The effects of nitrogen fertilization on the yield and quality of early potato (Solanum tuberosum L.) were studied at MTT Agrifood Research Finland during 1996-1997. Cultivars were harvested at three times. The experimental layout was a split-split-plot with harvest times as main plots and nitrogen fertilization and potato cultivars as the subplots. The fertilizer treatments were 60 and 120 kg N ha -1 and the cultivars tested were Timo, Gloria and Van Gogh. The harvest times were 57-62, 70-75 and 85-90 days after planting. Application of 120 kg N ha -1 intensifi ed canopy development and increased leaf area of the stands. At early harvest the tuber yield of all cultivars receiving the higher nitrogen application increased by 0.5-2.5 t ha -1 . The highest yielding cultivar was Timo. At last harvest, the higher nitrogen treatment increased yield by 3.0-6.2 t ha -1 . The highest yielding cultivars were Timo and Van Gogh. The dry matter content of tubers was very low, 13.8-17.2%, at the fi rst harvest and the higher nitrogen application reduced dry matter content by 0.3-1.0%. The highest fertilizer application rate resulted in the largest tuber size. Nitrogen application, however, affected the quality of potatoes by decreasing the dry matter content. The nitrate content in tubers increased signifi cantly with the increasing level of nitrogen. The range of nitrate content in tubers fl uctuated between 13 and 189 mg kg -1 fresh weight showing good controlling of nitrate values. Harvest time affected sucrose content and the reducing sugar content in tubers, but nitrogen fertilizer did not change the sugar content of tubers. As tuber yield and quality during a short growing season are affected mainly by intercepted radiation, methods to increase tuber yield should focus on reducing the time to emergence, improving haulm growth after emergence and increasing the harvest index.

No abstract

The effects various rates of nitrogen application on accumulation of dry matter and nitrogen in potato (Solanum tuberosum L.) were studied during a short growing period of 140-180 days, at MTT Agrifood Research Finland in 2000-2001. The treatments were 0, 60 and 120 kg N ha -1 and the potato cultivars tested were Van Gogh and Nicola. Four successive harvests were made during the course of the experiment to monitor changes in the accumulation of dry matter and nitrogen over the season. Applications of nitrogen substantially increased haulm dry matter accumulation and to an even greater extent their nitrogen contents. The highest dry matter values were generally registered at 120 kg N ha -1 . Dry matter and nitrogen content of haulms started to decline during the later part of season and most nitrogen was relocated to tubers. The results suggest that an application of only 60 kg N ha -1 was sufficient to promote rapid canopy development and there were only small reductions in dry matter and nitrogen accumulation until late in the season when the canopy started to senesce as nitrogen supply diminished. Tuber yield, plant dry matter and nitrogen accumulation at maturity were related to crop nitrogen supply. Although application of the high rate, 120 N kg ha -1 , resulted in a significant increase in dry matter accumulation, this was not reflected in the profit because the higher nitrogen application reduced dry matter content of tubers by 2.6% in 2000 and by 1.1% in 2001 relative to the use of 60 kg N ha -1 . Apparent fertilizer nitrogen recovery values on a whole plant basis ranged from 53 to 75%. The proportion of fertilizer recovered in tubers clearly declined with increase in nitrogen supply.

Commercial production of genetically modified (GM) potatoes (Solanum tuberosum L.) could represent a risk to conventional production if volunteer plants develop from tubers or true seeds that survive until the following growing season. We studied such risks under northernmost European conditions and monitored the effects of cultivar, tuber size and tuber depth in the soil on winter survival at MTT Agrifood Research Finland, Jokioinen (61806?N, 23802?E) from 2004Á 2007. Tubers of two non-GM cultivars, Saturna and Asterix, and two size classes, 25Á30 mm and 45Á50 mm, were planted at depths of 10 and 20 cm in autumn, soon after harvest. In winters 2004Á2005 and 2005Á2006 all tubers planted in the soil in autumn were killed by frost. In 2005Á2006, the field was covered by up to 30Á40 cm of snow and the minimum soil temperatures ranged between (0.4 o C and (0.9 o C, but only 0.0Á3.5% of the tubers survived and there was no difference between cultivars, tuber sizes and planting depths. Under laboratory conditions compared with (2.08C and (2.58C, treatment at (3.08C for 72 h resulted in significantly lower survival rate of the tubers (8.2%). Asterix, a late maturing table potato cultivar, was more resistant to low temperatures than the processing cultivar Saturna. In general, volunteer tubers are not currently a significant risk for coexistence of GM and conventional potato production in northern Europe due to the cold winter conditions but also due to possibilities to control the sporadic volunteers from the next crop. However, we noted that seedlings initiated from true potato seed are able to produce tubers despite the short growing season. Such a risk could be reduced by accepting only non-berry-producing GM cultivars for cultivation.

