The effect of different farming systems on potato tuber yield and quality
The world’s population is estimated to exceed over 9 billion people by 2050 (FAO, 2013), thus the demand for high yielding, good quality crops as well as the “challenges for the sustainability of the ecosystems” increases (Somers and Savard, 2015). Proper crop management is a key element in achieving high yields of good quality. Crop rotation, animal manures, and winter cover crops as catch crops (CC) play important roles in sustainable plant production systems because they provide nutrients for the system (Stark and Porter, 2005). CC and animal manures are mainly used by organic producers, because these are the main nutrient-rich sources for organic crop production. Animal manures are used by conventional producers only if, in addition to crop production, they have also livestock. Conventional producers, who grow only crops, largely depend on mineral fertilizers and different synthetic agrochemicals. According to Luik et al. (2008) conventional systems might not be sustainable in the long term, because they tend to be oversimplifi ed and maximally intensifi ed. But Edwards-Jones and Howells (2001) claimed that neither conventional nor organic farming systems (FS) are sustainable because both of them require inputs from non-renewable resources and, one way or another, they both impact on the environment. For organic producers there are also two main challenges, such as managing diseases and nutrients since nutrient availability is limited and there are only a few effective pesticides available that are allowed for use (Finckh et al., 2006). Also, Nelson et al. (2009) confi rm that in organic systems nutrient transformations almost exclusively relyon soil. In conventional systems, if there are problems with diseases or pest and with plant malnutrition, synthetic agrochemicals and mineral fertilizers can be provided throughout almost the entire growing season. Despite some limitations in organic farming, organic agriculture is based on its own self-regulating production system, and the concept of a farm is as an agro-ecosystem (Lammerts van Bueren et al., 2002). But organic agriculture alone does not provide a suffi cient amount of food for the growing population (Oliver and Gregory, 2015). In contrast, conventional agriculture depends mainly on external inputs, which makes it somewhat more vulnerable. To consider farming systems to be sustainable they must be “productive and maintain their contribution to society in the long term” (Gadanakis et al., 2015). In general, the demand for agricultural practices and food security that are more environmentfriendly is increasing rapidly, which favours the development of new 10 integrated farming systems (Duc et al., 2015). Such farming systems that use integrated management practices, such as crop rotations and organic (green manure crops, leguminous crops, CC) and inorganic fertilizers, will maintain soil as well as human health (Marsh, 2000; Oliver and Gregory, 2015). Future agriculture must also evolve towards climate-smart agriculture technologies, which are more adaptive to climate change by improving resource use effi ciency and ensuring food security (Zhang et al., 2015). Achieving food security does not only mean an adequate food supply but it also means that the food must be nutritious, of good quality (Wei et al., 2015). The potato is one of the most important crops worldwide, ranking fourth in annual production (Fernie and Willmitzer, 2001). The potato can be grown in harsher climates, and it is able to give, relatively quickly, high nutritious yields compared to any of the other major food crops (Lutaladio and Castaldi, 2009). However, to be productive, the potato needs signifi cant nutrient inputs to maintain its productiveness and quality. Crop management is the main factor that infl uences crop production and disease resistance (Larkin and Halloran, 2014; Olanya et al., 2014). Previous research has shown that FS affect tuber quality characteristics such as tuber nutrients (Järvan and Edesi, 2009) as well as starch and dry matter (DM) contents (Roinila et al., 2003). Plant nutrition is an important factor that infl uences natural disease resistance. If there is a defi ciency of essential elements susceptibility to potato diseases increases (Czajkowski et al., 2011), because the plant’s natural ability to fi ght them is lowered (Mulder and Turkensteen, 2005). Nutrients affect the plant physiology and thus potential for infection with pathogens (Dordas, 2008). At the European Association for Potato Research (EAPR, 2014) conference last year it was concluded that the agronomy side of potato production has gained too little attention over the past years and needs to regain its importance, because the agronomic side of potato production determines the potato performance parameters. Potato is a crop that has been studied in Estonia extensively because of its importance in Estonians everyday diet. The fi rst true Estonian potato scientist was