THE EFFECT OF CUTTING HEIGHT AND NITROGEN LEVEL ON THE YIELD, IN VITRO DIGESTIBILITY AND CHEMICAL COMPOSITION OF ITALIAN RYEGRASS SWARDS

Three cutting heights, 2±5, 7±6 and 12±7 cm (1, 2±5 and 5 in.) and three levels of fertilizer N, 168, 280 and 392 kg N/ha (150, 250 and 350 Ib N/ac) were imposed on a sward of Italian ryegrass (Lolium multiflorum) cv. Irish. Lowering the cutting height and increasing the level of applied N increased the yield of herhage DM. Increasing the level of applied N had a greater effect on the chemical composition of the herbage than altering the cutting height     

THE EFFECTS OF CHANGES IN HEIGHTS OF CUTTING AND GROWTH ON THE DIGESTIBLE ORGANIC MATTER PRODUCTION AND BOTANICAL COMPOSITION OF PERENNIAL PASTURE

Irrigated plots of a mixed sward of Lolium perenne, Paspalum dilatatum, Bromus unioloides, Dactylis glomerata and Trifolium repens were used in 2 experiments during 4 years. In the first experiment, die treatments comprised factorial combinations of heights of cutting of 3, 6 and 10 cm (1.2, 2.4 and 3.9 in.) above ground level, and heights of growth of 5, 13 and 20 cm (20, 5.1 and 8.0 in.) above the height of cutting. In the second experiment, 8 combinations of dose (3 cm or 1.2 in.) or lax (10 cm or 3.9 in.) cutting were applied at various times during each year. In the first experiment, DM production for cutting heights of 3, 6 and 10 cm was 50, 44 and 43 t/ha (198,17.5 and 171 ton/ac), respectively; the DOM production was 37, 32 and 32 t/ha (147, 12.7 and 12.7 ton/ac). DM production for growth heights of 5, 13 and 20 cm was 45, 46 and 48 t/ha (17.9, 183 and 191 ton/ac), respectively. DOM production, 34 t/ha (13.5 ton/ac), was not affected by height of growth. Percentages of protein (26, 22 and 20) and DOM (76, 72 and 71) declined as the height of growth was increased; but cutting height produced no significant effects in them. As cutting height was increased the percentage of clover declined (40, 31 and 23) and that of grasses increased (52, 66 and 72); diere were smaller changes with changes in height of growth. Hie second experiment showed that the difference between close and lax cutting became significant only when lax cutting was applied for at least half of the cuts each year. DM production was similar for treatments witii the same number of close or lax cuts, regardless of the time of year at which the two heights of cutting were applied.     

THE RESPONSE OF S24 PERENNIAL RYEGRASS SWARDS TO IRRIGATION

The response of established perennial ryegrass swards to irrigation was compared over 2 years. The swards received 250 (N₁) or 500 kg N/ha (N₂) and were cut 4 times each year. Water was applied in 5 irrigation treatments according to the potential soil water deficit: the soil was partially, or fully returned to field capacity after cutting; returned to field capacity after cutting and then whenever a 25 mm deficit arose; irrigated with 25 mm water whenever a 25 mm deficit arose independently of cutting; or irrigated at minimum intervals of 14 days, provided that the deficit was then at least 50 mm. There was little effect of irrigation on yield from the first cut in late May. Frequent irrigation gave the greatest increase in total annual yield (3.1 t/ha), hut partial irrigation after cutting was most efficient in use of water and equipment, provided that drought conditions were avoided. High concentrations of N in the herbage were associated with low DM yields, hut more N (percentage N DM yield) was recovered from the irrigated than from the unirrigated swards. More N was recovered than was applied in the N₁ treatment; less was recovered than was applied in N₂. In the N₁ treatment the nitrate concentration was <500 ppm hut it was 1000–4000 ppm in N₂. There was no consistent effect of irrigation on nitrate or K concentration.     