Peruna on rapsin rinnalla todennäköisin geenimuunneltu viljelykasvimme. Kun perunan tuotanto on alueellisesti keskittynyt Satakuntaan ja Pohjanmaan rannikkoalueille, muuntogeenistä perunaa joudutaan tulevaisuudessa viljelemään rinnakkain tavanomaisen perunan kanssa. Perunan muuntogeenisiä lajikkeita viljeltäessä on otettava huomioon tavanomaisten ja geenimuunneltujen lajikkeiden rinnakkaiselo. Muunneltua geeniainesta ei saa siirtyä tavanomaiseen perunan viljelyyn. Lajikkeiden sekoittuminen voi tapahtua siemeneriä siirreltäessä tai koneiden mukana. Toinen merkittävä riski ovat perunan korjuussa maahan jäävät mukulat ja niistä kasvavat jääntikasvit, joiden mukulat voivat sekoittua tavanomaisesti viljeltyyn perunaan. Maahan jäävä mukulamäärä voi olla suuri, jopa 20 000-40 000 kpl/ha. Mahdollinen riskitekijä geeniaineksen siirtymisessä on myös perunan botaaninen siemen. Perunan sukulaiskasvit mustakoiso (Solanum nigrum) ja punakoiso (Solanum dulcamara) eivät risteydy perunan kanssa eikä muuntogeenien leviäminen rikkakasvien kautta ole mahdollista. Gm-perunan viljely Euroopassa tullaan aloittamaan muuntogeenisten tärkkelysperunalajikkeiden viljelyllä. EU:ssa on parhaillaan käsiteltävänä hakemus Ruotsissa jalostetun muuntogeenisen Amflora-lajikkeen hyväksymiseksi viljelyyn. Lajike on entinen Prevalent-lajike, josta on kehitetty geenimuuntelun avulla tärkkelyksen koostumukselta poikkeava amylopektiinimuoto. Suomessa on kokeissa kotimaisia korkean tärkkelyspitoisuuden omaavia koelinjoja. Muualla kuin EU-alueella viljellään pienessä mitassa koloradokuoriaisenkestävää geenimuunneltua perunaa. Korjuussa maahan jäävät perunat tuhoutuvat talven aikana, jos lämpötila laskee useiden kuukausien ajaksi -1,0 oC alemmaksi. Pitkä kylmyysjakso lähellä jäätymisrajaa kuluttaa perunan liukoiset sokerit ja peruna tuhoutuu. Erillisissä kylmänkestävyyskokeissa kolmasosa mukuloista tuhoutui, kun lämpötila oli kahden vuorokauden ajan -2,0 - -2,5 oC. Kun lämpötila pidettiin 3-4 vuorokauden ajan -3,0 - -3,5 oC perunat tuhoutuivat täydellisesti. Lajikkeista Asterix osoittautui suuremman sokeripitoisuutensa ansiosta selvästi Saturnaa kestävämmäksi. Samasta syystä myös pieni mukulakoko (30 mm) oli suurta mukulakokoa (50 mm) kestävämpi. Perunan tärkeimmällä viljelyalueella Pohjanlahden rannikolla lumikerros jää useimpina talvina ohueksi ja jääntimukulat tuhoutuvat maan routaantuessa. Riski jääntimukuloiden säilymisestä lisääntyy, kun pysyvä lumipeite tulee ennen maan routaantumista. Botaaninen siemen ja siitä kasvava peruna eivät ole merkittävä riskitekijä tavanomaisen ja geenimuunnellun perunan rinnakkaiselossa. Muuntogeenisen lajikkeen siementen muodostuminen voidaan estää jalostamalla muuntogeenisistä lajikkeista koirassteriilejä. Jääntiperunan säilyminen maassa on mahdollista mallintaa maan lämpötilan perusteella ja laatia talven ilmastotietojen perusteella ennuste gm-perunan säilymisriskeistä eri osissa maata.