Growth and Yield Characteristics of Rice Directly Sown on a Well-Drained Paddy Field in Early Winter in the Cold Climate Region of Japan

Growth and Yield of Rice Directly Sown on a Well-Drained Paddy Field in Early Winter Using Multi Direct Seeder

This study aimed to experimentally determine the effectiveness of hill seeding in a well-drained paddy field using plowing and compaction systems by comparing the yield, quality, and lodging resistance under high-fertilizer conditions, to those of direct sowing in rows. The degree of lodging was found to be higher with hill seeding than with row sowing. There was a significant reduction in yield with row seeding. This was related to the lower percentage of ripened grain on the primary and secondary rachis branches of the panicle. Therefore, under high-fertilizer conditions, which promote lodging in rice directly sown in a well-drained paddy field using plowing and compaction systems, hill seeding has superior lodging resistance. This was due to the presence of shorter and thicker lower internodes in hill seeding compared to row seeding. Ripening capability was also maintained, which resulted in a higher yield and improved quality. Therefore, hill seeding is effective in obtaining stable and high yields of rice directly sown in well-drained paddy fields using plowing and compaction systems and of rice directly sown in flooded paddy fields.

We have discovered that some of the seeds lost their viability in the process of dormancy awakening. Following facts were found concerning this phenomenon. Dead seeds were found after one month from the beginning of dormancy awakening (either primary or secondary) in the storage within the soil under upland condition (70 to 80 per cent. soil moisture content of field capacity) at low temperature below 10°C (especially 10°C). Dead seeds did not differ from fresh seeds in the morphological appearance of the embryo at earlier time, but its dehydrogenase activity was missing. However, occurrence of dead seeds in the soil varied acording to the temperature and moisture content of the soil. In the storage under any moisture content of the soil at germination temperature and under submerged or air-dry condition at low temperature, dead seeds were not found. In well-drained paddy fields (submerged condition in rice season, upland condition after rice season), numbers of viable seeds decreased very rapidly during from winter to early spring. In poor-drained paddy fields (submerged condition in the whole year), numbers of viable seeds decreased very slowly because the seeds hardly died in the process of dormancy awakenig in winter. Accordingly, it was well established that longevity of seeds of barnyard grass are longer in poor-drained paddy fields than in well-drained paddy fields.

The lodging resistance as affected by dense sowing and the interrelationships of the traits related to the lodging resistance were examined in rice varieties under direct sowing culture on well-drained paddy field. The results obtained were summarized as follows: 1. Under sparse sowing condition (22.2 hills/m2), the severer lodgings were observed in longer culmed varieties. However, under dense sowing condition (200 hills/m2), the chief reason for lodging was the decrease in breaking strength of stem, and the additional one was the elongation of the basal internodes in long-culmed varieties. 2. The elongation of culm by dense sowing was attributed to the lengthening of lower internodes (N3∼N5). In some long-culmed varieties, the breaking internode came to one internode lower than usual by means of the elongation of the lower internode, and this resulted in the decrease of living leaf sheaths wrapped on the culm, which increased the stem strength. 3. By the research on the relationship between breaking strength and other characteristics, the following facts were made clear. (1) The decrease of breaking strength of the stem by dense sowing was related both to that of the culm and to that of the leaf sheath. Of the two, the latter gave larger influence than the former. There could be observed high positive correlation between breaking strength of stem (culm with leaf sheath) and that of leaf sheath. (2) The contribution rate of leaf sheath to breaking strength of stem amounted high, in some varieties attaining as much as 50-60%. This contribution value was shown larger in short-culmed varieties than in long-culmed varieties and greater in lodging resistant varieties than in lodging susceptible ones. Dense sowing made this rate decrease by diminishing the number of living leaf sheath wrapped on the basal internode. (3) Long diameter/short diameter ratio of culm was increased by dense sowing, and there could be observed negative correlation between this ratio and the breaking strength of the culm. Similar results were recognized also in the leaf sheath. (4) Starch grains were noticed in the culm of lodging resistant varieties, however, the effect of dense sowing on starch amount could not be made clear. 4. By multiple regression analysis, high multiple coefficients of correlation were shown between lodging resistance and four characters (plant height, fresh weight, breaking strength and length of lower internode). Also, high ones were observed between breaking strength of culm (also leaf sheath) and three characters (cross-sectional area, long diameter/short diameter ratio and amount of starch in culm), however, these multiple coefficients of correlation became low in long-culmed varieties under sparse sowing condition. 5. The results may be concluded as follows. One of the most effective method to hold lodging resistance larger is to increase both the living number of leaf sheath on the basal internode and the duration period of it, and the other is to inhibit the elongation of the basal internode, especially in long-culmed varieties.