THE EFFECT OF DEFOLIATION ON THE SEED-PRODUCING CAPACITY OF BRED VARIETIES OF GRASSES

Leafy grass varieties S24 perennial ryegrass, S26 cocksfoot, S215 meadow fescue and S51 timothy were cut in October and at various growth stages in spring; S53 meadow fescue was grazed at similar periods. Sub-plots were given different applications of N. The control plots had similar manurial treatments but were not defoliated. The seed yield of S24 following October cutting was significantly lower than the control in the first harvest year and significantly higher in the second; the mean yields over 2 years, as a result of cutting at this stage and before ear formation in March, were very similar to those of the control treatment. The mean yields from 3 harvest years for S26, S215 and S51 were generally improved by cutting in October and before ear formation, but cutting after ear formation reduced the number of heads and the seed yields. Extra N applied in conjunction with the defoliation had no significant effect on the number of seed heads or on seed yield. Double grazing of S53 in Sept. and Dec. reduced significantly its seed production in both harvest years. Application of N in spring gave a greater response than a similar application in autumn.     

THE EFFECT OF CUTTING AND NITROGEN TREATMENTS ON YIELD, PROTEIN CONTENT AND CERTAIN MORPHOLOGICAL CHARACTERISTICS OF TIMOTHY AND SMOOTH BROMEGRASS

Timothy and bromegrass were studied in pure sowings in a glasshouse, and each in a mixture with lucerne, dominated by the grass–fraction in the first crop year, in the field. In the glasshouse both species were cut 3, 5, or 6 times at a 2–in. and 6 times at a 3/4–in. stubble height. In timothy, cutting 6 times gave lower DM but higher protein yields than less frequent cutting. In bromegrass close cutting gave higher DM yields than lax cutting. The following results applied to both species: root weight decreased with increasing severity of defoliation, final tiller density was very low under close cutting, and a complete application of N at the time of sowing was superior to a split application.
In the field, the first cut was taken on 5 dates at intervals of 1 week, the second cut 6 or 8 weeks after the first cut, and the third cut 7 weeks after the second cut (for bromegrass mixture only). DM yield was generally the higher the later the first cut was taken and the longer the subsequent rest period. However, the opposite applied for best sustainment of yield. The 1 1/2–in. stubble treatments outyielded the 3 1/2–in. treatments. Generally, production of CP was influenced more by DM yield than by % content. Reduced removal of tiller primordia in the second cut led to higher third–cut yields, but at the cost of total yield. Difficulties in the control of shoot apex removal encountered in both glasshouse and field are discussed.     

THE RESPONSE OF S24 PERENNIAL RYEGRASS SWARDS TO IRRIGATION

Variations in soil-water and plant-water status were examined in swards of perennial ryegrass over a period of 2 years. Unirrigatcd swards were compared with swards partially irrigated after cutting and with swards fully irrigated after cutting and then again whenever a 25 mm potential soil water deficit (SWD) arose. Two levels of N were applied to the swards (N_j= 250 kg N/ha, N_T= 500 kg N/ha in each year). Frequent measurement of the water in the soil profiles beneath these swards with a neutron soil-moisture probe, enabled comparisons to be made of the actual SWD with the potential SWD on which the irrigation regimes were based. In the unirrigated swards the actual rate of water use by the swards fell below the potential rate of use at a potential SWD of approximately 50 mm. On the other hand, frequent irrigation at a potential SWD of 25 mm often failed to maintain the actual deficit within 25 mm of field capacity. Under both the unirrigated and the partially irrigated swards, greater use was made of the soil water below 30 cm depth in the N₂ treatment than in the N₁. The pressure-chamber technique proved particu larly suitable for measuring the variation in leaf-water potential (LWP) of grasses in the field. LWP was highest (least negative) at dawn and, provided that no dew was present on the leaves, was related to the actual SWD. There was no direct relationship between the daily minimum value of LWP and SWD, the former being determined largely by evaporative demand. However, LWP in frequently irrigated swards rarely fell below –15 atm, whereas much lower values were recorded in swards on drier soils. It is suggested that the effect of irrigation on plant-water stress may be most readily assessed from the LWP at dawn.     

THE EFFECT OF CUTTING HEIGHT AND CUTTING FREQUENCY ON THE PRODUCTIVITY OF AN ITALIAN RYEGRASS SWARD

Three cutting heights, 1, 3 and 5 in. (2.5, 7.6 and 12.7 cm), and three cutting frequencies, 3, 6 and 10 weeks, were imposed on a pure sward of Italian ryegrass (Lolium multiflorum) cv. Irish. Lowering the cutting height increased the yield of DM, digestible DM, crude protein and crude fibre. Increasing the interval between cuts increased the yield of DM, digestible DM and crude fibre. The results are discussed in relation to other research findings and to the management of short-term leys of Italian ryegrass.     

