It is intended to elucidate the interaction between photosynthesis and nitrogen metabolism in C_3 and C_4 plants. In the present study, the effects of nitrogen nutrition on photosynthetic rates (P_0), RuBP- and PEP-carboxylase activities and photorespiration rates were examined. Using newly expanded leaves of C_3 and C_4 plants grown at graded nitrogen level or at certain nitrogen level with ammonium or nitrate in culture solutions, their rates of apparent photosynthesis (P_0), nitrogen contents, RuBP- and PEP-carboxylase activities, CO_2 compensation points and the rates of photorespiration and dark respiration were measured. The results obtained were as follows: 1. Total nitrogen contents were highly correlated to P_0 of forage leaves. Both P_0 and Po per unit nitrogen increment were significantly higher in C_4 plants than in C_3 plants. 2. Reasons why P_0 of C_4 plants was enhanced more than that of C_3 plants with an increase of nitrogen content in leaves were (a) C_4 plants had higher proportion of soluble protein fraction to the total nitrogen compounds, (b) Activities of enzymes related to C_4 cycle remarkably increased with an increase of nitrogen content in leaves. 3. No significant differences were observed in P_0 of C_3 and C_4 plants between forms of nitrogen source. In C_3 plants, the rate of photorespiration, as determined by the rate of CO_2 released in CO_2 free air, of plants supplied with nitrate was approximately 30 percent lower than that of those supplied with ammonium. However, the rate of true photosynthesis was also lower in plants supplied with nitrate than with ammonium.

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To clarify the factors determining the number of heads per plant in relation to the degree of floral-induction in orchardgrass, the influence of floral-induction of main stem on heading behaviour of lateral tiller buds was investigated. Three clones of A-101 (early), L-102 (late) and EV72-7 (extremely early) were used. The details of growing procedure of materials had been described in the previous report of this series (III. Influence of fertilizer application on responsiveness to floral-induction treatment in aged plant. Bull. Natl Grassl. Inst. 17, 68-75.). Individual tillers separated from each clone were subjected to floral-induction treatment of 10℃ and 12-hour day-length for 7, 10, 14 and 21 days. After the treatment, they were grown under continuous light in a warm (25℃ day/15℃ night) glasshouse. Then the heading behaviour of the whole plants including lateral tillers, almost all of which left in the leaf sheaths of main stem during the treatment, was observed with special consideration to the position of nodes on main stem and the order of tillering (Figs.1 and 2). The periods of treatment required for the heading of main stem were 7 days in both of L-102 and EV72-7, and 14 days in A-101. When the period of treatment was not long enough to cause the heading of main stem, all the lateral tillers did not reach heading in all the clones tested. As the period of treatment became longer, the number of heads per plant became larger in each clone tested. But the tendency in the increase of the number of heads with lengthening the period of treatment was markedly different from clone to clone (Table 1). When the treatment was made for 21 days, only a part of the primary tillers reached heading and all the secondary tillers remained at vegetative stage in A-101 and L-102. In EV72-7, in contrast with the above two clones, all the primary tillers and about half of the secondary tillers reached heading and some of the tertiary tillers formed inflorescence primordia on their apices. As the position of nodes of main stem became lower, the lateral tillers of respective order reached heading earlier in each clone tested. The some uppermost primary tillers in A-101 and L-102, however, formed inflorescence primordia on their apices even though the immediately lower ones remained at vegetative stage. On the other hand, the heading was observed later in the lateral tillers of higher order than in those of lower order regardless of the clones tested (Table 2 to 5). From the above results, it was inferred that the differences among clones in the number of heads per plant at respective treatment-periods were attribuable to the following two factors ; (i) the degree of floral-induction of main stem, (ii) the dependence of lateral tillers on main stem in heading behaviour.

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This experiment was carried out to clarify the difference of morphological characteristics between survivor populations of orchardgrass, variety Masshardy in permanent meadow and pasture. The grasslands were managed as follows ; the meadow was harvested two times at July and September, and the pasture was grazed fifteen times by cattle from May to October every year in a rotational grazing system. Survivor plants of orchardgrass were collected from both ten years old meadow and pasture, and were grown under spaced plant conditions. The investigations were made on some morphological characters at full heading time during the second year after transplanting. It was found that there were differences in some characters between two survivor populations, however these differences were considered very small. The most noticeable difference was detected on the growth habit, and the population obtained from meadow was more high and erect plant type than those of pasture. The variance of plant height and flag leaf height on tiller was less in the population of meadow, and the variance of tiller angle decreased significantly in the pasture population. The results of this experiment indicate that selection has occured within the variety over a long period due to different farm practices.

