Yoshihiro Kaneta

Rice cultivar responses to elevated CO2 at two free-air CO2 enrichment (FACE) sites in Japan

There is some evidence that rice cultivars respond differently to elevated CO2 concentrations ([CO2]), but [CO2]×cultivar interaction has never been tested under open-field conditions across different sites. Here, we report on trials conducted at free-air CO2 enrichment (FACE) facilities at two sites in Japan, Shizukuishi (2007 and 2008) and Tsukuba (2010). The average growing-season air temperature was more than 5°C warmer at Tsukuba than at Shizukuishi. For four cultivars tested at both sites, the [CO2]×cultivar interaction was significant for brown rice yield, but there was no significant interaction with site-year. Higher-yielding cultivars with a large sink size showed a greater [CO2] response. The Tsukuba FACE experiment, which included eight cultivars, revealed a wider range of yield enhancement (3-36%) than the multi-site experiment. All of the tested yield components contributed to this enhancement, but there was a highly significant [CO2]×cultivar interaction for percentage of ripened spikelets. These results suggest that a large sink is a prerequisite for higher productivity under elevated [CO2], but that improving carbon allocation by increasing grain setting may also be a practical way of increasing the yield response to elevated [CO2].

Effects of preceding compost application on the nitrogen budget in an upland soybean field converted from a rice paddy field on gray lowland soil in Akita, Japan

Abstract The annual nitrogen (N) budget was measured in a soybean-cultivated upland field during the first year after conversion from a paddy field on gray lowland soil, which is typically found on the Sea of Japan side of northern Japan. Forage rice was cultivated on lysimeter fields for 4 consecutive years with applications of chemical fertilizer, immature compost, or mature compost (the control, immature compost, and mature compost plots, respectively), and then the fields were converted to upland fields for soybean (Glycine max [L.] Merrill cultivar Ryuho) cultivation. Input (seed, bulk N deposition, and symbiotic dinitrogen [N2] fixation) and output (harvested grain, leached N via drainage water, and nitrous oxide emission) N flows were measured, and the field N budget was estimated from the difference between the input and output. The soybean plants in the immature and mature compost plots grew well and had higher yields (498–511 g m)−2) compared to the control plot (410 g m)−2). Total N accumulation in the soybean plants derived from N2 fixation (g N m)−2) in the mature compost plot (27.7) was higher than those in the control (18.1) and immature compost plots (19.9). Percentages of soybean N accumulation derived from N2 fixation ranged from 53% to 74%. N derived from symbiotic N2 fixation accounted for more than 90% of the total N input, whereas harvested grain accounted for approximately 85% of the total N output. N leaching mainly occurred during the fallow period, accounting for 13–15% of the total N output. The annual N budgets were negative (−10.0,−14.2, and −6.4 g N m)−2 year)−1 for the control, immature compost, andmature compost plots, respectively). The Nloss from the immature compost plot was higher than that of the control plot, because the N output in harvested grain was higher, and the N input by N2 fixation was similar between plots. While the N loss from the mature compost plot was lower than that of the control plot because the N output in harvested grain was higher, as was the case in the immature compost plot, the N input by N2 fixation was also higher. Preceding compost application—whether immature or mature compost—to paddy fields increased the subsequent soybean yield during the first year after conversion. This result suggests that N loss and the following decrease in soil N availability in the field could be mitigated by increased N2 fixation resulting from mature compost application with an appropriate application practice.

Effects of Organo-mineral Complexes on Flocculation, Settlement and Vertical Distribution of Bioelements in Soil Suspensions