THE EFFECT OF FERTILIZER NITROGEN AND FREQUENCY OF DEFOLIATION ON YIELD OF GRASSLAND HERBAGE

The effects of 4 levels of applied nitrogen, ranging from nil to a maximum of 417 lb N/ acre/annum, in all combinations with 3 frequencies of defoliation, ranging from 2 to a maximum of 10 cuts per annum, on herbage production from a perennial ryegrass/ timothy/meadow fescue/white clover sward were measured. These treatments were operative for 2J years, and in a subsequent year the residual effect of cutting frequency was tested. Dry-matter yields of total herbage and of the clover fraction are quoted, together with N yields of total herbage. Yield response to N was higher than in some other experiments in the U. K. Cutting frequency had a very large effect and, in general, the longer the interval between cuts, the higher was the dry-matter (though not the N) yield. There was a marked interaction between cutting frequency and level of N: at the high cutting frequency, dry-matter yield increased linearly with increasing level of N; at the medium frequency, response tended to fall off at the highest level of N; at the low frequency, yield declined with increasing level of N beyond 139 lb N per acre per anum.     

REGROWTH OF S24 RYEGRASS AND ITS RELATION TO YIELD MEASUREMENT OF GRAZED SWARDS

The re growth of S24 ryegrass (Lolium perenne L.) plants was studied during 4 days, following defoliation to stuhble heights of 2, 4, 6, 8, 10 and 12 cm. The weight of regrowth produced by plants cut to 6-cm stubhie heights and higher was equal to the weight increment of uncut plants above the same heights. During the 4 days the weight of the stubble segment between 0 and 2 cm decreased in plants cut to 2 or 4 cm, but was maintained or increased in plants cut to 6 cm or higher. Weights of the 2- to 4- to 6-cm stubble segments were just maintained at the lower cutting heights, but were increased by the same amount as in uncut plants at the highest cutting height. The percentage of water-soluble carbohydrates in all stubble segments decreased following defoliation, but the percentage of N did not change. Root weights were either maintained or increased, depending on the severity of cutting. In relation to grazing experiments, it is pointed out that where DM disappearance is taken as the difference hetween yield on a protected site and residue on a grazed site, too close cutting of the sample areas will give an overestimate of yield.     

THE EFFECT OF HEIGHT OF CUTTING ON THE SUBSEQUENT GROWTH AND YIELD OF LUCERNE

Three experiments designed to test the effect of height of cutting of lucerne on subsequent yield are described and the results discussed. Extremely low cutting, at ground level, can cause the death of individual lucerne plants, but if such extreme cutting is avoided there is no evidence to show any advantage in leaving a long stubble. In fact, in a sward, the lower the cutting the greater is the yield to be expected.     

A COMPARISON OF THE GROWTH OF A CUT SWARD WITH THAT OF GRAZED SWARDS, USING A TECHNIQUE TO ELIMINATE FOULING AND TREADING

Plots of S24 perennial ryegrass were grazed fire times by sheep to stubble heights of 10–15 cm (treatment L), 5 cm (M) and 2 cm (S), other plots were cut (C) at approximately the same height as in M. the quantity of digestible organic matter (DOM) harvested by cutting at 5 cm was not significantly different from that harvested by grazing at the same average height there were only minor differences between grazing treatments in the amounts of DOM harvested, but the number of hours for which the sheep had to be maintained on the plots in order to graze the swards to the required heights increased 4-fold between treatments L and S. the results are discussed in relation to the total DOM harvested in each treatment.     

THE EFFECTS OF TYPE OF CUTTER AND HEIGHT OF CUTTING ON THE RECOVERY OF FOUR GRASS VARIETIES

S23 and S24 Lolium perenne and S37 and S143 Dactylis glomerata were cut to heights of 1 1/2 and 4 1/2 in. in a replicated experiment, using: a flail harvester, a reciprocating mower, and a reciprocating mower followed by a flail harvester to collect the wilted grass.
At the short cutting height there was a marked depression of regrowth of all grasses following the use of the flail harvester (P<0.01), compared with the other mowing treatments. No such effect was observed at the higher level of cutting. Close cutting with a flail forage harvester was shown to be detrimental to regrowth, but the reasons for this effect are not clear.     

