Abstract The flotation method of ultra-fine bubbles (UFB) aims to address pollution and has been used for combating the undesirable water conditions of contaminated soils. Hence, water containing UFB is gaining increasing attention for potential agricultural applications. Although certain hypotheses have been proposed, such as the collection of ions in water through the electrical characteristic of UFB, no clear experimental data have been provided. We found that improvement in turbidity may cause the adsorption of fine soil particles in the water by the UFB, thereby improving the quality of the water. The data from the paddy field showed that a decrease in turbidity (below 2 nephelometric turbidity units) occurred over a short period of time (3 days). UFB concentration is directly related to turbidity with a coefficient of determination of 0.93. This phenomenon was also observed through the distribution of bubbles and soil particles, where the average particle size increased because of the aggregation of soil particles and the decrease in turbidity in the paddy field, indicating that UFB collect soil particles and thereby improve water quality. Therefore, UFB are highly effective in cleaning rice field water and will be a preferred method for purifying the environment in the future.

Abstract The extensive and intensive use of herbicides has resulted in the spread of herbicide-resistant weeds in many crop production systems; therefore, it is imperative to devise new organic weed control methods. Recently, the application of spent coffee grounds (SCG) in agricultural fields has been found to inhibit plant growth and germination and is thus considered a potentially effective weed control measure. This study aimed to evaluate the effects of different amounts and methods of SCG application on weed growth through field experiments. The field experiments were conducted in an upland field converted from a paddy in western Japan. The results show that the plow-in application of over 10 kg m⁻² of SCG and mulching application of 20 kg m⁻² decreased the weed dry weight compared with the control. In addition, the growth of weed species of families other than Gramineae, such as wingleaf primrose-willow and horseweed, was not significantly affected by SCG application. Weed species of families other than Gramineae are dominant in some upland fields. Hence, the inhibitory effect of SCG on weeds may be lower in original upland fields than in the upland field converted from paddy field that was investigated in the present study. Overall, this study demonstrated that the plow-in application of 10 kg m⁻² of SCG every 4 mo was effective for weed control in an upland field converted from a paddy field. Because SCG worked against grass weeds under the specific conditions in this study, it would be valuable to explore other potential applications of this novel means of weed control.

Improving agricultural research and education is highly recommended to control agricultural development and environmental sustainability in Cambodia. Agricultural research mostly focuses on interviews with farmers as a first measure in developing countries, but a lack of quantitative accuracy remains one of the major constraints. In this situation, we conducted educational activities for master’s degree students of the Royal University of Agriculture (RUA) to append agronomic information with popular equipment in interdisciplinary fieldwork in Pursat Province, Cambodia. For the popular equipment, an RGB camera, a reflectometer as well as pH and EC meters were selected. The agronomic information collected by the students supported the results obtained during the interviews. For example, the difference in fertilizer application between the irrigated and nonirrigated areas was confirmed by the soil ammonium concentration evaluated with a reflectometer; the difference in rice growth among water conditions was confirmed by the leaf area percentage evaluated with an RGB camera. Since the majority of the students lacked agricultural and statistical knowledge, the agronomic information quantified by popular equipment provided proper educational materials. The interdisciplinary fieldwork also indicated serious problems in the study area, such as low beneficial crop production and environmental sustainability. To overcome these problems, improving agricultural education is required to foster skillful agricultural professionals, and the quantification of agronomic information is an essential issue.

Increasing the yield potential of rice (Oryza sativa) is the main objective of breeders and cultivators engaged in rice improvement programs. Erect panicle (EP) rice is generally high-yielding with panicles that remain non-curved until maturation. The aim of our study was to evaluate the association of agronomic traits with rice productivity in EP rice. Here, we used the recombinant inbred lines (RILs), crosses between Liaojing5 (erect panicle japonica type) and Wanlun422 (high-yielding indica type). The yield varied among the RILs, and the flag leaf length of EP RILs was negatively correlated with the yield; however, the correlation was not significant in the non-EP RILs. The flag leaf length of the EP RILs was also negatively correlated with biomass increase during the late ripening stage. This may reflect the canopy structure of the EP RILs with short flag leaves which had a larger leaf area index in the lower strata. Additionally, the chlorophyll content in the lower leaf significantly differed among the EP RILs with flag leaves of different lengths, resulting in a higher photosynthetic ability of the lower leaf of EP RILs with short flag leaves. In the present study, an EP line, which has the shortest flag leaf, showed a higher yield than Wanlun422 in both years. EP RILs with short flag leaves might show a higher canopy photosynthetic rate in the later ripening stage; therefore, this trait could be a potential phenotypic marker for achieving high yield of EP rice.

