In a farm-oriented enhancing aquatic system (FOEAS) paddy field and a conventional heavy-clay paddy field, we investigated the effect of high temperature during the ripening period on the yield and appearance quality of rice. The groundwater level of the FOEAS paddy field during the ripening period was maintained at 10–30 cm below the soil surface, while in the conventional paddy field, surface water was completely drained, remaining 30–50 cm below the soil surface, in late July. The sap bleeding rate of the plants in the FOEAS paddy high-temperature field was significantly higher than that in the conventional high-temperature paddy field. The difference was caused mainly by the increase in water uptake from soil below a depth of 12 cm in the FOEAS paddy field. Panicle temperature in the FOEAS paddy field was significantly lower than that in the conventional paddy field. The incidence of cracked, milky-white, and white-based rice kernels in the FOEAS paddy high-temperature field was significantly lower than that in the conventional high-temperature paddy field. In addition, the yield of rice in the FOEAS paddy field was higher than that in the conventional paddy field due to increases in the ripening rate and the thousand grain weight. The soil penetration resistance value in the FOEAS paddy field was equal to that in the conventional paddy field, confirming that the bearing capacity of the soil is suitable for machine harvest.
The results indicated that FOEAS in heavy-clay large-scale paddy fields is effective for conducting both large-scale mechanical work and maintaining the appearance quality of rice under high air temperature during grain filling.
In greenhouses cultivating eggplant in Kochi, Japan, a lengthening of productive growing periods and concomitant reduction in the frequency of desalting irrigation during fallow periods had resulted in nutrient accumulation in the soil. Excess nitrate in soil may suppress water and nutrient uptake by eggplant, resulting in unsatisfactory plant growth. The objective of this study was to assess rootstock eggplant growth and nutrient uptake under different soil NO3−-N and moisture content conditions in nutrient-accumulated soil.
Pot experiments in the glasshouse were carried out at three soil NO3−-N concentrations (13.4, 26.8, and 40.2 mmolc kg−1) and three levels of soil moisture (41, 51, and 61％ of maximum water holding capacity, designated as “dry,” “middle,” and “wet,” respectively).
The height of the eggplant was more in the treatment with lower NO3−-N concentration. High soil NO3−-N reduced eggplant stem diameters and shoot dry matter weight more distinctly in the “middle” treatment than in the “wet” treatment; this is because other ion concentrations are also raised in soil treated with high NO3−-N, resulting in reduced water uptake and disturbance of nitrogen metabolism. Suppression of eggplant growth due to high soil NO3−-N can be mitigated by maintaining soil moisture at a level high enough to keep the nitrate concentration below 37 mmolc L−1 in nutrient-accumulated soil.
To increase the yield of organic onion (Allium cepa L.) crops in Hokkaido, we conducted experiments on application of organic nitrogen fertilizers. The crop was cultivated under conditions of varying range of soil nitrogen fertility under the Japanese Agricultural Standard of Organic Agricultural Products. The main results obtained are as follows: (1) The onion yield was significantly higher after a single nitrogen fertilizer application in spring than after a split application (2/3 applied in the previous autumn and 1/3 applied in the spring of the current year). (2) There was no difference in onion yield when organic fertilizers with nitrogen content of ≥40 g kg−1 were used for the single fertilizer application in spring. However, the onion yield was lower after application of fertilizers with nitrogen content of approximately 20 g kg−1 than after application of fertilizers with nitrogen content of ≥40 g kg−1 . (3) We used the following formula to calculate the rate of nitrogen fertilizer application essential to obtain 44 Mg ha−1, the target yield of organic onion: (optimum nitrogen uptake–nitrogen uptake without nitrogen)/nitrogen fertilizer utilization rate. Using this formula, the rate of nitrogen fertilizer application was calculated to be 140 kg ha−1 when the soil nitrogen concentration was 50–70 mg kg−1 (according to the soil nitrogen diagnosis standard determined using the hot-water extraction method). When the soil nitrogen fertility was lower or higher than this range, it could be adjusted by increasing or decreasing the rate of nitrogen fertilizer application by 40 kg ha−1.
A rational fertilization method is required in the cultivation of lotus root (Nelumbo nucifera) for its stable production and the reduction of nutrient load in lakes and marshes. In this study, we established a rational and systematic method of fertilizer application for the cultivation of lotus roots. The standard yield from a given field was calculated as an average value of the yield per unit area for the past three years. The amount of nutrient absorption by lotus roots was then estimated on the basis of standard yield. Based on the results of a previous study, we experimentally formulated a specialized fertilizer that is compatible with the nutrient absorption properties of lotus roots. Using these processes, we established and verified a rational fertilization method for the cultivation of lotus roots. The yields and quality of lotus roots that were obtained using this fertilization method were comparable to those obtained using the standard fertilization method. This result indicates the validity of the fertilizer application method developed by us.