Growth prediction models are used nationwide to support rice cultivation management and to predict/evaluate rice production. Development prediction models are also used in Hokkaido. The development index (DVI) model is easy to use and has a high prediction accuracy. However, DVI models are limited to 4 rice cultivars with an earliness of “early to medium”. Therefore, we prepared the parameters of a DVI growth prediction model for rice cultivars with different levels of earliness for the Hokkaido region. During the preparation we encountered an issue because the development prediction model was not able to properly predict the difference in earliness between cultivars. This occurred due to a systematic estimation error, dependent upon the survey area of the growth data which was different between the cultivars. As a solution, we supplemented the growth data of the cultivars with the data of a “standard cultivar” to make the DVI model parameters. This was possible because the correlation between cultivars during the developmental stage of rice plants cultivated in Hokkaido is represented by a linear equation with a slope of almost 1. With the DVI model created using supplemented data, it became possible to accurately predict the difference in earliness between cultivars. This method is effective for creating development prediction models for cultivars whose developmental data is limited to survey areas and new cultivars with little data available.

View full abstract

　This study aimed to discuss an effective technique of CO₂ enrichment within a canopy of tomato grown by high-wire system in green house. Leaf area, photosynthetic photon flux density (PPFD), CO₂ concentration and photosynthetic rate were measured at different height above ground level in the tomato canopy. The leaf area of the middle (1.2 to 1.8 m) and lower layer (0.6 to 1.2 m) was larger than that of the upper layer (1.8 to 2.2 m). The PPFD from the upper to lower layer was decreased from 370 to 45 μmol m^-2 s^-1 in winter. However, CO₂ concentration varied little among the layers, and was below 400 μmol mol^-1 during the day. The maximum photosynthetic rate (P_max) of middle leaves was similar to that of upper leaves. The P_max of lower leaves were less than a half of the other leaves. The photosynthetic rates of middle and lower leaves were increased by 1.2 to 1.3 times with elevated CO₂ concentration from 400 to 800 μmol mol^-1 under low PPFD (e.g., 125 μmol m^-2 s^-1). Thus, it was considered that elevating CO₂ concentration at middle layer was appropriate for CO₂ enrichment within a canopy of tomato grown by high-wire system.

View full abstract

　Recently, many expensive devices with multiple-controls such as heating, ventilation and CO₂ application have been installed in green-houses which are mainly based on engineering, and less on using the characteristics of crop responses to the environment. In this paper, fertigation practices to lessen high temperature damage by using these characteristics are introduced.
　1) Cucumber plants grown in hydroponic systems had two peaks of nitrate absorption in a day: At around noon and early night. An anti-heat control was developed for fertigation using the early night peak. Water is used in lieu of midday solution to reduce plant water stress, and then high concentrated solution was supplied in early night to satisfy the daily nutrient demand of plants. It raised cucumber yield by 35 %. Yield even in nocturnal application of solution was 20-40 % more than in daytime application in cucumber and tomato plants.
　2) High soil temperature is decreased below furrow bottoms due to decrease in fluctuation. Yield in tomatoes planted in furrows 10 cm deep was 20 % more than in flat beds.
　3) In a trench house with depth 2 m and width 6 m situated in the north-south direction, papaya yield was three times as much as that in the normal green-house. Even in a trench house, papaya plants grown in the west side, where shading in the latter daytime decelerated plant water decreasing and soil temperature increasing, are superior in photosynthesis.
　4) Foliar water spray around 3 PM increased leaf water and yield in tomato, sweet potato and papaya plants due to accelerated root growth. However it decreased them in melon, cucumber and cabbage. Increasing of leaf negative-pressure to absorb water was higher in the former crops when leaf water was lost.
　These characteristics can be used for environmental controls in green-houses readily and cheaply.

View full abstract