Decrease In Dry Matter Accumulation Research Articles

Effects of hydrogen peroxide priming on yield, photosynthetic capacity and chlorophyll fluorescence of waterlogged summer maize.

Extreme rainfall events during the summer maize growth and development periods, which have induced losses in summer maize production. There was a completely randomized block experiment being designed with four treatments: waterlogging for 6 days at the V3 stage (C-W), H2O2-priming + non-waterlogging (H-CK), H2O2-priming + waterlogging for 6 days at the V3 stage (H-W) and control (C-CK). This study investigated the effects of H2O2 priming on yield and photosynthetic parameters of (Zea mays. L) summer maize hybrid DengHai605 (DH605) by measuring the leaf area index (LAI), soil and plant analyzer development (SPAD) value, stomatal morphology, gas exchange parameters, and chlorophyll fluorescence parameters. The results showed that the net photosynthetic rate (Pn) was decreased after waterlogging through the stomatal limitation of CO2 supply and reduction of PSII photochemical efficiency, which led to the decrease in dry matter accumulation and grain yield. H2O2 priming increased the number of opening stomas, the stomatal length, and width, thus increasing Ci by 12.1%, which enhanced the Pn by 37.5%. Additionally, H2O2 priming could improve the energy of dark reaction carbohydrates by increasing the light energy absorption and utilization, alleviating the function of PSII reaction centers, protecting the PSII receptor and donor side, and the electron transport chain. The φEo, φPo, φRo, and Ψo of H-W were increased by 89.9%, 16.2%, 55.4%, and 63.9% respectively, and the φDo was decreased by 23.5%, compared with C-W. Therefore, H2O2 priming significantly enhanced the PSII photochemical efficiency, and increased the CO2 supply in dark reactions to promote carbon assimilation, alleviating the waterlogging-induced damage to maize plant growth and grain yield.

Nitrogen and density treatment to improve resource utilization and yield in late sowing <italic>japonica</italic> rice

<p id="C3">Recently, the phenomenon of late sowing and late transplanting in rice is becoming more and more common in central Jiangsu, a rice and wheat double cropping system area, which is caused by climate change and the expanding of comprehensive rice-and-shrimp planting model. It will lead to the mismatch of rice growth period with light and temperature resources, restricting the stable high yield of rice. This study was conducted under the condition of late sowing and late transplanting (sowing date was June 12th, transplanting date was June 30th) and the seedling was transplanted by machine. Four nitrogen application rates (N₀: 0 kg hm^-2; N₂₄₀: 240 kg hm^-2; N₃₀₀: 300 kg hm^-2; N₃₆₀: 360 kg hm^-2) and three density treatments (D₃: 3 seedlings per hole; D₄: 4 seedlings per hole; D₅: 5 seedlings per hole) were arranged, and the suitable sowing period (May 29), conventional nitrogen application rate, and the seedling number per hole (N₃₀₀D₄) were taken as the controls. Our goal is to explore the effects of nitrogen fertilizer and seedling number per hole on the growth and yield formation in late-sown <italic>japonica</italic> rice, and to provide theoretical basis for improving yield potential and resource use efficiency in late sowing and late transplanting <italic>japonica</italic> rice in central Jiangsu province. The results showed that compared with CK, the yield of each treatment decreased, mainly because of the significantly reduced spikelet number under the late sowing and late transplanting condition. The highest spikelet numbers were 11.94% and 8.12% lower than those of CK in the two years. In addition, the utilization rate of temperature and light resources, nitrogen uptake, and nitrogen utilization rate decreased under late sowing and late transplanting treatment, leading to a decrease in dry matter accumulation and yield. The yield increased with the increase of nitrogen application rate and seedling number per hole under the late sowing and late transplanting condition, while there was no consistent with the trend under N₃₆₀D₅ treatment. We assumed that it was mainly due to the increased spikelet number, larger leaf area index at heading stage, the larger proportion of efficient leaf, and the extended growth period. In summary, the utilization of temperature and light resources and the dry matter accumulation at maturity stage was improved, and the decline in yield was alleviated. Nitrogen use efficiency increased first and then decreased with the increase of nitrogen rate, and N₃₀₀D₅ treatment reached the maximum. In general, under the late sowing and late transplanting condition, in order to alleviate the yield loss and reduce nitrogen fertilizer waste, we should increase the seedling number per hole and then increase the amount of nitrogen fertilizer.

