Kimihito Nakamura

Prospects for multifunctionality of paddy rice cultivation in Japan and other countries in monsoon Asia

This paper presents a study carried out by a group of Japanese researchers to critically review past researches and discussions on the multifunctionality of paddy rice cultivation, with the aim of describing the current status of the subject and providing options and potentials for future research and practices. The review was of over 200 documented articles on the major external functions. The results of this study revealed that the importance of multifunctionality is well perceived in Japan. The methodologies to measure and estimate the magnitude have been established for most functions. However, there is a need for more cases, to integrate all the functions at the local or regional scale to represent site-specific characteristics of multifunctionality. There is also a need to develop management practices to sustain and enhance the positive multifunctionality of paddy rice cultivation while minimizing negative effects to the environment, which may be brought into the agricultural policies. Except for Korea, Taiwan, and Japan, there are slightly different notions on multifunctionality in other monsoon Asia countries, but the gap in this notion is reducing following recent international activities.

Assessment of Root Zone Nitrogen Leaching as Affected by Irrigation and Nutrient Management Practices

et al., 1995), center-pivot fertigation (Spalding et al., 2001), groundwater table control (Drury et al., 1997), and reMultiple or split N fertilizer applications during a single cropping duced till or no-till practices (Power et al., 2001). Whatperiod is a recommended practice for controlling N (specifically ever management practices may be adopted, it is imporNO3–N) leaching into groundwater. Here, we demonstrate the benefit of split fertilizer applications in two typical upland soils of Japan tant to consider the simultaneous transport of water and (sand and Andosol) using a combination of a laboratory experiment N to evaluate the potential for NO3 groundwater poland modeling. Soil water flow and N transport properties of the soils lution. were measured using standard procedures. Transient N and water Numerous models have been proposed for modeling transport experiments were conducted in cylindrical soil columns unthe transport of N in soils. The conceptual N model by der single (lumped) and split NH4–N applications. The column experiTanji et al. (1977) is very simple with few input data ments were successfully simulated using Richards’ equation and an and is based on the principles of mass balance and steady advection–dispersion model with equilibrium nonlinear sorption constate. The extended conceptual model proposed by Tanji ditions and first-order transformation for N speciation. Using the et al. (1979) is also simple and is applicable to transient model for the two soils, several irrigation and fertilizer management conditions. The Nitrate Leaching and Economic Analyscenarios were then simulated based on 1992 through 2000 meteorological data to investigate the long-term effects of lumped and split sis Package (NLEAP) model combined with GIS is used fertilization schedules for a representative set of crop and irrigation to identify potential NO3 hot spots in shallow alluvial conditions. In comparison with lumped applications, split fertilizer aquifers under irrigated agricultural areas (Shaffer et al., applications were found to consistently reduce the amount of N leach1995, 1996; Follett, 1995). The SOILN model simulates ing, even though year-to-year differences of N leaching reductions daily N and C fluxes in agricultural systems, including between sand and Andosol were significant. For unstressed crops, the plant growth and N uptake (Jabro et al., 2001). actual reduction in N leaching are shown to depend on the timing of Nitrate leaching is considered to occur mainly during precipitation and irrigation events, on soil type, and on plant N uptake high precipitation or during irrigation; hence, transient behavior. However, across all scenarios, two split applications instead dynamic models of water and N transport and N transof a single, lumped application reduced the N leaching fraction by formation are more adequate to evaluate the risk of approximately one-third. In the sandy soil, a three-way split resulted in further leaching reductions compared with the two-way split. SixNO3 leaching into groundwater under various water and way split applications did not result in further N leaching improvefertilizer management scenarios. The Water Heat and ments in either sand or Andosol. After adjusting N application rates Nitrogen Simulation Model (WHNSIM), which simuto account for reduced N use efficiency, N leaching rates for unstressed lates transient water, heat, and N movements, including crops under lumped fertilization were found to be several times higher N transformations, satisfactorily predicted NO3 concenthan under split applications. tration in the soil solution and N uptake originating from experimental sites (Huwe and Totsche, 1995). Modeling of urea, NH4, and NO3 transport and transforG NO3 contamination is a common probmations conducted by Ma et al. (1999) includes urea lem in field crops and dairy areas of Japanese upand NH4 adsorption, urea diffusion and hydrolysis, diflands. Quantitative, technical information is needed to fusion of NH4 and NO3, nitrification, and denitrification help farmers make management decisions that support in flooded soil. Antonopoulos and Wyseure (1998) evalprofitable yields while avoiding environmental degradauated the transient water movement, mass transport, tion. Various management practices have been proposed and N transformations of restored and undisturbed soil. to control NO3 leaching. These include, for example, crop The HYDRUS code (Šimůnek et al., 1998, 1999) simulates rotation (Delgado et al., 2001), controlled-release fertilwater, heat, and solute movement in oneand two-dimenizer (Paramasivam et al., 2001), fine-tuned irrigation and sional variably saturated media. The solute transport equaNmanagementbasedonsoil testingprograms(Poweretal., tions incorporate the effects of zero-order production, 2001) or chlorophyll meter readings of the crop (Schepers first-order degradation, and first-order decay and production reactions that provide the required coupling between the solutes involved in the sequential first-order chain. K. Nakamura and T. Mitsuno, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, Japan, 606Several long-term studies have been conducted to 8502; T. Harter, Dep. of Land, Air and Water Resources, University of evaluate the effects of proposed best management pracCalifornia, Davis, CA, 95616; Y. Hirono, National Institute of Vegetable tices on NO3–N leaching, aquifer water quality, and crop and Tea Science, Kanaya, Shizuoka, Japan, 428-8501; H. Horino, Diviyields (e.g., Pang et al., 1997a, 1997b; Delgado et al., sion of Agriculture, Osaka Prefecture University, 1-1 Gakuen-cho, Sa2001; Jaynes et al., 2001; Paramasivam et al., 2001). Most kai, Osaka, Japan, 599-8531. Received 25 May 2004. Original Research Paper. *Corresponding author (ThHarter@ucdavis.edu). existing models have been evaluated on an annual or a crop season basis (e.g., Jabro et al., 2001; Delgado et Published in Vadose Zone Journal 3:1353–1366 (2004). al., 2001). Long-term studies are effective for evaluating