The production of pearl millet (Pennisetum glaucum (L.) R.Br.) is important in Namibia, in sub-Saharan Africa, owing to the prevailing low precipitation conditions. Most fields supporting crop production in northern Namibia are located in a network of seasonal wetlands. The aim of the present study was to evaluate the effects of ridging and fertilizer application on the yield and the growth of pearl millet in the seasonal wetlands under different rainfall conditions. The study was conducted for two years (2017–2018) in the experimental fields in northern Namibia, and yield, yield components, and growth parameters were evaluated in relation to the application of different fertilizers (manure and mineral) with and without ridge-furrows. Manure fertilizer application presented the highest yield in 2018, whereas mineral fertilizer application showed the highest yield in 2017. The proportion of rainfall was the highest during the mid-growth period in 2017, and the reproductive stage in 2018. Thus, pearl millet plants under manure fertilization overcame damage resulting from waterlogging stress during the seed setting stage by improving the soil and plant nutrient conditions. In contrast, the plants under mineral fertilization were more tolerant to large amounts of rain during the mid-growth period. In this study, yield was mainly determined by total dry weight, and it was closely related to panicle density in both years. Therefore, we concluded that fertilizer application, including additional fertilizer based on the growth diagnostic, could be important for improving crop production in seasonal wetlands.

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 treatments in 2014. LAI readings obtained by a plant canopy analyzer for non-destructive stratified measurements were relatively consistent with LAI estimations using the stratified clipping method for every cultivar and treatment. The parameters calculated using the statistical moment equations numerically showed the changes in LAI vertical distribution with plant growth up to the heading stage. The differences in the parameters also quantified the effect of cultivar, fertilizer, and plant density treatments. These results suggest that the non-destructive stratified measurements and the statistical moments evaluated in this study provide quantitative, reliable information on the dynamics of LAI vertical distribution. The method is expected to be utilized by researchers in various research fields sharing common interests.

Erect panicle rice cultivars utilize solar energy effectively and have improved ecological growing conditions. Among such cultivars, Shennong265 has been grown successfully throughout Northern China. Nevertheless, no studies have yet examined the relationships between crop dry matter productivity, weather conditions, and nitrogen uptake of the erect panicle type rice cultivar in Japan. The objective of our study was to evaluate the productivity of erect panicle rice Shennong265 in Western Japan under varied conditions. Three rice cultivars, Shennong265, Nipponbare, and Takanari were grown in the field under different fertilizer and plant density conditions in Western Japan using this information, we compared yield and growth characteristics of Shennong265 with those of Nipponbare and Takanari. Although Shennong265 had radiation use efficiency similar to that of the high yielding cultivar (Takanari) and much higher leaf nitrogen content than Takanari and Nipponbare, the average grain yield of Shennong265 grown under normal fertilizer and plant density conditions was approximately 6.9 t ha−1 as against 6.2 t ha−1 for Nipponbare and 9.6 t ha−1 for Takanari. These results suggest that, while Shennong265 has a high yield potential, the environmental conditions including climate, fertilizer, and planting period provided in this study were not suitable for achieving its maximum yield. The reduced performance of Shennong265 may be caused by insufficient fertilizer after heading and by shorter growth periods, as well as by the climate of Western Japan. Additional fertilizer application during the heading stage and earlier transplanting may be needed to obtain higher Shennong265 yields in Western Japan.

Mixed cropping is a cultivation method widely practiced in tropical regions. The newly developed close mixed planting technique mitigates the flood stress of drought-adapted upland cereal species by co-growing rice (Oryza sativa) plants under field flood conditions. We tested the hypothesis that O-2 was transferred from rice to upland crops using the model system of hydroponic culture. To confirm the hypothesis, the phenomena of O-2 absorption and release by plants were evaluated in a water culture condition without soil. Experiments were conducted in a climate chamber to estimate the amount of O-2 released from the roots of rice and pearl millet (Pennisetum glaucum) under both O-2 rich (20.0 +/- .0% conc. in phase I) and O-2-free dark (.8 +/- .0% conc. in phase II) conditions. The total O-2 change (between the two phases) in a single planting of rice and pearl millet was significantly higher than that of the mixed planting of rice and pearl millet, which indicated that O-2 was transferred from rice to pearl millet under a water culture condition. The result indicated that approximately 7 +/-mu M O-2 g fresh root weight(-1) h(-1) was transferred between the two plant species. O 2 transfer was confirmed between the two plant species in a mix cultured in water, implying its contribution to the phenomenon that improved the physiological status of drought-adapted upland crops under field flood conditions.

