Takahiro Shiono

INFLUENCE OF SUGARCANE BAGASSE-DERIVED BIOCHAR APPLICATION ON NITRATE LEACHING IN CALCARIC DARK RED SOIL

Application of biochar has been suggested to improve water- and fertilizer-retaining capacity of agricultural soil. The objective of this study was to evaluate the effects of bagasse charcoal (sugarcane [ L.] bagasse-derived biochar) on nitrate (NO) leaching from Shimajiri Maji soil, which has low water- and fertilizer-retaining capacity. The nitrate adsorption properties of bagasse charcoal formed at five pyrolysis temperatures (400-800° C) were investigated to select the most suitable bagasse charcoal for NO adsorption. Nitrate was able to adsorb onto the bagasse charcoal formed at pyrolysis temperatures of 700 to 800° C. Nitrate adsorption by bagasse charcoal (formed at 800° C) that passed through a 2-mm sieve was in a state of nonequilibrium even at 20 h after the addition of 20 mg N L KNO solution. Measurements suggested that the saturated and unsaturated hydraulic conductivity of bagasse charcoal (800° C)-amended soils are affected by changes in soil tortuosity and porosity and the presence of meso- and micropores in the bagasse charcoal, which did not contribute to soil water transfer. In NO leaching studies using bagasse charcoal (800° C)-amended soils with different charcoal contents (0-10% [w/w]), the maximum concentration of NO in effluents from bagasse charcoal-amended soil columns was approximately 5% less than that from a nonamended soil column because of NO adsorption by bagasse charcoal (800° C). We conclude that application of bagasse charcoal (800°C) to the soil will increase the residence time of NO in the root zone of crops and provide greater opportunity for crops to absorb NO.

Influences of feedstock and pyrolysis temperature on the nitrate adsorption of biochar

ABSTRACT Biochar (BC), charcoal produced through the pyrolysis of biomass, is reported to adsorb dissolved nitrate-nitrogen (NO3-N). The NO3-N adsorption properties of BC differ depending on the feedstock and the pyrolysis conditions, and the influences have not been systematically clarified. Therefore, we evaluated the dependence of feedstock and pyrolysis temperature on the NO3-N adsorption properties of BC. Wood chips [Japanese cedar [Cryptomeria japonica] (CE) and Japanese cypress [Chamaecyparis obtusa] (CY)], moso bamboo [Phyllostachys edulis] chips (MB), rice [Oryza sativa] husks (RH), sugarcane [Saccharum officinarum] bagasse (SB), poultry manure (PM) and domestic wastewater sludge (WS) were air-dried and heated in a batch-type carbonization furnace at pyrolysis temperatures of 400, 600 and 800°C, with a hold time of 2 h. Among the BC produced from each feedstock, the one produced at 800°C had the greatest NO3-N adsorption. The NO3-N adsorption by BC produced from wood-based biomass at 800°C was significantly higher than that of the BC produced from non-wood-based biomass at 800°C. Therefore, BC made from wood-based biomass at higher temperature can be adequate as soil amendment material for adsorption of NO3-N.

Effects of Biochar Produced From Sugarcane Bagasse at Different Pyrolysis Temperatures on Water Retention of a Calcaric Dark Red Soil

Abstract Biochar (BC) is a promising soil amendment that can enhance water retention and plant-available water capacity while mitigating CO2 emissions. We investigated the effect of sugarcane bagasse–derived BC on the water retention properties of a calcaric clay soil amended with 3% (wt/wt) BC produced at three pyrolysis temperatures (400°C, 600°C, and 800°C). For BC pyrolyzed at 800°C (BC800), water retention curves of soil amended at 1%, 5%, and 10% (wt/wt) were also measured. Water retention curves were measured immediately after amending soil with BC (all types and rates) and after a 180-day incubation period for soils amended with 3% BC. The hydrophobicity of BC pyrolyzed at 400°C (B400) was the highest of the three temperatures tested, resulting in the lowest water retained in soil amended with BC400, but only for measurements done before incubation. During incubation, the hydrophobicity of B400 decreased as the aliphatic compounds became exhausted by oxidation of the BC surfaces. The available water capacity of the clay soil increased significantly by more than 60% when amended with BC at rates greater than of 3% wt/wt (P < 0.05).

Evaluation of strips of centipede grass for sediment load reduction

Reddish sediment runoff from agricultural fields results in coastal environmental problems in Okinawa, Japan. Recent studies have demonstrated the effectiveness of strips of centipede grass (Eremochloa ophiuroides (Munro) Hack.), a perennial turf grass, in reducing the sediment loads from farmlands. However, sufficient information has not been provided to determine the appropriate strip specifications in the grass strip design. This study evaluated centipede grass strips for reduction of reddish sediment runoff from farmlands in Okinawa, Japan. A numerical model simulating the reddish sediment transport in the grass strip was constructed to determine the sediment removal efficiency of the strip. The model was verified using data obtained from field plot experiments with the grass strips under natural conditions. The sensitivity analysis of the model showed that the length of the grass strip (i.e. the dimension of the strip in the direction of flow) and unit inflow discharge have a great effect on sediment removal efficiency. The sediment removal efficiency obtained from the model simulation increased with the length of the strip and the increment of the efficiency decreased with the length of the strip. Therefore, these results indicate that the effective and efficient length of a centipede grass strip is 3 m for the reduction of reddish sediment loads under typical farmland conditions in Okinawa.

Modeling of Sediment Transport in Surface Flow with a Grass Strip

Reddish sediment runoff from land areas during rainfall causes environmental problems in coastal areas of the Okinawa region, Japan. Sediment delivered to the coastal areas causes water pollution, sedimentation and degrades the coastal ecosystems and fisheries resources. Agricultural fields are a major source of sediment runoff in the region (Yoshinaga & Onaga, 1993; Minami et al., 2002). Nakasonoe et al. (1998) reported that sediment from agricultural fields accounts for 70% of the total sediment runoff in the region. Countermeasures for runoff in agricultural fields are promoted as an important issue in the Okinawa region. Countermeasures so far proposed include terrace work, drainage canals, sediment ponds, grass strips, cover cropping, mulch farming, contour farming, deep tillage, crop rotation and green manure (Hudson, 1995; Morgan, 1995). The grass strip countermeasure involves installing grass bands at the downstream end of an agricultural field to reduce the amount of non-point source pollutants, such as sediment and nutrients from an agricultural field into the stream (Dillaha et al., 1989). Grass strips are currently installed by prefectural governments assisted by the Ministry of Agriculture, Forestry and Fisheries as public work projects for water conservation, and also as a measure to help conserve agricultural land, water and the environment in rural areas. Grass strips can also be installed by farmers themselves as one of agricultural activities. There are various factors affecting how effectively grass strips reduce sediment runoff, such as flow rate of inflowing water, sediment properties, slope conditions and features of the grass (Haan et al., 1994). When installing grass strips as a countermeasure for sediment runoff, various conditions must be taken into consideration. In designing grass strips, it is necessary to know the quantitative relationships between the various factors influencing grass strips and their effects on reduction of sediment runoff, and to determine appropriate and reasonable parameters for installing grass strips. In previous studies, Sugawara et al. (2001), Osawa et al. (2005) and Shiono et al. (2005) conducted field experiments in Ishigaki Island and the northern part of the Okinawa Main Island, and reported their results on the effects of grass strips for reducing reddish sediment runoff. Shiono et al. (2007) also reported the influence that the length of grass strips in the direction of flow and particle sizes of sediment flowing into grass strips have on the ability of grass strips to reduce reddish sediment runoff. These results were obtained from field