Effects of Charcoal-treated Soils on Plant Growth and Nutrient Leaching 木炭による土壌処理が作物生育及び養分流出に及ぼす影響

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1 Effects of Charcoal-treated Soils on Plant Growth and Nutrient Leaching 木炭による土壌処理が作物生育及び養分流出に及ぼす影響 Kingshuk ROY *, Sadao NAGASAKA * and Shigeo ISHIKAWA * ロイキンシュック * 長坂貞郎 * 石川重雄 * Abstract: The leaching of nutrients from agricultural land is a major concern in Japan as well as many other countries. Experiments were conducted with two representative farmland soils, Kuroboku (Andosol) and Kunigami Maji (Ultisol). The soils were treated by mixing with charcoal that was processed at three different grain sizes, and Komatsuna (Brassica rapa var. perviridis) plants were grown in these charcoal-treated soils and a non-treated control. Plant growth parameters and discharge water in each condition were analyzed periodically throughout the observation period. The results showed that the addition of 1% charcoal grains (by volume) of particle size less than or equal to 5 mm was effective in both soil types from the perspectives of plant growth and nutrient leaching. Key Words: wood charcoal, farmland soil, plant growth, nutrient leaching, downstream pollution 要旨 : 農地からの養分流出問題は日本のみならず世界各国で注目されている研究課題である 本研究では 土性の異なる 2 種類の農地土壌 ( 黒ボクと国頭マージ ) に粒径別処理した 3 種類の木炭を混合させ 木炭処理法の違いが栽培作物の生育度合いと養分流出防止にどのような影響を及ぼすかについて実験的に調べた 実験期間中には 各栽培ポット内における作物生育関連の主な要因および各種処理土壌から流出した水中の主要なイオン濃度を定期的に測定した 結果として 両種の供試土壌においても 作物生育及び土壌養分の流出に対しては 5mm 以下の粒径をもつ木炭添加処理が効果的であることが分った キーワード : 木炭 農地土壌 作物生育 養分流出 下流汚染 INTRODUCTION In addition to its primary use as a fuel, charcoal has historically been used as a soil improver in many parts of the world (Hutterer, 1983; Wood & Baldwin, 1985; Glaser et al., 21). In Japan, although the use of rice husk charcoal and various ashes in agricultural fields dates back several centuries (Miyazaki, 1697), the of wood charcoal to soil was reported only few decades ago (Kishimoto & Sugiura, 1985; Nishio & Okano, 1991). In recent years, effective forest management has become a major concern in Japan, and there is a need to effectively utilize a huge surplus of forest residues (Harada, 2; Yoshioka et al., 25). Therefore, increased demand for wood charcoal (also termed biochar) can promote appropriate forest management. The effects of charcoal vary according to the raw materials, production methods and types of charcoal, and when it is applied to agricultural soil; biochar shows positive effects on certain physical, chemical, and biological properties of soil (Tryon, 1948; Ogawa & Okimori, 21; Kolb et al., 29). In addition, because charcoal is a porous material with high water- and air retention capacities, the addition of charcoal to agricultural soils increases water holding capacity and decreases nutrient leaching (Laird et al., 21). Both factors have become of interest to soil- and water conservationists in recent years, who have investigated means of reducing pollution load to downstream waterways from non-point-sources such as agricultural land. While many plant- and soil scientists recommend the use of charcoal for soil improvement, and to achieve better plant growth (Steiner et al., 27; Glaser et al., 22), less attention has been given to quantifying nutrient leaching from agricultural soils * College of Bioresource Sciences, Nihon University 環境情報科学学術研究論文集 26(212) 21

2 Table 1 Major properties of the soils (in-situ condition) used in the experiment Soil type Kuroboku soil (Andosol) Kunigami Maji soil (Ultisol) Particle size distribution Particle Three phase distribution Sand Silt Clay density Solid Liquid Air SHC EC OMC (ignition loss) % g cm -3 % cm s -1 ds m -1 % SHC and OMC denote Saturated Hydraulic Conductivity, and Organic Matter Content, respectively. ph (KCl) treated with charcoals. A review of the literature found no previous comparative study of the most suitable form/size of charcoal grains to simultaneously promote plant growth and reduce nutrient leaching. Soil texture has an important influence on the extent of nutrient leaching/retention in agricultural land (Major et al., 29). Therefore, we selected two common agricultural soils in Japan with different textural classes, and plants were grown with the addition of charcoals processed at three different particle size ranges. This study aimed to determine the most suitable form of charcoal treatment in agricultural soils. The study assessed the extent to which the different charcoal-treated soils contribute to plant growth and reduce the leaching of nutrients especially inorganic nitrogenous and other major ions that are responsible for water pollution. 