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Compost application can enhance soil fertility and is consequently presumed to increase crop production in Japan's paddy-upland rotation fields. This study aimed to evaluate the effects of rice straw compost (RSC) application on available soil nitrogen (Av-N) levels and rice and soybean plants in a paddy-upland rotation field using data obtained from a long-term field experiment. Data collected between 2005 and 2020 were analyzed from a long-term paddy rice – upland soybean rotation field. The experimental design employed a split-plot arrangement, with RSC application (with and without RSC) representing the whole plot, N fertilizer application (no nitrogen vs. standard fertilizer) representing the split-plot, and years representing the replication factor. The datasets included eight years of rice and soybean cultivation, and the chemical properties of postharvest soil spanned 16 years. The data was analyzed via analysis of variance. Applying RSC increased the Av-N concentration significantly by 63%–67%. The RSC application significantly increased the N concentration in rice shoots at the mature stage by 8%–12% but decreased it in soybean shoots after the seed emergence stage by 4%–8%. Consequently, the rice yield displayed clear responses to RSC application, whereas the soybean yield did not. The lack of soybean yield response might be due to an inhibitory effect of the Av-N gain attributable to the RSC application on biological nitrogen fixation. While applying compost can enhance Av-N content as well as rice productivity in paddy-upland rotation fields, its impact on soybean productivity requires careful evaluation. [ABSTRACT FROM AUTHOR]

To investigate how the long-term application of inorganic fertilizer and organic amendments affects the turnover rates of organic matter in physico-chemically fractionated components in paddy soils and how their rates are related to their amounts, we studied the effect of variable management of inorganic fertilizer and organic amendments for > 50 years on the ∆14C values of accumulated soil organic carbon (SOC) in fractionated components of 5 soil samples from three paddy fields. SOC was fractionated into four components based on their physico-chemical properties: (1) light fraction (LF) derived from plant residues, (2) heavy fraction (HF) containing stable aggregates, (3) oxidizable fraction (OxF) and (4) non-oxidizable fraction (NOxF) forming organo-mineral complexes with fine-textured minerals. The ∆14C values were determined by accelerator mass spectrometry using graphitized samples. The ∆14C values of SOC in NOxF (from −305‰ to − 90.5‰) were much lower than those of HF (from −123‰ to − 3.7‰) and OxF (from −215‰ to 21.0‰). Lowest values for NOxF suggested slowest turnover rates as expected, and higher and comparable values for OxF and HF implied much faster turnover rates of SOC in OxF compared with upland soils. This could be one of the characteristics of SOC dynamics in paddy soils, probably reflecting repeated puddling of plow layer soils. ∆14C values in all the fractions increased in response to the application of inorganic fertilizer and organic amendments, suggesting faster turnover rate. Soils with clayey and weathered characteristics had the lowest ∆14C values, or slowest turnover rates among the study fields. The relationship between the ∆14C value and the amount of accumulated C for HF, OxF and NOxF indicated that the more the SOC accumulated, the faster the turnover rate of the SOC was, regardless of the fractions, and the relationship of the HF was considerably different from those of OxF and NOxF. In conclusion, these results can be the basis for understanding the C dynamics and for improving soil fertility status and soil C sequestration in paddy soils. [ABSTRACT FROM AUTHOR]

To investigate how the long-term application of inorganic fertilizer and organic amendments affects the accumulation of organic matter in physico-chemically fractionated components in paddy soils and how the accumulation is determined by soil properties and anthropogenic carbon input, we studied the effect of variable management of inorganic fertilizer and organic amendments for > 50 years on the amounts of accumulated soil organic carbon (SOC) in fractionated components in three paddy fields. SOC was fractionated into four components based on their physical and chemical properties: (1) light fraction (LF) derived from plant residues, (2) heavy fraction (HF) containing stable aggregates, (3) oxidizable fraction (OxF) and (4) non-oxidizable fraction (NOxF) forming organo-mineral complexes with fine-textured minerals. On average, the amount and percentage of accumulated C in the four fractions were as follows: OxF (6.63 gC kg−1soil, 46%) > NOxF (5.32, 35) > LF (1.68, 12) > HF (1.12, 7.2), suggesting about 80% of SOC was in fine, stable fractions. The amount of accumulated C in all fractions increased slightly with the application of inorganic fertilizer, while it increased considerably with the use of organic amendments. In addition, the application of fertilizers and amendments raised the proportion of C content in LF and HF, which are labile and related to soil fertility. Stepwise multiple regression analysis using two principal component analysis scores of soil properties and anthropogenic C input further revealed that the labile fractions (LF and HF) were more strongly determined by the management of fertilizers and amendments, while the stable fractions (OxF and NOxF) were more strongly determined by soil-specific properties, mainly the amorphous nature of the soil. These results indicate that the use of certain amounts of organic amendments would be recommended to carry out rational management to improve soil fertility and C sequestration in paddy fields, with the application of amorphous minerals as an additional option. [ABSTRACT FROM AUTHOR]

