Kazunori Kohyama

Nitrogen and phosphate balance on crop production in Japan on national and prefectural scales

Trends in nitrogen (N) and phosphate (P) balance for several crops were calculated for the nation and by prefecture for 5-year periods from 1985 to 2005. Prefectural chemical N and P fertilizer applications for paddy rice and upland crops declined but applications for vegetable crops increased during the period like as national trends. Prefectural chemical N and P applications for tea, orchard and forage remained unchanged in line with national trends. Manure N and P applications for each crop did not follow the trends for chemical fertilizer. Although chemical fertilizer application declined, N and P crop withdrawal for paddy rice, upland crops and tea increased as a result of optimizing fertilizer timing and placement. Nitrogen and P balance for each crop indicated a surplus; P surplus was larger than N surplus, because of higher P input and lower crop P withdrawal. Chemical N fertilizer determined N surplus except for forage, which was determined by manure application. Therefore N surplus on paddy rice, upland crops, orchard and tea declined and increased on vegetables. Forage recorded an N deficiency in two 5-year periods nationally because of low manure input. Because P balance was also determined by chemical P fertilizer, the P surplus for paddy rice and upland crops declined and the P surplus for vegetables increased during the period. Total P surplus was reduced on paddy rice and upland crops. Trends for chemical fertilizer, manure and N and P balance varied widely among prefectures, especially for P. Crop withdrawal of N and P varied relatively little. Although prefectural trends did not always follow the national trend, we could conclude that the negative environmental effects of Japanese crop production have diminished recently, and an improvement in N and P balance in vegetable production can be expected.

Areas of increasing agricultural abandonment overlap the distribution of previously common, currently threatened plant species.

Human-driven land-use changes increasingly threaten biodiversity. In agricultural ecosystems, abandonment of former farmlands constitutes a major land-use shift. We examined the relationships between areas in which agriculture has been abandoned and the distribution records of threatened plant species across Japan. We selected 23 plant species that are currently identified as threatened but were previously common in the country as indicators of threatened plant species. The areas of abandoned farmlands within the distribution ranges of the indicator species were significantly larger than the proportion of abandoned farmland area across the whole country. Also, abandoned farmland areas were positively correlated with the occurrence of indicator species. Therefore, sections of agricultural landscape that are increasingly becoming abandoned and the distribution ranges of indicator species overlapped. These results suggest that abandoned farmland areas contain degraded or preferred habitats of threatened plant species. We propose that areas experiencing increased abandonment of farmland can be divided into at least two categories: those that threaten the existence of threatened species and those that provide habitats for these threatened species.

Influence of Agricultural Activity on Nitrogen Budget in Chinese and Japanese Watersheds

Abstract To analyze the effect of agricultural activity on nitrogen (N) budget at the watershed scale, a comparative study was conducted at two Japanese watersheds, the Shibetsu River watershed (SRW) and Upper-Naka River watershed (UNRW), and one Chinese watershed, the Jurong Reservoir watershed (JRW). The total area and the proportion of agricultural area (in parentheses) of the watersheds were 685 (51%), 1 299 (21%), and 46 km2 (55%) for SRW, UNRW, and JRW, respectively. The main agricultural land use in SRW was forage grassland, while paddy fields occupied the highest proportion of cropland in UNRW (11% of total area) and JRW (31% of total area). The farmland surplus N was 61, 48, and 205 kg N ha−1 year−1 for SRW, UNRW, and JRW, respectively. The total input and output for the whole watershed were 89 and 76, 83 and 61, and 353 and 176 kg N ha−1 year−1 for SRW, UNRW, and JRW, respectively. The proportion of discharged N to net anthropogenic N input was 31%, 37%, and 1.7% for SRW, UNRW, and JRW, respectively. The two watersheds in Japan showed similar proportions of discharged N to those of previous reports, while the watershed in China (JRW) showed a totally different characteristic compared to previous studies. The high N input in JRW did not increase the amount of discharged N at the outlet of the watershed due to high proportions of paddy fields and water bodies, which was an underestimated N sink at the landscape scale.

