Possibility of No-Input Farming in Lowland Rice Fields in Japan from the Viewpoint of Sustaining Soil Fertility

In Japan, the area of low-input rice production is gradually increasing with a growing public interest in the quality and safety of our staple food. In an extreme case, rice has been grown over years without using any chemical fertilizers and agrochemicals. However, it is uncertain how much and how long such no-input farming can sustain rice yield and soil fertility. To better understand the sustainability of no-input rice farming in Japan, I briefly review previous results obtained from the long-term field experiments. The topics are (1) rice yield and soil fertility under no-input farming, (2) the environmental factors affecting rice growth and soil fertility under no-input farming, and (3) the dynamics of soil K under continuous rice cropping. The corresponding conclusions are as follows: (1) rice yield and soil fertility under no-input farming in Japan were influenced by various environmental and management factors operating at regional and field scales; (2) the input of K through irrigation and the high-clay content in soil were considered the key environmental factors that enable to sustain no-input farming; and (3) soil K depletion caused by long-term exhaustive cropping should be assessed by monitoring the decrease of soil nonexchangeable K rather than that of exchangeable K

An Overview of the Effects of Heat Treatments on the Quality of Organic Wastes as a Nitrogen Fertilizer

Sewage sludge is often heat-dried to eliminate water and pathogens. However, heat-drying can also change the form of nitrogen (N). To improve our understanding of this phenomenon, we examined the heat-induced changes in the rate of N mineralization from soils and organic wastes. Published results revealed that the response to the heating temperature differed between soils and organic wastes. As the heating temperature increased to 200°C, the rate of N mineralization increased in soils but decreased in organic wastes. In organic wastes such as sewage sludge, the content of mineralized N tended to decrease sharply when heating temperatures increased to 150–200°C. Furthermore, our results obtained from heat-drying of sewage sludge at 180°C indicated that the rate of carbon (C) mineralization decreased with increasing heating period after the sludge temperature reached 180°C. The C in sewage sludge heated at 180°C for 120 hours after complete drying contained more humin and aromatic C than that in sludge that was heat-dried at 180°C without the additional heating period. These results suggest that the heat-drying treatment can be divided into the drying and denaturing periods and that the temperature of the sludge, not that of the reactor, affects the quality of the end-product

An Overview of the Studies on Biochar Fertilizer Carried Out at the Beginning of the Twentieth Century in Japan

Biochar is a recently coined term for charred organic matter used as a soil amendment. Although the term is relatively new, the substance has been used for a long time throughout the world, including Japan. After we read a Japanese book entitled Nibai Shukaku Tenri Nouhou (How to Double Crop Yield by Almighty Farming System) originally published in 1912, we found that there were conflicting opinions between the author (Mr. Katsugoro Oyaizu) and soil scientists of the time (Dr. Gintaro Daikuhara and others) on the benefits of the use of biochar fertilizer. Previous publications on this topic have been written in Japanese from a sociological viewpoint. By referring to the literature published at the beginning of the twentieth century in Japan, we attempt to shed light on the conflict between traditional knowledge of biochar fertilizer and new concepts of soil science imported from the Western countries. We also describe briefly the socioeconomic impacts on the use of biochar fertilizer in the later generations

コンケン ドジョウ ノ ヨウブン ドウタイ ニ カンスル ケンキュウ

京都大学0048新制・課程博士博士(農学)甲第9148号農博第1209号新制||農||831(附属図書館)学位論文||H13||N3579(農学部図書室)UT51-2001-K355京都大学大学院農学研究科地域環境科学専攻(主査)教授 小﨑 隆, 教授 櫻谷 哲夫, 教授 關谷 次郎学位規則第4条第1項該当Doctor of Agricultural ScienceKyoto UniversityDA

Soil color analysis for statistically estimating total carbon, total nitrogen and active iron contents in Japanese agricultural soils