A study on the relationships between canopy architecture and yield of rice sown directly requires experimentation with population density of different magnitude and basal nitrogen levels. A lowland rice cultivar, Yamabiko, was sown directly in a square design at five population density levels (1600, 400, 100, 25 and 6.25 plant/m2 at seedling stage) having two nitrogen levels as basal dressing (0 kg-N/10a : 0-N plot and 10 kg-N/10a : 10-N plot) on a well-drained paddy field in 1972. Each plot was replicated three times. Plants were grown on available soil moisture for one month. Thereafter, field was flooded with irrigation water which was kept stagnant in the field till dowgh-ripe stage. The leaf stratified structure of each plot was evaluated on the basis of F1 and F2 scores obtained by the multivariate analysis method as described in part I14). The relationship between the leaf stratified structure and yield was analysed and the results were compared with those of a rice community of transplanting culture reported in two previous papers14, 15) in order to find the characteristics of the structure of this rice community sown directly. The results are as follows : 1. The relationship between F1 or F2 score and the leaf stratified structure and the seasonal trend of leaf stratified structure were virtually the same as those of two previous papers (Tables 1 and 2 ; Figs. 1, 2 and 3). 2. The yield (winnowed paddy) was maximum at 400 plant/m2 density level both in 0-N and 10-N plots and the yield of 10-N plot was about 19% higher than that of 0-N plot (Table 3). 3. The leaf stratified structure and top dry weight appeared to be independent of each other. 4. Positive correlation between yield and top dry weight at each growth stage was found in 0-N and 10-N plots. The correlation was higher at later stage of plant growth, and it was always higher in 0-N plot than in 10-N plot (Table 4). 5. The correlation between yield and F1 or F2 score was high and positive at the young panicle formation stage only in 0-N plot and at all stages except active-tillering in 10-N plot (Table 5). This trend was similar to that reported in part I, presumably due to the similarity of the weather between these experiments. 6. The relative strength of correlation between yield and F1 or F2 score compared with correlation between yield and top dry weight (see part II15)) was greater in the communities with larger leaf area index (LAI), which include 10-N plot or later stage of plant growth. By contrast, in the communities with smaller LAI, the relative strength was small. The smaller the LAI was, the higher was the change of this relative value (Figs. 4 and 5). 7. The comparison of the leaf stratified structure of a rice community sown directly with that of a transplanted community15) shows that the former structure had a tendency to have a high leaf weight percentage (see part I for the definition) in the lower stratum at the active-tillering stage and in the upper stratum after the young panicle formation stage (Fig. 6). The results of No. 1, 3, 5 and 6 are the same as those of two previous papers14, 15). It is therefore suggested that the relationship between the leaf stratified structure and yield of rice is little influenced by the differences in cultural methods as well as the yearly variations in the environmental conditions. It was observed that F1 and F2 factors maintained their individual characteristics in the three experiments. Thus, it is concluded that the statistical method used in the series of this study is very useful for analysing canopy architecture of rice community and for investigating the yielding ability of rice from the viewpoint of canopy architecture.

Vertical changes in bacterial and archaeal communities (mainly methanogen) with soil depth in three Japanese paddy fields (Tatsuta, Nagakute and Ichinomiya, Aichi prefecture) were investigated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and quantitative PCR. All fields were located in an alluvial area and the soil texture differed among the layers. The Nagakute and Ichinomiya paddy fields were well-drained paddy fields (Gray Upland soil and Gray Lowland soil, respectively), whereas the Tatsuta paddy field was a wet paddy field (Gley soil). The amount of extracted DNA drastically decreased below a depth of 20 cm and remained at a low level in the deeper layers in all fields. Numbers of mcrA genes, encoding the methyl-coenzyme M reductase α subunit of methanogenic archaea, drastically decreased with depth in the Nagakute and Ichinomiya paddy fields; high numbers of mcrA genes were retained through the layers in the Tatsuta paddy field. Cluster analysis of the DGGE band patterns of the bacterial and archaeal communities showed that their patterns in each field were initially divided into two groups, upper and lower layers, except for the bacterial community in the Tatsuta paddy field. These differences in the communities roughly corresponded to the distribution of the rice roots. Sequencing analysis of representative DGGE bands of the archaeal communities showed that diverse methanogens belonging to members of Methanomicrobiales, Methanosarcina spp., Methanosaeta spp., Methanocellales and Methanobacteriaceae inhabited the plowed soil layer, whereas uncultured members in the cluster ZC-I group of Methanosarcinales were more predominant beneath the plowed soil layer. Archaeal members other than methanogens inhabited the deeper layers of the Nagakute and Ichinomiya paddy fields. These results showed that the populations and compositions of bacterial and archaeal communities in paddy fields distinctly varied with soil depth, and indicated that the distribution of rice roots and the groundwater level might affect the populations and compositions in the subsoil.