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This experiment was carried out in order to know the relationship between the efficiency of solar energy utilization and the dry matter production in orchardgrass. The varieties examined were Pennlate, Latar, Hokkai-1, Potomac, Chinook, Kitamidori, Daprime, S143, Apanui and Frode. The main results obtained were summarized as follows :1. The efficiency of solar energy utilization (Eu) can be expressed in the following formula ; Eu=Efficiency of intercepting energy (Ei)×Efficiency of energy conversion (Ec)=Ei×Ec 2. It was found that the relationship between Ei and leaf area (F) can be expressed by the following equation (Fig.1) ; Ei=1-exp (-K'・F) K': The light diminution coefficient (Regression coefficient between increase in leaf area and degrease in relative light intensity at ground level). 3. Eu averaged through the whole examined period was different among varieties. It was in the range of 1.82% (Pennlate) to 1.00% (S143), and the mean value of 10 varieties was 1.47% (Table 1). 4. Eu of the tiller weight type varieties and the medium type varieties were increased up to LAI 10 to 11, but Eu of the tiller number type varieties reached the maximum at approximate LAI 7. This fact suggests that the tiller number type varieties may be more productive under frequent cutting (Fig.2). 5. Highly significant correlation was found between the dry matter production and Eu during the growing season. Eu indicated significant correlation with both Ei and Ec for the earlier stage of the season, but only Ec for the latter half. E_i was related closely with LAI, and Ec was related with specific leaf weight (SLW) and K' (Fig.3, Fig.4, Table 2). 6. To clarify the relative contribution of LAI, SLW and K' to Eu, the multiple regression analysis was applied. Eighty six to 93% of the variation among varieties were accounted for by LAI, SLW and K'. The ratios of standard partial regression coefficients of 3 characters were 60:30:10 at the early stage of growth, but 37:43:20 at the late stage of growth

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In order to obtain basic data for clarifying energy passage in a grassland ecosystem, determination of calorific values were carried out on several species under various conditions. Furthermore, energy storage in plant materials on a unit land area were calculated to ascertain the dynamics of energy mass in a pasture system and to compare variations between different pasture systems. The results obtained are as follows ; 1) Yearly averaged calorific value on a DW g basis was 4, 301 cal for orchardgrass in a cutting system, and 4, 375 cal (light grazing plot) and 4, 369 cal (heavy grazing plot) for a mixed community of grasses and legumes in a grazing system. 2) Leaf blade possessed the highest energy value among the components of orchardgrass. 3) Calorific values among six dominant species examined in grazing grassland show decreasing tendencies in a Zoysia japonica>white clover≒Kentucky bluegrass≒Sasa nipponica>red top≒orchardgrass>tall fescue sequence. 4) Estimated energy storage on a unitgro und area basis was high in grazing pasture (ranging from 4, 100 to 7, 600Kcal/m^2 for the light grazing plots, from 2, 800 to 6, 000Kcal/m^2 for the heavy grazing plots), however, values for an orchardgrass cutting field ranged from 1, 900 to 4, 100Kcal/m^2.

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This experiment was carried out to investigate the variation of seasonal growth pattern among the natural populations of timothy (Phleum pratense L.). Seven and ten populations which were collected from the northern and southern areas of Hokkaido respectively, were grown in the experimental field at Sapporo. In the fourth year after seeding, from the restarting of growth in early spring to seed maturing in mid-summer, two vigorous tillers on each of ten plants per population were cut off at one week interval at the soil surface and their dry weight was measured. Logistic equation, w=A/[1+κ・exp (-λt)], was fitted to a series of observed values of weight of a tiller between May 12 and July 28 and three parameters characterizing growth pattern, intrinsic growth rate (λ), maximum growth rate (MGR) and the time at which growth rate reaches the maximum (T at MGR), were estimated in each population (Table 1). The MGR and λ tended to be larger in the southern group than in the northern group. Furthermore, except for one population of the southern group, all populations of that group reached the maximum growth rate earlier than any population of the northern group. The growth rate approximated by logistic equation was higher in the southern group during the early half of the growing period, but in the northern group during the late half of the growing period (Fig.3). From May 12 to May 19, leaf weight increased in the southern group but did not in the northern group (Fig.1) and thus their relative growth rates differed significantly in this period (Table 3, Fig.4). Allometry coefficient of stem and leaf development was not different among the populations and stem weight increased in proportion to about a square of leaf weight (Fig.5). It was suggested by these results that the differences in seasonal growth pattern of tiller between northern and southern populations were largely due to the time lag of developmental stage resulting from the difference in the time of leaf growth commencement under low temperature conditions in early spring.