1. MATERIALS AND METHODS All of the experiments and analyses in this study were carried out in a glasshouse and an analysis lab within the campus of the College of Bioresource Sciences, Nihon University in Fujisawa city, Japan. 1.1 Charcoal processing and plant growth experiment Komatsuna (Brassica rapa var. perviridis), also known as Japanese Mustard Spinach, was used as the test plant for the study. This plant grows well in acidic soil and is widely used in experimental studies. Two different types of soils were used as growing media. One type of soil, commonly known as Kuroboku soil (Andosol) was collected from farmland within the university campus (farmland number: 43), while the another type, known as Red Yellow soil or Kunigami Fig. 1 Outline of the experimental design, showing replications and treatments Maji soil (Ultisol) was collected from farmland in Onna village, located in Okinawa prefecture; the major properties of the soils are shown in Table 1. Charcoal intended for agricultural/horticultural uses, which is commonly found in gardening shops, was used to treat the soil after simple processing. Charcoals were broken up into pieces with a hammer and then the crushed charcoals were passed through sieves to divide the particles into three different specific physical particle size ranges, namely: 1) less than or equal to 1 mm; 2) greater than 1 mm but less than or equal to 5 mm; and 3) greater than 5 mm but less than or equal to 8 mm. The charcoal was processed in this way before adding it to the soil because the different particle sizes have differing specific surface areas; this was expected to influence the retention/depletion properties of water and nutrients in the soils. The processed charcoal grains were then mixed with both soil types at 1% by volume, as this mix ratio was previously reported to be effective for vegetable growth (Tsukagoshi et al., 25). Plastic pots (Sanko Inc., 5SR, volume 16 cm 3 ) were filled with the charcoal-treated soils (and non-treated control 22 環境情報科学学術研究論文集 26(212)

3 samples for both soil types) at in-situ dry densities of.6 g cm -3 and 1.1 g cm -3 for Kuroboku soil and Kunigami Maji soil, respectively. A total of 32 pots were used, 16 for each of the two major soil types. Each major soil type included 4 treatment sub-groups (3 charcoal-treated soils plus 1 untreated control); each charcoal-treatment sub-group comprised 4 individual pots: triplicates planted with Komatsuna (Brassica rapa var. perviridis), and 1 with no-plant. Fig. 1 shows details of the treatments and replications of the experiment. Komatsuna seedlings were germinated in a box with vermiculite, and were then transplanted to the selected pots when they reached an average height of approximately 4 cm. Prior to transplantation, a small amount of organic lime was added to Kunigami Maji soil, which had a low ph (4.7). No amendment for ph was necessary for Kuroboku soil. The pots were then labeled and placed randomly in a glasshouse, where the average daily maximum/minimum temperature and relative humidity ranges were recorded as 48/7 and 2 8% during the observation period (October 2, 211 to January 27, 212). Several parameters related to plant physiology and soil characteristics were measured: shoot length (cm), leaf-stock diameter (mm), number of leaves, soil moisture (%), soil EC (dsm -1 ), and soil hydraulic conductivity (cm s -1 ). Shoot lengths (cm) were measured using a measuring scale. Soil moisture and EC were recorded using a W.E.T sensor (Daiki Rika Kogyo Co.) coupled to a Time Domain Reflectometer (TDR). These parameters were measured weekly, whereas the hydraulic conductivities of charcoal-treated soils were measured once using a falling-head permeameter (DIK-45, Daiki Rika Kogyo Co.) based on Darcy s. In addition, leaf-diameter, and the fresh and dry weights (g) of root- and shoot parts of each plant were measured immediately after the end of the experiment. Diameter (mm) for every single leaf-stock was measured by using digital vernier calipers (CD-2CP, Mitutoyo Corp.). Fresh weights (g) were determined using a digital balance after separating the root and shoot parts, whereas dry weights were obtained after oven-drying at 7 for 3 days. Moisture contents for every whole plant were calculated from the measured data. It is noted here that, due to a sudden temperature increase resulting from a fire accident that occurred inside the glasshouse on November 2, 211, the shoot parts of all the plants were dried up. However, we continued the experiment after relocating the plants to an adjacent glasshouse where the environmental conditions matched the original glasshouse. The Komatsuna plants regained their health, grew new leaves within a few days, and we restarted our measurements and observations. In analysis of aboveground plant data, we used the parts that regenerated following relocation. Plant data were analyzed using MiniTab statistical software. All data sets were tested for normality and homogeneity of variances. One-way ANOVA was used to compare treatments and Tukey s range tests were used to examine the significance of the differences found. All statistically significant differences were tested at P<.5 level. 