Keisuke Katsura

Rice Adaptation to Aerobic Soils: Physiological Considerations and Implications for Agronomy

Abstract Aerobic culture is a water-saving technique for direct-seeded rice cultivation. Growing rice under continuously unsaturated soil conditions can maximize water-use efficiency and minimize both labor requirements and greenhouse-gas emissions. Under a temperate climate, aerobic culture can produce a rice yield greater than 9 t ha–1 especially in central Japan (11.4 t ha–1). Aerobic culture using large-scale center-pivot sprinklers is being established in the central United States, where yields can surpass 10 t ha–1. However, yields remain at less than 8 t ha–1 in the tropics. The high yield of Japanese aerobic culture is mainly attributed to vigorous nitrogen uptake during the reproductive stage, which allows rice plants to produce more spikelets and biomass. Fertilizer management for aerobic culture must satisfy both the nitrogen demand and control spikelet density to achieve an appropriate sink–source balance. Unfortunately, the poor development of the root system in rice limits its water uptake from unsaturated soil. Adaptive responses such as adventitious root emergence, lateral root branching, and deep root penetration would protect the plants against dehydration stress in aerobic culture. Intermediate plant height with a few large tillers rather than semi-dwarf stature with profuse tillering should be a suitable plant type for aerobic culture, and plants should show leaf expansion despite fluctuations of soil moisture. The development and identification of suitable genotypes and crop management options are underway worldwide for more resource-use efficient and productive aerobic rice culture.

Soil color analysis for statistically estimating total carbon, total nitrogen and active iron contents in Japanese agricultural soils

Abstract Soil color originates mainly from organic matter, iron mineralogy and moisture content. We aimed to find a suitable method to measure soil color sensitively and to evaluate the extent to which the color parameters can be useful for statistically estimating total carbon (C), total nitrogen (N) and active iron (Fe) contents in Japanese agricultural soils. A soil color reader (SPAD-503) was applied to two sample sets: (1) 100 surface soils collected throughout a 0.5-ha paddy field (field scale) and (2) 147 surface soils collected from agricultural fields in Japan (national scale). For analysis with this instrument, about 2 g of air-dried, finely-ground samples were packed firmly in a plastic cell, and their colors as they appeared on windows in both sides of the cell were measured. A CIE 1976 (L*, a*, b*) color space was used for color description. For the field-scale samples, the values of the coefficient of variation were around 15% for total C, total N and acid oxalate extractable iron (Feo). The L* value (lightness) was negatively correlated with the content of total C and total N (R2 = 0.18** and 0.26**, respectively), and the b* value (yellowness) was positively correlated with the Feo content (R2 = 0.59**). For the national-scale samples, the values of the coefficient of variation were around 60% for total C, total N and Feo. The L* value was negatively correlated with the content of total C and total N (R2 = 0.70** and 0.59**, respectively), but the b* value was not correlated with the content of Feo (R2 = 0.00). When the analysis was limited to 65 samples frequently used for paddy fields, the b* value was positively correlated with the Feo content (R2 = 0.52**). In conclusion, the proposed method enabled us to measure soil color sensitively with a small sample size. The L* and b* values obtained can be useful for rapid estimation of total C, total N and Feo contents in agricultural surface soils in Japan.

The effects of the photoperiod-insensitive alleles, se13, hd1 and ghd7, on yield components in rice

Flowering time is closely associated with grain yield in rice (Oryza sativa L.). In temperate regions, seasonal changes in day length (known as the photoperiod) are an important environmental cue for floral initiation. The timing of flowering is important not only for successful reproduction, but also for determining the ideal balance between vegetative growth and reproductive growth duration. Recent molecular genetics studies have revealed key flowering time genes responsible for photoperiod sensitivity. In this study, we investigated the effect of three recessive photoperiod-insensitive alleles, se13, hd1 and ghd7, on yield components in rice under Ehd1-deficient genetic background conditions to ensure vegetative growth of each line. We found that se13-bearing plants had fewer panicles, hd1-bearing plants showed decreased grain-filling percentage, and ghd7-bearing plants appeared to have fewer grains per panicle and fewer secondary branches. Our results indicate that the pleiotropic effects of photoperiod-insensitive genes on yield components are independent of short vegetative growth. This will provide critical information which can be used to create photoperiod-insensitive varieties that can be adapted to a wide range of latitudes.

