Growth disorder of sorghum have been reported in upland fields of Kagoshima and Miyazaki prefecture since 1967. Although several workers presented hypotheses on the cause of growth disorder of sorghum, no satisfactory explanation is offered for the occurrence of growth disorder of sorghum. In 1990, growth disorder was observed in sorghum planted in the field of Osumi Branch, Kagoshima Agricultural Experiment Station. The present paper reports relationship between soil chemicals and nematodes, and growth disorder in sorghum. Growth disorder occurred in sorghum in the field where sorghum was planted continuously or twice in the past five years. Levels of pH, nitrogen, phosphorous and CaO, MgO, K2O, Fe, Cu in the sick soil were almost similar to those in the healthy soil. Levels of Fe, Zn, Cu and B in stems and leaves of plants showing disorder were higher than those of plants showing normal growth. Application of phosphorous, potassium and boron had no effect on the growth of plants showing disorder. Plant-parasitic-nematodes were detected from both the sick and the healthy soils. However, there were not large differences in the number of nematodes between the sick and the healthy soils. The growth disorder did not occur even though when the nematodes separated from the sick soil and plant roots were inoculated to the soil. The results obtained suggested that nutrient deficiencies and plant-parasitic-nematodes are not major factors causing growth disorder in sorghum but that suggested that possibily of soil born disease by continuaus croping, owing to the growth disorder was decrease by fumigation of Chloropicrin in the sick soil, also growth disorder was not occurred in the virgin soil.

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Response of grazing behaviour and nutritional component of pasture plant to topdressing of N and P_2O_5 fertilizer were examined using yearling race horse grazing sward. Nitrogenous and phosphorus fertilizer were treated 0, 2, 4 and 6 kg per 10 a respectively in each experimental sward. Results obtained were summarized as follows : 1) Just after the topdressing, horses were grazed down only none or low level fertilized plot and not grazed high level fertilized plot at all. 2) After several days horses grazed on more and more high level fertilized plot. 3) Under the continious set grazing not only sward canopy maintained lower but also maintained nutritional component of pasture plant constantly, even in high level topdressed plot.

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The heading habit and seasonal growth of twenty six clones of tall fescue were investigated for three years at two locations, Nishigoshi and Aso. In the statistical analysis all effects, except reprications, were considred fixed. The analysis of variance revealed significant differences among genotypes for heading date and scores of vigor in every seasons. Also, the interactions of genotypes×locations and those of gentypes×locations×years were significant for heading date and vigor in every season (Table 3,7). Principal component analysis was applied to the genotype×environment interaction matrix. In the result of principal component analysis for heading date in six environments, first component scores mean the yearly fluctuation of genotypes in Nishigoshi, and second ones mean those in Aso (Table 5, 6). In the case of vigor in 20 environments, first component shows genotypes×locations interaction, second one shows the seasonal growth of genotypes, and third one appears to indicate genotypes×locations inteaction in the relation between vigor in initial growth stages and that of perennial growth stages (Table 9). The clones which showed good growth at both locations were originated in the populations of Kyushu or the cultivars bred in U.S.A. (Fig. 2). Two clones originated in Algerian populations showed good growth at Nishigoshi and poor growth at Aso (Fig. 1). We need to investigate adapatability and stability of tall fescue clones from the results of evaluation tests for several years at two or more locations. The clones which exhibited remarkable interaction of genotype×environment on heading habit might cause to drift on the genetic characters of synthetics presupposing random mating amang the clones. Whereas the clones which exhibited interaction on vigor might improve stability of synthetics.

