Nitrogen (N) is normally applied twice during sugarcane cultivation on Negros Island in the Philippines. As the first application is carried out during the early growth stage, there is a high possibility that N is not absorbed sufficiently by the sugarcane and a large amount of N may be leached with percolating water. To investigate this leaching, we monitored the vertical movement of soil water and soil solutes using GS3 dielectric moisture and electrical conductivity (EC) sensors in a sugarcane field on Negros Island. The monitoring was conducted after the first N application at different application rates (50% or 100% of the recommended rate) and timings (immediately or 30 days after planting [DAP]). The EC values increased when 100%-N was applied immediately after planting, indicating that N leached into the deeper soil layer. The monitoring results suggest that the applied N did not remain in the root zone (due to leaching) and was not replenished until the second application, when the absorption ability of the sugarcane was high. Conversely, when 100%-N was applied at 30 DAP, the applied N remained in the root zone until the second application. When 50%-N was applied at 30 DAP, the increase in EC was small compared to the 100%-N application. These results indicate that applying N immediately after planting at the recommended rate led to an insufficient nutrient supply for the sugarcane, as well as the loss of N fertiliser via leaching.

Fertilizer application during sugarcane cultivation is a main source of nitrogen (N) loads to groundwater on small islands in southwestern Japan. The aim of this study was to quantify the effect of reducing the N fertilizer application rate on sugarcane yield, N leaching, and N balance. We conducted a sugarcane cultivation experiment with drainage lysimeters and different N application rates in three cropping seasons (three years). N loads were reduced by reducing the first N application rate in all cropping seasons. The sugarcane yields of the treatment to which the first N application was halved (T2 = 195 kg ha−1 N) were slightly lower than those of the conventional application (T1 = 230 kg ha−1 N) in the first and third seasons (T1 = 91 or 93 tons ha−1, T2 = 89 or 87 tons ha−1). N uptake in T1 and T2 was almost the same in seasons 1 (186–188 kg ha−1) and 3 (147–151 kg ha−1). Based on the responses of sugarcane yield and N uptake to fertilizer reduction in two of the three years, T2 is considered to represent a feasible fertilization practice for farmers. The reduction of the first N fertilizer application reduced the underground amounts of N loads (0–19 kg ha−1). However, application of 0 N in the first fertilization would lead to a substantial reduction in yield in all seasons. Reducing the amount of N in the first application (i.e., replacing T1 with T2) improved N recovery by 9.7–11.9% and reduced N leaching by 13 kg ha−1. These results suggest that halving the amount of N used in the first application can improve N fertilizer use efficiency and reduce N loss to groundwater.

The second of the United Nations' 17 Sustainable Development Goals aims to end hunger, achieve food security and improve nutrition, and promote sustainable agriculture. However, it is well known that the agricultural potential in developing regions including Africa has not been fully realized because adverse environments and changing climate conditions impose abiotic (e.g., low soil fertility, droughts) and biotic (e.g., pests, diseases) stresses on plant growth and development. To ensure food and nutrition security in such regions, the Environmental Stress-tolerant Crops project, the High-yielding Biomass Crops project and the Pest and Disease Control project in the Program for Stable Agricultural Production at the Japan International Research Center for Agricultural Sciences aimed to develop technologies and crops with high productivity and adaptability to adverse environments and changing climate conditions. In order to develop crops with environmental stress tolerance and disease resistance, we have clarified and used the genes and loci involved in these traits toward the development of breeding materials. And in order to develop technology for effectively controlling transboundary pests, we have elucidated the ecology of their occurrence and developed pest management technology based on that information. We hope that these materials and technologies will contribute to achieving food and nutrition security in developing regions.

Erianthus arundinaceus, a warm-season perennial species in the Gramineae family, is currently being considered as a bioenergy crop candidate due to its capacity for high yields. Several experiments to explore this possibility have been conducted in Nasushiobara, Japan, where the mean minimum air temperature in January over the last three decades has been − 4.4 °C. Some accessions and breeding lines have demonstrated overwintering abilities, and annual dry matter yields of up to 52 t ha−1 were recorded in the 7th year after planting. Cutting to a 0.05-m height in February contributed more to subsequent regrowth and yield than did similar cutting in November. However, when performed in November, cutting to a 0.3-m height was more beneficial to subsequent regrowth and yield than cutting to a 0.05-m height. Allowing the foliage to run dry during winter led to a dry (approximately 70% dry matter ratio) biomass harvest in late winter. During winter, nutrient remobilization within the plants decreases nutrient removal from the soil. Although nitrogen fertilizer use efficiency was quite high (60%), only 20% of the nitrogen in an individual plant in the 2nd year after planting originated from fertilizer. This was likely due to a large amount of nitrogen obtained from non-fertilizer sources, i.e., soil and stored in the stubble from the previous harvest. Future experiments should focus on designing a fertilizer application program that could lead to sustainable and long-term high-yield E. arundinaceus biomass production in temperate zones.

