Response of potatoes to organic fertiliser rate: Yield, tuber quality and nutrient uptake

Potatoes were grown during spring-summer 2003 and 2004 at the experimental farm of CCORAV located at Grotte di Castro, Viterbo, Central Italy to evaluate the impact of 5 rates of a guano-based organic fertiliscr on yield, tuber quality, nitrogen uptake, and nitrogen use efficiency. A randomized complete 1 block design with four replicates was used to compare 5 rates (0, 0.5, 10, 15, 20 t ha(-1)) of a guano-based fertiliser (10.0N-1.3P-2.5K). Rate of organic fertiliser did not affect yield of large size tubers (diameter > 75 mm) and small size tubers (diameter < 45 mm). Increasing the fertiliser rate increased linearly the marketable yield of medium size tubers (diameter 45-75 mm) and total marketable yield. There was a linear relationship between leaf N concentration at blooming stage and fertiliser rates, which suggested that the effect observed on marketable yield was probably due to N status. Tuber nitrogen uptake increased by increasing fertiliser rate while the opposite was observed for nitrogen use efficiency.