The effect of height and frequency of mowing on the yield and composition of perennial ryegrass—white clover swards in the autumn to spring period

Ninety-six plots (3 × 2 m) of well-established perennial rye grass/white clover pasture were mown to heights of 2·7 (Low) or 3·96 (High) cm (rising plate meter) at 14-, 28-, 84- or 112-d intervals in autumn-winter. A 7-, 14- and 28-d mowing interval was superimposed in spring on each autumn–winter mowing interval treatment with the low and high mowing heights altered to 2·92 and 4·80 cm, respectively.
With the low cutting height, accumulated herbage DM was more than doubled (1806 ± 79 kg DM ha^-1) compared to a 'high' (754 ± 49 kg DM ha^-1) cutting height in autumn–winter and this was due to increased harvesting efficiency rather than growth as estimated by leaf extension. Although defoliation interval had no effect on DM yield, the grass component increased and clover decreased. The composition effect carried over into spring. On average, 3·5 tillers were produced over winter for each ryegrass tiller present in autumn and tiller densities were higher in spring. Tillers produced over autumn–winter contributed more than 60% of ryegrass growth by early spring.
In early spring (16–30 September), the low cutting height increased herbage DM yield, in mid-spring (1–14 October) it reduced DM yields particularly in combination with short defoliation intervals, while in late spring (14 October to 11 November) cutting height had no effect on DM yields.
Over the entire spring period there was a very marked effect of defoliation interval on DM yields.     

SOME EFFECTS OF GRAZING MANAGEMENT ON THE YIELD AND ITS COMPONENTS OF SOME PASTURE GRASSES

A study was made to determine the effects of grazing to a height of 1 in. when the swards reached heights of 3 and 9 in. on the dry matter production, LAI, tillering and rate of leaf production of new and old tillers in the spring–summer and autumn–winter seasons of 3 pasture species growing in association with white and red clovers. In both seasons the herbage yield under 9–1 management was higher than that under 3–1 and was significantly greater in the spring-summer season. Differences in DM production between cocksfoot, tall fescue and Ariki ryegrass failed to reach significance.
Light utilization under the 2 management systems was considered to be inefficient. In the autumn-winter period there was a linear relationship between the LAI and DM production in all treatments.
The rate of leaf production per tiller was significantly higher in cocksfoot than in ryegrass and tall fescue in both seasons.
New tillers had a significantly higher rate of leaf production than old tillers in the spring-summer period, but not in autumn-winter. The numbers of grass tillers and rooted nodes of clover were significantly higher under 3–1 than under 9–1 and were influenced by season.     

不同铲蔸深度对甘蔗根系形态和生理特性的影响

以云蔗07-2800为材料,在收获期设置4个不同铲蔸深度（5、0、-5、-10 cm）,研究不同铲蔸深度对甘蔗伸长期根系形态特征和生理特性的影响。结果表明：铲蔸深度对伸长期甘蔗生物量有极显著影响（P<0.01）。铲入地下5 cm处理甘蔗伸长期地上部生物量干重极显著高于其他处理,各处理间根冠比差异较大。在伸长期甘蔗总根长、根系总表面积和根系总体积均呈现增长趋势,且在伸长中期和后期,铲入地下5 cm处理的总根长、根系总表面积和根系总体积均极显著高于其他处理。同一时期各处理根系丙二醛（MDA）含量高低表现为5 cm>-5 cm>0 cm>-10 cm,根系超氧化物歧化酶（SOD）和过氧化物酶（POD）活性高低总体表现为伸长后期>伸长中期>伸长早期。根系超氧化物歧化酶（SOD）、过氧化物酶（POD）和硝酸还原酶（NR）酶活性高低均表现为5 cm<0 cm<-5 cm<-10 cm的趋势。蔗蔸铲入地下5 cm处理的甘蔗生物量最大,产量最高,说明该处理可有效促进宿根甘蔗根系生长、发育,增加深层根系总量,提高根系抗逆性生理指标含量与活性,提高甘蔗植株对水分、养分的利用效率,增产增效。在甘蔗机械化管理收获技术水平不断提高和宿根蔗年限不长的背景下,宿根蔗采用入土5 cm铲蔸作业,具有较好增产效果和大面积推广应用的前景。     

