Results

A basic yield determining factor is - in addition to the soil type - the available growing period. The potato haulms can - depending on weather conditions - be infested at an early growing stage by late blight. If late blight destroys the haulms, the tubers will not grow anymore. Pre-sprouting the seed potatoes can start the growing faster and develop earlier, which helps to secure yields. Farmers, who pre-sprouted their seed potatoes had an additional yield over the years of 16 percent on average. Irrigation of the potatoes resulted in significantly higher yields (up by 25 percent) and stabilized the yield level, which is of great advantage especially on lighter, sandy soils with a low water holding capacity. Contemporary irrigation reduces the infestation with wireworms. This decreases the sorting and increases the proportion of marketable potatoes.

A sensory panel of experts has been trained to evaluate the sensory quality. The expert panel should classify the taste attributes sweet, bitter, chestnut to musty and detect their intensities. Also, it should help to identify batches of potatoes with sensory deficiencies. So in 2007, potato batches of the variety Princess were often ranked highly bitter. This was caused by the weather conditions. They led to an infestation by late blight at an early growth stage and, thus to a die-off of the potato crops. These physiologically immature potatoes showed not only a bitter taste but also very low starch content and often high nitrate levels.

The results of this farm-practice focused project to improve organic potato production show that an intensive cooperation between farmers, advisers and scientists generate valuable insights. They immediately benefit the agricultural practice, because they directly find the way into the advisory practice.

The project results were also used to revise the brochure for organic potato cultivation, which is edited by FiBL, Bioland Beratung, Kompetenzzentrum Ökolandbau Niedersachsen (KÖN) and Bio-Austria in cooperation with the Thünen-Institute of Organic Farming and is now available free of charge for everyone.

Background and Objective

The external quality characteristics of potatoes include a uniform tuber shape, no damage and very smooth skin without black scurf or scabs. The "inner quality", however, includes the value-adding and value-reducing ingredients - a starch content which corresponds to the variety, low nitrate content and a high sensory quality, whereby, i.a. the taste experience is meant. Here taste is defined as the overall sensory experience that the consumer perceives through the interaction of taste, smell and tactile sensitivity. It consists of many components such as sugar, starch, organic acids, etc., but also of a huge number of flavours, most of which are volatile compounds and are perceived by our smell receptors. All this depends on many factors: the choice of variety and the site and weather conditions are important, as are the agronomic measures of the farmer and the storage conditions. Our aim was to identify factors which significantly improve the external and internal qualities of potatoes, in particular the sensory qualities. We have derived cultivation recommendations for farmers from our results in order to be able to offer the consumer higher-value quality. An adequate yield must be achieved for economic viability.

Approach

In the joint project, coordinated by the Thünen-Institute of Organic Farming, Bioland-Beratung, Ökoring Niedersachsen, and Marktgenossenschaft der Naturland Bauern together with the Qualitäts-Management-Beratung für Öko-Produkte and the ttz Bremerhaven, nearly a total of 300 samples of the three potato varieties Princess, Nicola and Ditta were collected and analyzed, mainly in the North and South of Germany, over the project period of three years. All the management data of the potato cultivation were requested from the farmers: Which soil tillage or organic fertilizers were used? Were the potatoes pre-sprouted or irrigated, etc.? Also, the weather conditions in the different regions and years were taken into account. All cultivation and quality data formed the basis for the web-based benchmarking system developed within the project.