The accident caused at the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant by the Great East Japan Earthquake of 11 March 2011 resulted in radioactive fallout over a wide area of eastern Japan. Production of bioenergy crops and their conversion to energy may be one way to resume agricultural production at an early date and to put renewable energy to practical use. We examined yearly changes in radioactive cesium concentrations in the harvested parts of six perennial Gramineae candidate bioenergy crops and the distribution of the cesium in plant organs and rhizosphere soil layers under no-till conditions in an experimental field 112km from the nuclear power plant. Average radioactivity of the sum of cesium-134 and cesium-137 in the harvested parts (foliage) of the six bioenergy crops on the day of harvest declined considerably from 193.3Bqkg(-1) in 2011 to 31.6% of the 2011 level in 2012, 28.8% in 2013 and 28.7% in 2014. Radioactivity was higher in the underground plant parts (subterranean stem and root) than in the aboveground parts (foliage and stubble). In 2014, radioactivity in the untilled rhizosphere soil was higher in the shallow layer (0-5cm from the soil surface) than in the deeper layers, indicating that rainfall and perennial bioenergy crop cultivation for more than 3years had a limited effect on the soil distribution of the fallout. These results provide unique and specific information on radioactive cesium transfer to bioenergy crops and could help in the planning of feedstock supplies in radiation-polluted areas.

Nitrogen (N) is a major essential element for all organisms, and generally the amount of available N (mainly inorganic nitrogen such as nitrate or ammonia) in soil is limiting factor for natural and agricultural plant production [40]. Biological nitrogen fixation (BNF) is a process by which atmospheric dinitrogen (N2) is reduced into 2 molecules of ammonia (NH3) by the enzyme nitrogenase with 8H+, 8eand 16 Mg ATP. BNF have important role in N cycle in both global ecosystem and agro-ecosystem. Based on the data compiled by Bezdicek and Kennedy in 1988 [11], about 175 million metric tons of nitrogen per year is estimated to be fixed in global ecosystems, in which 90 million metric tones in agricultural land, 50 million metric tones in forest and non-agricultural land, and 35 million metric tones in sea. At that time, nonbiological nitrogen fixation was estimated about 50 million metric tones per year by industrial nitrogen fixation mainly for the synthesis of ammonia fertilizer, and about 20 million metric tones by combustion, and about 10 million metric tones by lightening. In 2009, the production of N fertilizers increased to 106 million metric tones (FAOSTAT), but the amount of BNF still exceeds over non-biological nitrogen fixation.

ミネラルバランスに留意した飼料用サトウキビの施肥方法の開発の一環として,製糖用に準じた現行の施肥方法の区 (対照区) に対して,カリ施肥量を減らした処理区 (カリ減区,無カリ区) を設け,多回株出し栽培での飼料用サトウキビの生育,養分濃度および土壌の養分含量の推移を調査し,カリ施肥量の低減の可能性を検討した.対照区と比較してカリ減区や無カリ区ではミネラルバランスの指標であるK/(Ca+Mg)当量比が低く,株出し2回目以後は施肥処理による有意差が認められた.これはカリ減肥によりK濃度が低下し,吸収の拮抗関係にあるCa,Mg濃度が増加したためであり,カリ減肥を継続することでK/(Ca+Mg)当量比の改善が可能と判断された.一方で,カリ減肥ではKの収奪が大きいため土壌の交換性Kが低く推移し,多回株出し栽培で収量の低下が認められた.また,株出し7回目に無カリ区にカリ施肥をしたところ,施肥量の増加に伴い生草収量が増加した.このため,多回株出し栽培ではカリ減肥の継続は困難であり,現行のカリ施肥量を維持すべきと言える.また,対照区でも土壌の交換性Kが低下傾向にあることから,堆肥などでKを還元することが多回株出しでの収量維持に重要と考えられた.肥料の3要素のうちNは現行の施肥量が適正であるが,Pは投入が過剰であった.対照区でも株出し栽培の継続により収量低下が認められており,その原因として土壌の交換性Ca,Mgの低下が推察されることから,苦土石灰を施用するなど3要素以外の収支への留意も必要と言えた.

