K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y nitrogen and irrigation management of potatoes Sarah Sinton, Bruce Searle

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y N and water are the main drivers Both N and water in the right amounts are needed to grow a great potato crop. Optimise tuber yield and quality. Accurate irrigation enhances N uptake. Minimise wastage, leaching. Crop needs change every year.

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y How crops are managed Focus has been on maximising yields. Putting plenty of N on to cover all bases. Potato roots can reach 70 cm.

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y Yields, N applied, N left Location Gross yield (t/ha) Side- dressed N (kg/ha) N left in soil to 80cm (kg/ha) Low NGrower NLow NGrower N Canty Waikato

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y How crops are managed Focus has been on maximising yields. Putting plenty of N on covered all bases. How much N is already in the soil? How much will be mineralised? The Potato Calculator.

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y Full Senescence Full Canopy Emergence Canopy development

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y 100% partitioned to tops 25% tops 75% tubers 100% tubers tuber initiation tuber biomass tops biomass Thermal time Biomass Partitioning of resources

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y The soil model Saturated Field capacity Wilting point

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y Early deficit , Canterbury Yield reduction between 4.5 and 14.6 t/ha

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y Later deficit , Canterbury Yield reduction between 0.5 and 6.3 t/ha

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y How crops are managed Focus has been on maximising yields. Putting plenty of N on covered all bases. How much N is already in the soil? How much will be mineralised? Experience with Canterbury crops. Emphasis on N when in fact water was limiting.

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y Lysimeter installation

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y Rainfall and drainage 90 mm drainage 210 mm drainage N treatments appliedN at planting

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y N Leached at 80cm Leaching from N already in the soil Leaching from N at planting N treatments applied Leaching from N treatments

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y Final points You need to understand the interaction between the crop, soil and weather to best optimise N and water use. You need to know: - What the soil can supply - How much is needed (if there’s a shortfall) - When to apply them The Potato Calculator can help you do this.

K N O W L E D G E A N D V A L U E F R O M S C I E N T I F I C D I S C O V E R Y Acknowledgements Sustainable Farming Fund HortNZ Ballance Agri-Nutrients McCain Foods Ltd Environment Waikato Horizons Hawke’s Bay Regional Council HortResearch CFR Eurogrow Many potato growers > A decade of Public Good money for earlier research