The erect panicle (Ep) type is an important characteristic for japonica super rice in Northeast China and plays a significant role in enhancing yield. The Ep type is considered to be a genetic ideotype resource to the japonica super rice group by virtue of its agronomic advantages such as grain number per panicle and biomass. This study addresses the effects of nitrogen and planting density conditions on yielding performance regarding panicle type (PT) using the recombinant inbred line (RIL) population derived from the cross between an Ep variety Liaogeng 5 and non-Ep variety Wanlun 422. The genetics underlying the Ep type proved to be robust not only for panicle-type optimization but also plant height, panicle length, flag leaf length and seed density. We also found that regardless of nitrogen and density, correlation between harvest index (HI) and plant height was not significant in Ep type whatever the nitrogen and density. The application of Ep type provides a potential strategy for yield improvement by increasing biomass through HI maintainable in rice.

Food security has become a serious concern recently in Southeast Asia. The reduction of agricultural land because of economic development is decreasing the food supply. Simultaneously, due to rapid population growth, the food demand is increasing. Therefore, to ensure a stable food supply, it is important to estimate the supply capability of rice, which is the staple food in most Asian countries. In this study, a crop model (SIMRIW-RS) that can combine remote sensing data with a crop model (SIMRIW) was used to estimate rice yield at a regional scale. This model was applied to the estimation of rice yield in paddy fields located in the suburbs of Vientiane, Laos. Satellite (COSMO-SkyMed) -derived data for leaf area index (LAI) were integrated into SIMRIW-RS, and the transplanting date detected by COSMO-SkyMed was used to set the starting date of the simulation. Results were verified by surveying farmers. Transplanting dates were detected with high accuracy in all but a few fields. On the basis of the results of regression analysis between actual LAIs and the corresponding backscatter coefficients of COSMO-SkyMed, we suggest that COSMO-SkyMed can estimate LAIs at early growth stages when LAI is small. The results of yield estimation after integrating the LAIs derived from COSMO-SkyMed data into SIMRIW-RS indicated that the estimation accuracy of the rice yield was improved compared with the estimation result without adjusting parameters in the model, and this held so long as LAI was retrieved with high accuracy by satellite data. However, when LAI could not be estimated accurately, integration has the potential to worsen the model's accuracy compared with the estimation result without any such readjustment. This study therefore indicates that SIMRIW-RS has the potential to estimate rice yield accurately when the LAI of rice is estimated with high accuracy from satellite data.

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 development, leaf area index (LAI) growth, dry matter production and yield formation) and has 2 representative field parameters and 5 representative cultivar parameters. The parameters that were determined with the data from previous field studies seemed to be reflected with field and cultivar characteristics, and differences in the rice growth and production among the fields and cultivars were well explained by the model. The application of the model on a regional scale using remote sensing is discussed.

Rice is the most important crop in Lao People's Democratic Republic (Lao PDR). The improvement of its productivity is strongly recommended, but information about its growth characteristics in farmers' fields is limited. This study evaluated the dynamics of the leaf area index (LAI) and analyzed the relationship between the rice productivity and soil in farmers' fields in Vientiane province, Lao PDR. Because the LAI in the farmers' fields increased almost linearly, a straight-line regression was used for the analysis. The rice yield in the farmers' fields ranged from 63.8 g m(-2) to 411.8 g m(-2) and correlated with the LAI during the later growth stage. The variability in the LAI was explained by the LAI growth rate but rarely by the effective accumulated temperatures from the estimated transplanting date. The LAI growth rate was associated with the nitrogen and carbon content in the soil. These results suggest that the rice productivity in farmers' fields is governed by the soil fertility through LAI growth, and that LAI monitoring is an effective tool to evaluate the production.

Rice is by far the most important crop in Cambodia. The improvement of its productivity is strongly recommended, but information about cultivation environment, management and their effects on rice production in farmers' paddy fields is quite limited. This study periodically measured the leaf area index (LAI) by using a plant canopy analyzer and conducted yield, water, soil and management investigations in 77 farmers' paddy fields in the Bakan district, Pursat province, Cambodia in 2014. Because the LAI showed linear growth in almost all farmers' fields, the LAI growth rate was determined by linear regression. The grain yield ranged from 70.8 gm(-2) to 499.0 gm(-2) and was positively correlated with the maximum LAI. The variability in the maximum LAI was mainly explained by the LAI growth rate, while the growth period had a significant correlation with the maximum LAI only in the broadcast fields, where earlier planting led to larger LAI. The result of the ANCOVA shows that the LAI growth rate was affected by seeding date, water status and soil condition (C content and C/N ratio) while the effect of planting method (transplanting/broadcasting) and N fertilizer was non-significant. The non-significance of effect of N fertilizer may imply the timing or method of application is improper. The results suggest that the key means to improve rice productivity are effective application of fertilizer and selection of planting methods dependent on the soil fertility, together with water-saving irrigation method. (C) 2016 Elsevier B.V. All rights reserved.