Dolomite [CaMg(CO3)2] is used widely for soybean, Glycine max (L.) Merr. production in Japan to amend soil pH, although magnesium (Mg) in the dolomite can inhibit soybean growth and yield. The aim of this study was to determine the effect of Mg on soybean production in a paddy – upland rotation field in 2019–2020 by comparing the application of dolomite and calcite (CaCO3). The field test included three replications with three lime applications: control (no lime), dolomite, and calcite. The amounts of calcite and dolomite applied in each year were 253 and 259 g m−2, respectively. The soil pH was almost similar following the applications of calcite and dolomite, whereas the soil exchangeable Mg content was higher following the dolomite application than following the other applications. The shoot weight from the flowering stage to the harvest stage (R8) was significantly higher following the calcite application than following the other applications. However, the shoot weight at only R8 was significantly higher following the dolomite application than following the control application. In 2019–2020, the highest soybean yield was resulted from the calcite application (355 g m−2) followed by the dolomite application (312 g m−2) and the control application (260 g m−2). The severity of soil-borne diseases was lower following the dolomite application than following the control application, and even lower following the calcite application. Thus, the application of dolomite increased soybean yield by improving soil pH; however, Mg in the dolomite inhibited a further increase in soybean yield in a paddy – upland rotation field. [ABSTRACT FROM AUTHOR]

In Japan, soil pH is primarily measured using water with a solid-to-liquid (SL) ratio of 1:2.5, whereas soil pH measurement methods vary by country. Although some soil pH estimation models for each country have been developed to convert soil pH measured by other methods, suitable models for soils in Japan remain unidentified. Therefore, we propose models for estimating the various soil pH values from those measured by water with an SL ratio of 1:2.5. We collected a dataset of 192 topsoil properties in paddy-upland rotation fields in eastern Japan. The dataset comprised soil pH, electrical conductivity (EC, SL ratio of 1:5), particle density, silt and clay content, and total carbon. Soil pH was measured using distilled water (DW), 0.01 M calcium chloride (CaCl2), and 1 M potassium chloride (KCl) with an SL ratio of 1:1 (pH-1DW), 1:2.5 (pH-2.5DW, pH-2.5CaCl2, pH-2.5KCl), and 1:5 (pH-5DW, pH-5CaCl2, pH-5KCl). The comparison of linear regression models showed that the models comprising pH-2.5DW and intercept were sufficiently accurate to estimate pH-1DW and 5DW. However, to estimate pH-CaCl2 and pH-KCl, the models comprising pH-2.5DW, EC, and intercept were sufficiently accurate. From the study results, we proposed the following equations: pH-1DW = 1.10 × pH-2.5DW − 0.69 (R2 = 0.92, RMSE = 0.19); pH-5DW = 0.80 × pH-2.5DW + 1.32 (R2 = 0.86, RMSE = 0.16); pH-2.5CaCl2 = 0.93 × pH-2.5DW + 1.75 × EC − 0.44 (R2 = 0.94, RMSE = 0.14); pH-5CaCl2 = 0.83 × pH-2.5DW + 2.19 × EC + 0.29 (R2 = 0.88, RMSE = 0.20); pH-2.5KCl = 0.92 × pH-2.5DW + 2.86 × EC − 0.97 (R2 = 0.93, RMSE = 0.15); pH-5KCl = 0.88 × pH-2.5DW + 2.94 × EC − 0.57 (R2 = 0.93, RMSE = 0.15). [ABSTRACT FROM AUTHOR]

To prove the hypothesis that paddy rice utilizes soil nonexchangeable potassium (neK) and causes associated structural changes in clay minerals, K status and clay mineralogy of 22 surface soils from three paddy fields under long‐term fertilizer management for 51–93 years were investigated. Soil neK content was determined as the difference between 1 mol L−1 hot HNO3 extractable K and 1 mol L−1 ammonium acetate exchangeable K. Clay mineralogy was identified by X‐ray diffraction (XRD). The radiocesium interception potential (RIP), an index of frayed edge sites in the interlayer sites of 2:1 type clay minerals, was also determined. The neK contents under the ‐K and NPK treatments were considerably lower than those under the unfertilized treatment in all the fields, indicating the exploitation of soil neK by rice. XRD analysis of the clay samples revealed 7% shift from the 1.0 peak to 1.4 nm one under the ‐K treatment compared with the unfertilized one, and the amounts of neK were negatively correlated with those of RIP (p <.01), suggesting the expansion of interlayer spaces of the 2:1 type phyllosilicates such as mica due to the release of neK. In addition, the neK content positively correlated with K balance of the long‐term experiments (p <.05). The differences of neK between unfertilized K and ‐K treatments corresponded to 22–157 kg K ha−1, or 0.42–1.68 kg K ha−1 year−1. In conclusion, utilization of considerable amount of soil neK under K depleted conditions should be considered to establish sustainable K management for paddy rice. [ABSTRACT FROM AUTHOR]

