YIELD AND QUALITY RESPONSE OF CRISPING POTATOES (SOLANUM TUBEROSUM L.) TO APPLIED NITROGEN

The nitrogen (N) requirements of two Australian crisp potato (Solanum tuberosum L.) varieties, Bliss and Dawmor, were compared with Atlantic in experiments over three years on loamy sands and sands in the south west of Western Australia. There was a significant response of yield to rate of applied nitrogen (N) and variety on all sites and a significant nitrogen by varietal interaction on sands. Yield increased to a maximum with rate of applied N and then decreased above this rate on sites on loamy sands and or reached a plateau with no yield decrease (exponential response) at high rates of applied N on sands. Nitrate (NO3)- N concentration (mg kg-1 DW) in petioles required for maximum yield of Atlantic decreased linearly (P 0.05) from 23,947 at the 10 mm tuber stage to 13,052 at the 60 mm tuber stage, in Dawmor from 22,429 to 14,644 and in Bliss from 20,202 to 12,597 over the same tuber stages. Bliss tubers had the highest specific gravity (SG) on both soil types and Dawmor the lowest on loamy sands. The effect of rate of applied N and variety on crisp cooking color, internal defects (hollow heart and internal brown spot) of tubers and tuber nutrient concentration is also discussed.