Modeling the effects of cool water on growth and grain yield in rice

水温(Tw)通过多种生长过程限制水稻产量。根据不同Tw条件(17~26℃)下的田间试验，建立了一个简单的Tw对水稻生长发育和产量影响的模拟模型。该模型涵盖了Tw对植株发育速度、叶形、分蘖和茎伸长的影响。叶面积估计是根据主茎上的叶数和分蘖数的乘积得出的。辐射利用效率表示为发育阶段的函数。收获指数是小穗结实率的函数，小穗结实率是用降温天数估计的，根据发育中的穗的垂直位置，根据Tw或气温来估计。1990-1999年，我们在北海道的四个地点(Pippu、Iwamizawa、札幌和Oono)测试了该模型。估计的产量与测量的产量基本一致，范围为19-677 gm^-2&gt；，均方根偏差(RMSD)为79 gm^-2&gt；(n=33)。基于热平衡的Tw估算模型(Kuawgata等人)2001年)估计四个地点的相对标准偏差约为1℃，残留物没有指示性趋势。据估计，札幌过去10年的平均Tw比Ta高3.8℃，Tw之差相当于粮食产量的约300gm^-2&gt；这表明北海道水稻产量受到显著的“水毯”影响。产量的区域差异主要归因于太阳辐射，但风速对Tw也有显著影响。模拟表明，在其他气候条件不变的情况下，气温每升高3℃，札幌市的Tw将增加1.3℃，粮食产量将增加6%。

Water temperature (Tw) can limit rice yield via various growth processes. A simple simulation model was developed to evaluate the effects of Tw on rice growth and yield based on the field trials conducted under different Tw conditions (17-26℃). The model covers the effects of Tw on the developmental rate, leaf appearance, tillering and culm elongation. Leaf area estimates were derived from a product of leaf number on the main culm and tiller number. Radiation use efficiency was expressed as a function of developmental stage. Harvest index was determined as a function of spikelet fertility, which was estimated with the cooling degree-days based on either Tw or air temperature depending on the vertical position of the developing panicles. We tested the model at four locations (Pippu, Iwamizawa, Sapporo and Oono) in Hokkaido for 1990-1999. The estimated yields were generally in good agreement with the measured yields that ranged from 19 to 677 gm^<-2> with the root mean square deviation (RMSD) of 79gm^<-2> (n=33). The Tw estimation model based on the heat balance (Kuawgata et al. 2001) estimated those at the four locations with a RMSD of about 1℃ with no indicative trend in the residuals. Tw averaged for the past 10 years was estimated to be higher than Ta by 3.8℃ in Sapporo, the Tw difference being equivalent to about 300 gm^<-2> of grain yields indicating the marked "water blanket" effect on rice productivity in Hokkaido. The regional yield variation was largely attributed to solar radiation, but wind speed that affects Tw also had a significant effect. A simulation indicated that a rise in air temperature by 3℃ could result in a 1.3℃ increase in Tw and a 6 % increase in grain yield in Sapporo, if other climatic conditions were unchanged.