Effects of organic (Italian ryegrass and Bokashi) and chemical fertilizer on growth, yield, and grain quality of rice (Oryza sativa L.) were compared under different planting densities in 2013/2014 and 2014/2015. Italian ryegrass was incorporated into the soil as green manure. Bokashi (a mixture of organic materials) was applied as basal dressing. To measure yield and its components, 30 hills were chosen for each treatment. Rice grains were harvested from each treatment to assess the grain quality and to evaluate accumulation structures using a scanning electron microscope. Bokashi treatment increased panicle number per hill, ripened grain percentage, panicle number per m², and grain yield compared to no fertilizer treatment at normal planting density. Chemical fertilizer treatment increased plant length at high planting density. Italian ryegrass and Bokashi treatments promoted the taste point (taste score as reference) by reduction of amylose and protein contents at normal planting density in contrast to chemical fertilizer. 1000-grain weight, panicle number per m², and grain yield were higher at high planting density than at normal planting density. However, high planting density decreased panicle number per hill and spikelet number per panicle. It also enhanced the amylose content of rice grain. Scanning electron microscopic observation revealed that chemical fertilizer treatment marked up protein bodies and their traces on amyloplasts. However, Bokashi treatment produced large amyloplasts, which included many starch granules. These results show that Italian ryegrass and Bokashi can offset reductions of chemical fertilizer and can lead to sufficient starch accumulation structures in rice grains. Graphical Abstract (Kakar et al.)

Paddy field runoff containing plastic capsules that are used to coat fertilizers has been receiving increased attention. However, the behavior of these capsules, especially their degradation behavior, has not been extensively investigated. We divided the capsules in runoff into two categories: “floating capsules after ploughing” and “floating capsules discharged via pipes at the exits of paddy fields”. The behaviors of the capsules in both types of runoff were monitored in 2022 and 2023 at four paddy fields in Fukushima and Miyagi prefectures in northern Japan. Sampling of capsules in paddy biomass and soil, and comparisons of capsule weight to biomass weight showed that a decrease in plastic capsule weight reflected a decrease in capsule runoff. However, the emergence of clear effects showed a delay of 2 to 3 years, as explained by carbon isotopic analyses. The decrease in the weight of the plastic capsules could be attributed to a combination of capsule degradation and the release of urea inside the capsules, which was also explained by carbon isotopic analyses. Three types of degraded capsules were found: shrunken, broken, and spherical. Statistically significant differences among the weights of each type found.

The Fukushima nuclear accident caused widespread radiocesium contamination, and subsequent decontamination reduced soil fertility by removing nutrient-rich topsoil. Although biological amendments have been widely investigated for soil improvement, their potential to restore crop productivity in decontaminated Fukushima soils remains poorly understood. This study evaluated a Bacillus-based biofertilizer (Yume-Bio) and an Aspergillus fermentation product (kouji) as biological amendments for restoring crop productivity in decontaminated soils. Pot and field experiments were conducted to assess their effects on the growth, mineral nutrition, and seed yield of Perilla frutescens grown in decontaminated Fukushima soils. In pot experiments, Yume-Bio showed no significant effects on plant growth, although slight root improvement was observed. In contrast, application of kouji alone or in combination with Yume-Bio significantly enhanced plant growth, increasing leaf number by 112% and improving biomass production. Nutrient accumulation was also promoted, with total N and Fe increasing by 170% and 194%, respectively. In field experiments at two sites in Fukushima, treatment effects were limited and generally non-significant. These results indicate that kouji has potential to enhance plant growth under controlled conditions, while the effectiveness of biological amendments under field conditions remains site-dependent, highlighting the need to optimize application strategies under heterogeneous soil conditions.