Tohoku University · Agricultural and Biological Sciences
Professor Koki Homma's research lab specializes in agricultural systems and environmental sustainability, focusing on the impacts of climate change, soil variability, and management practices on rice and soybean production in tropical and subtropical regions. The lab integrates remote sensing, especially UAV-based imaging and radiative transfer modeling, with field-based crop and soil measurements to assess crop productivity, stress responses, and resource use efficiency. A key research direction involves developing non-destructive methods for monitoring canopy structure and plant health, such as leaf area index (LAI) vertical distribution, to support precision agriculture. The lab also investigates climate-resilient crop management strategies, including optimal transplanting dates, fertilizer application, and breeding for heat and disease tolerance.
Figures are computed from collected data and may differ slightly.
Mini-watersheds called Nongin Thai are geographical components of rainfed lowland rice culture in Northeast Thailand, and constitute distinct units in understanding environmental constraints for low and unstable rainfed rice production there. The toposequential variation of soil fertility and its relation to rice productivity within mini-watersheds, was examined by phytometry of sampled soils and field measurements of rice growth and yield. The phytometry experiment with irrigated potted rice us
Reflectance and vegetation indices obtained from aerial images are often used for monitoring crop fields. In recent years, unmanned aerial vehicles (UAVs) have become popular and aerial images have been collected under various solar radiation conditions. The value of observed reflectance and vegetation indices are considered to be affected by solar radiation conditions, which may lead to inaccurate estimations of crop growth. In this study, in order to evaluate the effect of solar radiation cond
近年わが国では夏期の気温が上昇傾向にある. こうした高温化傾向に向けた水稲生産の品種および耕種的な対応に資するために, 1964年から2003年までに生じた水稲栽培における気象変化を定量化し, それが水稲生産に及ぼした影響を解析した. この40年間で夏期の大気二酸化炭素濃度は45ppm上昇し, 最高気温は約0.8℃, 最低気温は約1.1℃上昇した. またこの期間に品種および作期の変化により関東以西で出穂盛期が1～2週間早期化したが, それにより出穂前の気温は低下し, 出穂後の気温と日射量は増加する傾向がみられた. これらによる水稲生産性の増加率は地方によって異なるが, 二酸化炭素の増加によるものが2.5％, 気候変化によるものが-6.0～3.1％, 早期化によるものが-0.5～6.8％であると見積もられた. このうち気候変化については, 関西以西において日射量の増加によるプラスの影響が, 気温の上昇により打ち消されていたことがわかった. 分散分析と重回帰式を用いた分析により, 出穂盛期後10から30日までの平均最低気温が1℃上昇することにともない一等米比率は平均で3.57％低下し, 同
Monitoring the vertical distribution of leaf area index (LAI) is an effective method for evaluating canopy photosynthesis and biomass productivity. In this study, we proposed a novel method to characterize LAI vertical distribution non-destructively by utilizing LAI-2200 plant canopy analyzer, followed by the application of statistical moment equations. Field experiments were conducted with 5 rice cultivars under 2 fertilizer treatments in 2013 and with 3 rice cultivars under 3 plant density tre
Environmental resources for rainfed rice production show large variability even within a small area in Northeast Thailand, and it is said that farmer’s management is well adapted to the variability. This study evaluated transplanting date and nitrogen (N) fertilizer rate in the management to improve rice productivity. The effect of transplanting date and N fertilizer rate on rice productivity was analyzed by investigating rice growth, and also by dividing rainfed rice fields located in a mini-wa
Red crown rot (RCR) is a soil-borne disease that damages soybean growth and decreases yield. Infected plants show earlier defoliation and pencil-like roots, sometimes resulting in mortality. This disease became common relatively recently, and information about its field-scale appearance is insufficient. Insufficient data is a major constraint when planning countermeasures. In this study, unmanned aerial vehicle (UAV)-acquired images were used to visualize the spatial and time series variation in
Rice is not merely a staple food but an important source of income in Cambodia. Rapid socioeconomic development in the country affects farmers’ management practices, and rice production has increased almost three-fold over two decades. However, detailed information about the recent changes in rice production is quite limited and mainly obtained from interviews and statistical data. Here, we analyzed MODIS LAI data (MCD152H) from 2003 to 2019 to quantify rice production changes in Pursat Province
To evaluate rice production and management on a regional scale, a simulation model combined with remote-sensing is recommended. This study aimed to develop a simulation model for use with remote-sensing (SIMRIW-RS) to evaluate the field-to-field variation in rice production on a regional scale. This model was developed based on a simulation model for rice weather relations called SIMRIW and its derived models. The model consists of 6 components (water budget, nitrogen uptake, phenological develo
地球環境変化に対する作物応答を明らかにするために, 高温・高CO2濃度環境がイネ群落の蒸散とガス拡散抵抗に与える影響を調査した. CO2濃度をそれぞれ365と700μL L-1に設定した2棟の温度傾斜型CO2濃度制御チャンバー(TGC)の各々に3温度区(実験期間内平均気温29.8, 30.4, 32.5℃)を設け, 水稲品種アキヒカリとIR36を栽培し, 実験に供試した. 各温度・CO2濃度処理区で8月2日(幼穂形成期)から8月22日(出穂期)まで, 乾湿球温度, 群落表面温度(Tc)と純放射量を測定し, また, ミクロライシメータ法を利用して蒸発散量(E)も測定した. Eの測定値と微気象データをもとに得られた水蒸気と熱輸送に対する空気力学的拡散抵抗(ra)は, 全処理区, 全計測期間を通じてほぼ一定値の11.7sm-1で推移した. このra値とTcおよび微気象データを熱収支式に代入し, Eおよび群落拡散抵抗(rc)を求めたところ, Eの推定値とライシメータ法による実測値は, 両品種とも非常によく一致した. 両品種のrcは全ての温度・CO2濃度処理区において, 全天日射量が500W m
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