Monitoring leaf growth is a useful method for evaluating crop growth. In this study, frequent measurements of the rice canopy were conducted with a plant canopy analyzer, and parameters were estimated by applying several equations to evaluate leaf growth. The applicability of this evaluation method is discussed based on the statistical analysis of parameters. Experiments were conducted for 6 rice cultivars under 5 treatments in 2 years. Parameters describing the dynamics of leaf growth were obtained by applying 4 mathematical growth models in which the independent variable was the effective accumulated temperature. The parameters numerically represented the dynamics of leaf growth in each cultivar and treatment. In particular, maximum LAI and interception growth rates (MLGR and MIGR) which were obtained by applying logistic function to leaf area index (LAI) and diffuse non -light intercepted (DIFN), respectively, showed no interaction between the cultivar and environment. The lack of interaction may indicate that these parameters typically characterize cultivar and growth environments. The differences in the parameters could also be used to quantify the effect of basal fertilizer application on leaf growth enhancement and that of additional fertilizer on the extension of this enhancement. These results suggest that the applied method for parameterizing leaf growth based on frequent measurements with a canopy analyzer is suitable for evaluating the effects of genotype, management and the environment because it facilitates measurements in many plots. (C) 2015 Elsevier B.V. All rights reserved.

Increasing the yield of rice per unit area is important because of the demand from the growing human population in Asia. A group of varieties called erect panicle-type rice (EP) achieves very high yields under conditions of high nitrogen availability. Little is known, however, regarding the leaf photosynthetic capacity of EP, which may be one of the physiological causes of high yield. We analyzed the factors contributing to leaf photosynthetic rate (P-n) and leaf mesophyll anatomy of Nipponbare, Takanari, and Shennong265 (a EP type rice cultivar) varieties subjected to different nitrogen treatments. In the field experiment, P-n of Shennong265 was 33.8 mu mol m(-2) s(-1) in the high-N treatment, and was higher than that of the other two cultivars because of its high leaf nitrogen content (LNC) and a large number of mesophyll cells between the small vascular bundles per unit length. In Takanari, the relatively high value of P-n (31.5 mu mol m(-2) s(-1)) was caused by the high stomatal conductance (g s;.72 mol m(-2) s(-1)) in the high-N treatment. In the pot experiment, the ratio of P-n/C-i to LNC, which may reflect mesophyll conductance (g(m)), was 20-30% higher in Nipponbare than in Takanari or Shennong265 in the high N availability treatment. The photosynthetic performance of Shennong265 might be improved by introducing the greater ratio of P-n/C-i to LNC found in Nipponbare and greater stomatal conductance found in Takanari.

Rice is the most important crop in Lao People's Democratic Republic (Lao PDR). Synthetic aperture radar (SAR) is proposed as a more suitable method to evaluate rice growth in this area because it is independent from cloud and solar illumination. This study analyzed the relationship between the back scattering coefficient (BSC) in SAR images and leaf area index (LAI) of rice. Here, we discuss the applicability of SAR to estimate LAI and its growth rate in farmers' fields in Lao PDR. 30 farmers' paddy fields were selected for surveying throughout the growth period in the wet season of 2013, and both LAI and normalized difference vegetation index (NDVI) were measured at 4 time periods before the heading period for each field. X-band SAR images from the COSMO-SkyMed system (SAR) were used in this study. BSC was significantly correlated with LAI and NDVI. BSC at 28 of 30 fields was positively correlated with days after transplanting (DAT), and 10 of these results were significant. The increased rate in BSC obtained at the fields where BSC and DAT had a significant correlation, were significantly correlated with that in LAI. This finding suggests that if SAR images demonstrate significant increases of BSC against DAT, the increased rate may also represent LAI growth rate, although uncontrollable water levels and weeds occasionally interrupt observation. This study demonstrates the capacity of SAR to evaluate rice production in developing countries. (C) 2015 Elsevier B.V. All rights reserved.