Abstract.The response of overwintering nymphs of Strophingia ericae (Curtis) (Homoptera: Psylloidea) to long and short photoperiods over a range of temperatures was investigated to determine the interaction between these factors and winter development as a regulatory mechanism of their life cycle. Strophingia ericae was successfully reared from egg to adult in a long photoperiod (LD 18:6 h) at 10, 15 and 20°C on its host plant Calluna vulgaris. Although development time was longer at 10 than at 15 or 20°C (≈ 263 days compared with ≈ 155 and ≈ 159 days, respectively), there was no interruption in development at any of these temperatures, indicating that there was no obligatory diapause. However, short photoperiod (LD 12:12 h) inhibited development of overwintering fifth instars collected from the field in early winter. Those collected in September and kept at 15°C developed to adult in ≈ 120 days in a short photoperiod (LD 12:12 h) compared with ≈ 40 days in a long photoperiod (LD 18:6 h). Inhibition became weaker in December and disappeared by January, when fifth instars developed to adult at the same rate in both long and short photoperiods (≈ 30 days). A similar photoperiodic response was observed when the experiment was repeated at 10°C, although development times were consistently longer. The observation that insects collected from the field in early winter were able to resume development immediately on transfer to favourable conditions (15°C and LD 18:6 h photocycle) suggests that there is a photoperiodically induced quiescence (rather than a true diapause) in overwintering S. ericae, which becomes progressively reduced as winter proceeds.It was concluded that the life cycle of the upland and possibly the lowland form of S. ericae is regulated by a winter‐active photoperiodic inhibition of development, which effectively synchronizes the emergence of the adult stage with higher spring temperatures and renewed host plant growth.

In direct-seeding cultivation of rice, it is possible to save working time for growing and transplanting seedlings. In Hokkaido, where the management area of one farm is larger than that of other parts of Japan, the area of direct-seeding cultivation in large-sized paddy fields with groundwater level control systems has been increasing. Irrigation requirements increase in some cases of direct-seeding compared with the transplanting cultivation. To disseminate direct-seeding in an area it is necessary that the increases in irrigation requirements be within the permissible range of the irrigation of the area. The authors compared three cultivation methods: direct-seeding in non-puddled submerged paddy fields, direct-seeding in well-drained paddy fields, and transplanting cultivation, by using a large-sized block paddy field with the groundwater level control system facilities in Moseushi Town of Hokkaido. The following were clarified: 1) The difference in infiltration was small between the transplanting and direct-seeding cultivation methods. 2) The water supply volume, which is the sum of the irrigation requirement and the effective rainfall, of the three methods had very few differences in the period from the initial water intake and the re-submerging of the field because the groundwater level in the vicinity of the field was comparatively high and the infiltration was small. 3) The quantity of water intake during the period of shallow water management in direct-seeding cultivation is comparable to the puddling water requirement in transplanting cultivation.

Various foreign sources of information have recently shown us that the application of 2.4-D (2.4-dichlorophenoxy acetic acid) is effective for the weed control. Therefore, the writer tested a possibility of adopting this method in paddy condition. From several varied experiments, a spray of 0.05-0.1 percent 2.4-D in the form of either sodium or ammonium salt in water at the rate of 75-150 liters per 10 ares on weeds between the growing rice plants on well-drained paddy field in the mid-or late July has given desirable results, this method was so effective that, with the exception of Echinochlon Crusgalli Beauv. all kind of weeds such as Aneilema Keisak Hassk., Monorkoria vaginalis presl., Lindernia Pyxidaria all., Rotala indica Koehne. ver. uliginasa Miq. cyperus difformis L. Fimbristylis miliacea Vahl., Elatine orientalis Makino, Echipta alba Hassk., Hleocharis acicularis R. Br., etc., were killed within 1-2 weeks, nevertheless no injury to the rice plants was recognized. It may be recommended for the control of weeds on th paddy field to apply 50-75gr of 2.4-D per 10 ares, as it gave as much rice yield as that of the ordinary weeded plot. 37.5gr per 10 ares (0.05 percent solution at the rate of 751. per 10 ares) seemed to be too small doses and 150 gr. per 10 ares too much dose, each of which decreased the rice yields 15 percent and 10 percent respectively as compared with the ordinary weeded plot, although the rice yields of both plots was superior to that of the unweeded plot which about 35 percent less yield than the control.