Yield and dry matter productivity of Japanese and US soybean cultivars

Abstract The difference in yields of cultivars may be causing difference in soybean yield between Japan and the USA. The objective of this study was to identify the effect of the cultivar on dry matter production and to reveal the key factors causing the differences in yield by focusing utilization of solar radiation in recent Japanese and US soybean cultivars. Field experiments were conducted during two seasons in Takatsuki, Japan (34°50′), and in a single season in Fayetteville (36°04′), AR, USA. Five Japanese and 10 US cultivars were observed under near-optimal conditions in order to achieve yields as close to their physiological potential as possible. The seed yield and total aboveground dry matter (TDM) were measured at maturity as long as radiation was intercepted by the canopy. The seed yield ranged from 3.10t ha−1 to 5.91t ha−1. Throughout the three environments, the seed yield of US cultivars was significantly higher than that of Japanese cultivars. The seed yield correlated with the TDM rather than the HI with correlation coefficients from .519 to .928 for the TDM vs. .175 to .800 for the HI, for each of the three environments. The higher TDM of US cultivars was caused by a higher radiation use efficiency rather than higher total intercepted radiation throughout the three environments. The seasonal change in the TDM observed in four cultivars indicated that dry matter productivity was different between cultivars, specifically during the seed-filling period.

Simple method for measuring soil sand content by nylon mesh sieving

Abstract A rapid and reagent-free method for measuring soil sand content is presented. In this method, a 20-µm-opening nylon mesh cloth was used for wet sieving of the sand fraction, and the difference of the soil weight before and after sieving was measured with an electric balance. Once air-dried, 2-mm sieved samples are prepared, the analysis can be completed within 2 d and 50 samples can be handled together by one person. The accuracy of this method was evaluated using five agricultural surface soils with various textural classes. The sand content obtained from the proposed method agreed well with that from the conventional method. Repeatability and reproducibility of the proposed method were high for sandy soils and were moderate for a clayey soil. The sensitivity of the method was further evaluated by analyzing 100 surface soils collected from a single paddy field having a similar textural class. The regression analysis of data between the proposed and conventional methods yielded an R2 value of 0.83 and a slope of 1.04. The slight overestimation by the proposed method suggested a systematic error, originating probably from the lack of pretreatment to remove organic matter. Limited to agricultural soils containing total carbon (C) of less than 5%, the proposed method would be useful not only for scientific investigation but also for educational purposes.

A Multichannel Automated Chamber System for Continuous Measurement of Carbon Exchange Rate of Rice Canopy

Recent studies on high yielding rice suggest that the yield potential is more limited by source production than by sink size (Peng et al., 1999). The source production in the fi eld depends primarily on the canopy carbon exchange rate (CER) which itself is a highly integrated process as a function of plant factors such as photosynthetic and respiratory properties, leaf area index, canopy architecture, and environmental factors. For increased source production in rice, it is important to identify the factors that limit CER under fi eld conditions. This necessitates the measurement of crop canopy CER under fi eld conditions. Various systems have been developed and utilized for the measurements of crop canopy CER; those included the closed chamber (Takeda, 1961; Saitoh et al., 1998), open-top chamber (Collins et al., 1995) and aerodynamic CO2 fl ux measurement systems (Inoue et al., 1958; Toda et al., 2000). Each of these systems has advantages and disadvantages. While the aerodynamic system allows measurement of CER under nondisturbed natural conditions, it requires a suffi ciently large fetch, which limits its applicability for genotypecomparative CER measurements. The closed chamber system may give accurate CER data, but its requirement of air conditioner to suppress inside temperature rise not only makes the system costly but also creates a chamber environment largely different from the fi eld, which was referred to as the chamber effect (Kobayashi, 2001). The open-top chamber system has intermediate characteristics between the above two systems, but possible mixture of outside air with the inside air limits the accuracy of CER measurements. Thus, an ideal crop CER measurement system may be such that allows accurate, long-term and simultaneous CER measurements on different genotypes under fi eld-like conditions with modest construction costs. Employing the periodically closing chamber method that has been frequently utilized for measurements of methane emission rate from soil-plant system (Wassmann et al., 2000; Nishimura et al., 2004), we developed a multichannel automated chamber system for continuous measurement of CER of rice canopy. This system was applied for long-term CER measurements for three rice cultivars. The chamber effects accompanying this system were evaluated by comparing the estimated biomass production from CER measurements with that measured by periodic harvesting of the rice crop grown outside the chamber. This paper describes the system and its characteristics.

Agronomic Traits for High Productivity of Rice Grown in Aerobic Culture in Progeny of a Japonica Cultivar and a High-Yielding Indica Cultivar

Abstract Aerobic rice culture is a promising way to save water and achieve a high yield. The present study was conducted to identify the agronomic traits required for high rice productivity in aerobic culture using chromosomal segment substitution lines (CSSLs) obtained as progeny from the cross between Sasanishiki (japonica), as the recurrent parent and Habataki, a high-yielding indica cultivar with high spikelet production ability, grown under flooded and aerobic conditions in 2009 and 2011. Grain yields of the CSSLs in aerobic culture were similar to or higher than those in flooded culture in 2009, but were similar to or lower than those in flooded culture in 2011. There were significant effects of genotype and water environment on grain yield in both years. Most of the CSSLs had a higher grain yield than Sasanishiki in aerobic culture, whereas their average was close to that of Sasanishiki in flooded culture. Rice plants grown in aerobic culture had larger biomass production, which enabled most of the CSSLs to produce more spikelets per unit area and maintain single-grain weight, thereby producing a higher grain yield than Sasanishiki. These results suggest that high spikelet producing ability would promote high grain yield in aerobic culture.