Spatial prediction of radioactive Cs concentration in agricultural soil in eastern Japan

Abstract As a result of the accident at the Fukushima Dai-ichi Nuclear Power Station (FDNPS) operated by the Tokyo Electric Power Company, radioactive cesium (Cs) was released into the surrounding environment. To determine the extent of decontamination required in agriculture fields and to consider management options, we surveyed and measured soil Cs concentrations in 3461 agricultural fields, and used these data to construct a distribution map of radioactive Cs concentration in agricultural soil in eastern Japan. Soil Cs concentration was positively correlated with radiation dose (r2 = 0.89, n = 2199). This linear correlation was affected to some extent by soil surface condition, soil group and land use type. Linear regression analysis was conducted by land surface condition, soil type and land use type. We constructed a soil Cs concentration map by regression and by a regression-kriging (RK) method that combines regression equations with ordinary kriging of the regression residuals. Prediction accuracy of the RK was higher than that of the regression; we therefore adopted the RK. Total radioactive Cs concentration in soil was highest in the 20-km evacuation zone surrounding FDNPS, and tended to be higher to the northwest of FDNPS than in other directions. About 5900 ha of paddy fields and 3000 ha of upland fields in Fukushima Prefecture were above contamination level 2 (> 5000 Bq kg−1), and were mostly distributed in the evacuation zone.

Factors controlling organic amendment application rate and long-term change in application rate in Japanese paddy field using longitudinal questionnaire survey dataset (the Basic Soil Environment Monitoring Project, Stationary Monitoring, 1979–1998)

Using data from a longitudinal survey (the Basic Soil Environment Monitoring Project, Stationary Monitoring, 1979–1998, launched by the Ministry of Agriculture, Forestry and Fisheries of Japan), it was found that livestock possession, soil type, utilization form of paddy fields and full-/part-time status of farmers were important factors controlling application rates of organic amendments (OA) in Japanese paddy fields. When data points were categorized in terms of these four factors, application rate of livestock waste compost (LWC) on the basis of fresh weight (FW) varied remarkably. Application rates of LWC decreased during the survey period, whereas rice straw residue (RSR) application rates increased. The smallest LWC application rate (average 0.3 ± 0.2 Mg FW ha−1 for the period between 1994 and 1998) was found among rice (Oryza sativa L.) single-cropping, poorly drained lowland paddy soils (PDLPS) including Histosols, with full-time farmers possessing no livestock. Even among rice single-cropping, the application rate was clearly larger (average 10.6 ± 0.5 Mg FW ha−1 for the period between 1979 and 1983) for non-poorly drained lowland paddy soils (non-PDLPS), with full-time farmers possessing livestock. Much greater than this was the LWC application rate for converted paddy fields (average 29.9 ± 4.3 Mg FW ha−1 for the period between 1989–1993), non-PDLPS, with full-time farmers possessing livestock. Accordingly, this study emphasizes the importance of categorizing data points at least in terms of soil type, utilization form of paddy fields, livestock possession and part- or full-time farming status when constructing an inventory, exploring changes in OA application rate, and making policy.

Phosphate adsorption coefficient can improve the validity of RothC model for Andosols

The conventionally-modified RothC model for Andosols required pyrophosphate-extractable aluminum (Alp) for changing humus decomposition rate of the original RothC model. However, any Japanese soil database, which were derived from national soil survey projects, did not have the Alp dataset, and thus the conventionally-modified RothC model required Alp prediction from soil organic carbon (SOC) content. From this reason, there is a risk of Alp prediction error in the run-up to predict the SOC turnover. Objectives of this study were (1) to explore the alternative soil property for re-modifying the conventionally-modified RothC model and (2) to validate the re-modified model against long-term experimental data sets of Japanese Andosols. Phosphate adsorption coefficient (PAC), which is an indicator of the content of amorphous aluminum (Al) and iron (Fe) compounds, was tested to replace Alp using three Andosols database. A stability factor, H(f), was defined as the factor needed to divide the decomposition rate constant of the humus pool so that the modeled SOC level matched the measured level. Phosphate adsorption coefficient showed positive correlation with the H(f). The H(f) was regressed by the exponential equation using PAC as an independent variable, and its R 2 value was higher than in the Alp derived regression. We incorporated the PAC derived regression into the original RothC model as the PAC-modified RothC model. From the comparison of the models validity, the PAC-modified RothC model showed low mean error with low root mean square error in the long-term experimental data sets. These results indicate that PAC can replace Alp for changing the decomposition rate of humus pool in RothC model with accuracy enhancement.

