Case Study on the Use of the Leaf-Count Method for Drip Fertigation in Outdoor Cucumber Cultivation in Reconstructed Fields Devastated by a Tsunami

Abstract

Drip fertigation was tested in fields using a nitrogen fertilization method based on leaf increments, with the aim of increasing the cucumber yield in outdoor fields restored after the tsunami disaster in Rikuzentakata City, Iwate Prefecture, in 2011. The 2016 test site (Takata field) was restored as a paddy field, and there were problems with water retention and gravel contamination. The condition of the 2017 test site (Yonesaki field) was better than that of the 2016 site. The drip fertigation method increased cucumber yield by 93% and 27% in the Takata and Yonesaki fields, respectively, when compared to the yield from fields cultivated conventionally. Drip fertigation enables the constant supply of liquid fertilizer to the rhizosphere, and the easy application prevents the scarcity of fertilizer, especially at later stages of growth. In contrast, a real-time soil diagnosis, using the Dutch 1:2 soil–water extract method, was unsuccessful due to flooding, especially in the Takata field. As the purpose of this method is not to reduce the amount of nitrogen provided, but to increase the yield, and because it is difficult to precisely control the application of fertilizer due to precipitation, we suggest that the real-time soil diagnosis and feedback should be omitted to further simplify fertilizer application.