Soil color originates mainly from organic matter, iron mineralogy and moisture content. We aimed to find a suitable method to measure soil color sensitively and to evaluate the extent to which the color parameters can be useful for statistically estimating total carbon (C), total nitrogen (N) and active iron (Fe) contents in Japanese agricultural soils. A soil color reader (SPAD-503) was applied to two sample sets: (1) 100 surface soils collected throughout a 0.5-ha paddy field (field scale) and (2) 147 surface soils collected from agricultural fields in Japan (national scale). For analysis with this instrument, about 2 g of air-dried, finely-ground samples were packed firmly in a plastic cell, and their colors as they appeared on windows in both sides of the cell were measured. A CIE 1976 (L[*], a[*], b[*]) color space was used for color description. For the field-scale samples, the values of the coefficient of variation were around 15% for total C, total N and acid oxalate extractable iron (Feo). The L[*] value (lightness) was negatively correlated with the content of total C and total N (R[2] = 0.18** and 0.26**, respectively), and the b[*] value (yellowness) was positively correlated with the Feo content (R[2] = 0.59[**]). For the national-scale samples, the values of the coefficient of variation were around 60% for total C, total N and Feo. The L[*] value was negatively correlated with the content of total C and total N (R[2] = 0.70** and 0.59[**], respectively), but the b[*] value was not correlated with the content of Feo (R[2] = 0.00). When the analysis was limited to 65 samples frequently used for paddy fields, the b[*] value was positively correlated with the Feo content (R[2] = 0.52[**]). In conclusion, the proposed method enabled us to measure soil color sensitively with a small sample size. The L[*] and b[*] values obtained can be useful for rapid estimation of total C, total N and Feo contents in agricultural surface soils in Japan

Significance of Plant-induced Solubilization of Soil Nitrogen: A Case of Komatsuna Plants Grown in Fertilized Soils

Plant-induced solubilization of soil nitrogen (N) is a key process for plants to utilize the recalcitrant form of N. Toevaluate its contribution to plant uptake, the factors affecting the contribution and the forms of N solubilized by plants, we analyzed the results of a pot experiment in which komatsuna (Brassica rapa L. var. peruviridis) was grown in 3 different soils applied with 5 types of sewage sludge as a source of N for plants. The amount of N solubilized by plants, which was defined experimentally as the difference in the amount of solubilized N between the planted and unplanted treatments, varied with the soil types more than the types of sewage sludge. This accounted for 30% (Arenosol), 15% (Fluvisol) and 1.6% (Andosol) of the amount of N uptake on average. These percentages were high when the level of soil soluble N after the experiment was below approximately 30 mg kg-1. Sequential analyses of insoluble N in soil after the experiment indicated the occurrence of plant-induced solubilization of both bio-soluble and acid-soluble N in many of the Arenosol and Fluvisol treatments and that of acid-soluble N in the Andosol treatments. The plant-induced solubilization in the Andosol resulted in the accumulation of more labile bio-soluble N rather than enhanced plant uptake. For komatsuna grown in fertilized soil, the depletion of soluble N in the root zone seems to be important for the increase in the contribution of the plant-induced solubilization to uptake but not for the occurrence of the solubilization

Farm-Scale Estimation of Total Nitrogen Content in Surface Paddy Soils by Extraction with Commercially Available Hydrogen Peroxide

We recently proposed a simple method for estimating total nitrogen content in paddy soil. In this method, soil is extracted with a commercial 3% hydrogen peroxide (H₂O₂) solution at 25 °C for 40 h, and electrical conductivity (EC (H₂O₂)) of the extract is measured. This study aimed to further evaluate the method’s applicability to soil samples collected at the farm scale by using the original and six additional H₂O₂ solutions that are locally and commercially available. The results obtained with the original solution indicated that the determination coefficients between EC (H₂O₂) and total N were statistically significant at all farms examined: Moka, 0.78 (n = 13); Kyoto, 0.50 (n = 16); Kizu, 0.43 (n = 89); and Kawatabi, 0.25 (n = 18). The EC of the tested H₂O₂ solutions varied from less than 0.05 to 1.4 mS cm−1 because of the addition of different stabilizers. EC (H₂O₂) values obtained with the less stabilized H₂O₂ solutions (one from Japan, one from USA, and the analytical grade 6% solution) agreed well with those obtained with the original solution. Thus, the proposed method can be useful for estimating the farm-scale variation in soil total N, provided a H₂O₂ solution with a low EC (<0.2 mS cm−1) is used for the extraction