Distribution and Quantity of Root Systems of Field-Grown Erianthus and Napier Grass

Cellulosic bioethanol produced from non-edible plants reduces potential food-fuel competition and, as such, is receiving increasing attention. In the raw material production of cellulosic bioethanol, the aboveground biomass of plants is entirely harvested;consequently, the plant roots represent the major source of organic matter incorporated into the soil. We selected Erianthus and Napier grass as the raw materials for cultivation in Asia. However, information about whether these 2 species provide sufficient root volume to sustain soil fertility is limited. Therefore, we examined the spatial distribution of the roots of these 2 plants, and quantified root mass and length. Erianthus and Napier grass were either grown in fields or greenhouses in Tokyo (Japan) and Lampung (Indonesia), and then their roots were exposed from adjacent soil profiles. Both species developed large, deep roots, penetrating 2.0-2.6 m deep into the soil. Root depth indexes showed that the roots of both species penetrated much deeper into the soil compared to monocot crop species, being more comparable to dicot species. Erianthus developed a root mass and length of 384-850 g·m-2 and 28.8-35.8 km·m-2, while the values for Napier grass were 183-448 g·m-2 and 15.6-43.6 km·m-2, respectively. These values exceeded the maximum values previously recorded for common crop species. Our study confirmed that Erianthus and Napier grass develop deep root systems, with substantially large biomass;hence, we suggest that both plants supply root biomass in large quantities, representing possible major sources of soil organic matter.

Performance of Four Rice Cultivars Transplanted Monthly over Full Year under Irrigated Conditions in Tanzania

In Tanzania, the phenology and seasonal variations of the yields of different rice cultivars have rarely been studied, especially under fully-irrigated conditions. A trial was conducted to identify the most suitable calendar for rice production in Tanzania under fully-irrigated conditions. Four popular rice cultivars, NERICA1, Wahiwahi, IR64 and TXD306, were transplanted monthly from January to December 2011. The four cultivars recorded similarly higher or lower yields than the annual means when transplanted in July （0.50-0.57 kg/m2） and April （0.07-0.31 kg/m2）. A yield-ranking analysis showed that plants transplanted in July was the most productive while those transplanted in April was the least productive, and also revealed a yield-seasonality for irrigated rice in Tanzania, a low-yield season （April-May）, a high-yield season （June-August）, and an unstable-yield season （September-March）. These yield seasons would appear to be closely linked to seasonal temperature variations. When transplanted in April-May, plants were exposed to very low temperatures between panicle initiation and flowering, apparently reducing yield through cold-induced sterility. Those transplanted in June-August prolonged their growth under relatively low temperatures and increased yield through increasing biomass production. In September- March, yield levels varied greatly due to the shortened phenological growth durations at higher temperatures. We conclude that under fully-irrigated conditions in Tanzania, rice should be transplanted in July to ensure the maximum production and yield stability. The yield-seasonality suggests that implementing measures to protect plants from low and high temperature stress at critical phenological stages may allow year-round rice production under fully-irrigated conditions in Tanzania.

Responses of Root Hydraulic Properties and Transpirational Factors to a Top Soil Drying in <i>Cajanus cajan</i>and <i>Sesbania sesban</i>

Responses of leaf area (LA), stomatal conductance (gs), root length (RL) and root hydraulic conductance per unit of root length (Lpunit) to top soil dryness were investigated. Pigeon pea (Cajanus cajan) and sesbania (Sesbania sesban) were grown in a vertical split-root system. From sixty-six days after sowing, the top soil was dried while the bottom soil was kept wet. Pigeon pea increased LA while maintaining leaf water potential (ΨL) by reducing gs. Increased transpirational demand through canopy development was compensated for by increasing water extraction in the bottom soil. This was achieved by increasing not only RL but also Lpunit. Sesbania kept constant levels of gs, causing a transient reduction of ΨL. ΨL of sesbania was, then, recovered by increasing only RL, but not Lpunit, in the bottom soil while suspending LA extension, suggesting that sesbania regulated only the root area to LA ratio. This study demonstrated a species-specific significance of Lpunit and coordination among Lpunit, RL, gs and LA in exploitation of wet-deeper soils in response to top soil dryness.

Cultivation of <i>Erianthus</i>and Napier Grass at an Abandoned Mine in Lampung, Indonesia

The production of cellulosic bioethanol from non-edible plants is drawing increasing attention, as it potentially avoids food-fuel competition. Because growing such plants on farmland indirectly reduces food availability, the plants should be grown on marginal, non-arable lands. In this study, we evaluated the growth of cellulosic energy crops at a former mining site in Indonesia. This mine was abandoned because it contained few mineral deposits, and exposed subsoils rather than toxic soils prevented revegetation. In the first trial, growths of two energy plant species Erianthus spp. and Napier grass (Pennisetum purpureum) were compared with that of maize (Zea mays) at the mine site and a nearby degraded farm. Erianthus and Napier grass produced 11.7 and 22.5 t·ha-1 of shoot dry matter at 8 months after planting (MAP) in the farm respectively while maize plants failed to establish, but none of the three species grew at the mine. In the second trial, two-week-old seedlings of Erianthus and Napier grass rather than stem cuttings as used in the first trial were planted at the mine site. Erianthus and Napier grass produced 16.3 and 24.0 t·ha-1 of shoot dry matter over the course of 18 months, respectively. Application of organic fertilizer significantly increased shoot dry matter to 18.9 and 39.6 t·ha-1 in Erianthus and Napier grass, respectively. During the 18-month growth period, both of the energy plants significantly increased soil carbon at the 0 - 0.3 m depth from 0.33% to 1.15% - 1.23% when chemical fertilizer was applied and to 0.67% - 0.69% when both chemical and organic fertilizers were applied. From 0 - 5 MAP, soil surface level dropped by 28.0 - 34.7 mm in plots without plants due to soil erosion. In contrast, both of the energy plants significantly reduced the drop of soil surface level to 16.0 - 19.3 mm in plots with chemical fertilizer alone and to 18.0 - 20.7 mm in plots with chemical and organic fertilizers. Proportions of small soil particles, that would be easily detached and transported by water flow compared with large particles, were larger in the planted plots than the no-plant plots at 16 MAP. The results suggest that successful cultivation of energy plants on abandoned mine sites is possible, particularly if seedlings are transplanted and the crops are fertilized with organic fertilizer. In addition, the cultivation of Erianthus and Napier grass has positive impacts on soil quality that may contribute to their sustainability as crops and to the conservation of the local ecosystem.

Identifying potential field sites for production of cellulosic energy plants in Asia

Cellulosic bioethanol produced from non-edible plants avoids food-fuel competition.Growing such plants on marginal non-arable lands also avoids the use of farmland.In this study,attempts were made to identify potential field sites for cellulosic bioethanol production in Asia.In this study,GIS databases containing information about requirements such as land use,landform,and climate were superimposed.Areas with terrestrial constraints were then removed from the candidate field sites using a terrain slope database.The remaining lands were evaluated using a net primary production(NPP)database.Of these areas,southern and eastern India,northeastern Thailand,and southern Sumatra(Indonesia)had high NPP.In the 2nd phase,local information regarding infrastructure,and agriculture were analyzed.Field-establishment feasibility was high for eastern India and southern Sumatra.Potential field sites were then located in satellite images of these two areas.In the 3rd phase,soils around potential sites were evaluated.Local residents were interviewed to estimate the cost of producing plants for biomass energy.Sites selected using this simple method are suitable for biomass production.