Consumers interest for organic agriculture and environmental-friendly agricultural products is increasing. Nevertheless, cultivation protocols in organic farming are not sufficiently standardized to guarantee product quality stability, a parameter which is critical for further expansion of this niche market. Variable responses in terms of quality and quantity of the harvested product often arise from complex interactions between agronomic and environmental factors. Here we report on the effects of different levels of nitrogen fertilization (0, 50, 150, 200 kg N ha−1) and irrigation regime (50% and 100% replenishment of the evaporation determined using a Class A pan, plus a non-irrigated control) on yield and accumulation of primary metabolites of two potato cultivars (Agria and Merit) grown under conventional and organic farming systems. Organic farming caused a 25% marketable yield reduction with a higher percentage of large tubers under conventional farming, whereas irrigation increased the marketable yield and the percentage of large tubers. Nitrogen fertilization affected the marketable yield and significantly interacted with the irrigation regime in modifying potato yield and quality. Farming protocol, cultivar, irrigation and nitrogen fertilization all affected both amino acid contents and composition with a significant decrease of most essential amino acids in coincidence with highest nitrogen levels. An increased water availability caused an accumulation of reducing sugars in potato tubers only in organic farming, whereas such accumulation was not observed under conventional farming. These results indicate that cultivar-specific genetic determinants and cultivation factors, including the farming system, may strongly and specifically interact to affect important quality parameters of potato tubers. This should be considered to improve quality standards in organic farming.
source: European Journal of Agronomy