Makoto Kitou

Characteristics of synthetic soil aggregates produced by mixing acidic “Kunigami Mahji” soil with coal fly ash and their utilization as a medium for crop growth

Abstract This study was carried out to examine the characteristics and potential utilization of synthetic soil aggregates (SSA) produced by mixing acidic “Kunigami Mahji” soil in Okinawa, Japan, with waste materials, such as coal fly ash, used paper and starch, as media for crop growth. A series of different SSA were produced by incorporating various percentages (i.e. 0, 20, 40, 60, 80 and 100%) of coal fly ash into the “Kunigami Mahji” soil with used paper and starch. The particle density and bulk density of the original “Kunigami Mahji” soil were 2.67 and 1.23 g cm−3, respectively. The increased percentages of added coal fly ash, used paper and starch significantly decreased the particle and bulk densities of SSA compared with the original “Kunigami Mahji” soil because of the low particle and bulk densities of the coal fly ash (2.10 and 0.96 g cm−3, respectively). The SSA particle density varied between 2.39 and 2.14 g cm−3, and bulk density varied between 0.72 and 0.81 g cm−3, depending on the additional percentages of coal ash from 20–100%. Maximum water-holding capacity and saturated hydraulic conductivity were increased with the formation of SSA with coal fly ash, used paper and starch binder compared with the original “Kunigami Mahji” soil. The saturated hydraulic conductivity values of the SSA increased because of their low bulk density compared with the original soil. The addition of coal fly ash, used paper and starch to the acidic (pH = 4.62) “Kunigami Mahji” soil to form SSA increased the pH (6.70–9.96), electrical conductivity, exchangeable cation concentration and cation exchange capacity. The addition of coal fly ash up to 60% increased the aggregate strength. The growth and yield of komatsuna and soybean crops with SSA as a crop growth medium was assessed. Both crops showed the highest growth and yield when grown with SSA containing 20% of coal fly ash. Synthetic soil aggregates containing more than 20% of coal fly ash reduced plant growth and yield. Therefore, SSA produced from “Kunigami Mahji” soil with 20% of coal fly ash, used paper and starch can be successfully used as a medium for crop growth.

Use of synthetic soil aggregates as a containerized growth medium component to substitute peat in the ornamental plant production

This study investigates characteristics and utilization of synthetic soil aggregates (SA) formed by low productive acidic soil with paper and starch waste for production of French marigold (Tagetes patula) as a partial peat substitution in growing substrate. Five different growth substrates utilized in this study were: (i) Peat only, (ii) peat 75%: SA 25%, (iii) peat 50%: SA 50%, (iv) peat 25%: SA 75%, and (v) SA only. Peat 75%: SA 25% enhanced substrate physical and chemical properties into the established ideal substrate range. Plant height, numbers of flowers, fresh shoot weight, dry shoot weight, root length, fresh root weight and dry root weight of French marigold grown in the substrate of peat 75%: SA 25% increased by 13.28, 23.07, 28.51, 27.41, 6.66, 68.33 and 7.40%, respectively, compared with peat substrate. Peat 50%: SA50% gave similar growth parameters to peat only substrate. Nitrogen (N) content of plants grown in peat 75%: SA25% was higher than peat substrate. Cu, Fe, Mn and Zn concentrations in all plant shoots were in the normal range and well below the phytotoxic range. Therefore, growth substrates with 25% and 50% SA can be recommended as the most effective substrates to substitute expensive and less available peat from an environmental point of view.

Effect of Synthetic Soil Aggregates as a Soil Ameliorant to Enhance Properties of Problematic Gray (“Jahgaru”) Soils in Okinawa, Japan

Synthetic aggregates (SA) were developed using low productive red soil, paper, and starch waste and then utilized as a soil ameliorant to improve poor physical and chemical properties of a gray soil (“Jahgaru”). The gray soil was amended with SA at 10, 20, 30, 40, and 50% and then used for the cultivation of French marigold (Tagetes patula). The SA addition enhanced bulk density, porosity, water‐holding capacity, hydraulic conductivity, pH, organic matter, and carbon (C) content of original gray soil. Plant height, number of flowers per plant, shoot fresh weight, shoot dry weight, root length, root fresh weight, and root dry weight in 30% of SA addition were the greatest and were increased by 1.5, 2.9, 3.5, 4.7, 3.4, 4.3, and 9 times, respectively, compared to gray soil. It can be concluded that developed SA can be utilized as a soil ameliorant to improve poor physical and chemical properties of gray soil.