Julius Aamisepp who promoted the cultivation of potato and its research. The fi rst fertilization experiments were conducted by Arnold Piho in 1960–1980 which also included the potato crop. The latest potato fertilization research has been made by Kuldkepp et al. 11 (1999), by Astover and Roostalu (2003), by Järvan and Edesi (2009), by Toomsoo and Leedu (2002), by Toomsoo et al. (2009; 2012). However, such complex potato fertilization research (under different organic and conventional farming systems) presented in current thesis has not been made before in Estonia. Earlier potato research has had mainly domestic importance. In the past, besides potato fertilization, the effect of different potato pre-planting thermal treatments on the tuber yield formation has been studied by Viacheslav Eremeev. Also there has been some potato disease related research by Mati Koppel who studied the potato soft rot (Erwinia/Pectobacterium spp.) disease and by Eve Runno-Paurson who investigated the potato late blight (Phytophthora infestans). The potato meristem multiplication has been studied by Viive Rosenberg and Marje Särekanno. Potato research related to plant breeding has been conducted by Aide Tsahkna and Mati Koppel. There are many other great potato researchers in Estonia who are a true experts in their fi eld of study. Crop rotations are important tools that affect potato productivity (Carter et al., 2003) and diseases (Peters et al., 2004). Catch crops are essential to avoid nutrient losses (Stark and Porter, 2005). Brassica crops used as CC have, furthermore, been found to have a disease suppressing effect (Cohen et al., 2005). Since the potato is a high nutrient demanding crop, additional mineral or organic fertilizers must be provided. Despite nitrogen (N) being a basic potato nutrient, the selection of its appropriate application rate for the potato is quite diffi cult, due to signifi cant variation (Zebarth et al., 2009). The appropriate N demand can vary among many factors such as climatic conditions during the growth period, crop management practices the previous crops cultivated. Addressing all the aforementioned factors should ensure high potato yields of good quality. Currently, these are the following gaps in our knowledge: (i) how the yield increase through different agronomic practices affects the potato tuber mineral elements concentrations (which are considered tuber nutrients) (White et al., 2009) and overall crop quality (Wang et al., 2008), (ii) how crop rotations infl uence tuber quality parameters (Mohr et al., 2011), and (iii) how the plant nutrition and crop rotations together affect the occurrence of tuber diseases (VanderZaag, 2010). The focus of much research tends to be on organic or conventional management systems separately, it is important to investigate their infl uence together comparatively (Bernard et al., 2014). Thus, the overall aim of this thesis is to 12 investigate how different organic and conventional management practices under the same crop rotation infl uence tuber quality characteristics as well as yield.Käesoleva doktoritöö raames uuritakse, kuidas erinevad viljelussüsteemid (neli tavaviljeluse süsteemi koos suureneva mineraalse lämmastiku normiga vs kaks mahesüsteemi koos vahekultuuride ja sõnnikuga), mis järgivad sama külvikorda (punane ristik, talinisu, hernes, kartul, oder punase ristiku allakülviga) mõjutavad kartuli kogu ja kaubanduslikke saake, mugulate toiteainete (N, P, K, Ca, Mg), nitraatide (NO3–), tärklise ja kuivaine sisaldust kui ka mugulahaiguste nagu harilik kärn (Streptomyces spp.), hõbekärn (Helminthosporium solani), kuivmädanik (Fusarium spp.) ja märgmädanik (Pectobacterium spp.) esinemist, mida määratletakse ka kui mugulate kvaliteedinäitajaid. Antud töö peamine hüpotees on, et kartuli saagikus ning mugulate toitainete, nitraatide, kuivaine ja tärklise sisaldus kui ka mugulahaiguste esinemine sõltuvad kõik viljelussüsteemist, külvikorrakultuuridest ning kliimatingimustest. Tulenevalt töö hüpoteesist oli uurimustöö eesmärkideks täpsemalt (i) hinnata viljelussüsteemi mõju kartuli saagierinevustele, (ii) uurida, kuidas erinevad viljelussüsteemid mõjutavad mugulate makrotoitainete kontsentratsiooni kui ka kuivaine ja tärklisesisaldust (iii) ning mugulahaiguste esinemist. Uurimistööst ilmnes, et uuritavate aastate keskmisena oli viljelussüsteemidel usutav mõju kartuli saagikusele, mugulate N, NO3–, P ja Mg sisaldustele kui ka mugulahaiguste nagu kuivmädanik, hõbekärn ja harilik kärn (madala nakkustasemega) esinemisele. Seega viljelussüsteemide toitainetega varustatus kui ka nende allikas võivad suuresti mõjutada mõningaid mugulate kvaliteedinäitajaid. Mugulate K, Ca, tärklise ja kuivaine sisaldused kui ka märgmädaniku esinemine vastupidiselt ei olnud mõjutatud erinevatest viljelussüsteemidest ning nende toitainetega varustatusest, kui välistatakse kasvuaasta ilmastikutingimuste mõju. See, kuidas konkreetne süsteem mõjutab mugulate kvaliteediomadusi, on otseselt mõjutatud ka kasvuperioodi keskkonnatingimustest.