Rapid measurement of radiocesium in water using a Prussian blue impregnated nonwoven fabric

We developed a rapid method for concentrating and measuring radiocesium (134Cs and 137Cs) dissolved in fresh water using nonwoven fabric impregnated with Prussian blue (PB) as a radiocesium absorber in combination with gamma-ray spectrometry using a germanium (Ge) detector. Utilizing this method, dissolved radiocesium in a 20–100 L freshwater sample could be concentrated within a period of 20–60 min by passing the sample through 10–12 columns, connected in series, that had been fitted with nonwoven fabric disks impregnated with PB. Laboratory tests using water samples containing known amounts of radiocesium confirmed that the overall recovery rate of the isotope was 100%–108%, and that the first six columns recovered 84%–97% of the isotope. The detection limit of this method was determined to be 0.002 Bq/L with a sample of 100 L and measurement time of 43,200 s. In comparison with traditional methods using ion-exchange resin, co-precipitation with ammonium phosphomolybdate, etc., our method has the advantages of reduced cost and a significantly shorter concentration time. Since water samples can be treated in short periods of time, it is now possible to conduct radiocesium pre-concentration in situ, thus eliminating the need to transport large-volume water samples to laboratories.

Effects of different application timings of methane fermentation digested liquid to paddy plots on soil nitrogen and rice yield

Treatment of animal and food wastes using a methane fermentation technique is drawing considerable public attention as a suitable option for the utilization of biomass resources. The application of a fermentation byproduct (methane fermentation digested liquid) as an agricultural fertilizer has been investigated. Determining the appropriate timing required for applying digested liquid on a rice (Oryza sativa L.) paddy plot is important. The concentrations of soil nitrogen (N) components and rice yield should be considered because digested liquid contains both inorganic and organic N. This study compares the N transformation and the rice yield and growth at different application times over a period of 3 y. The effects of the timing of basal application on soil N were different and the timing that maximized the rice yield was different in each year. Days before ponding (DBP) affected soil N before mid-summer drainage, and rice growth rates at the panicle formation stage and the ear emergence stage. The effects of DBP disappeared before harvest. The results indicated that sufficient potentially mineralizable N existed regardless of DBP, and the effect of DBP lessened after the mid-summer drainage, which coincides with the period when N uptake is most active.