Sodium nitroprusside application enhances drought tolerance in marjoram herb by promoting chlorophyll biosynthesis and enhancing osmotic adjustment capacity

Sodium nitroprusside (SNP) has a decisive function for mitigating water deficit; nevertheless, the specific roles of SNP on chlorophyll biosynthesis, water relation, and osmotic adjustment in marjoram (Origanum marjorana L., Lamiaceae) have not well been established. To assess the function of SNP in alleviating water stress (50% of field capacity), potted marjoram herbs were subjected to watering regimes (well-watered or water-deficit) with or without SNP concentrations (0, 30, 60 μM). Drought caused a significant reduction in water potential (Ψw), osmotic potential (Ψs), turgor potential (Ψp), relative water content (RWC), photosynthetic pigment, chlorophyllide (chlide)a, chlideb, chlorophyll (chl)a/chlidea, chlb/chlideb, and ions, however increased pheophytina (pheoa), protoporphyrin (Proto), Mg-protoporphyrin (Mg-proto), and protochlorophyllide (pchlide). Conversely, osmotic adjustment (OA) was improved, associated with the hyper-accumulation of osmotic adjustment solutes (OAS) leading to an increase in water saturation deficit (WSD), which induced a decrease in dry matter accumulation and shoot fresh weight. Application of SNP decreased Ψw, Ψs, and Ψp and WSD while maintained higher RWC, comparing the plants devoid of SNP supplementation. Supplementary SNP additionally motivated the energetic buildup of various OAO in drought-affected plants that improved OA aptitude, improved water retention capacity, and increased plant growth. Additionally, SNP application increased chlorophyll, carotenoid, pheoa, chlidea, chlideb, chla/chlidea, chlb/chlideb, and decreased Proto, Mg-proto, pchlide, and ions. The findings of the present study clarified that the SNP application improved drought tolerance of marjoram plants, through maintaining ion homeostasis, enhanced OA capacity, increased OAO accumulation, and stabilized chlorophyll biosynthesis.

PLOUGH PAN IMPACTS MAIZE GRAIN YIELD, CARBON ASSIMILATION, AND NITROGEN UPTAKE IN THE CORN BELT OF NORTHEAST CHINA

This study aims to investigate the responses of carbon assimilation, grain yield, leaf stay-green rate, nitrogen uptake and distribution to soil compaction in the hard plow pan caused by repeated use of tractor-driven cultivator in Northeast China. The typical hybrid maize variety “Zhengdan 958” was exposed to two treatments of simulated plow pan (SP) and simulated subsoiling (SS, control) in pot experiments from 2012 to 2014. Compared with SS, SP significantly reduced net photosynthetic rate (Pn) during growth stage, leading to a decrease in dry matter accumulation (DMA) and grain yield (GY) in three consecutive experimental years. Leaf stay-green degrees (LSD), which showed a fast descending trend from 20 days after silking (DAS), significantly decreased in the later filling stage under SP treatment. The translocation efficiency of the stored N (TEN) in stalk and leaf to the grain during pre-silking was enhanced, whereas leaf and grain N concentration (LNC/GNC), together with N accumulation amounts at maturity were significantly reduced under SP treatment. Also, plough pan reduced the N distribution to the organs of stalk, leaf and grain. In conclusion, subsoiling is a possible way to delay leaf senescence and achieve higher DMA and GY, and increased grain N in the corn belt of Northeast China.

