Shuichi Miyagawa

EFFECTS OF SILICATE MATERIALS ON GROWTH AND GRAIN YIELD OF RICE PLANTS GROWN IN CLAY LOAM AND SANDY LOAM SOILS

The usefulness of silicate materials in rice cultivation has been reported by a number of authors. However, very little has been done to study recycling of silicon (Si)-rich plant residues, such as the use of rice chaffs as soil amendments. Pot experiments were conducted in a green-house at Gifu University in 1997. In this investigation, powdered rice chaff (Cp) and normal rice chaff (Ch) were mixed in a fertile clay loam soil and an infertile sandy loam soil, with or without a biodecomposer (Wara soil). Calcium silicate was also applied to the soils for comparison. For both types of soils, six treatments were replicated four times giving 48 pots (24 × 2) in total with a randomized complete block design. Rice plants (Oryza sativa L. cv. Hatsushimo) were grown in pots filled with the soils as treated above, and the growth and Si and nitrogen (N) contents in the plants and grain yield were determined. Application of rice chaffs had little effect on plant height, but slightly increased the number of tillers per pot. The total N content of the plants was decreased in the clay loam soil but not in the sandy loam soil, but the Si content in the plants, grown in both soils, was increased. The effect of Cp and Ch on the Si content of plants was significantly enhanced by the addition of the biodecomposer. Both organic and inorganic silicate materials increased the number of grains and the dry weights of grains. The application of Cp together with the biodecomposer was the most effective. Cp could be used instead of inorganic Si fertilizer, providing a sustainable Si recycle system in rice cultivation.

Indigenous utilization of termite mounds and their sustainability in a rice growing village of the central plain of Laos

BackgroundThe objective of this study was to investigate the indigenous utilization of termite mounds and termites in a rain-fed rice growing village in the central plain of Laos, where rice production is low and varies year-to-year, and to assess the possibility of sustainable termite mound utilization in the future. This research was carried out from 2007 to 2009.MethodsThe termites were collected from their mounds and surrounding areas and identified. Twenty villagers were interviewed on their use of termites and their mounds in the village. Sixty-three mounds were measured to determine their dimensions in early March, early July and middle to late November, 2009.ResultsEleven species of Termitidae were recorded during the survey period. It was found that the villagers use termite mounds as fertilizer for growing rice, vegetable beds and charcoal kilns. The villagers collected termites for food and as feed for breeding fish. Over the survey period, 81% of the mounds surveyed increased in volume; however, the volume was estimated to decrease by 0.114 m3 mound-1 year-1 on average due to several mounds being completely cut out.ConclusionIt was concluded that current mound utilization by villagers is not sustainable. To ensure sustainable termite utilization in the future, studies should be conducted to enhance factors that promote mound restoration by termites. Furthermore, it will be necessary to improve mound conservation methods used by the villagers after changes in the soil mass of mounds in paddy fields and forests has been measured accurately. The socio-economic factors that affect mound utilization should also be studied.

Hydropriming effects on carbohydrate metabolism, antioxidant enzyme activity and seed vigor of maize ( Zea mays L.)

Two cultivars of seeds from the National Corn and Sorghum Research Center (NCSRC) and a Private Company (PC) were hydroprimed for 3 to 12 h, then artificially aged at 42C, 100% RH for 96 h. The germination of NCSRC unprimed seeds after accelerated aging was greater than the PC seeds caused by its initial ascorbate peroxidase (APX) activity. Hydropriming for 3 to 9 h prevented any loss in germination due to the aging process. However, this effect was inhibited by hydropriming for a longer duration. The amelioration of the aging process may be due to a reduction in oxidative stress by antioxidant enzymes. Superoxide dismutase (SOD) and APX may play a role in NCSRC, but APX only contributed in PC seeds. The high amylase activity with remaining glucose content may associate to improve germination in the hydroprimed with aged seeds. Hydropriming periods of greater than 9 h resulted in loss of seed germination after accelerated aging. This result was caused by a reduction in sucrose and raffinose content. The sharply increased amylase activity for both cultivars and the decreased activities of SOD and APX in NCSRC and APX in PC may also indicate the loss of primed seed vigor.