THE EFFECT OF CUTTING COCKSFOOT (DACTYLIS GLOMERATA L.) GROWN FOR PRODUCTION OF SEED

An experiment is described in which cocksfoot, grown for production of seed, was cut annually for 3 years in either autumn, winter or spring. No significant increases in yield of seed/ac were obtained from any treatment compared with an uncut control, and a cut in late April in one year seriously reduced the yield of seed. Additional N applied after a defoliation in October did not increase the yield of seed compared with that from plots which were cut at the same time but not fertilized. The production of tillers was not affected by cutting on any date. The percentage fertility of tillers was increased by cutting in the first year, when the number of tillers was smallest; the fertility was less consistently affected in the second year, and was generally unaffected in the third year. The weight of seed produced per ear was usually reduced by the cutting treatments. In the third year of the experiment it was shown that the penetration of light to the base of the shoots was increased substantially by defoliation, but it is deduced that maximum interception of light by the whole plant is more important for the production of seed than increasing by cutting that proportion which penetrates to the base of the plant.     

THE EFFECT OF DRILL WIDTH ON THE SEED PRODUCTIVITY OF LEAFY VARIFTIES OF THREE GRASS SPECIES

Three leafy grass varieties, S215 meadow fescue, S37 cocksfoot and S51 timothy. were subjected to four dril spacings of 6, 15, 24 and 36 in. under two levels of nitrogen application. Over three harvest years, meadow fescue gave better seed yields with 6- and 15-in, drill spacings. Cocksfoot gave very similar yields from 1.5, 24- and 36-in, drills but a signincantly reduced yield from 6-in, spaced drills. Timothy produced significantly higher yields at the 24 in spacing.
The three varieties showed a significant response to nitrogen application.
Aphids seriously affected the vegetative growth of meadow fescue and timothy at the wider spacings, but the 6-in. drills m boths species remained relatively free of aphid attack, as also did the cocksfoot block.     

不同刈割周期、留茬高度对4种柱花草属牧草产量的影响

利用正交试验研究了不同刈割周期、留茬高度对4种柱花草属牧草产草量的影响。试验表明,草种和刈割周期对草产量的影响显著,留茬高度对草产量影响不大,各因素对草产量的影响为：RA＞RC＞RB,即品系＞刈割周期＞留茬高度。极差分析得出各因素的最优水平为：A2品系,GC1581柱花草; B4留茬高度,40 cm;C2刈割周期,60 d。     

The effect of frequency and height of defoliation on the production and persistence of 'Grasslands Matua' prairie grass

The performance of prairie grass ( Bromus willdenowii Kunth) cv. Grasslands Matua was examined under mowing at five defoliation intervals (10, 20, 30, 40 and 50 d) and two defoliation heights (3 cm and 8 cm). Annual and seasonal production of both the total herbage and of Matua, and the proportion of Matua in the sward, increased with less frequent defoliation. To a lesser extent, increasing the height of defoliation increased dry matter yield. Matua tiller numbers were increased by less frequent defoliation and were greater under the 8 cm than the 3 cm defoliation height. To increase prairie grass production and persistence, rest intervals between grazings of 40 to 50 d are recommended, or alternatively, a management involving silage or hay cutting offers scope.     

THE EFFECT OF NITROGENOUS FERTILIZER ON THE RATE OF GROWTH OF ITALIAN RYEGRASS

The rate of growth of Italian ryegrass in the spring was measured by recording dry-matter yield at weekly intervals over periods of 6 weeks. There were 3 levels of applied N: 25, 75 and 125 lb/ac. Yield increased fairly slowly in the first 2 weeks and level of applied N had little effect. In the final 4 weeks the grass grew at a faster and fairly constant rate, which was very much affected by the level of N. Grass receiving 25 lb N produced 2900 lb of dry matter/ac in 6 weeks, 75 lb N 4400 Ib, and 125 Ib N 4700 lb. By the end of the first week, % N and % nitrate-N were higher at the 75 lb than at the 25 lb N level and by the end of the second week they were higher at the 125 lb than at the 75 lb N level. The effect of weather factors and the question of predictability of yield are discussed.