1.2 Water sampling and chemical analyses The bottoms of the plastic pots were sealed with round-cut pieces of synthetic artificial grass to minimize soil outflow along with water. Each pot (with or without plant) had a saucer to collect the drained water. As the soils used in this experiment were collected from farmland (in-situ), they had already received different organic and inorganic inputs prior to our charcoal treatments. Therefore, the day prior to seedling transplantation, baseline nutrient leaching was assessed in each charcoal-treated/non-treated condition. The same quantity of water was applied to each pot, and water samples were collected from the discharged water that collected in the saucers. We also used a liquid, HYPONeX (N:P:K=6:1:5), which was applied twice (dosage per : 4mL per liter of water) during the observation period, to facilitate plant growth and also to assess nutrient leaching while the plant utilized the nutrients with the course of time and growth in each pot. The first of with water was also done the day before the seedling transplantation (October 19, 211), and water samples were collected accordingly. Although each pot was watered equally each day, care was taken that the quantity of discharge-water was minimized and did not overflow any saucer. In addition, samples of discharged water were collected from each saucer on December 6, 211, and then again on the following day (December 7, 211), during the second of. Water samples were collected again in the same way at the end of the experiment 環境情報科学学術研究論文集 26(212) 23

4 (January 27, 212). Water samples were stored in a dark chamber of a refrigerator (below 1 ), and were then analyzed in the laboratory using atomic absorption spectrometry (TOA, auto sampler ICA-545). Our study focused mainly on those nutrients leached from agricultural soils that are detrimental to downstream water. The analysis therefore emphasized the concentrations of nitrogenous ions (NO3-N, NO2-N, NH4-N), while other major ions (Na +, K +, Mg 2+, Ca 2+, Cl - and SO4 2 - ) were also investigated to determine whether the available ion concentrations in soil-water had any effect on plant growth. We used tap water throughout the experiment, and therefore the same ions were also analyzed in the tap water. 2. RESULTS AND DISCUSSION 2.1 Plant growth Table 2 summarizes the plant physiological data, showing average values of the replications in each treatment. Only the number of leaves in Kuroboku soil were found to be statistically significant (P<.5). Considering these values along with those of the other parameters (P>.5) as shown in Table 2, the addition of charcoal grains (less than or equal to 1 mm) to Kuroboku soil was found to be the only treatment that improved the overall growth of Komatsuna. In the Kunigami Maji soil, the charcoal treatments showed no significant improvement in plant growth compared with the non-charcoal plants. However, among the charcoal- Fig. 2 Concentrations of ions in tap water and treatments, the addition of charcoal grains with small particle size (smaller than or equal to 5 mm) was found to be better for plant growth than the larger sizes (larger than 5mm but smaller than or equal to 8 mm). 2.2 Chemical analyses Fig. 2 shows major ion concentrations of and irrigation water. Among the analyzed ion components, concentrations of nitrogenous components in discharges, i.e., nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N) and nitrite nitrogen (NO2-N), are graphed in Figs. 3(a,b)-4(a,b). Comparison of the temporal outflow of ions before and after every /irrigation showed that the major leaching component differed with soil type (texture), but that the quantities of nitrogenous ions for both Kuroboku and Kunigami Maji soils treated with Table 2 Physiological parameters of Komatsuna plants, showing average values for different treatments c in the treatment column denotes charcoal particle size, while the letters (a and b) alongside numeric values denote significant differences (p<.5) for each treatment (Tukey s range test). 24 環境情報科学学術研究論文集 26(212)