Adverse effect of increase in minimum temperature during early grain filling period on grain growth and quality in indica rice (Oryza sativa) cultivars

Increasing global temperatures have a deterimental effect on rice quality besides leading to yield penalty. Past data shows that minimum temperature has increased more than maximum temperature in India as well as other parts of the world. The effect of this increase in mean minimum temperature on grain growth and quality of indica rice (Oryza sativa L.) cultivars is obscure. Our study submits the evaluation of grain quality of early, mid-early and medium duration indica rice cultivars to moderate increase in mean minimum temperature from anthesis to maturity in two seasons (kharif 2014 and 2015) . Early duration susceptible cultivars, Vandana and Parijat were significantly affected during the early phase of grain filling resulting in 4.6 and 6.4% decline in test weight and 12-18% in high density grains respectively, when the mean minimum temperatures were ≥ 25°C. Slower grain growth rate under elevated mean minimum temperature accounted for decrease in dry matter accumulation in these cultivars. In general, percentage chalkiness was less in all the indica cultivars. Head rice recovery was not affected but amylose content reduced in all cultivars with a significant effect on Bakal and Sahbhagi Dhan when minimum temperatures increased by more than 23°C. Rice cooking temperature determined by alkali spreading value was not stable across the environment in early duration cultivars, Vandana and Parijat. Increase in mean minimum temperature elicited the vulnerability of early duration indica cultivars, by adversely affecting quality traits like test weight, high density grains and gelatinization temperature.

Responses of Nitrogen Metabolism, Uptake and Translocation of Maize to Waterlogging at Different Growth Stages.

We performed a field experiment using the maize hybrids DengHai605 (DH605) and ZhengDan958 (ZD958) to study nitrogen uptake and translocation, key enzyme activities of nitrogen metabolism in response to waterlogging at the third leaf stage (V3), the sixth leaf stage (V6), and the 10th day after the tasseling stage (10VT). Results showed that N accumulation amount was significantly reduced after waterlogging, most greatly in the V3 waterlogging treatment (V3-W), with decreases of 41 and 37% in DH605 and ZD958, respectively. N accumulation in each organ and N allocation proportions in grains decreased significantly after waterlogging, whereas N allocation proportions increased in stem and leaf. The reduction in stem and leaf N accumulation after waterlogging was mainly caused by a decrease in dry matter accumulation, and a reduction in N translocation from stems and leaves to grains after waterlogging. Additionally, waterlogging decreased the activity of key N metabolism enzymes (nitrate reductase, glutamine, glutamate synthase, and glutamate dehydrogenase), and the most significant reduction in V3-W with a decrease of 59, 46, 35, and 26% for DH605, and 60, 53, 31, and 25 for ZD958, respectively. Waterlogging disrupted N metabolism, hindered N absorption and transportation, and decreased maize yield.

Weed interference on growth and yield of transgenic maize

Plants kept under competition tend to modify their morphology to optimize the use of production factors. This study aimed to evaluate the effects of competition between transgenic maize and five weed species on the growth and yield of transgenic maize hybrid. The experiment used a randomized block design with four replicates in a factorial 5 x 2 + 6 scheme consisting of a combination of maize under competition with five weed species (Bidens pilosa, Commelina benghalensis, Brachiaria brizantha, Sorghum arundinaceum and Ipomoea triloba) in two weed densities (15 or 30 plants m-2) plus six treatments corresponding to maize and weed species without competition. All the means for dry matter accumulated by maize plants in the stem and leaf in the density of 15 plants m ² were higher than the means for plants in coexistence with 30 plants m-². Number of kernels, diameter and length of cob were not affected by competition with weeds. The weeds that most interfered with maize biomass production were S.arundinaceum and B.brizantha. Leaf dry mass accumulation was more sensitive than the production of stem. It was observed that maize was usually very competitive with weeds, and there was a strong decrease in dry matter accumulation of all the weeds in the study when in coexistence with the crop.

