べたがけに伴う温度変化とコマツナの生長との関係の簡易モデルによる解析

Abstract

The effect of row cover on the growth of Komatsuna (Brassica campestris L. rapifera group) was evaluated using a simple model describing the relationship between temperature and leaf growth. The model was developed from a growth chamber experiment and shows that a) relative leaf area growth rate (RLGR) varies inversely as the 0.6th power of leaf area (LA) and b) RLGR is related to temperature by a sigmoid curve. Separate field experiments were carried out over six periods of growth and the parameters of the model were derived so as to fit the model to the results of these experiments. The growth-promoting effect of row cover was best described when the model was driven by soil temperature rather than air temperature, and it was therefore concluded that the growth-promoting effect of row cover strongly depends on its ability to warm the soil. The model-aided analysis of field-grown Komatsuna showed that leaf growth under row cover was stimulated most at lower temperatures and in the earlier growth stages. The effect of temperature was explained by the relationship between soil temperature and RLGR, in which the temperature-stimulation of RLGR decreases at higher temperatures. The effect of early growth stage was due to the enhanced rate of soil warming that results from better penetration of solar radiation to the soil surface when canopy leaf area is relatively undeveloped. Although both of these effects are already known empirically, the model-aided analysis used in the present study is able to explain them quantitatively.