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As a part of the study on the adaptability of timothy cultivars to environmental conditions and breeding of timothy of high quality, the effects of low solar radiation stress of short duration on growth and in vitro DMD were examined using the following cultivars : Kunpu (extremely early maturing), Senpoku (early), Nosappu (early), Erecta R.v.P. (medium) and Hokushu (late). Four clones of each of the cultivar were transplanted in a Wagner pot (1/5,000 a) that had been filled previously with a gleyic ordinary andsols, and cultivated outdoors for 50 days. At transplanting, each pot received 1 g of ammonium sulfate, 2g of superphosphate of lime and 0.2 g of potassium sulfate. Three levels of shading treatment ernployd in this study were non (S0), 52% (S1) and 80% (S2). Ten days after the transplantation, these plants were cultivated using S0. After treatment of 20 days, all pots were returned to S0 and cultivated for an additional 20 days. Two replications of each cultivar were then arranged in a split plot experiment design : main plot was solar radiation levels and split plot was cultivars. Extremely early maturing and early maturing cultivars showed large differences in total plant weight and foliage weight between S0 and the low solar radiation treatments at the completion of the test, while the other cultivars demonstrated only slight differences. At the period of 11 to 20 days after the low solar radiation treatment, RGR of Nosappu was highest for S0 and lowest for S2, while that of Erecta R.v.P. was highest for S2 and lowest for S0. At the period of the solar radiation treatment, Kunpu showed a large difference in NAR between S0 and the low solar radiation treatments, while Hokushu showed only a slight difference. RGR, NAR and LAR throughout the whole test period varied according to the cultivars used. The differences in LAR between the treatments were smaller than those of RGR and NAR at the period of the low solar radiation treatment. In the present test, low solar radiation treatment for 10 days resulted in poor growth thereafter, in particular extremely early maturing and early maturing cultivars at S0. It seems to be the low NAR at the period of 11 to 20 days after the low solar radiation treatment. RGR was more strongly affected by NAR than LAR. These data including dry weight, RGR, NAR and other characteristics suggest that medium maturing and late maturing cultivars would exhibit the highest resistance to low solar radiations, while those of extremely early maturing and early maturing cultivars were lowest among the cultivars tested. Each cultivar showed its highest DMD at S0 throughout the whole test period. Among all the cultivars tested, DMD decreased due to the low solar radiation treatments, which might result from a decrease in the non-structural carbohydrate content of the plant. The interaction between the low solar radiation treatment and cultivar in DMD showed no significance.

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Application of raw dairy manure causes a serious problem of weed seed dispersal to crop lands. The objective of this study was to clear the effect of exposure to anaerobic fermantation on the survival of seeds of broadleaf dock (Rumex obtusifolius L.) contained in dairy slurry. Two fermentation temperatures (35 and 42.5℃) and 3 retention time (10, 15, and 20 days) were applied to determine the percentage of seed germination, assuming that the anaerobically stabilized waste would be applied as a manure after release of methane gas. The results were summarized as follows : 1. Anaerobic fermentation lowered the seed survival ratio of broadleaf dock. 2. Exposure to temperature of 42.5℃ decreased the seed survival ratio more than 35℃. 3. Compined fermentation with temperature of 42.5℃ and retention time 10 days completely suppressed seed viability. From these findings, it is suggested that anaerobic fermentation may have a similar effects on other seed types.

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Methods for predicting the heading date of timothy(cv. Senpoku) 1st crop were investigated on 1km^2 plots in the Konsen District of Hokkaido, Japan. 1) Effect of air temperature (DVR(T)) and day length (DVR(L)) on plant developmental rate (DVR(T,L)) were calculated nonparametricaly from data collected for 12 years (1980-91)on a timothy 1st crop sward that was renovated at 3 years interval. DVR(T, L)=DVR(T)+DVR(L) (1) Σ^^<D_k>__<i=1>DVR(T_i, L_i) = 1 (2) where D_k is number of days from sprouting date to heading date. The error in predicting heading date was smaller when both daily mean air temperature (DMT) and day length were used than when DMT was used alone. Better prediction was obtained when the calculation was started at sprouting began than at the date that snow cover disappeared. 2) DMTs in each 1km^2 area were estimated from DMTs at surrounding national observatory (AMeDAS station) and normal DMTs obtained from a national meteorological data bank. The errors in estimating DMTs increased with altitudes. Because most grasslands of the district located at low altitudes, the accuracy of estimated DMTs was considered satisfactory for predicting the heading date of the timothy cultivar studied. 3) A raster map of predicted heading dates for timothy in the Konsen District was drawn for 1992, using estimated DMTs and DVR (T, L) derived from equation (1) and (2). Because we could not know the sprouting date of timothy in each 1km^2 area in the Konsen district, we started the prediction calculation on April 18, which was the observed sprouting date at Konsen Agricultural Experiment Station. Difference of starting date did not appreciably affect the predicted heading date. Predicted heading dates calculated by the proposed method need to be compared with actual heading dates in the field.

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In order to clarify how much intraspecific variation in competitive ability exist in single grass species and which traits are responsible for it, we compared competitive ability of eighteen cultivars of D. glomerata when combined with weakly and strongly competitive cultivars of tall fescue (Festuca arundinacea Schreb.) for a period of two years under fertile soil conditions in experimental fields. Shoot and root morphological traits of each cultivar were also measured under pot conditions. Relative competitive ability was assessed by aggressivity, 1/2 (relative yield of focal species-relative yield of neighbouring species). The results obtained were as follows : (1) There were large differences in competitive ability between cultivars in both D. glomerata and F. arundinacea. The difference was more apparent in the second year than in the first year. (2) For D. glomerata, competitive ability in the first year was correlated only with the seedling emergence time. In the second year, most of the variation in competitive ability between cultivars was explained by shoot and root morphological traits. Competitive ability correlated positively with root DW, mean tiller weight and mean root weight. (3) For F. arundinacea, the strongly competitive cultivar had larger seeds, faster seedling emergence, larger root weight but smaller shoot DW than the weakly competitive cultivar.