Temporal and Spatial Profiling of Root Growth Revealed Novel Response of Maize Roots under Various Nitrogen Supplies in the Field

A challenge for Chinese agriculture is to limit the overapplication of nitrogen (N) without reducing grain yield. Roots take up N and participate in N assimilation, facilitating dry matter accumulation in grains. However, little is known about how the root system in soil profile responds to various N supplies. In the present study, N uptake, temporal and spatial distributions of maize roots, and soil mineral N (Nmin) were thoroughly studied under field conditions in three consecutive years. The results showed that in spite of transient stimulation of growth of early initiated nodal roots, N deficiency completely suppressed growth of the later-initiated nodal roots and accelerated root death, causing an early decrease in the total root length at the rapid vegetative growth stage of maize plants. Early N excess, deficiency, or delayed N topdressing reduced plant N content, resulting in a significant decrease in dry matter accumulation and grain yield. Notably, N overapplication led to N leaching that stimulated root growth in the 40–50 cm soil layer. It was concluded that the temporal and spatial growth patterns of maize roots were controlled by shoot growth and local soil Nmin, respectively. Improving N management involves not only controlling the total amount of chemical N fertilizer applied, but also synchronizing crop N demand and soil N supply by split N applications.

Nitrogen fertiliser rate and post-anthesis waterlogging effects on carbohydrate and nitrogen dynamics in wheat

Waterlogging is predicted to increase in both magnitude and frequency along with global warming, and will become one of the most severe adversities for crop production in many regions. Nitrogen is considered to be an effective up-regulatory nutrient for crops grown under stress and non-stress conditions. In this study, we try to evaluate N fertiliser effects on contents of carbohydrate and N dynamics, dry matter accumulation in shoot, yield under post-anthesis waterlogging. Waterlogging after anthesis significantly reduced grain yield due to decrease in thousand-kernel-weight and in grain number per spike. High N fertiliser application aggravated grain yield loss due to post-anthesis waterlogging. These yield losses were related to the decreases in dry matter accumulation, redistribution of stored photosynthate to the grain, and the conversion capacity from carbohydrate to starch in grain. The decrease in dry matter accumulation could be attributed to the reduced activities of Pn (photosynthesis) and SPS (sucrose phosphate synthase) in the flag leaf, while the low capacity in starch synthesis could be explained by the reduced activities of sucrose synthase (SS) and soluble starch synthase (SSS) in grain. Total N uptake in shoot was also reduced, which could contribute to the losses in biomass and yield by waterlogging. The decrease in Pn was inconsistent with the increase in N content in the flag leaf at high N fertiliser application under post-anthesis waterlogging.

Accumulation of abscisic acid in cotton fibre and seed of normal and abnormal bolls

Cotton (Gossypium hirsutum L.) yield and quality is affected by altered fruiting patterns with progress in season. The present study was conducted to analyse normal and altered (abnormal) boll (fruit) development at maturation phase. Both normal and abnormal bolls of the same age groups were analysed for growth in terms of dry weight, water content and endogenous abscisic acid (ABA) content of fibre and seed. Endogenous level of ABA was estimated by using antibodies raised against ABA–protein conjugate. To amplify the reaction, indirect ELISA (Enzyme Linked Immuno Sorbent Assay) was performed. A marked decrease in dry matter accumulation (DMA) of seed and fibre was observed in abnormal bolls as the season progressed. Fibre from the abnormal bolls showed marked variation in endogenous ABA content, however, in abnormal seeds water content and endogenous abscisic acid content showed significant variation compared to that of normal bolls. From the results, it is concluded that a marked decrease in seed dry weight may be because of a decrease in water content and accumulation of higher endogenous abscisic acid content, whereas, the major reason for reduced fibre weight may be due to accumulation of endogenous abscisic acid.