Crop growth was enhanced in fields previously cultivated with host plants colonized by arbuscular mycorrhizal fungi (AMF), compared with fields previously cultivated with non-mycorrhizal plants. To clarify the effect of previous cropping on the community structure of AMF in soybean roots, soybean were grown in fields which were cultivated after mycorrhizal plants, non-mycorrhizal plants, or left in uncropped condition over three years (in 2004, 2006, and 2007) in two different soils (Thapto-upland Wet Andosol and Low-humic Andosol). The partial region in the 18S rDNA of AMF from soybean roots was amplified by a nested PCR method using primers specific for AMF and sequenced. The sequence homology search and phylogenetic analysis revealed that the AMF community in soybean roots was unaffected by the preceding crop. Further, it was shown that the AMF phylotype "Glo-B1", which included Glomus sp. ZJ (AB076344), was the most frequently detected, irrespective of the preceding cropping system. However, in 2007, the community structure of AMF in the soybean roots from the Low-humic Andosol field, which had been used as grassland for several years, was relatively different from that of the Thapto-upland Wet Andosol fields. It was implied that the AMF community could be affected by environmental condition or long-term vegetation.

To estimate potential nitrogen-fixing endophytes in sugarcane and sweet potatoes, we used a cultivation-independent approach. The expression (RNA) of dinitrogenase reductase gene (nifH) was investigated by reverse transcription-polymerase chain reaction as well as DNA searches. Gene fragments corresponding to nifH were amplified from mRNA and DNA obtained from stems of pot-grown sugarcane and stems and tubers of field-grown sweet potatoes in Japan. Sequence analysis revealed that large numbers of the clones were homologous to the nifH sequences of rhizobia. Moreover, the expression of nifH genes in the stems of sugarcane was correlated with the nitrogen fixation assessed by the 15N-dilution method. These results suggest that the detection of expressed nifH genes from the host plant tissues enabled an efficient estimate of nitrogen fixation.

The accident at the Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Company, Inc.) caused by the Great East Japan Earthquake of 11 March 2011 resulted in radioactive fallout that caused heavy damage to agricultural production over a wide area of eastern Japan. Production of biofuel crops and their conversion to energy may be one way to resume agricultural production at an early date and to put renewable energy to practical use. This study addressed two concerns relevant to this scenario: (i) the degree of transfer of radioactive cesium from the soil to biofuel crops; and (ii) evaluation of gasification technology from the standpoint of removal of cesium contained in the biomass. Sixteen lines of Gramineae crops grown in an experimental field 112km from the nuclear power plant contained 143.4-600.4Bqkg(-1) dry matter (DM) of radioactive cesium, the arithmetic average being 285.9Bqkg(-1) DM. The crops included, inter alia, Erianthus arundinaceus (Retz.) Jesw., Miscanthus spp., maize (Zea mays L.) and sorghum (Sorghum bicolor Moench), all of which were cultivated without tillage in 2011. A comparison of Miscanthus spp. that overwintered between 2011 and 2012 revealed that radioactivity decreased from 146.1 to 229.3Bqkg(-1) DM (arithmetic average: 193.3Bqkg(-1) DM) to 53.0-81.0Bq kg(-1) DM (arithmetic average: 66.0Bqkg(-1) DM). A simplified laboratory-scale experiment revealed that the stable isotope of cesium attached to pulverized biomass of Japanese cedar (Cryptomeria japonica D. Don) and E.arundinaceus was completely trapped in gasification system and gas purification system. This result indicates that cesium was not transferred to the gas that was produced for fuel. Gasification using polluted biomass will be practical after further studies have addressed problems related to issues such as scale-up, troubleshooting continuous runs and disposal of radioactive wastes.

飼料用サトウキビ品種KRFo93-1において，生育とK/（Ca+Mg）当量比で示されるミネラルバランスの関係について検討した．生育の程度は株あたり乾物重で評価した．試験1では新植における生育に伴うK/（Ca+Mg）当量比の変化について，また試験2では生育期間の異なる場合におけるK/（Ca+Mg）当量比について検討した．試験1，2ともに試験開始前の土壌の交換性K，Mg，Caは栽培基準に照らして適正な値であった．新植における地上部のK，Mg濃度は生育が進むにつれて有意に低下し，K/（Ca+Mg）当量比も生育に伴って低下した．また，乾物重とK/（Ca+Mg）当量比の間には有意な負の相関関係が認められた．同様に生育期間の異なる場合においても，乾物重とK/（Ca+Mg）当量比の間には有意な負の相関関係が認められた．K/（Ca+Mg）当量比の基準値は2.2とされるが，試験1，2ともに基準値を超える例は認められなかった．以上のことから，土壌のミネラルバランスが適正な条件においては，K/（Ca+Mg）当量比は基準値の2.2を下回り，また，生育に伴いK/（Ca+Mg）当量比が低下することが明らかとなった．

