Masamichi Ohe

Role of Belowground Parts of Green Manure Legumes, Crotalaria spectabilis and Sesbania rostrata, in N Uptake by the Succeeding Tendergreen Mustard Plant

Using symbiotically N2-fixing legumes as green manures is a way to supply N from the atmosphere to cropping ecosystems. Usually whole plants of the green manure are incorporated into soil; hence, the belowground parts as well as the aboveground parts would contribute to N transfer to succeeding crops. However, little is known about the contribution of the belowground parts alone. We assessed N transfer from belowground parts compared to whole plants of two legumes, Crotalaria spectabilis and Sesbania rostrata. Each of the legumes was grown approximately for 3 months in a 1/2000a Wagner pot filled with soil media, and then the roots alone (R) or shoot and root (S + R) were harvested and incorporated in the pots. Tendergreen mustard (Brassica rapa) as the succeeding crop was grown for 66 days in these pots without additional fertilizer. Although the amount of N in green manure in S + R pots was approximately 4-fold higher than that in R pots, differences in N uptake by tendergreen mustard between the S + R and R pots were smaller (1.7-fold for C. spectabilis and 2.3-fold for S. rostrata). This means that N recovery rate by tendergreen mustard was significantly higher in R than in S + R pots with either green manures. Differences in C/N ratio of the green manures could not likely explain the higher N recovery rate in R pots. Bioassay of the aqueous extracts from the green manure with lettuce seedlings suggested that growth inhibitory effects might be responsible for the lower recovery rate in S + R treatment.

Ecophysiological Traits of Field-Grown Crotalaria incana and C. pallida as Green Manure

Abstract To evaluate the growth capacity and some chemical characteristics of two Crotalaria species, C. incana and C. pallida, used as green manure, we conducted a field experiment at Osaka, Japan. Both Crotalaria species exhibited vigorous vegetative growth, and leaf area was expanded in C. pallida and branching was promoted in C. incan. Top dry weight and nitrogen content of C. pallida were twice as high as those of C. incana at 87 and 120 days after transplanting (DAT), and the lower values in C. incana were attributed to drastic defoliation of lower leaves due to earlier anthesis from mid-July. Several indicators for rapid decomposition of the plants used as green manure, such as C/N ratio, lignin (L) content and L/N ratio at 56, 87 and 120 DAT, were significantly higher in C. pallida than in C. incana. However, these values might not be critical for nitrogen mineralization after incorporation of the materials into soil. To evaluate the qualitative traits of the two species as green manures, the materials were mixed with soil at a rate of 20 g fresh weight per pot, and seeds of wheat were sown at 10 and 30 days after mixing the green manure (DAM). The growth and nitrogen uptake of wheat grown on the soil mixed with C. pallida were inferior to those of wheat grown on the soil mixed with C. incana on both sowing dates, and the difference between the effectiveness of the two species as green manure was larger in the wheat sown on 10 DAM than on 30 DAM. The possible increase in nitrogen supply and growth inhibition by incorporation of these materials to wheat plants were discussed.

Tricalcium phosphate solubilization by root nodule bacteria of Sesbania cannabina and Crotalaria juncea

Genus Sesbania and Crotalaria have high ability to symbiotically fi x atmospheric nitrogen, and to sustain soil productivity when incorporated into soil (Shioya et al., 1990). In our previous studies, we evaluated the contribution of these two legumes used as green manure plants to growth of the succeeding crops (Daimon, 2006). These plant species have also been studied on P (phosphorus) acquisition ability under low P conditions. For instance, Tanaka et al. (1999) reported that S. rostrata exudes malonic and malic acids, having a role of solubilizing Al-P in the medium, in response to lower P level. Various bacteria and fungi in different soils have been reported to solubilize the sparingly soluble P (Barea et al., 2002). The solubilization of P by root nodule bacteria such as Rhizobium, Bradyrhizobium and Mesorhizobium, which solubilize rock phosphate, hydroxyapatite, and/or tricalcium phosphate has been reported (Halder and Chakrabartty, 1993; AbdAlla, 1994; Peix et al., 2001). However, little is known about the ability of rhizobia of Sesbania cannabina and Crotalaria juncea. In this study, we examined the possibility of releasing P from tricalcium phosphate, which is sparingly soluble P in arable land, by the root nodule bacteria with these two green manure legumes.

Effects of Deep-Flooding Irrigation on Growth, Canopy Structure and Panicle Weight Yield Under Different Planting Patterns in Rice

Abstract For rice cultivation in Japan, deep-flooding irrigation is used as a growth control method. To clarify the effects of deep-flooding cultivation under the different planting-pattern, we arranged conventional (Con, 22 hills m-2), narrow (Nar, 33 hills m-2) and very narrow (broadcast direct-seeding Model:BDSM, 100 hills m-2) planting plots under shallow-flooding (SF: 5 cm) and the deep-flooding (DF: 27 cm) conditions from active to maximum tillering stage and evaluated the growth, panicle weight yield, panicle components and community structure. DF was effective in controlling the weak tiller over the whole planting plots arranged. The panicle weight yield (m-2) was high in DF and high yield was kept even in BDSM. The panicle weight yield (m-2) increasesin DF was based on the panicle weight (panicle-1) increased by increasing secondary rachis-branches and their grains (Con and Nar), or on the panicle numbers (m-2) increase (BDSM). Shoot nitrogen content (tiller-1), reported to have the correlation with panicle components, was high in the Con and Nar in DF, and this might contribute to the increase in secondary rachis-branch grains. In BDSM in DF, the marked decrease in the percentage of productive tillers and serious lodging observed in SF were improved. The lodging resistance value in DF was higher than that in SF over the whole planting plots. The light transmission in DF was superior to that in SF in spite of the large LAI. Thus, the growth improving effect of DF was obvious over the wide planting pattern range.

Seed Germination and Coleoptile Growth of New Rice Lines Adapted to Hypoxic Conditions

We investigated the morpho-physiological traits of rice (Oryza sativa L.) during the germination and post-germination phases to explore avoidance of hypoxic conditions. We compared four lines selected for anaerobic germination (AG lines) with the variety IR42. The germination capacity of AG lines was higher than that of IR42. The germination percentages and coleoptile elongation differed among the four AG lines; IR06F459 showed the fastest germination and rapid coleoptile elongation. The coleoptiles of IR06F459 were significantly longer than those of IR42. The α-amylase activity in germinating seeds was significantly higher in IR06F459 than in IR42. At 2 days after sowing, the sucrose and glucose concentrations in germinating seeds were higher in IR06F459 than in IR42. These results show that IR06F459, an AG line with a long coleoptile, has high α-amylase activity and high sucrose and glucose concentrations in germinating seeds. These attributes partly explain its vigorous germination and coleoptile growth under hypoxic conditions.