Sorghum Intercropping Effects on Yield, Morphology, and Quality of Forage Soybean

Shading patterns when two forage species are intercropped may be different than in a monocrop environment. Our objectives were to quantify yield and forage quality response of forage soybean [Glycine max (L.) Merr.] intercropped with forage sorghum [Sorghum bicolor (L.) Moench] and compare to the measurements of monocrop soybean. Soybean plants were harvested from the middle portion of individual rows in plots containing only soybean and from plots having alternating soybean and sorghum rows spaced 76 cm apart. Morphological and forage quality measurements were determined on leaf and stem fractions. Morphological measurements included main stem length, node number, leaf area ratio (LAR), specific leaf weight (SLW), and stem diameter. Forage quality constituents included in vitro dry matter disappearance (IVDMD), neutral detergent fiber (NDF), hemicellulose, and cellulose, and crude protein (CP) concentrations. Intercropped soybean had 6 more plants m−1 of row, less advanced morphological development, and 2.3 Mg ha−1 less dry matter than monocrop soybean. Leaf IVDMD, NDF, hemicellulose, and cellulose did not differ between intercrop and monocrop soybean. However, stem IVDMD was 33 g kg−1 greater for intercropped than monocrop soybean, reflecting the 36 g kg−1 decrease in NDF concentration. Intercropped soybean was lodged both years more than monocrop soybean, which may have been due to the significant decrease in stem NDF. Leaf CP concentration was 25 g kg−1 greater for monocrop soybean than intercropped soybean; however, stems from intercropped soybean had 12 g kg−1 greater CP than monocrop soybean stems. Soybean exhibited a high degree of morphological plasticity, presumably in response to increased competition for solar radiation. Although forage quality of intercrop soybean was greater than monocrop soybean, intercropping forage‐type soybean with another tall‐growing forage does not appear to be practical because of the decrease in dry matter accumulation.

Relative toxicity of cadmium, lead, and zinc on barley

The relative toxicity of cadmium (Cd), lead (Pb), and zinc (Zn) on the growth performance of barley (Hordeum vulgare L.) was measured. Lead and Zn resulted in an increase in dry matter production at the lower additions. All the Cd and the higher Pb and Zn additions resulted in significant decreases in growth over the controls, the roots showing a greater decrease in dry matter accumulation than did shoots. Roots accumulated higher amounts of Cd, Pb, and Zn in direct proportion to that soil‐applied. A significant inverse relationship between relative yield and tissue element concentration was observed. Toxicity occurred in the following order: Cd > Pb > Zn. Threshold concentration, critical tissue concentrations, and loading rates to produce a 10% yield reduction were also calculated. Our study indicates the possibility of estimating barley yield based on plant tissue Cd, Pb, and Zn concentrations.

Uptake of mannitol from the media by in vitro grown plants

Higher plants grown in vitro are very seldom fully autotrophic. Therefore, such cultures are usually supplied with exogenous sugars. However, at higher sugar concentration a decrease in dry matter accumulation is observed which can be explained by a decrease in osmotic potential of the medium. To test this explanation a series of experiments with mannitol, a sugar alcohol often used for simulation of osmotic stress, were performed with excised wheat embryos, rape seedlings and potato stem segments grown in vitro. As the presence of mannitol in the medium caused a significant decrease in dry matter accumulation, the content of mannitol in the shoot tissues was determined using HPLC analysis to estimate the uptake and transport of mannitol from roots to shoots. Mannitol contents up to 30% of dry weight in wheat and 20% in rape and potato shoots were found, indicating that mannitol is easily taken up by in vitro plants and transported to shoots. There were no large changes in the content of glucose, fructose and sucrose caused by the presence of mannitol in the tissues. These data show that mannitol can not be used as an inert osmoticum in in vitro studies.