Yields from rice plants cultivated under tree canopies in rainfed paddy fields on the central plain of Laos.

Abstract Many trees are left uncut in the paddy fields of many villagers in central Laos. Yields of rice in rainfed paddy fields interspersed with trees in central Laos were investigated in relation to shading and soil fertility from trees. Grain yield of rice plants cultivated in close proximity to tree trunks (CTP) was higher than that of the plants cultivated far away from the tree trunks (FTP) in 5 fields but lower in 7 fields. The effects of individual trees on rice yield varied among trees of the same species over the course of the three-year study period. No relationship was observed between the changes in photosynthetic photon flux density (PPFD) due to interception by the tree and the ratio of grain yield of CTP to that of FTP. A significant negative relationship was observed between grain yield of FTP and the ratio of grain yield of CTP to that of FTP, suggesting that yield of CTP under some trees is not lower than that of FTP when the latter was low.

Effects of Soil Fertility Management on Growth, Yield, and Water-Use Efficiency of Maize (Zea mays L.) and Selected Soil Properties

Maize was grown for two cropping years to investigate the supplementary effect of inorganic fertilizer with cow dung on growth, yield, water-use efficiency, and soil properties. Five treatments were imposed: unfertilized control and four different fertilization packages comprising two different levels of inorganic fertilization with cow dung as supplements, sole inorganic fertilizer, and sole cow dung. Results analyzed after the two cropping years showed significant differences in growth and yield. A reduction in yield was observed for the unfertilized plots, whereas yields in the plots of supplemented inorganic fertilizer with cow dung increased and were significantly at par with the sole inorganic fertilizer plot. Water-use efficiency was improved for the fertilized plots. Significant improvement was observed in the water-stable aggregates with plots that received cow dung as organic manure either in part with inorganic fertilizer or as sole cow dung.

Effects of soil moisture and temperature on decomposition rates of some waste materials from agriculture and agro-industry.

Abstract The effect of soil moisture and temperature on decomposition of waste materials, bagasse, coir dust, rice chaff and rice straw, in soil were examined by measuring the decrease in weight of and CO2 generation from each waste material. The rate of the decrease in weight increased as temperature rose, and was highest in rice straw followed by bagasse, rice chaff and coir dust in this order, irrespective of soil moisture and temperature level. In all waste materials, the rate of decrease in weight was highest in the soil holding the water equivalent to field capacity (saturated soil) followed by submerged soil and dry soil in this order. CO2 generation rate was also highest in rice straw followed by bagasse, rice chaff and coir dust. It was highest in saturated soil followed by half-saturated or submerged soil and dry soil in this order. The rate of CO2 generation from rice straw in saturated soil was highest at the initial period of incubation and it decreased thereafter, but the rate in submerged soil was highest at 40 and 20 days after the start of incubation at 20 and 35ºC, respectively. The rate of CO2 generation from coir dust and rice chaff was very low at all soil moisture levels at either 20 or 35ºC. The content of total N in the waste materials was positively and significantly correlated with the rate of decrease in weight in saturated and submerged soils at a moderate temperature (Oct. – Dec.), and in submerged soil at a high temperature (Aug. – Oct.). It was also significantly correlated with CO2 generation rate in submerged soil at 20ºC. Holocellulose and hemicellulose contents were negatively and significantly correlated with CO2 generation rate in dry soil at 20ºC. Lignin content was also significantly and negatively correlated with CO2 generation in dry soil at 35ºC.