Many kinds of sugarcane hybrids and relatives were planted in two sites, Tsukuba and Nasushiobara, in the northern Kanto region of Japan to evaluate their overwintering ability and biomass production. JW49 (Saccharum spontaneum L.), US56-15-2 (S. spontaneum L.) and Ponape Hurukimura (Saccharum barberi Jeswiet) were able to overwinter in the field experiment conducted in Tsukuba, but not in Nasushiobara. In the field experiment conducted in Nasushiobara, only two lines, JW599 (Saccharum spontaneum L.) and JW630 (Erianthus spp.), overwintered. JW630 also showed good ratooning ability in Tsukuba, even though the results were obtained from the experiment without replication. The newly planted JW599 and JW630 were small in the first year, but from the second year the biomass production of the ratoon plants became huge. The dry matter yields of JW599 and JW630 in the first year were 0.07 and 0.13 kg per hill, respectively, and the average dry matter yields of JW599 and JW630 during three years of ratoon cultivation were 1.46 and 2.63 kg per hill per year, respectively. Assuming that they are planted at 1.5-m inter-row intervals and 0.3 m inter-hill intervals, and each hill can accumulate the same dry matter yield, the dry matter production of the ratoon plant of JW599 and JW630 is estimated to be 32.5 and 58.4 t/ha, respectively.

To explore the presence and expression of the nifH gene of diazotrophic endophytes in sugarcane ( Saccharum spp. hybrids) cv. NiF8, we conducted pot experiments for two seasons in a glasshouse from 10 June to 17 September (high temperature and long days) in 2005 and 1 September to 9 December (low temperature and short days) in 2006. The expression of nifH genes in the stems and roots of sugarcane plants at 50 (or 59) and 100 days after transplanting was investigated by reverse transcription (RT)–PCR and by examining the nifH nucleotide sequence diversity. N 2 fixation was assessed by the 15 N-dilution method. The nifH RNA sequences in the stems and roots of the first experiment were similar to those of Bradyrhizobium sp. and Azorhizobium caulinodans . In the second experiment, nifH expression from these bacteria was not detected in the stems. nifH gene expression in the stems was in accordance with 18–24% N derived from air in the high-temperature season and negligible in the low-temperature season. Both the proliferation of N 2 fixers and expression of the nifH gene indicated that bacteria similar to rhizobia may contribute to N 2 fixation in sugarcane under our experimental conditions.

As the Thai economy grew rapidly after 1985, agriculture became more intensive through the increasing use of chemical fertilizer and mechanization. This study aimed to analyze the nitrogen (N) cycle related to agricultural activities in Khon Kaen Province in Thailand during 1990–1992 and 2000–2002, and on the changes in utilization of local organic resources and the N load to the environment. A model of the N cycle was constructed including compartments for farmland, crop yield, crop residue, food factory, livestock, humans, market, hydrosphere and atmosphere. N flows among the compartments in the model were estimated from data derived from Thai agricultural statistics, related reports and journal articles, interviews with farmers and food factory staff, field observation and information from Thai experts. N flow through livestock declined because of a decrease in the number of buffalo raised, which reduced the production of animal manure. N returned to farmland in crop residues increased because sugarcane cultivation, and crop residues, increased and the burning of rice straw decreased. An increase in chemical fertilizer application increased N input to farmland for crop production. N balance in farmland changed from −27 kg ha−1 year−1 in 1990–1992 to +6 kg ha−1 year−1 in 2000–2002, which improved soil N depletion. Because N leaching and erosion from farmland were low, water pollution in farmland is expected to be low. Human waste was not used or treated, and water pollution from human waste would be expected in housing areas. Analysis of indices of the N cycle showed that the stock of soil N in farmland supported agricultural production in 1990–1992, and that N inflow from outside the area (chemical fertilizer) supported agricultural production in 2000–2002. However, efficiency of N use for agricultural production did not improve.

Eight high biomass sugarcane clones and two commercial sugarcane cultivars were planted in upland and paddy fields in Tsukuba in 2003-2005 to identify a new crop suitable for abandoned paddy fields in the Kanto region of Japan. The paddy field was flood irrigated until harvest in 2003 and 2004. In 2005, the paddy field was flood irrigated for one month after transplantation and then the water was drained to above ground level to maintain an ill-drained condition. The highest dry matter (DM) yield of the high biomass clones was over 40 Mg/ha in the upland field, and even in the ill-drained paddy field, all high biomass clones achieved almost 30 Mg/ha. Because DM yield of feed-use rice cultivars is reported to be around 20 Mg/ha, DM yield of high biomass clones grown in ill-drained conditions would exceed that of feed-use cultivars grown in a flooded condition. Average DM yield, stalk number and plant length of the high biomass clones grown in the ill-drained paddy field were better than those grown in the flood-irrigated condition. Although the average DM yield in the paddy field was lower than the upland field every year (P < 0.01), the average proportion (paddy/upland) of DM yield in 2005 when the paddy field was in the ill-drained condition was 0.79, whereas it was 0.59 in 2003 and 0.54 in 2004 when the paddy field was flood irrigated. The results suggest that sugarcane and high biomass clones can be grown in ill-drained paddy fields with good yields; however, cultivars with improved initial growth rates and winter survivability are necessary for the Kanto region.