Growth of florets of sunflower ( Helianthus annuus L.) in relation to their position in the capitulum, shading and nitrogen supply

Florets at different positions in the capitulum of sunflower grow to different sizes and produce seeds with different weights. Competition between florets during their growth is thought to contribute to size differences and this has been studied in relation to changes in environmental conditions experienced by the plants. The imposition of shading (20% full sunlight) at the end of floret initiation decreased dry matter accumulation by the whole plant, although teh areas of leaves still expanding increased. The distribution of dry matter between plant organs was changed by shading, and competition between the capitulum and leaves was apparent. This, and the decrease in dry matter accumulation, decreased the receptacle area available for floret growth, with the result that florets in all positions were smaller. Changes in N supply had smaller effects on organ growth than shading. Nitrogen concentrations in leaves, capitulum bracts, receptacle and florets were increased by shading but were not affected by N supply rates. Attempts to change dry matter distribution between capitulum and leaves by removing half the leaves as they unfolded were not successful, but th experiment did confirm the apparent competition between the capitulum and the leaves. There were no direct effects of the environmental factors on floret growth but it was controlled by the available receptacle area which was affected by plant dry matter accumulation and the internal competition between the capitulum and leaves. Competition between florets in different positions remained unchanged in changed environmental conditions. It is suggested that the competitive hierarchy between florets is a consequence of their sequence of initiation; the outer florets are initiated before the inner ones and whilst they are growing always have a superior competitive ability.

Effects of soil type, mineral nutrition and salinity on greenhouse‐grown muskmelon in winter1

Abstract Greenhouse experiments under winter conditions were conducted to examine the effects of soil type, mineral nutrition and salinity on vegetative growth and. fruit yield of ‘Galia’ muskmelon (Cucumis melo L.). Growth in a calcareous soil or in sand, under low nutrition level or with 200 mM NaCl added during fruit maturation, imposed significant stresses on the plants expressed by (a) a decrease in dry matter accumulation in vegetative organs, in fruit number and size, and (b) an increase in dry matter percentage in leaf blades and stems. Despite the significant differences in vegetative growth of plants grown in heavy soil vs sandy soil, and in high nutrition vs low nutrition levels, the distribution of dry matter among vegetative organs (leaves, stems and roots) was affected only slightly. Sandy soil, low nutrition and high salinity decreased branching, and thus the distribution of dry matter between the main shoot and the branches. Dry matter percentage in leaf blades and stems was a sensitive pa...

Varietal differences in the response of potatoes to repeated short periods of water stress in hot climates. 2. Tuber yield and dry matter accumulation and other tuber properties

The effect of repeated short periods of water stress during the hot season on six potato cultivars was investigated. The number of tubers per plant tended to decrease in response to water stress in cultivars which had more than 9.8 tubers per control plant (Desiree, Alpha, Elvira). In the other cultivars, no consistent effect of water stress on tuber number per plant was observed. Except for Spunta, the percentage of large tubers (>60 g/tuber) was reduced in the water-stressed plants. Consequently, the average weight of these tubers was greater than that of tubers harvested from the unstressed plants, indicating that the sink force of the individual tuber was not impaired by drought. However, tuber yield per plant was reduced due to drought in all cultivars tested. The smallest decrease in dry matter accumulation as well as the greatest lowering of the osmotic potential in the tuber tissue was found in Alpha. No consistent effect of water stress on the percentage of misshapen and sprouting tubers was observed, indicating the marked effect of the high temperature on these traits.

Micronutrients and nitrogen metabolism

Deficient as well as toxic levels of micronutrients either Co, Cu, Mn, Mo or Zn in the growth medium resulted in a significant decrease in dry matter accumulation and amount of total as well as protein N, increase in the content of total N and water-soluble protein content and caused some change in protein amino acid composition in maize plants as compared to the control. Activity of alkaline aminopeptidases was significantly higher due to deficiency or toxicity of the elements. Sephadex fractionation and gel acrylamide electrophoresis of tissue extract revealed the dominance of low-molecular-weight proteins in maize shoots in both the situations. The results of the present investigation suggest that restriction in protein synthesis under the deficiency as well as toxicity of micronutrients in the growth medium is associated with the accumulation of low-molecular-weight in the plant tissue.