Delineation of Japanese soil temperature regime map

The soil temperature regime map provides for utilitarian classification that can be superimposed on soil classification to permit more precise interpretations and assessments of land use. The objects of this study are (1) to clarify the relationship between soil temperature and meteo-geographical factors, and then (2) to delineate detailed soil temperature regime map (1 km grid) as Japanese land resources inventory. There was a parallel relationship between mean annual soil temperature (MAST) and mean annual air temperature (MAAT), but this relationship was affected to some extent by the mean annual wind speed and mean annual global irradiation in this study. Furthermore, the difference between MAST and MAAT [Diff(MAST–MAAT)] showed the highest correlation with elevation. The map of RK_Diff(MAST–MAAT) was computed using this meteo-geographical relationship with the regression-kriging approach, and then the map of MAST and the soil temperature regime map were delineated using the map of MAAT and the RK_Diff(MAST–MAAT). The root mean square error of this delineation procedure was 0.47°C. It was clear that the majority of the Japanese soils had “mesic” soil temperature regime, and Japanese agricultural land was mainly distributed at “mesic” area and followed by “thermic”, “frigid”, and “hyperthermic” area. For promoting this land resource inventory, the soil temperature regime map will be uploaded on “Soil Information Web Viewer (http://agrimesh.dc.affrc.go.jp/soil_db/)”, which is provided by the National Institute for Agro-Environmental Sciences.

Relationship between nitrogen and phosphate surplus from agricultural production and river water quality in two types of production structure

Abstract We examined the relationship between nitrogen (N) and phosphate (P2O5) surplus derived from agriculture and river water quality. We selected two river basins; one was a paddy farming area (Omoigawa) and the other was an intensive livestock husbandry area (Nakagawa). Nitrogen and P2O5 surpluses, defined as the difference between their input and output on regional farmland, from farmland in Omoigawa were twice those of Nakagawa; the surpluses came mainly from chemical fertilizer use. Although N and P2O5 surpluses in Nakagawa were lower, Nakagawa had a large amount of non-utilized livestock excreta, twice the N surplus on farmland in Nakagawa. Residual N and P2O5 in the river basin, caused by surplus and non-utilized livestock excreta, were approximately 20% and 40%, respectively, higher in Nakagawa than in Omoigawa. Outflows of N and P2O5 to river water were higher in Omoigawa than Nakagawa. By excluding domestic sewage N and P2O5 in river water, we calculated the loads of non-point source N and P2O5. Non-point source N and P2O5 were higher in Omoigawa than Nakagawa. This inverse result might be caused by the different source of residual N (i.e. chemical N fertilizer or livestock excreta).

Radiocesium interception potential of agricultural soils in northeast Japan

ABSTRACT The health risks associated with the long-term intake of radiocesium from food have been of great concern since the Fukushima Daiichi Nuclear Power Station accident in 2011. Therefore, evaluating the phytoavailability and mobility of radiocesium in soil and determining the ability of soil to fix radiocesium are important research topics. The capacity and selectivity for 137Cs sorption in soil is evaluated on the basis of the radiocesium interception potential (RIP). Here, we measured the RIP of 925 farmland soil samples collected from Fukushima Prefecture and surrounding regions and plotted the values on a soil classification map and a surface geological map. The RIP values ranged from 73 to 12700 mmol kg−1, and a wide range was also observed among samples with identical soil types and geological features; however, the RIP values were significantly low for Andosols (P ≤ 0.05). In addition, soils that did not contain vermiculite, illite and smectite had low RIP values. All measured RIP values were negatively correlated with the total C content and phosphate absorption capacity and positively correlated with the clay, silt, and exchangeable K and Ca content (P ≤ 0.01). However, the relationship between the RIP and the measured soil properties, except for the exchangeable K content, is strongly dependent on the soil classification and clay mineral composition. Therefore, the soil properties that most significantly influence the RIP values are probably differences in the soil parent materials, which influence the soil classification and clay mineral composition.

5- and 10-km mesh datasets of agricultural land use based on governmental statistics for 1970–2005

Land use data serve as an essential part of large-scale ecological research, such as landscape ecology and macroecological studies. For agricultural fields in Japan, existing time series statistical records can be used to convert map data according to a map of municipality units. In this data paper, we determined the areas of agricultural land use in Japan from 1970 to 2005, excluding small islands, at spatial resolutions of 5- and 10-km mesh grid units, which are often referred to as the Five-fold Mesh and Japanese Second-order Mesh, respectively. The elements considered included total farmland, paddy fields, dry farmland, and orchards. In 2005, we included abandoned agricultural areas because the related data were available in the agricultural statistical records. The source data came from the Census for Agriculture, Forestry and Fisheries conducted by the Ministry of Agriculture, Forestry and Fisheries, Japan. The Datum was the Japanese Geodetic Datum 2000 (JGD2000). All of the datasets have open data licenses under the rules of the Creative Commons CC-BY 4.0 International (https://creativecommons.org/licenses/by/4.0/legalcode).