The Potassium Absorption Capacity of Witloof Chicory (Cichorium intybus L.) in Modelled Salt Accumulated Field Made by Excessive Application of Methane Fermentation Digested Slurry

The Methane Fermentation Digested Slurry (DS) contains sufficient nitrogen and other fertilizer components, thus several studies have been conducted on the development of practical techniques to use DS for horticultural productions (Möller and Müller, 2012; Endo, 2014). In practice, there are several studies for a more efficient use of DS as a fertilizer for realizing a sustainable production of various horticultural crops, such as tomato (Solanum lycopersicum L.), cabbage (Brassica oleracea L.), Komatsuna (Brassica rapa) and cucumber (Cucumis sativus L.) (Endo et al., 2002; Tokuda et al., 2010; Fujikawa and Nakamura, 2010; Yoshino et al., 2012). On the other hand, it has been recognized that, in Japan, the problem of remanence and accumulation of fertilizer components in the soil is getting conspicuous, not only for indoor fields but also for open field horticultural production, being the cause of this problem an excessive use of fertilizers, both chemical and organic (Tanimoto, 1991). In particular, the organic fertilizers, such as compost and DS derived from livestock wastes, especially for cow manures, contain a high concentration of potassium among the three major plant macronutrients. This specific chemical constitution leads consequently to the potassium accumulation in the soils when we use it based on the required amount of nitrogen (Goto and Eguchi, 1997; Oyanagi et al., 2002). In order to make the best use of organic fertilizers for an efficient production of horticultural crops, it is necessary to develop practical solutions which can avoid potassium accumulation in the soils. The accumulation of salts, including potassium, tends to break the balance of mineral absorption by crops. This may lead to a yield decreasing, a deterioration in quality and negative impacts to livestock animals such as grass tetany when used as a forage crop; consequently, the importance of effective solutions to evade salt accumulation in the soils has been recognized (Ito et al., 1981; Eguchi, 1993). The major techniques recently used for salt removal from salt accumulated soils are: 1) excessive irrigation or flooding, including dumping the snow into the field (Aragaki et al., 1986); 2) dilution of salts by removing surface soils, soil dressing and plowing to replace surface soil with subsoil; 3) organic matter application which aims to increase chemical, physical and biological soil buffering capacity (Ikeda et al., 1994); and 4) growing a “Cleaning Crop”, which has an excessive salt absorption capacity from the soils, e.g. grass for forage or green manure. The most common method with comparative ease is probably the flooding (excessive irrigation): However, it has been reported that this technique has several problems, such as impacts on the ground water quality by the leaching of nitrate nitrogen or sulphate ion (Yanagase et al., 2005). Furthermore, researches have clarified until now that this technique can lead to the emission of a large amount of ni-