuts 72 334 543 34 436 -335

Wheat -36 29 752 68 435 -315

Cotton -23 273 501 70 362 -365

RESULTS ON YIELDS: EAST (V7)

CropSeed (kg ha-1)

Biomass (kg ha-1)

Actual Pot Actual Pot

Wheat 5432 8000 15520 20000

Maize 9896 14500 17062 26500

Fallow

Groundnuts 2619 4500 7483 14500

RESULTS ON YIELDS: WEST (V6)

CropSeed (kg ha-1)

Biomass (kg ha-1)

Actual Pot Actual Pot

Peas 3428 4000 7617 9500

Groundnuts 3971 4500 11346 14500

Wheat 5845 8000 14256 16000

Cotton 0 6500 14084 18500

Season Pivot Dual crops Peak period(days) ET rate (mm day-1)

1West Peas 50 5.9

East Wheat 50 6.2

2West Groundnuts 70 5.5

East Maize 45 7

3West Wheat 50 6.5

East Fallow

4West Cotton 50 6

East Groundnuts 70 4

CONCLUSION

Thank you