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The radiocesium interception potential (RIP) of bulk soil (RIP) can reliably be used to predict the magnitude of soil-to-plant radiocesium transfer. There has been some controversy about which soil properties control the RIP, although the RIP is theoretically proportional to the amount of frayed edge sites in micaceous clay minerals. The RIP was determined for 97 paddy soils in three regions (Hama-dori, Naka-dori, and Aizu) in Fukushima Prefecture, Japan, and the relationships between selected physicochemical properties and the RIP were analyzed. The mean (± standard deviation) of the RIP for the 97 soils was 1.67 (±0.87) mol kg, and the range was 0.34 to 5.36 mol kg. Pearson correlation analysis revealed that the RIP positively correlated best ( < 0.01) with the clay fraction K content as a mass fraction of the bulk soil (clay-K) and negatively correlated with the total C content and the phosphate absorption coefficient ( < 0.05). Therefore, clay-K, an indicator of the amount of micaceous clay minerals in a soil, was confirmed as being useful for estimating the magnitude of the RIP for paddy soils in Fukushima. The RIP was invariably low if either the total C content exceeded 6.0% or the phosphate absorption coefficient exceeded 1500 mg kg, suggesting that these parameters could be useful for screening soils with particularly low RIP values.

Improved recovery of fertilizer nitrogen (N) would permit a reduction in the rate of application of fertilizer, which would save resources and decrease N outflow from paddy fields into adjacent bodies of water. Contact application of controlled‐availability fertilizer (CAF) to plant roots (i.e. “co‐situs application”) is a possible method to increase the recovery of fertilizer N by plants. We investigated the effects of co‐situs CAF application on the uptake of fertilizer and soil N and the yield of paddy rice (Oryza sativa L.) in seven soils with different levels of available N. The experiment was conducted in a paddy field in which the plow layer soil had been replaced with the sample soils. The uptake of fertilizer N increased to 4.5–5.3 g m−2 (65–75% recovery) with co‐situs application (7 g N m−2) from 1.9–2.6 g m−2 (27–37% recovery) with conventional readily available fertilizer (RAF). The increased uptake of fertilizer N was not significantly correlated with available soil N. However, the uptake of soil N decreased by 0.2–1.6 g m−2 with co‐situs CAF application, and the decrease in soil N uptake was greatest in soils with the highest available N. The net (total) N uptake after co‐situs application was 0.9–2.4 g m−2. Brown rice yield was strongly related to N uptake in the RAF and CAF plots. Nitrogen application rates could be reduced by 19–53% with co‐situs application, while still providing a N uptake equal to that with conventional RAF application. However, the potential reduction in the application rate of N was smaller in soils with more available N.

This study clarified suitable times for the single spraying of a fruit cluster with forchlorfenuron (1-(2-chloro-4-pyridyl)-3-phenylurea, CPPU) to reduce radial fruit cracking during tomato production under a rain shelter. We examined the relation between fruit development at the time of CPPU spraying and the occurrence of radial fruit cracking. The rate of occurrence was reduced in fruits that had been sprayed when they were 1.5-6.5 cm in diameter. The CPPU spraying time was regarded as the time when the maximum fruit diameter in the truss is 3.0-4.9 cm, with the minimum fruit diameter being about 1.5 cm. Actually, radial fruit cracking was clearly reduced by CPPU spraying at the time with a 3.0-4.9 cm maximum fruit diameter, although the reduction was somewhat unclear by spraying at the time of flowering or at the time with a maximum fruit diameter of 1.0-2.9, 5.0-6.9, or 6.0-7.9 cm. The reduction of radial fruit cracking by CPPU spraying was regarded as attributable to the increase in cell numbers near the fruit epidermis. The CPPU spraying did not significantly affect the harvested fruit number, average fruit weight, or total fruit yield. The marketable fruit yield increased along with the reduction of radial fruit cracking by CPPU spraying. The shape and quality of fruits sprayed with CPPU and untreated fruits were equivalent.

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