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Tropical pasture legume Siratro (M. atropurpureum cv. Siratro), which has shown greater potential in dry matter production in South-Western Islands of Japan, was grown in pure stands and in mixed stands with Rhodesgrass (C. gayana cv. Pioneer) and were compared with Rhodesgrass grown in pure stands applied with four levels of nitrogen regarding in vitro dry matter digestibility (IVDMD) of plant top, digestibile dry matter (DDM) yield, nitrogen concentration in plant top, and nitrogen yield. IVDMD which was higher in Siratro than in Rhodesgrass was decreased in both species during the periods of higher temperature and fewer rain fall. Annual yields of DDM amounted to 660-790kg/10a in pure stands of Siratro and 550〜670kg/10a in mixed stands of Siratro and Rhodesgrass in the second year, being equivalent to the yields in pure stands of rhodesgrass applicated with 24〜34kg N/10a in the pure stands. Nitrogen concentration in plant tops was also higher in Siratro than in Rhodesgrass showing lower values during the periods of higher temperature. Annual yields of N amounted to 38〜42kg/10a in pure stands of Siratro and 24〜31kg/10a in mixed stands of Siratro and Rhodesgrass in the second year, being equivalent to the yields in pure Rhodesgrass applicated with 45〜78kg N/10a in the pure stands. With these results above, Siratro appeared as a promised legume for growing in South-Western Islands of Japan.

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A sand culture pot experiment investigated effects of harvesting intensities on vegetative regrowth, nodule development and effeciency of N_2-fixation in Desmodium intortum cv. Greenleaf. Expansion of leaf area and dry matter of plant top and root systems increased at higher clipping height and more so when leaves remained on the stubble were not removed. Nodule development was affected by harvesting treatments in the same manner with plant dry weight, but their recovery rates were faster than plant dry weights in all treatments. Rates of acetylene reduction also changed in the same manner with plant dry weight. Rates of hydrogen evolution and efficiencies of N_2-fixation have dropped for a short period after harvest and increased again, but a definite trend was not observed in both parameters among harvesting treatments. A comparison of the present data with other reports suggested that Greenleaf desmodium tended to persist in lower clipping heights as compared to Leucaena and Siratro. The data also suggested that harvesting treatment affected efficiency of N_2-fixation for long periods.

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In the present study, Job's-tear millet as a forage was cutivated in order to clarify the herbage productivity and the suitablity in chemical composition. Fodder Job's-tear millet, cultivar Okayama Zairai, was sown on May 20 in 1982, at 0.8kg seed with drilling per are in a well-draind paddy field. The amounts of nitrogen, phosphorus and potassium applied before sowing and after the first cropping were each 2.0 and 1.5kg per are as compound fertilizer (15-15-15). Watering was practiced by intermittent irrigation thoughout seasons from the five-leaf stage. Fodder Job's-tear millet was cut at the heading stage (21/July) for the first cropping and at the milk-ripe stage (22/Sept.) for the second cropping. Investigation was performed periodically at intervals of one week during growing seasons. The following results were obtained: 1) Fodder Job's-tear millet was grown vigorously under submerged paddy condition. The total yield was 1, 029kg per are in green herbage and 192kg in dry matter. 2) The range of crop growth rate (CGR) during first cropping was 17〜37DM・g^<-1>・m^<-2>・day. The optimum leaf area index was estimated about 6.8 from the relation between CGR and mean leaf area index (Fig.1). 3) In the chemical composition, the contents of crude protein, crude fat, NFE, crude fiber and crude ash were 11.1, 3.7, 40.2, 32.0 and 13.0% at the first cropping, and 8.3, 2.5, 43.4, 33.8 and 12.0% at the second cropping, respectively. The contents of calcium, phosphorus, magnesium and potassium were 0.28, 0.16, 0.17 and 3.02% at the first cropping, and 0.38, 0.13, 0.14 and 2.28% at the second cropping, respectively. The contents (%) of calcium, phosphorus, magnesium and potassium varied during herbage seasons, in the range from 0.38 to 0.24, 0.25 to 0.11, 0.29 to 0.13 and 4.33 to 1.88 respectively. The contents of phosphorus, magnesium and potassium in the herbage decreased slowly with advancing maturity, but that of calcium increased. 4) It is judged from the above results that fodder Job's-tear millet showed a high herbage productivity under a submerged paddy field, but its contents of inorganic elements such as calcium, phosphorus and magnesium are below the mineral requirment for milking cow.