Studies on the Short Period Cultivation of Direct-Sown Rice Plant : 6. Effect of the sowing time on the plant growth and rice yield in the late seasonal cultivation

This experiment was carried out in order to make clear the relation of the sowing time to plant growth and rice yields in the late seasonal cultivation. Varieties used for this experiment were Yukara (extremely short-term variety) and Fujiminori (short-term variety). Seeds were sown at six times from late June to early August. The authors tested the growth and yields affected by variations in sowing time. The results are summarized as follows: 1) Grain yields decreased with the delay in sowing time. It was explained that the reduction in yields was caused by decrease in the dry matter accumulation in panicles and in the ripening grade (the weight of 1, 000 kernels x the percentage of ripened grains). 2) The decrease in dry matter accumulation in panicles with the delay in sowing time was due to the reduction in the rate of dry matter production during the ripening period. The reduction in the rate of dry matter production during the ripening period was due to the decrease in the net assimilation rate and the amount of leaves, and affected equally by the decrease in the net assimilation rate in the case of Yukara and by the decrease in the net assimilation and the amount of leaves in the case of Fujiminori, respectively. 3) There were no grain yields when the heading time was so late (Fujiminori, sown on 8 August) as ripening was completely disturbed by unfavourable weather conditions. The decrease in grain yields with the delay in sowing time in Fujiminori was greater than in Yukara. 4) The decrease in ripening degree caused by the delay in sowing time was due to the lowered ratio of the quantity of dry matter accumulation in panicles to the number of hulls per unit area. Namely, it was due to the fact that the decrease in the quantity of dry matter accumulation in panicles per unit area was greater than the decrease in the number of hulls per unit area.

Studies on the Short Period Cultivation of Direct Sown Rice Plant : 4. Effect of the sowing time on the plant growth and rice yields

This experiment was carried out in order to make clear the relation of the sowing time to the plant growth and rice yields. Sample varieties used for this experiment were extremely early-maturing varieties (Yukara and Sasahonami) and early-maturing varieties (Fujiminori and Koshijiwase). Seeds were sown in varied seeding density ranging over four times from the late May to early July. The authors tested the growth and yields affected by variations in sowing time. 1) Grain yields decreased linearly with the delay in sowing time, showing a decrease of 0.3 to 0.45 kg. per are per day. The decrease in yields from the yields in late May sown was at the rate of 0.5 to 0.9 per cent. This was thought that the reduction in yields was caused by decrease in the dry matter accumulation in panicles and by failure in full-ripeness. 2) The decrease in dry matter accumulation in panicles with the delay in sowing time was due to the reduction in the rate of increase in dry matter production during the ripening periods. The lowering of increasing rate in dry matter during the ripening periods was due to the decrease in the net assimilation rate and leaf dry weight, and affected greatly by the decrease in the net assimilation rate in the case of extremely early-maturing varieties and by the decrease in the leaf dry weight in the case of early-maturing ones. 3) The failure in full-ripeness by the delay in sowing time was due to the lowered ratio of "the quantity of dry matter accumulation in panicles per unit area" to "the number of hulls per unit area". namely, it was due to the rate of decrease in the number of hulls per unit area was less than that of decrease in the quantity of dry matter accumulation in panicles per unit area. 4) During the ripening period, the leaf dry weight in extremely early-maturing varieties were less than in early-maturing varieties, but net assimilation rate in extremely early-maturing ones was higher than in the early-maturing ones. As a result, no significant differeces were found in the rate of increase in dry matter weight between both varieties. Consequently, in the variation of sowing date no significant differences were found in yields between extremely early-maturing varieties and early-maturing ones. 5) Yukara showed higher yield than Sasahonami, and Fujiminori than Koshijiwase. This was ascribed to the fact that Sasahonami was very poor in ripeness (excess of hulls) and the dry matter increasing rate for Fujiminori was high throughout the entire plant growth period. There were generally a few differences in yields according to seeding density.