Decadal sustainability of spatial distribution of soil properties in a paddy field as a fingerprint reflecting soil-forming factors and field management

Abstract Spatiotemporal variations of soil properties were measured in a Japanese paddy field in order to evaluate how they were created and sustained through various field managements. The field was subjected to land consolidation during 1960s, heterogeneous application of manure in the late 1970s and land leveling in 1986, 1987 and 2003. Surface soils were collected from throughout the field in 2002 and 2012, and the physicochemical properties were analyzed. Additional analyses were carried out for relative altitude in 1986, 1999 and 2012, and soil hardness in 2012. In the field examined, the distribution of field attributes reflected past field managements. The heterogeneous distribution of relative altitude was partly explained by the passage of agricultural machinery, whereas the heterogeneous distribution of soil organic matter was partly explained by both past and recent applications of animal dung manure. In general, the measured soil properties were maintained from 2002 to 2012, and the pattern of spatial distribution did not change significantly for many of the properties. The correlation coefficient of the distribution patterns between 2002 and 2012 was highest for yellowness (0.95), followed by sand (0.90), acid-oxalate extractable iron (Fe; 0.88), available phosphorus (P; 0.87), redness (0.82), lightness (0.77), sand-size organic matter (0.74) and total nitrogen (N; 0.72). Land leveling carried out in 2003 barely influenced the distribution of these properties. Among these properties, soil color parameters and sand content can be measured rapidly without reagents and will be useful for characterizing paddy fields according to the distribution of stable soil properties. The analysis of the natural abundance of 15N in soil was also effective to suggest the contribution of the application of animal dung manure to the accumulation of soil organic matter at a within-field scale. It can be concluded, as a general rule, that each paddy field has its own fingerprint which is unveiled by precise soil sampling and analyses of stable properties.

The early flowering trait of an emmer wheat accession (Triticum turgidum L. ssp. dicoccum) is associated with the cis-element of the Vrn-A3 locus

Key messageWe identified a novel allele of the Vrn-A3 gene that is associated with an early flowering trait in wheat. This trait is caused by a cis-element GATA box in Vrn-A3.AbstractTo identify novel flowering genes in wheat, we investigated days from germination to heading (DGH) in tetraploid wheat accessions. We found that the tetraploid variety Triticum turgidum L. ssp. dicoccum (TN26) harbors unknown genes that surpass the earliness effect of the early flowering allele Ppd-A1a harbored by TN28 (T. turgidum L. ssp. turgidum conv. pyramidale). Using recombinant inbred lines resulting from a cross between TN26 and TN28, we performed a quantitative trait locus (QTL) analysis for DGH. We identified a QTL for earliness in TN26 on chromosome 7AS, the chromosome on which Vrn-A3 is located. By sequence analysis for the Vrn-A3 locus in both TN26 and TN28, we identified a 7-bp insertion that included a cis-element GATA box sequence at the promoter region of the Vrn-A3 locus of TN26. Based on an expression analysis using sister lines for Vrn-A3, we suggest that the early flowering trait of TN26 was caused by the GATA box in Vrn-A3. In addition, we identified tetraploid wheat as a useful genetic resource for wheat breeding.

Grain yield responses of lowland rice varieties to increased amount of nitrogen fertilizer under tropical highland conditions in central Kenya

Abstract Tropical highland conditions in Mwea Kenya, ensure the high radiation and the large day–night temperature differences. Such conditions are generally believed to promote rice growth and yield, but the current grain yield is lower than the expectation. In the current standard N fertilizer practice in Mwea, 75 kg nitrogen (N) ha−1 is applied in three splits at fixed timing. The effects of increases in N fertilizer amount (125, 175, and 225 kg N ha−1) on rice growth and yield were evaluated to test the hypothesis that unachieved high rice grain yield in Mwea is due to insufficient amount of N fertilizer. Two popular lowland varieties in Mwea (Basmati 370 and BW196) and two varieties reported as high yielding in other countries (Takanari and IR72) were used. Shoot dry weight (DW) increased with increases in the amount of N fertilizer applied in three splits at fixed timing, irrespective of variety. It reached approximately 20 t ha−1 under increased N conditions (>75 kg N ha−1) in several cases, indicating that high biomass production could be achieved by increasing N application rate. However, the increased biomass did not increase grain yield, due to decreased grain filling under high N conditions in all varieties. Thus, N amounts above 75 kg ha−1 were ineffective for increasing grain yields in Mwea, where N fertilizer was applied in three splits at fixed timing. Increasing influence of low temperature under high N conditions may be one of the reasons for the decreased grain filling in Mwea.