Ny giv for midtnorsk øko-potet med tidlige sorter og god agronomi?

Summary

The project “Organic potatoes in Mid-Norway – the potential of early cultivars and good agronomy” (POTETGIV) was funded by the Regional Research Council Møre and Romsdal, with cofunding from the County Governor of Trøndelag/Trøndelag County Council and the County Governor of Møre og Romsdal/ Møre og Romsdal County Council. The aim was to study if early potato varieties could produce acceptable yields of potatoes which could perform well during storage in a traditional potato storage cooled by controlled ventilation, when no fungicides were used against late blight (Phytophtora infestans). Late blight is a major problem in organic growing of potatoes in the region of Mid-Norway, which comprises the counties Trøndelag and Møre og Romsdal. The study was carried out as a field experiment with 4 varieties at two sites in Trøndelag (Levanger, Byneset) and one site in Møre og Romsdal (Sunndal) in the growing season of 2019. The farmers hosting the field experimental sites assisted in the field work by carrying out soil tillage and weed harrowing and are kindly acknowledged also for inviting the public to open field days in June 2019. The experimental work was carried out by the Norwegian Agricultural Extension Service (in Norwegian: Norsk landbruksrådgivning, NLR) Trøndelag, assisted by Landbruk Nordvest in Sunnndal (local division of NLR). The potatoes were stored in Sunndal with Sunndalspotet AS, who was responsible for assessing the quality of potatoes during storage. Norwegian Centre for Organic Agriculture (NORSØK) coordinated the project activities, and a general aim of the project was to increase the interest for growing organic potatoes in this region of Norway. Mid-Norway has a significant organic production in general, but a scarce area of farmland used to grow organic potatoes. Only 18.5 out of totally about 1700 hectares were used for organic potatoes in 2018, and in 2019 this area decreased to 12.5 hectares. The main reasons are that one large costumer (a hospital) stopped their former practice of purchasing organically grown potatoes, and organic potatoes have not been prioritised as a product by the retail sector. Only about 1% of the total consumption of potatoes in Norway is from organic potatoes, whereas for carrots, about 5% are organic.
To study whether early potato cultivars may give satisfactory yields before infestation of late blight, and be used for storage over winter, we designed a field experiment with four treatments: Early and late planting of seed potatoes which were, or were not, pre-sprouted (kept cool, in light) before planting. We wanted to test if application of early cultivars may be a good strategy for growing organic potatoes, since they may possibly produce a reasonable yield before the first attack of late blight. By such attack, the leafy canopy must be removed to avoid infestation on the rest of the canopy and the tubers. Light treatment, and early planting of seed potatoes will also support early growth. We wanted also to study of the shelf life of the tubers was sufficient for storage over winter before consumption. The cultivars were Hassel, Solist (yellow), Juno and Rutt (red). Very surprisingly, the summer of 2019 was quite dry, and no infestation of late blight occurred. Hence the canopy was removed in mid-August, well before senescence. Yields were recorded shortly after removal of canopy, and again in September when the temperature had decreased and become acceptable for storage without active cooling. We wanted to study if the remaining stalks had some effect on the growth of potatoes after removal of the canopy. The cultivar Hassel produced the highest yields, on average 50 tons per hectare. The other cultivars produced about 45 tons. We did not find increased tuber yields at the second harvest. For early planted potatoes, we found a positive effect of light treatment. On average for all treatments and potato cultivars, potatoes with light treatment gave 49 tons, and without light treatment 47 tons per hectare. For late planted potatoes, there was no positive effect of light treatment. The proportion of large potatoes (> 60 mm) increased after removal of potato canopy, when the potato plants remained in the field for several weeks. Growers need to be aware and consider removal of canopy to control the proportion of large tubers, not only to control late blight. Surface scurf was the most serious reason for out-sorting during quality assessment after storage to January-February. The proportion of potatoes being sorted out (not possible to sell as food quality) ranged between 9 and 13% for the three experimental sites. The incidence of surface scurf decreased with more organic matter in the soil. Solist and Hassel performed well during storage, and more than 50% of the tubers were found to be satisfactory for marketing in late April. This is comparable with potato cultivars normally grown for storage, such as Folva. For Rutt, only 34% of the tubers were acceptable for marketing, and for Juno, which is the earliest cultivar tested here, 0% of the tubers were acceptable for marketing in late April because they had begun to sprout.
We conclude that growing Hassel or Solist, with early planting after light treatment, may give good yields of organically grown potatoes in Trøndelag and Møre og Romsdal which may perform as well as conventionally grown storage varieties of potato during storage over winter. This is useful knowledge for producers of organically grown potatoes in Mid-Norway. Retail actors have a potential to do more active marketing of organically grown potatoes, in this region and in Norway in general. Possibly, sales could increase if premium prices, which are currently close to 90% as compared with conventional prices, are somewhat reduced. Premium prices tend to increase along the distribution chain, and the prices to consumers end up very high.
A video from the project (in Norwegian) is available at this link: https://youtu.be/mwMXkOSBB_U