Soil organic matter that could be combined with soil particles into large aggregates, may reduce soil erosion. However, soil organic matter itself is a possible source of water pollution. The objective of the present study was to analyze organo-mineral complexes and their effects on flocculation and settling characteristics of soils. Particle-size fractionation and flocculation/settlement experiment were conducted by using 7 types of soil samples (smectic heavy clay soils with 5 types of agricultural practices, alluvial clay loam soil, and volcanic heavy clay soil). All the samples were taken from paddy fields in Japan. Particle size fractionation showed that short-term (4 years) organic matter application to the smectic soil had increased the number of coarse organic particles. Puddled ponding water in the smectic heavy clay field under 4 years of organic matter application led to the highest levels of total organic carbon and particulate organic carbon among the sampling fields. Therefore, the coarse organic particles were considered to be easily suspended by puddling. The high floatability of coarse organic particles was consistent with their low density and weak association with minerals. Flocculation/settlement experiments showed the significant effect of pH decrease by organic matter application on the settlement of the smectic soil particles. The alluvial soil, volcanic soil, and smectic soils under continuous (4 years and 19 years) organic matter application could form large floes even at 50 mM NaCl, while the smectic soils under conventional tillage, no-tillage, and no-puddling required more than 200 mM NaCl for rapid settlement. Sodium pyrophosphate treatment of the dispersive soils resulted in higher concentrations of carbon and nitrogen in the upper layer (0–4 cm) of their suspension after 8 h of settlement, although the treatment had reduced the organic matter content of the soils. The reduction in the hetero-flocculation of the soil particles with different charge characteristics was considered to be the possible process for the increased dispersibility of the soils by the removal of organo-mineral complexes, because the smectic soil did not show a rapid settlement at the average point of zero salt effect for the whole soil components. Based on the settlement profiles, we estimated that the reduction of nutrient losses (suspended load) from surface ponding water in puddled fields was 74–112 kgC ha−1 and 6–7 kgN ha−1 by 8 h of settlement, and at least 100–157 kgC ha−1 and 9–10 kgN ha−1 by 8 h of settlement with an improvement in the pH and electrolyte concentrations.

Effect of soil physical properties on soybean nodulation and N2 fixation at the early growth stage in heavy soil field in Hachirougata Polder, Japan

Abstract We studied the effect of the soil physical properties on soybean nodulation and N2 fixation in the heavy soil of an upland field (UF) and an upland field converted from a paddy field (UCPF) in the Hachirougata polder, Japan. Seeds of the soybean cultivar Ryuho were sown in each field with or without inoculation of Bradyrhizobium japonicum A1017. The soybean plants were sampled at 35 (V3) and 65 (Rl) d after sowing (DAS), and then nodulation and the percentage of N derived from N2 fixation in the xylem sap were determined. The soil physical properties were different between UF and UCPF, especially the air permeability and soil water regime. Nodule growth was restricted in UCPF irrespective of rhizobial inoculation, though rhizobial infection was not inhibited by the unfavorable soil physical conditions. Soybean plant growth was closely related to the nodule mass and N2 fixation activity, and the inoculation of a superior rhizobium strain was effective only at 35 DAS. These results indicate that soybean nodulation and N2 fixation was considerably affected by the physical properties of heavy soil, and that it is important to maintain the N2 fixation activity and inoculate the soybean plants with a superior rhizobium strain at a later growth stage in order to increase soybean production in heavy soil fields.

Effects of hairy vetch foliage application on nodulation and nitrogen fixation in soybean cultivated in three soil types

We investigated the effects of applying hairy vetch foliage on nodulation and atmospheric nitrogen (N2) fixation in soybean cultivated in three soil types in pot experiments. Soybean plants were grown in Gley Lowland soil (GLS), Non-allophanic Andosol (NAS), and Sand-dune Regosol (SDR) with hairy vetch foliage application in a greenhouse for 45 days. In GLS, the nodule number was not influenced by the application, however, nodule dry weight and N2 fixation activity tended to increase. In NAS and SDR, nodule formation was depressed by foliage application. Soybean plant growth was promoted in GLS and SDR but not in NAS. These promotive effects of hairy vetch foliage application on soybean plant growth in GLS were considered to be mainly caused by the increase in N2 fixation activity of the nodules, whereas it was considered to be mainly caused by the increase in nitrogen uptake activity of the roots in SDR. The varying effects of hairy vetch foliage application on soybean nodulation may be due to soil chemical properties such as pH and cation exchange capacity, which are related to soil texture. Therefore, we conclude that it is important to use hairy vetch for soybean cultivation based on the different effects of hairy vetch on soybean plant growth in different soil types.