Pythium iwayamai, P. okanoganense and P. paddicum, the main causal organisms of Pythium snow rot, were isolated from rotted leaves of wheat and barley grown in 122 paddy fields and 7 upland fields between 1982 and 1986. P. paddium was the dominant pathogen in ill-drained paddy fields in the previous season. From well-drained paddy fields, all three pathogens were isolated independently or simultaneously. On the other hand, P. iwayamai was the dominant pathogen in upland fields. The results indicate that distribution of the pathogens may vary with the degree of drainage in the fields.

The relationship between snow tolerance and growth characteristics in early winter was investigated using 41 varieties of broad bean. Varietal differences in snow tolerance were detected after 36 and 61 days of continuous snow cover. After 61 days of snow cover, only 2 varieties survived and 39 varieties were injured seriously. After 36 days of snow cover, 4 varieties were injured seriously but 37 varieties survived. The 41 varieties examined were classified into 3 groups based on their snow tolerance; hardy, intermediate and susceptible. To breed a snow tolerant variety, varieties in each group were bred under similar environmental condition. Several significant correlations were recognized between the degree of snow injury and some growth characteristics in early winter. The hardy varieties had a short plant length, light fresh and dry weights of foliage, high percentage of dry weight of foliage and late floral differentiation, whereas the susceptible varieties showed opposite tendencies. In the susceptible group, floral differentiation started in the early stage of growth and the floral buds developed markaedly before winter, suggesting that the susceptible varieties belong to spring type of broad bean. These results show that the varietal difference in snow tolerance of broad bean is closely correlated with the development of floral differentiation and morphological characters at early winter.

Several experiments were carried out to investigate the mechanism of decrease of rice yield in ill-drained paddy field. The results were summarized as follows : 1. No difference of rate of growth of the plant in cooler seasons were recognized between on well-drained and on ill-drained paddy fields, but as it became warmer, the plant grown in the former showed more rapid growth than that in the latter, and at the harvest time the culm length, number of panicles and kernel yield in well-drained paddy fields were greater than that in the ill-drained. 2. The higher the soil temperature in summer, the heavier became the decay of r0ot caused by bad aeration in ill-drained paddy fields as compared with that in well-drained fields. 3. The remarkable outbreak of sesame spot disease and stem rot in ill-drained paddy fields might be attributable to the retardation of absorption of nutritive elements, especially of potassium and silica, caused by injuries in roots.

To understand the growth habit of rice plants under direct seedling cultivation on well-drained paddy fields, physiological and ecological characteristics were compared among directly seeded and transplanted rice cultivar Whasungbyeo. Photosynthesis and respiration were lower in direct seeding cultivation (DSC) than in mechanical transplanting cultivation (MTC). Chlorophyll content and root activity were lower in DSC than in MTC from the tillering to heading stages, while they were higher 15 days after heading in DSC. The stomatal resistance of the upper leaves was higher in DSC than in MTC from the tillering to heading stages, however, it was higher in MTC than in DSC 15days after heading. The specific leaf area was higher in MTC than in DSC from the tillering stage to 15 days before heading, and was lower in MTC from the heading stage to 15 days after heading. The length of leaf blade and internode were longer in DSC than in MTC except the flag leaf and first internode. Partial dry weight was high in the upper part in MTC and lower part in DSC. CGR, RGR, NAF and LAI were higher in DSC than in MTC from the tillering to heading stages. The number of spikelets, yield and ripened grain ratio were higher in DSC than in MTC, while the number of panicles was higher in MTC.

In Japan, the extent under paddy is approximately three million hectares and the average yield per hectare is about 3000 kg, though high yield gives as much as over 7000 kg per hectare. It is at present a serious problem as to what methods we can use to obtain a high yield of rice. Generally, in well-drained paddy fields where the system of double-cropping is practised, rice is cultivated under a flooded condition in summer, and upland crops such as barley or wheat is cultivated under upland condition in other seasons.

Progress of the growth stages of direct-seeded rice on a well-drained paddy field and transplanted rice on a flooded paddy field with cropping season