Leaf dynamics is one of the important characteristics in rice (Oryza sativa L.) because it determines dry matter productivity. Nevertheless, few studies have evaluated the genotypic variation in leaf dynamics. This study conducted one-week-interval nondestructive measurements by using plant canopy analyzer, and parameterized leaf dynamics for a rice diversity research set of germplasm (RDRS) and high yielding varieties. Three year experiment in Kyoto University showed large genotypic variations in 5 indexes of leaf dynamics, which consisted of 4 parameters from the nondestructive measurements (relative growth rate of LAI, the maximum growth rate of light interception, days to 80% coverage and extinction coefficient) and LAI at heading from destructive measurement. The significant differences among genotypic groups were observed in relative growth rate of LAI, the maximum growth rate of light interception, days to 80% coverage. High-yielding varieties released by IRRI had higher values of the maximum growth rate of light interception, suggesting that the varieties have been improved in terms of canopy development. In contrast, since Takanari and Milyang23 didn't have extreme characteristics in leaf dynamics, further improvement may be possible.

研究代表者は現在までに作物の生育動態に関する定量的評価手法の開発を行ってきたが，この手法では群落閉鎖後の生育状態に関する評価は難しく，また，広域評価も困難であった．そこで本研究では，生育期間を通して作物の生育情報を収集するための手法を開発し，さらに手法の広域展開可能性を検討することを目的として，以下の解析・実験を行った． ①生育期間を通した生育情報収集技術の開発：広範な栄養環境下で多様なイネ6品種を用いて行った3か年の栽培試験結果から，現在までに開発してきた生育動態を評価するパラメータのうち被覆率増加に関するパラメータがバイオマス生産をよく反映していることがわかった．さらに，これらのパラメータに加えて，群落閉鎖後の葉身窒素含量のような品種固有の生理パラメータを利用することで，収量の推定精度が改善されることを示唆した． ②ドローン計測による被覆率計測手法の検討：収量変動の大きい圃場でダイズの栽培試験を行い，異なる距離からのドローン撮影による被覆率計測を試みた．近距離（約7m）からのドローン計測と比較して，遠距離（約20m）からの計測による収量推定精度が高かった．遠距離からの撮影は雑草等の誤差要因を小さくすることが明らかとなり，より簡易的に広域のデータ収集が可能であることを示した． ③機械学習を利用したササゲ収量推定精度の検証：西アフリカでササゲ20品種を用いた栽培試験を行った。通常マメ科は水平葉であるため，被覆率を生産性評価に利用することは難しいが，本研究対象地域のような低生産性地域では被覆率が重要なパラメータであることがわかった．簡易的な3時期の非破壊的な被覆率計測によって，対象地域のササゲ収量を高精度で推定できることが示された．ここでは，4手法の機械学習を試し，手法による推定精度の違いを検出することができた．

新型コロナウイルス（Covid-19）禍により渡航が制限されたため、オンラインによりナミビア、ボツワナ、日本の3ヵ国での試験や研究成果を詳細に打ち合わせ、以下の研究と、研究成果の共同執筆・国際会議での報告などを実施した。① 接触混植試験：ナミビア北部では、ソルガムとトウジンビエの接触混植が農家の自助努力などにより徐々に広がりを見せている。そこで、ナミビア大学オゴンゴ校内の附属農場施設内で、トウジンビエとソルガムの接触混植試験を実施した。農家圃場においても栽培を希望する農家に種子を提供し、農家圃場における栽培試験を実施した。② 亀裂施肥試験：本試験のためにナミビア国で作成した新型の亀裂施肥機をベースにして日本ではコストを考慮し、亀裂処理に特化した新型アタッチメントを作成した。その走行試験を神戸大学等で実施し、今後の普及を検討中である。 ③ ボツワナ大学では、ナミビアから導入したイネ品種群の栽培試験を2019/2020作付け期に開始し、2021/2022まで3か年に渡る栽培トライアルを継続中である。2021/2022からは小規模フィ―ルドでの作付けを開始し、種子の更新と栽培試験を拡大した。 ④ ナミビアとボツワナの研究サイト周辺の農家圃場では季節湿地が形成されるためメタン発生の増大が懸念される。そこで地球温暖化の進行を阻止するためウルトラファインバブル水灌漑によるメタン削減の可能性を議論し、現地への導入を目指したフィールド試験を日本で開始した。 ⑤ 研究成果5報の原著論文がアクセプトされた。 ⑥ 国際学会（アジア作物学会議）で４報の口頭発表と、国内学会（日本作物学会）で２報の口頭発表を実施した。