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This experiment was undertaken to clarify the silage quality and the feeding value of soiling crop and silage in Job's-tear millet. Fodder Job's-tear millet which have mentioned in the previous paper was harvested at the heading and the flowering stage for soiling, and at the heading and the milk-ripe stage for silage in the first and the second cropping, respectively. Each digestibility of chemical composition was estimated by the conventional collection trials with sheep. The results are summarized as follows: 1) Each silage quality which were prepared at the heading and the milk-ripe stage was ranked "good" or "excellent" grade without reference to the first or the second cropping. 2) Each digestibility of chemical composition except crude fat in soiling crops and silages decreased with advancing maturity. The digestibility of crude protein in silages was higher in the first cropping than in the second one. 3) In the digestible nutrients of soiling crop, each DCP and TDN content of the first and second cropping was 7.7 and 7.2%, and 62.9 and 60.0% at the heading stage, and 6.4 and 5.8%, 55.6 and 55.0% at the flowering stage, respectively. On the other hand, each DCP and TDN content of silages at the heading stage was 8.0 and 59.6% in the first cropping, and 6.8 and 58.1% in the second one. Also, each DCP and TDN content at the milkripe stage was 6.4 and 53.4% in first cropping, and 5.4 and 53.4% in the second one, respectively. Therefore, DCP and TDN contents in soiling crops and silages decreased with advancing maturity. 4) Each range of NDF, ADF, AD-lignin and silica contents in soiling crops was 65.3 to 71.4%, 40.3 to 49.3%, 6.1 to 10.1% and 4.9 to 10.2%, respectively and increased with advancing maturity. Each digestibility of NDF and ADF in soiling crops and silages decreased rapidly with advancing maturity.

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In order to investigate the effect of addition of glucose at ensiling and pre-wilting to medium moisture level on the disappearance of nitrate and the bacteriological changes with special reference to the changes in nitrate reducing bacteria during ensilage, Italian ryegrass containing large amounts of nitrate was ensiled in laboratory silos. In each experiment, the silos were kept at 28℃ in the incubator in triplicate and opened at 3, 7, 15 and 60 days after ensiling. The results obtained from this experiment were as follows: 1. The silages without glucose addition (control) were of extremely poor quality, rate of nitrate disappearance being from 97.0 to 100%. The glucose-added silages and the medium moisture silages were of good and medium quality, respectively. The rate of nitrate disappearance in glucoseadded silages was 4.4 to 28.2%, but that in medium moisture silages was different in two experiments, being 100 and 38.2%. 2. In the first few days after ensiling, a rapid decrease of nitrate reducing bacteria occurred in all silages, but the extent of the declining was in different among three treatments. Counts of nitrate reducing bacteria in the medium moisture silages were largest and those of the glucose-added silages were smallest. 3. In the glucose-added silages, rapid growth of lactic acid bacteria occurred, the counts reaching to a peak at 3 to 15 days after ensiling. The counts of lactic acid bacteria in the control silages at 60 days considerably decreased and the level was lower than those in medium moisture silages.

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This paper described the palatability of orchardgrass which was cultivated with the different levels and types of nitrogen fertilizer under the condition shading 50% of solar radiation with cheese-cloth. Fertilization was designed as follows, at the experiment of the different nitrogen levels, 0.2 and 1, 2kg of nitrogen/are were applied with urea at each of four dressings in a year, and at the experiment of the different types of nitrogen fertilizer, 0.4kg of nitrogen/are was likewise given with urea, ammonium sulfate or ammonium nitrate. Palatability was evaluated with a two-choice preference method in cut-feeding tests using sheep, and chemical composition of these forages was compared with each other. The palatability of orchardgrass varied considerably by means of application rates or types of nitrogen fertilizer. The orchardgrass applied low level of nitrogen (0.2kg/are) showed higher palatability than the one with high level of nitrogen (1.2kg/are). And the orchardgrass applied ammonium sulfate showed higher palatability than the ones applied urea or ammonium nitrate. In general, the forage plants of high palatability tended to accumulated relatively large amounts of 85% ethanol soluble- and total soluble-carbohydrate, and to contain far less total nitrogen and nitrate nitrogen than the forage plants of low palatability. It appears that the nitrate nitrogen is particularly an important substance affecting the palatability of shaded forage plants, because the difference above 0.23 unit of nitrate nitrogen concentration in the tested forage plants caused sheep to discriminate palatable and unpalatable ones, whereas no any distinction on palatability occured in the cases of below 0.11 unit of them.

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