Onion (Allium cepa L.) production in converted paddy fields has been increasing in Japan in order to meet increases in domestic demand. The Hokuriku region is characterized by plentiful snowfall and widely-spread, heavy clayey fields, which are limiting factors in the yield of autumn planted onion. Unsurprisingly, this region has a lower onion yield compared to the average onion yield in other parts of Japan. In this study, we evaluated the effect of polyethylene film mulching and the basal application of various slow-release fertilizers on the yield of onion in a heavy clayey field over a period of four years in Joetsu, Niigata prefecture. Plants were seeded in 448-cell trays in early September of each year and were then transplanted in mid-to-late October into rows covered with or without black polyethylene mulching film. Within each mulch or no-mulch row, fertilizer application was tested. The conventional application subplot (CV) received a basal application of fertilizer at transplanting and a follow up topdressing in the spring. In the other subplots, any of the slow-release fertilizers (i.e., various types of coated urea or calcium cyanamides) were applied at transplanting along with the same basal fertilizer as the CV subplot. The results are summarized as follows:

1) Although mulching led to a significantly higher yield than no-mulching did in two of the four trials, this increase in yield effect was not observed in the other two trials.

2) With the basal application of some kinds of coated urea or calcium cyanamide, the onion yield was comparable or higher than the CV onion yield in three of the four trials.

3) Among the examined coated urea, LPS40 seemed to be the most appropriate fertilizer to be applied with basal fertilizer in this region.

We developed a simple device to determine soil gas diffusion values. The operating principle is the same as the McIntyre and Phillips design in which a gaseous tracer is supplied to the confined core of a probe that is inserted into the soil. The diffusion coefficient is obtained from the rate of decline of the tracer gas in the core. We used a semiconductor gas sensor and iso-butane (2-methylpropane) gas to measure the concentration of the tracer gas in order to eliminate the need for gas chromatography and to minimize the amount of tracer gas required. Our device can quantify the gas diffusion coefficient of Toyoura standard sand as accurately as Osozawa and Kubota's method, which is the most widely-used laboratory method. The semiconductor gas sensor requires preheating to obtain a stable output and a period to equilibrate with the ambient soil humidity before measurement, as the sensor is sensitive to humidity. The sensor output can determine the concentration of iso-butane using an exponential function. Additionally, the sample must be kept wet for measurement, because iso-butane is absorbed on the surface of the air-dried portion of Toyoura standard sand.

Organic farming is promoted as a way to produce food while minimizing harm to ecosystems. We examined the feasibility of an organic rice (Oryza sativa L.)–rice–soybean (Glycine max (L.) Merr.) rotation system, using the application of common organic materials to produce standard yields of each crop in the Ibaraki prefecture, Japan. Using applications of rice bran, soybean curd residue, leftover grains, and other organic materials, we were able to adjust the nitrogen (N) and phosphate (P₂O₅) application rates to less than 7.4±0.20 g m⁻² and 8.6±1.93 g m⁻², respectively, in place of inorganic fertilizer in rice production from 2009 to 2018. Since three years after the start of the organic system, the brown rice yields with winter flooding reached 530 and 580 g m⁻² in 2012 and 2013, respectively. The yields were 350–490 g m⁻² from 2015 to 2018. The weight ratio of grain to straw and the percentage of ripened grains were lower than conventional values in the cited document, and the protein concentrations in the brown rice were generally lower than the upper limit recommended for fine taste. The soybean yields were relatively stable (190–270 g m⁻²) with only plowing hairy vetch (Vicia villosa Roth) used as a green manure in 2011, 2014, and 2017. No increasing or decreasing trends were recognized in total carbon or N concentrations in the soil during the experimental period, although both showed increases in the spring after winter flooding. Soil available N increased from 2009 to 2012, but a declining trend was not recognized after that. Available P remained low during the experiment. The present practice supported an adequate rice and soybean yield and conserved soil available N. We concluded that more N supply around the heading stage could be effective to increase rice yield.