Search

We have investigated the effectiveness of a new soybean fertilization technique, named crack fertilization, which involves the application of nodule bacteria on biochar to soybean roots through cracks formed between planting rows during midterm tillage. In the present study, the factors and timing of crack fertilization were investigated in an upland field converted from a paddy. The variables investigated were: 1) crack formation without the application of any agricultural materials, and 2) the application of biochar or 3) nodule bacteria on biochar into cracks. The treatment periods were: 1) before sowing, 2) during midterm tillage, and 3) during both periods. The combination of crack fertilization and reduced tillage was also tested. The method of crack fertilization that increased yield was the combination of crack formation and the application of biochar, and the most effective period for the treatment was before sowing in the reduced tillage field. Seed yields in conventional and reduced tillage fields were comparable in the upland field converted from the paddy. These results suggest that the application of biochar into cracks after scratching the soil surface to remove weeds before sowing is a practical method of increasing soybean yield in upland fields converted from paddies.

A field experiment was conducted to examine the possibility of introducing winter legumes, hairy vetch and faba bean, as green manures to turmeric cropping in a temperate region. Hairy vetch shoots were incorporated to determine the effect of N and P added as green manure. Higher values in plant height and number of leaves of turmeric were observed in the treatment with incorporation of hairy vetch than in that without incorporation (no-incorporation) throughout the growth periods. The differences in total amounts of N and P of turmeric between incorporation and no-incorporation treatments were the highest on 15 October, when the amount was increased by 8.0 g N and 1.1 g P m–2 compared with the no-incorporation treatment. From September to October, curcumin content rapidly increased with rhizome thickening, and gradually increased. We also quantified the N and P contribution from faba bean residues to the succeeding turmeric. The total amounts of N and P in turmeric cultivated after incorporating shoot and root residues into previously cultivated faba bean field were 2.5 g N and 1.0 g P m–2, respectively, larger than incorporating only roots. In previously fallow field, the incorporation of the shoot increased the total amount of N and P in tumeric by 4.5 g and 1.9 g m–2, respectively, compared with that without incorporation. In the second year after incorporation, growth and nutrient uptake of the turmeric crop did not significantly differ from those without incorporation. In the temperate region, these winter legumes would be used as basal organic matters for turmeric production.

The important role of auxin polar transport in the early growth stage of etiolated maize (Zea mays L. cv. Honey Bantam) seedlings was intensively studied. Rapid growth in the basal region of coleoptile and the apical region of mesocotyl was observed in etiolated maize seedlings in the dark. Indole-3-acetic acid (IAA) applied to the top of coleoptile substantially promoted the growth of coleoptile and mesocotyl dose-dependently, suggesting that endogenous IAA is responsible for the growth of coleoptile and mesocotyl in etiolated maize seedlings. Polar transport of radiolabeled IAA ([14C]IAA) in the coleoptile segment was significantly higher than that in the mesocotyl segment from etiolated maize seedlings. Auxin polar transport in the coleoptile and mesocotyl segments from etiolated maize seedlings increased with the growth of the seedlings from which the segments were excised. Maximum expression of the gene (ZmPIN1a) closely related to auxin polar transport was observed just prior to maximum levels of auxin polar transport in the coleoptile and mesocotyl segments. In addition, the growth rate was well correlated with the auxin polar transport and the expression of ZmPIN1a gene in coleoptile and mesocotyl of etiolated maize seedlings. These results strongly suggest that auxin polar transport regulated by ZmPIN1a protein is essentially required for the growth of coleoptile and mesocotyl in the early growth stage of etiolated maize seedlings.

Legume-grass mixed cropping may alleviate N starvation when incorporated as grass green manure which has a higher C/N ratio than legume manure. We focused on N and P absorption of oat in mixed cropping with hairy vetch, and investigated the effect of the mixedcropping green manure on the growth and nutrient uptake of the succeeding corn. The total N and total P contents of oat mixed-cropped with hairy vetch were higher than those of sole-cropped oat, and dry weight in addition to N and P contents of oat were greatly increased by cutting mixed-cropped hairy vetch before blooming. Sole cropping of hairy vetch was the best green manure to enhance the growth and nutrient uptake of the succeeding corn crop, but mixed cropping of oat with hairy vetch was also highly effective. Further investigations are needed to determine the long-term effect of mixed cropping green manure on N and P sequestration as soil organic matter.