Arsenic (As) and cadmium (Cd) are harmful to humans, and their concentrations in rice are affected by the water management strategies used in paddy fields. Water management, however, is considered a burden for farmers, and thus an efficient strategy by which to decrease As and Cd concentrations in brown rice is desired. The purpose of this study was to estimate the effects of water management on the total As and Cd concentrations in brown rice during the 3 weeks before and after heading on a weekly basis. Moreover, the study aimed to determine the differences in this effect among soil types and cultivars. Pot cultivation experiments of rice were conducted by applying two levels of weekly flooding or draining to an L12 orthogonal table, and their effects each week on the As and Cd concentrations in brown rice were identified. Redox potentials of soils decreased during flooding and increased during draining, but the decrease during flooding in Andosols was slower than that in Fluvisols. For the plants growing in Fluvisols, the total As and Cd concentrations in the brown rice increased and decreased with flooding, respectively, and an opposite trend was observed with draining. In the Japonica varieties 'Koshihikari' and 'Hitomebore,' water management during the first week from 0 to 2 days after heading had the greatest impact on As and Cd concentrations. However, in the Indica variety 'Takanari,' the weeks that most affected the As and Cd concentrations were the second and first week from the day after heading, respectively. In the Andosols, the Cd concentration was changed by water management as in the Fluvisols, but the same was not found for the As. This suggests that the effect of water management on the As concentration in brown rice could be nullified by the Andosols ability to absorb As. However, it was also possible that the effect of water management could not be detected due to the low As concentration of the Andosols. These results provide insights that will help to efficiently reduce As and Cd concentrations using information on the rice variety and soil type. [ABSTRACT FROM AUTHOR]

There have been few studies in Japan on the effects of the application of lime materials, especially in regard to the soil calcium-to-magnesium ratio (Ca:Mg). The aim of this study was to explore the effects of changes in the soil Ca:Mg on soybean growth via pot and field tests over two growing seasons: 2018–2019. The field tests were conducted in two different fields, one in each year, and the soil for the pot tests in both years was collected from the respective fields used in the field tests. In the pot test from 2018 to 2019, we adjusted the soil Ca:Mg ratio and soil pH using Ca(OH)2 and CaSO4, with three conditions: control (pH = 5.2, Ca:Mg = 1.3), CaMg (pH = 5.0, Ca:Mg = 2.6), and CaMg + pH (pH = 5.7, Ca:Mg = 2.4). Moreover, we added two further conditions for the pot test in 2019: CaCO3 (pH = 5.9, Ca:Mg = 1.8) and dolomite groups (pH = 6.4, Ca:Mg = 1.3). In the field test, we adjusted only the soil Ca:Mg ratio using phosphogypsum and had two conditions: control (pH = 5.0, Ca:Mg = 1.1) and gypsum (pH = 4.7, Ca:Mg = 1.9). In both tests, the application of Ca except for dolomite contributed to the increase in the concentration and uptake of Ca both in the whole plants and some parts of the soybean plants. Likewise, application of Ca except for dolomite contributed to a significant increase in the total number of pods. The weight of seeds and the total dry weight in the CaMg + pH and CaCO3 groups and in the gypsum plot were significantly higher than were those in each control group. Thus, the study suggests that the Ca:Mg ratio in soils with a low Ca:Mg ratio may limit soybean growth to a greater extent than does the soil pH. However, the effect of the interaction between the soil Ca:Mg ratio and soil pH on dry-matter production of soybeans was different between the pot and field tests, and further studies were needed to clarify the discrepancy. [ABSTRACT FROM AUTHOR]