Growth and Nutrient Accumulation of Winged Bean and Velvet Bean as Cover Crops in a Subtropical Region

We examined biomass dry matter and nutrient uptake of live plant parts, leaf area index, and litter of winged bean (Psophocarpus tetragonolobus) and velvet bean (Mucuna pruriens) 12, 18, 24 and 30 weeks after sowing (WAS). The two plants had similar leaf and stem+petiole biomasses. At 30 WAS winged bean had a significantly lower pod yield than velvet bean. Between 18 and 30 WAS, winged bean produced less litter than velvet bean due to differences in growth stages. The total mulch of live parts and litter of winged bean and velvet bean completely covered the ground by 18 and 12 WAS, respectively. Compared to velvet bean, the leaf and stem+petiole of winged bean had a significantly higher N concentration; significantly higher N uptake at 24 and 30 WAS; significantly lower C/N ratio; and significantly higher P, K and Mg concentrations. In winged bean, P uptake was significantly higher in the leaf at 30 WAS and in the stem+petiole at all harvesting times. The total biomass of the leaf, stem+petiole and litter of winged bean was 317–561 g DM m-2, and their N content was 12.3–17.7 g m-2. The total biomass of live parts and litter of winged bean might be sufficient to suppress weeds and increase soil N. Winged bean is an appropriate legume cover crop and green manure due to its longer growing period and superior ground-covering ability and high N input.

Potential growth of hairy vetch as a winter legume cover crops in subtropical soil conditions

Abstract Soil acidity is one of the most serious causes of land degradation and limits crop production in subtropical agriculture. A number of legumes have adapted to P-limiting conditions, and the aim of the present study was to select an appropriate species for use as a winter legume cover crop under subtropical soil conditions in Okinawa, where P deficiency stems from soil acidification. Four vetch and four clover species were examined in pot trials. Of these, hairy vetch (Vicia villosa Roth) was found to be the most tolerant of P-limiting conditions. The shoot biomass of hairy vetch was also generally higher than that in the clover species when the P supply was non-limiting in the spring season. Hairy vetch was then compared in a pot trial with four clover species for an extended period of growth with adequate P supply. The N fixing activity of hairy vetch in the vegetative stage was 3.2-fold greater than that of the clover species. Nitrogen and P uptake in shoots and roots was significantly higher in hairy vetch than in the clover species in the vegetative and flowering stages. The C/N ratio in the shoots and roots of hairy vetch tended to be lower than that in the clover species. Shoot K uptake by hairy vetch was significantly higher in the vegetative stage than that in the clover species. In a field trial, shoot biomass and nutrient uptake of hairy vetch were similar on four different subtropical soils with pH values ranging from 5.7 to 7.5. Hairy vetch is an appropriate winter legume cover crop to improve subtropical soils by increasing organic matter and supplying nutrients to the subsequent crop.

Characteristics of Surface Sediments along a Creek in a Mangrove Forest

The mangrove habitat is referred to as an advancing coast, where the land advances toward the sea due to soil sedimentation. In the present study, physico-chemical and mineralogical characteristics of surface sediments in a mangrove forest were investigated to evaluate the mechanism of accumulation of surface sediments from the viewpoint of colloid chemistry. A mangrove forest in the Fukido River basin, Ishigaki Island was selected as the study site. Six locations along the river in the forest were selected, and samples of surface sediments (0.5 cm thick) were collected at 4 points (a point on the water side of the bank directly in the river water (hereafter referred to as “0 m from the river water”), a point on the bank at a distance of 0.5 m from the river water and points at distances of 5.5 m and 10.5 m into the forest from the river) of each location (total 24 points). The soil texture of the surface sediments considered of HC at nearly all the sampling points, and more clay tend to accumulate on the water side of the bank of about 200 m upstream from the downstream end of the study area. The silt fraction of the surface sediments contained quartz at a rate of about 70% along with feldspar and a small percentage of cristobalite. In the clay fraction, the contents of kaolinite and illite were slightly higher than the contents of vermiculite and vermiculite-chlorite intergrade. The mineral composition was similar at all the points, suggesting that the minerals were carried from the upper reaches of the river and were deposited in the study area. Both the pH and EC values of the surface sediments tended to decrease toward the upper reaches of the river and to be higher on the bank than at the points farther into the forest. The total carbon content, organic carbon content, total nitrogen content and total phosphate content tended to be higher on the bank at about 200 m upstream from the low end of the study area, indicating a larger accumulation of organic matter at this site. High clay and high organic matter contents were observed on the bank at this location. From the above evidence, it was suggested that organo-mineral complexes were likely to accumulate in mangrove surface sediments.