Browsing by Author "Pakarinen, Aku"

Modern agriculture uses great amounts of fertilizers. A large portion of these fertilizers leaches from the fields to the surrounding environment and causes eutrophication of water ecosystems. Fertilizers are an expense for the farmer. Sustainable agriculture aims to minimize the use of fertilizers by using natural processes and nutrient circulation. Crop rotation is an important tool in sustainable agriculture. In crop rotation different crop species are cultivated alternately in the same field. Arbuscular mycorrhizal (AM) symbiosis is one of the world’s most important symbioses — 80 % of land plants form it. AM symbiosis enhances host plant’s nutrient uptake and provides nutrients from low concentrations in the soil. The important role of AM symbiosis in agriculture is widely recognized. However, the effect of different crop sequences on soil AM fungi is poorly studied, especially in boreal climate. In this thesis, I study the effect of four different preceding green manure crops (white lupin Lupinus albus, french marigold Tagetes patula, crimson clover Trifolium incarnatum and common vetch/hairy vetch Vicia sativa/V. villosa) on the AM colonization rate and diversity in onion (Allium cepa) roots and rhizosphere. White lupin does not form a mycorrhiza, unlike the other three preceding crops in the experiment. Onion is one of the most cultivated vegetable crops in Finland and is particularly dependent on its AM symbiont. My thesis is based on a field experiment executed in Natural Resources Institute Finland’s study field, in Mikkeli, eastern Finland, from 2017 to 2018. One of the four preceding crops was sowed in each cultivated row for 2017 growing season. Preceding crops were ploughed into the soil in autumn 2017. Onion was cultivated in all rows in 2018 growing season. I studied the effect of different preceding crops on the AM colonization rate in onion roots with microscopic methods. I studied the effect of preceding crops on the AM diversity in onion roots and rhizosphere with molecular methods. The preceding crop did not have an effect on the AM colonization rate, nor did it affect the AM diversity in onion roots or rhizosphere. Unlike in previous studies in warmer climates, the non-mycorrhizal preceding crop white lupin did not have a negative impact on the soil AM community. My study suggests that non-mycorrhizal preceding crops can be used in crop rotations, in the climate conditions of eastern Finland, especially in combination with mycorrhizal plants. Future studies should investigate the effect of longer crop rotations on the soil AM fungal communities.