2015 Volume 14 Issue 4 Pages 349-356
To expand the use of digestive liquid (DL) from methane fermentation, we examined whether DL could be used as a fertilizer in hydroponics. Because DL contains a large amount of NH4-N, plants would suffer from severe damage due to NH4-N and NO2-N if grown in nutrient solutions containing DL. Nitrifying bacteria propagated in sand filters equipped in some hydroponic facilities might prevent the accumulation of NH4-N and NO2-N, so the nitrification performance of the filter was monitored. The nitrifying capacity of a mature sand filter with a 0.0079 m2 filtration area was 180 mg・day−1 N. NO2-N tends to accumulate when NH4-N is highly loaded on the filtration system. Komatsuna (Brassica rapa L. Perviridis Group) plants were grown hydroponically using completely nitrified DL as fertilizer. The shoot fresh weight was comparable to that of the conventional cultivation method if phosphate and microelements were added to the nitrified DL-based nutrient solutions. Komatsuna plants were also grown in the NFT system equipped with sand filters and nutrients were replenished by the untreated DL during the cultivation period. The plant height was slightly lower than that with the conventional cultivation method, although the shoot fresh weight of both showed no significant difference. When DL was used for the nutrient solution, a large amount of K, Na, or Cl accumulated, presumably having negative effects on the plant height. Further study is needed to resolve the problems related to the accumulation of some nutrients in order to achieve the practical use of DL in hydroponics.