5 Concentration (mg L -1 ) a. PLANT no2-n NO 2 no3-n NO 3 NH4+-N 4 Concentration (mg L -1 ) b. NO PLANT NO no2-n 2 NO no3-n 3 NH4+-N 4 Before Before Fig. 3 (a, b) Nitrogenous ions discharged from Kuroboku soil Concentration (mg L -1 ) no2-n NO 2 no3-n NO 3 NH4+-N 4 a. PLANT Concentration (mg L -1 ) no2-n NO 2 no3-n NO 3 NH4+-N 4 b. NO PLANT Before Before Fig. 4(a, b) Nitrogenous ions discharged from Kunigami Maji soil Table 3 Cumulative leaching of all measured ions throughout the experiment Soil type Kuroboku soil (Andosol) Kunigami Maji soil (Ultisol) Treatment No charcoal c 1 mm 1 mm < c 5 mm 5 mm < c 8 mm No charcoal c 1 mm 1 mm < c 5 mm 5 mm < c 8 mm Plant/ no-plant NH4-N NO3-N NO2-N Na + K + Mg 2+ Ca 2+ Cl - SO4 2- mg L -1 No plant Plant No plant Plant No plant Plant No plant plant No plant Plant No plant Plant No plant Plant No plant Plant c in the treatment column denotes charcoal particle size 環境情報科学学術研究論文集 26(212) 25

6 charcoal grains of less than 1 mm to 5 mm tended to decrease more gradually than other conditions, for both the soils with and without plants. Table 3 shows the amounts of all the major ions accumulated throughout the observation period. Kuroboku soil with both plant and no-plant discharged much NO3-N, whereas the Kunigami Maji soil discharged most NH4-N (Table 3). This variation is possibly due to differences in the soils properties, such as hydraulic conductivity and OMC (organic matter content). Kuroboku soil was rich in OMC (Table 1), and the average coefficient of hydraulic conductivity in Kuroboku soil ( cm s -1 ) was higher than that in Kunigami Maji soil (4 1-4 cm s -1 ), which might facilitate soil microorganisms oxidizing the ammonium form to nitrate-nitrogen. Although the concentration levels of major ions (Na +, K +, Mg 2+, Ca 2+, Cl - and SO4 2- ) other than the nitrogenous compounds differed, neither of the soils had an effect on plant growth, as the average EC values for both soils were less than the salinity level (2 ds m -1 ) that would inhibit plant growth. CONCLUSIONS From this study, it can be concluded that the benefit to plant growth from adding charcoal to soil is dependent upon the soil type (texture), and requires a specific size of charcoal particles, such as the positive effect observed from adding charcoal grains smaller than or equal to 1 mm to Kuroboku soil. However, relatively small grains of charcoals (less than or equal to 5 mm in our study) generally have the potential to reduce nutrient leaching from soil, which could thereby lessen the pollution load from farmlands to downstream waterways. However, as agricultural soils, even with similar textural classes, have differing organic matter/humus contents, the effect of micro-organism activities and therefore predisposition to accumulate/discharge nutrients from soil also varies. Therefore, to differentiate the individual effect of charcoal, further analyses are required of every soil component. Long-term field experiments/observations could also determine the appropriate frequencies of charcoal addition; otherwise, smaller particles of charcoal could reduce water infiltration capacity, leading to increased salinity, and may ultimately inhibit plant growth. ACKNOWLEDGEMENTS The authors would like to acknowledge first Ms. Haruka Koyama and Ms. Misato Kawasaki, two graduate students from the senior author s lab, for their continuous assistance in carrying out the experiments. We also wish to thank Dr. Y. Yanagisawa and Dr. N. Kurauchi from the College of Bioresource Sciences, Nihon University, for their cooperation and willingness to discuss issues and provide feedback where essential. We are also grateful to the anonymous journal referees, for their valuable comments and suggestions. REFERENCES Glaser, B., Haumaier, L., Guggenberger, G and Zech, W. (21) The Terra Preta phenomenon: a model for sustainable agriculture in the humid tropics. Naturwissenschaften, Vol. 88, No. 1, pp Glaser, B, Lehmann, J. and Zech, W. (22) Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal- a review. Biology and Fertility of Soils, Vol. 25, No. 4, pp Harada, T. (2), Energy use of biomass from forest. Research Journal of Food and Agriculture, 23 (6), pp [in Japanese]. Hutterer, K. L. (1983) The Natural and Cultural History of Southeast Asian Agriculture: Ecological and Evolutionary Considerations. Antropos, 78, pp Kishimoto, S., Sugiura, G. (1985) Charcoal as a soil conditioner. 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(1948) Effect of Charcoal on Certain Physical, Chemical, and Biological Properties of Forest Soils, Ecological Monographs, Ecological Society of America, Vol. 18, No. 1, pp Wood, T. S. and Baldwin, S. (1985) Fuelwood and Charcoal Use in Developing Countries. Annual Review of Energy, Vol. 1, pp Yoshioka T., Hirata S., Matsumura Y., Sakanishi K. (25) Woody biomass resources and conversion in Japan: The current situation and projections to 21 and 25. Biomass and Bioenergy, Vol. 29, pp 環境情報科学学術研究論文集 26(212)