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Characterization of forage biomass on pastures is complicated by both temporal and spatial variability that result from variation in vegetation patch sizes. These factors, along with topography, kind of animal, fence location, salt placement, and water location, result in non-uniform grazing by animals. Currently accepted methods for biomass estimation of herbaceous standing crop assume a normal distribution. This assumption may not be tenable, because the probability density function for biomass changes as defoliation (grazing) occurs. In this study, the three-parameter Weibull distribution was evaluated and compared to the normal for modeling the distribution of Agropyron cristatum biomass as a function of grazing intensity and time. Weibull parameters, estimated using probability weighted moments (PWM), described all 12 observed biomass distributions at the α=0.05 level of significance based on the Kolmogorov goodness-of-fit test. In contrast, the normal distribution was only able to describe 75% of the observed biomass distributions.

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A laboratory experiment was carried out to investigate the relationship between uprooting strength and root length in seminal root of 8 temperate grass species (14 varieties) with emerged seedlings when sown on the surface of yellow paddy field soil and Kuroboku soil under 25℃ and 100% RH. The volume of clod of soil particles, bound by both root and coleorhiza hairs, was measured with a few grass species. The figures were related to the differences in anchoring force of the seedling roots depending on grass species and the soil types. 1. The elongation of the seminal root penetrated into yellow paddy field soil was 4-6 mm per day in orchardgrass, perennial ryegrass and Italian ryegrass as compared to 2-3 mm in tall fescue and smooth bromegrass. All these species were similar within the range of 8-10 g in uprooting strength. Seminal root of Kentucky bluegrass and timothy grew to 2 mm in length and with ca. 4 g of the uprooting strength. 2. The uprooting strength of grass seedlings was closely related to the length of penetrating seminal root (r=0.757, p<0.01). 3. Although seminal root of tall fescue grew longer and grasped larger clod in Kuroboku soil than in yellow paddy field soil, it showed similar to or slightly lower uprooting strength than those in the latter soil. 4. The volume of soil clod and uprooting strength of surface-sown grass seedlings were related to penetrated root length. Three milimeter of seminal root length had an uprooting strength three times as strong as the adhering strength of coleorhiza hairs.

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Clone structure of a perennial ryegrass (Lolium perenne L., tetraploid cv. Friend) population was studied using starch gel electrophoresis for a 4-yr-old sward. The sward consisted mosaicly of two patch types, one with distinct stands of L. perenne and. one with dense clumps of that. In the patch with distinct stands, two 1×1 m^2 quadrats were placed and determined for the phenotypes or genotypes of all stands by two enzyme systems (PGI and GOT). Of 54 genets detected over two quadrats, nine ones contained two or more ramets which were distributed closely each other. In the densely aggregated patch where it was hard to distinguish ramets, five 25×40 cm^2 quadrats were excavated intact and mapped for the position of the clumps (i. e. ramet aggregation). Electrophoretic analysis showed that the genets tend to form the discrete spatial units, with high density of genet (ca. 132 genets m^<-2>). Analysis of the genet composition within 10 large stands specified that six ones consisted of two or more genets. These results suggest that this L. perenne population may be maintained partly by aerial tillering, and that intermixed genets may occur frequently.

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We examined the seedling recruitment of a perennial grass, Phleum pratense, in a simulated sward to test the idea that the occurrence of seedling recruitment is possible for perennial grasses under the condition received with a frequent removal of the above-ground vegetation after their seed rain. Establishment and demography of P. pratense seedlings were monitored during April to December 1984 (to March 1985 for two quadrats) in the sward. The seedlings established frequently and played a role as important members of the population. Sixty seedlings (58.8% of overall seedlings monitored) survived to December and they as a pool increased gradually its dry matter weight up to 13.9% of the overall dry weight of the P. pratense population. Three plants within the two quadrats which recruited from seedlings were in heading stage in March 1985. Many small-sized openings, which had been created from plant-plant competition, occurred within the quadrats. Most of openings were, however, unutilized by seedlings during the study period. Survivorship and size of seedlings were partly dependent on the micro-scale extent of the coverage by the surrounding adult plants. These facts strongly suggested that there is a condition under which seed reproduction plays an important role in maintaining the population size of perennial grasses, and the condition in question is one with a frequent removal of the above-ground vegetation after the seed rain.

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