Effects of powdered rice chaff on growth and yield of rice under different soil pH conditions

Abstract A recent rapid reduction in soil pH has been attributed to fertilizer mismanagement. The decomposition and consequent nutrient release from silicate rich organic material such as powdered rice chaff (Cp) could be affected by such reductions in pH. In the present study, rice plants were grown in either Cp or calcium silicate (Si-Ca) under various soil pH ranging from 5.5 to 7.5. The results show that the pH of soils gradually decreased at different growth stages in the case of pH 6.5 with Cp treatment. On the other hand, pH gradually increased at different growth stages of the rice plants when soil pH was initially 5.5, both with Cp and with calcium silicate. Nitrogen (N) and silicon (Si) contents of the plants decreased gradually with growth stage after the maximum tillering stage. The relationship between Si and N content in the plant at maximum tillering stage showed contradictory results. Si content was higher at pH 6.5 and at pH 5.5 with both Cp and calcium silicate treatments. On the other hand, N content was higher at pH 6.5 and at pH 7.5. Yield and yield components were significantly higher at pH 7.5 with Cp. These results suggest that Cp can be used as an alternative source of inorganic Si fertilizer. The mechanism by which the Cp acts under different pH nutritional conditions is unclear.

Effect of Supplementing Inorganic Fertilizer with Organic Fertilizer on Growth and Yield of Rice-Cowpea Mixed Crop

Abstract With the renewed interest in mixed cropping and the increasing awareness of environmental degradation arising from high chemical inputs, this experiment was conducted to assess the effect of supplementing inorganic with an organic fertilizer on the growth and yield of rice and cowpea under the mixed cropping system. Treatments comprised six sole crops and three mixed crops, each under 100% NPK (C), 50%NPK+ 50% cow dung (CCD) and cow dung alone (CD). The fertilizer treatments did not significantly affect cowpea performance. However, the number of panicles per hill and the number of spikelets per panicle of rice were higher under mixed cropping than under sole cropping. On the average, rice grain yield was significantly lower under the mixed cropping than under the sole cropping. The land equivalent ratios increased under all the fertilizer treatments indicating the efficiency of the mixed-cropping system. The results of the experiment suggest that rice– cowpea mixed cropping under CCD and CD is a viable production option.

Soil Productivity after Decomposition of Waste Materials under Different Soil Moisture and Temperature

Abstract Productivity of the soil with waste material (WM), i.e., bagasse, coir dust, rice chaff and rice straw decomposed for two months at various temperatures and soil moisture were investigated by analyzing the chemical properties and growth of maize cultured on the soil for 45 days. The soil with decomposed WM (WM soil), tended to show lower pH values than the soil without WM soil (control) as a whole. The values of electric conductance were higher in WM soil, especially in the soil with decomposed rice chaff and rice straw referred to as rice-chaff and rice-straw soils, respectively. The total N content tended to be higher in the WM soil except for coir dust soil. The total C content tended to be higher in all WM soils. The difference in the content of total N and total C between WM and control soils was remarkable in bagasse soil. The change of the chemical properties of the soil did not apparently correlate with the rate of CO2 generation during incubation of WM soils, but pH, electric conductance, content of total N and total C contents were higher in the soils generating CO2 at a rate of 40 to 80 ppm min−1, in bagasse or rice straw soils. The dry matter production of maize on WM soils was positively correlated with the rate of CO2 generation. It was suggested that the WM soils generating little CO2, such as the soil with bagasse or rice straw decomposed in a dry condition, tended to inhibit maize growth owing to low pH and shortage of available nitrogen by rapid decomposition just after the start of maize growth. The wet WM soils generating CO2 format a rate of 40 to 80 ppm min−1, e.g., bagasse and rice straw soils might be favorable for dry matter production of maize.

Effects of trees planted on levees on rice yields in rain-fed paddy fields of northeast Thailand

Abstract Trees are increasingly being planted on the levees of paddy fields of rice (Oryza sativa L.) in northeast Thailand. We investigated and compared the yields of rice grown in rain-fed paddies under and far from canopies of three different tree species: eucalyptus (Eucalyptus spp.), mango (Mangifera indica L.), and the indigenous neem tree (Azadirachta indica A. Juss). Rice yields tended to decrease near trees of all types at five sites, but there was no change in yields at the remaining 11 sites during the 3-year study. The reduced yields likely resulted from lower aboveground biomass, leading to fewer rice panicles and spikelets, particularly near trees with a dense canopy. Extremely low yields were observed near eucalyptus in paddy fields suffering from severe drought. These results, as well as information provided by farmers’, suggest that eucalyptus trees may have detrimental effects on rice and should not be planted on the levees of paddy fields with relatively low productivity.