Siderite (FeCO3), a type of carbonate mineral, is very occasionally recognized as a nodule in anoxic soils and sediments. During siderite formation, elements are expected to be accumulated or excluded between siderite and bulk soil. Therefore, we verified the affinity of 40 elements for siderite found in the gley horizon of a smectite-rich paddy field in northeastern Japan from the elemental concentration of the soil and the siderite dissolved in 2.88 mol L−1hydrochloric acid (10% HCl). The concentration ratio of the target element of the soil to the siderite was expressed by the product of the dimensionless R0value and ratio of titanium (Ti) concentration of the soil to the siderite (Csiderite/Csoil) = R0(Tisiderite/Tisoil). The affinity of each element for the siderite was analyzed by comparing the R0values. In comparison with Ti used as the reference element, P, Cr, Co and Mo were accumulated (R0 > 1.0), and alkali metals, such as Li, Na and K, and chalcophile elements, such as Cu, Zn, Cd and Pb, tended to be equal or excluded from the siderite (R0≦1.0). Of the group 2 elements, Ca, Sr and Ba were accumulated, while Mg was excluded. The affinity of Mn for siderite exceeded that of Fe as the main component of the siderite, which reflects the fact that siderite was formed in a fresh water condition. The siderite size did not influence the elemental affinity. Observation of micromorphology using a scanning electron microscope showed that the siderite nodules were aggregations of siderite particles and clays, suggesting that the siderite grew by taking in clay around it. The rare earth element (REE) distribution pattern showed a tendency not to increase linearly but to increase with forming a concave curve at the intervals of the four elements with the increase of atomic number (i.e. tetrad effects). Although these findings are from the lower horizons of anoxic soils, the elemental affinity for siderite of this study is useful in order to elucidate the complex elemental dynamics in the anoxic environment. [ABSTRACT FROM AUTHOR]

To reduce the availability of soil cadmium (Cd) to soybeans (Glycine max(L.) Merr.), we employed a liming by partial mixing (PM) technique in two drained paddy fields on Gray Lowland soils, which had 0.1 mol L–1hydrochloric acid-extractable Cd concentrations as high as 1.08 and 1.40 mg kg–1. Among the different application methods tested, PM application (PM2) using a width of 20 cm and a depth of 20 cm was found to be most appropriate for reducing the seed Cd concentration and to obtain the optimum yield at Site A. Under PM2, a liming rate of 38% of that for broadcast incorporated into the surface 15 cm layer (Bc) was suitable to reduce the seed Cd concentration at Site A, whereas the lime rate with PM2 was set at 50% of that for Bc (PM2-50) at Site B due to the higher availability of soil Cd. The root system was limited within the range of lime and fertilizer application for PM2 as well as PM2-50; thus, the lime and fertilizer were supplied successfully to the rooting zone. The soil pH value was lower under PM2 at Site A and PM2-50 at Site B compared with Bc, whereas the seed Cd concentration was lower for PM2 and PM2-50. This may be explained by the intensive uptake of calcium and magnesium with PM2 as well as PM2-50. The seed Cd concentration in the cultivar “Ryuhou” at the target pH of 6.5 was approximately 30% lower with PM2-50 than Bc at Site B. In addition, the average seed Cd concentrations in one cultivar and two lines, characterized by the lower Cd uptake with higher retention in roots and higher accumulation in leaves, were approximately 40% lower compared with “Ryuhou.” Thus, the combination of liming with PM2-50 at the target pH of 6.5 and a low-Cd cultivar (or lines) minimized the seed Cd concentration. The highest seed Cd concentration was found in the first year of soybean cultivation, which was considered to be caused by the release of Cd from organic nitrogen compounds during the nitrogen mineralization process. [ABSTRACT FROM PUBLISHER]

No-tillage (NT) management is a promising method to sequester soil C and mitigate global warming caused by agricultural activities. Here, we report 4 years of continuous soil respiration rates and weekly nitrous oxide (NO) and methane (CH) emissions in NT and conventional-tillage (CT) plots in a typical Japanese volcanic soil. Overall, the soil respiration, NO emission, and CH uptake decreased significantly in the NT plot. A difference in soil respiration and NO emission between the two plots began after the tillage treatment and the incorporation of crop residues and fertilizers, whereas the CH uptake did not vary significantly during the fallow period after the treatments. The NO emission was higher from the CT than from the NT plot during the fall. The overall lower CH uptake in the NT than in the CT plot likely resulted from a combination of decreased soil gas diffusivity and higher mineral N content at the soil surface. Higher soil respiration and NO emission occurred in the NT plot in the summer of 2003 and were plausibly caused by an increase in the soil moisture content that resulted from lower temperatures during July and August; the higher soil moisture must have accelerated the decomposition of organic matter accumulated in the topsoil. These results indicate that NT management is generally effective for the mitigation of the total GWP by reducing soil respiration and NO emission in temperate regions; however, NT management may increase rather than decrease these emissions when fields experience cool summers with frequent rainfall. [ABSTRACT FROM AUTHOR]