1. 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

2. 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

3. BACKGROUND

4. ORANGE-RIET

5. VAALHARTS

8. CASE STUDY: VAALHARTS (V6 & V7)

9. VAALHARTS

10. IS DUAL CROPPING UNDER CENTRE PIVOTS A JUSTIFIABLE IRRIGATION PRACTICE?

11. Soil properties Soil depth 0- 0.30.3-0.60.6-.90.9-1.2 1.2- 1.5 1.5-1.8Mean Clay content (%)56.589910.58 Bulk den (kg m -3 )1605165316261627165416561636 K sat (mm h -1 )39.834.5---24.332.9 pH (H 2 O)77.57.88.1 87.7 CEC (cmol c kg -1 )2.932.5 2.83 EC e (mS m -1 )7383.377.184.479.788.581 SAR1.251.741.711.811.882.081.74 MATERIAL AND METHODS: Soil information

12. Agronomic practices (East) Season1234 Crop rotationWheatMaizeFallowGroundnuts CultivarDuzziePannar 6126Aqua Planting date12 June 200715 Dec 20075 Nov 2008 Harvesting date29 Nov 200712 June 200825 July 2009 Planting density 150 kg ha -1 80 000 plants ha -1 114 kg ha -1 Total kg N ha -1 222225104 Total kg P ha -1 4033 Total kg K ha -1 50 52 Pest management -Eptam Treflin Temik Harnas Hammer Cultivation practices Plough, tiller & plant Bale, plough, disc, till & plant Disc, plough, till, & plant

13. Agronomic practices (v6, west) Season1234 Crop rotationPeasGroundnutsWheatCotton CultivarSolaraAquaDuzie - Planting dateJuly 2007Dec 2007June 2008Dec 2008 Harvesting date14 Nov 2007May 20081 Dec 200825 July 2009 Planting density 120 kg ha -1 150 kg ha -1 18 kg ha -1 Total kg N ha -1 93168209247 Total kg P ha -1 17303833 Total kg K ha -1 50405052 Pest management Galliant- Buctril MCPA Treflin Temik Roundup Metamidofos Cultivation practices Burn, plough, wonder till & plant Bale, burn, rip & plant Burn, wonder till & plant Bale, burn, rip & plant

14. 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

15. MATERIAL AND METHODS: Measurements

16. Rainfall Irrigation Soil water Water table depth East

17. Rainfall Irrigation Soil water Water table depth West

18. RESULTS ON SWB: EAST (V7) Crop∆WRIETD Wheat6120444166497-21 Maize1135026641417-147 Fallow211210460-54 Groundnuts3626040243281-302

19. RESULTS ON SWB: WEST (V6) Crop∆WRIETD Peas13202344414964 Groundnuts7233454334436-335 Wheat-362975268435-315 Cotton-2327350170362-365

20. RESULTS ON YIELDS: EAST (V7) Crop Seed ( kg ha -1 ) Biomass ( kg ha -1 ) ActualPotActualPot Wheat543280001552020000 Maize9896145001706226500 Fallow Groundnuts26194500748314500

21. RESULTS ON YIELDS: WEST (V6) Crop Seed ( kg ha -1 ) Biomass ( kg ha -1 ) ActualPotActualPot Peas3428400076179500 Groundnuts397145001134614500 Wheat584580001425616000 Cotton065001408418500

22. SeasonPivotDual crops Peak period (days) ET rate (mm day -1 ) 1 WestPeas505.9 EastWheat506.2 2 WestGroundnuts705.5 EastMaize457 3 WestWheat506.5 EastFallow 4 WestCotton506 EastGroundnuts704

23. CONCLUSION

24. Thank you