A fiber reinforced plastic (FRP) pot, equipped with a slanted pipe through which water is supplied, has been used for assessment of rice herbicides. This pot may also be useful for controlling water table in upland conditions. In this experiment, early growths of soybean and morning glory grown under waterlogging and excess soil water conditions were evaluated. The waterlogging condition was attained by adjusting the top of the slanted pipe to soil surface level, and excess soil water condition (0.2 m3 m−3) by adjusting to 15 cm below the soil surface. The water content of the soil did not fluctuate during the treatment. Shoot growths of soybean and morning glory were poorer under waterlogging than excess soil water condition. The present experimental procedures using a FRP pot could be available for evaluation of wet damage of field crops grown under ill-drained field.

Enhancement of nitrogen fixation activities by a cultivation technique is one of the potential targets to improve soybean yield in Japan. A cultivation technique named “crack fertilization” is described and the nodulation control by this technique is analyzed by experiments in two fields with different soil and environmental conditions, and a root box experiment. Crack fertilization is a technique that utilizes the irregularly shaped soil cracks formed by subsoiling just before the flowering stage of soybean, and introduces root nodule bacteria, fertilizers, and so on to the deep subsoil layer. Production of ureide-form nitrogen at six weeks after the crack fertilization (only nodule bacteria application to the subsoil layer) was 1.4 times higher than the control in the Hikone field. Acetylene reduction activity at four or eight weeks after the crack fertilization (application of both nodule bacteria and low level of fertilizer to the subsoil layer) tended to be higher than in the control in both fields. In the root box experiment, nodule number was four times higher than that in the control at the lower portion of the root system, where modified crack fertilization treatment was conducted, and the acetylene reduction activity was increased significantly by the treatment. These results indicated that the soybean nodulation control, i.e., timing and position of nodulation, as well as the enhancement of nitrogen fixation activity could be achieved by this crack fertilization technique.

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.

Hairy vetch (Vicia villosa Roth) has the potentials for preventing soil erosion and suppressing weed growth as a winter cover crop. We evaluated the additional N supplied by this crop harvested at different growing stages to the succeeding sorghum in pot experiments. Hairy vetch was grown in 1/5000a Wagner pot, and shoots (S) and roots (R) were mixed separately or together (S+R) into the soil on 30 March, 18 April and 2 May. After incorporation of the plants, seeds of sorghum were sown in the pots. Dry weight and N content of hairy vetch increased throughout the growing period. The value of nitrogenase activity in root nodules peaked on 18 April and then drastically declined. When hairy vetch was harvested on 30 March, N content of sorghum in the S pots was definitely less than that in the R and S+R pots. When hairy vetch harvested on 2 May, however, the N content in the S pots was similar to that in the S+R pots, and it was significantly higher than that in the R pots. Although N input from hairy vetch was higher in the S pots than in the R pots, N uptake by sorghum was not reflected in those values. The belowground parts of hairy vetch may have a considerable effect on N uptake of sorghum when using this plant species as green manures.

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.

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.

In Crotalaria juncea L., adventitious buds were formed in cotyledonary expiants cultured on 0.8% agar-solidified 1/2 MS basal medium containing B5 vitamins, 1.0 or 0.5 mg L–1 NAA, 5.0 or 10.0 mg L–1 BA and 3% sucrose. The frequency of adventitious bud formation was 30-45% in all combinations of NAA and BA. In histological observations, prominent mitotic figures were observed in several cells of the subepidermal palisade layers on the adaxial side of the expiants in contact with medium after 3 days of culture. Calli were formed within 6 days of culture. After 10 days of culture, numerous mature tracheary elements were produced at random in the proliferated regions, and cell divisions at the superficial region led to the formation of the meristematic structure. The shoot apex of the seedling produced numerous trichomes from superficial cells, but the adventitious bud formed on the cotyledon produced no trichomes. Initiation of the meristematic region in the expiant could be used as a target site for gene transfer experiments.

The effect of nitrate in the culture solution (0.7, 3.5, 7.0, and 14.0 mM N) on the growth, root nodule formation and nitrogenase activity of the peanut (cv. chico) inoculated with Bradyrhizobium sp. was examined at early developmental stages. The amount of nitrogen derived from fixation and its percentage to total nitrogen in the nitrate-fed plant were evaluated using 15N labeled nitrate. The dry weight and total nitrogen content of the plant at 40 days after transplanting (day 40) varied with the concentration of nitrate in the culture solution. Both of them were higher in the plants grown in the presence of nitrate at the concentrations above 0.7 mM. On the other hand, the number and fresh weight of nodules, and acetylene reduction activity per plant were the lowest in the presence of nitrate at 14.0 mM, relatively high at 0.7 mM, and the highest at 3.5 mM. The proportion of N derived from atmosphere to total nitrogen in the plants examined at days 18 and 33 was 23–31% in the presence of nitrate at 3.5 and 14.0 mM. However, the proportion examined at day 48 was as high as 57–58% at 3.5 mM, and it was only 22–24% at 14.0 mM.