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.     

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

Residual response to an initial application of nitrogen was measured in 3 years and was found to be quite large, e.g. a response of 8 Ib DM per extra Ib N at the first harvest, when applying 125 Ib N/ac (140 kg/ha) rather than‘75 Ib (84 kg/ha) and allowing 6 weeks' growth, was increased to 21 Ib DM when yield from residual cuts was taken into account. Response was large in relation to the amount of N estimated to have been left behind after the first harvest. Marginal recovery of N, already quite high at the first harvest, was increased to a little over 90% when yield from residual cuts was taken into account Recovery, however, was lower than this when 10 weeks' growth was allowed before the first harvest, and it seems that, in this case, some N may have been lost from the system. A supplementary experiment suggested that the residual effect of N on DM yield could be obscured to some extent by fresh applications of N.     

氮肥对套作大豆干物质积累与分配的影响

在麦/玉米/豆种植模式下,研究了施氮量对套作大豆干物质积累与分配的影响.结果表明,随着施氮量的提高,大豆LAI增大,叶片衰老延缓,在盛荚期保持更大的叶面积,有利于干物质的积累.适宜的施氮量(≤135 kg/hm2)在大豆结荚期后能协调植株各部分干物质的输出率,对套作大豆有明显的增产作用;高氮处理(180.225 kg/hm2)促使植株茎、叶干物质量在始熟期积累过多,而干物质的输出率降低,导致源/库比例不协调,对豆荚的贡献率降低,产量降低.就不同器官而言,叶片对籽粒的贡献率大于茎秆对籽粒的贡献率.干物质量与产量构成因素存在明显相关,在套作大豆苗期,根、茎干物质量与充实度、产量显著正相关;在套作大豆生育中、后期,叶片干物质积累量与产量构成因素呈显著负相关.综上所述,适宜施氮量(45～90 kg/hm2)提高干物质的贡献率,减少大豆秕粒,有利于套作大豆获得高额产量.     

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

This paper describes the rate of growth of Italian ryegrass in the spring, measured by recording DM yield at weekly intervals up to 10 weeks. There were 3 levels of applied N: 25, 75 aud 125 lhJac (28, S4 and 140 kgJha). Rate of growth declined after the sixth week at all 3 levels of N. Grass receiving 25 Ib N produced 5000 Ib DMJac (5600 kgJha) in 10 weeks, that receiving 75 lb N 6800 Ib (7700 kgJha) and that receiving 125 lb N 7100 lb (8000 kgJha). The DM content of herbage fell after the first week and subsequently increased steadily up to 10 weeks; the fall was least marked and the rate of increase most rapid at tbe lowest level of N. In vitro digestibility (measured in one year only) was much affected by stage of growth and little affected by level of N.     

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.     

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

In an experiment described earlier (13), the N content of Italian ryegrass in spring reached a high value one or two weeks after applying N and then fell quickly at first and then more slowly. After 10 weeks average N content (in DM) was 0.6% from an application of 25 lh N/ac (28 kg/ha), 0.9% from 75 lb N (84 kg/ha), and 12% from 125 lb N (140 kgJha). Nitrate-N content fell more abruptly and tben remained fairly constant. Percentage nitrate–N (in DM) fell below 0.10% during the second week after an application of 25 lb NJac, during the third week after 75 lb N, and during the fifth week after recciriag 125 lb N. The yield of N increased during the first 5 or 6 weeks, remained fairly constant for 3–5 weeks, and then hegan to fall. During the ninth and tenth weeks, the crop lost an average of 9 lb N/ac per week (10 kg/ha) after an application of 75 Ib N/ac and 12 lb N/ac per week (13 kg/ha) after 125 Ib N.     

THE EFFECT OF WHITE CLOVER ON THE PRODUCTION OF YOUNG AND OLDER GRASSLAND COMPARED TO THAT OF NITROGEN FERTILIZER

The result of a study over many years on the effect of white clover (Trifolium repens L.) and nitrogen fertilizer on the production of young and old grassland are discussed. In young and old grassland, clover and N fertilizer increased production and N content. The effect of clover on production was somewhat greater in young grassland than in old. This difference was associated with a difference in the clover percentage in the sward. Statistical treatment of the results of similar studies by other workers showed that, given equal percentages, the clover in an older sward clearly had a greater effect than the clover in the first few years after sowing. Variation in the production of both young and somewhat older grass/clover swards are mainly due to differences in the clover percentage.     

THE EFFECT OF NITROGEN APPLICATION AND AUTUMN MANAGEMENT ON AUTUMN GROWTH, WINTER 'BURN' AND SPRING GROWTH OF LOLIUM PERENNE L. AT ABERYSTWYTH, EDINBURGH AND CAMBRIDGE.

A trial was carried out to find management practices which would permit the best discrimination for winter performance of erennial ryegrass cultivars. Due to the mild winter experienced only a few of the plants were killed outright. The cultivars were therefore assessed for percentage of green herbage and for spring growth. There were four sites: an upland and lowland site at Aberystwyth and one site each at Edinburgh and Cambridge. At all sites two N rates (totals of 125 or 550 kg/ha in the first year after sowing) and 5 autumn cutting treatments were used to give differences in the amounts of herbage remaining at the onset of winter. The last dates of defoliation in the autumn were: C₁ end of August; C₂ end of September; C₃ end of October; C₄ mid-November; C₅ was cut on all these dates. Four cultivars (Grasslands Ruanui, S321, Premo and Argo) which differed in their autumn growth potential, frost susceptibility and degree of winter dormancy were grown. The autumn yield of S321 was, in general, higher than that of the other cultivars but there were interactions with N, management and location. The data on percentage of herbage remaining green in February illustrated differences due to the siting of the trial. In the conditions prevailing the two Aberystwyth sites facilitated greater discrimination between cultivars than those at Edinburgh and Cambridge. In three of the four sites the management which produced most winter ‘burn’(including both that due to natural senescence and that due to winter damage) involved accumulation of herbage in the autumn but there were considerable sites × managements interactions. For example at Cambridge management produced no significant effect whereas at the Aberystwyth lowland site frequent defoliation in the autumn had more effect than allowing herbage to remain uncut after the end of August. High N significantly decreased the percentage of green herbage only at the two Aberystwyth sites. Over five-fold differences in spring yield were obtained, the heaviest yields being recorded at Edinburgh and Cambridge. However, there were large interactions between environments and cultivars; for example the higher N rate reduced spring yield at Aberystwyth but increased spring yield at Edinburgh and Cambridge. Premo and S321 had similar yields in spring at the Aberystwyth lowland and Cambridge sites but Premo was higher yielding than S321 at the Aberystwyth upland site and at Edinburgh. The large environmental effects and their interactions with cultivars illustrate the difficulties of cultivar assessment and the dangers inherent in national recommendations for grass cultivars.     

THE EFFECT OF WHITE CLOVER, FERTILIZER NITROGEN AND SIMULATED ANIMAL RESIDUES ON YIELD OF GRASSLAND HERBAGE

An experiment is described which measures the effects of white clover, fertilizer nitrogen and simulated animal residues, alone and in all combinations, on total herbage production from a perennial ryegrass sward. Yields of oven-dry herbage and of nitrogen are quoted. Two cuts were taken in the seedling year and four to six in each of three full harvest years.
Yield response to fertilizer nitrogen was similar to that in some other experiments in the U.K., while the beneficial effect of clover on yield was rather greater.
Negative nitrogen ± clover and positive nitrogen ± animal residues interactions were found throughout the yield data. There was a positive clover ± animal residues interaction in the first harvest year (dry-matter yield only), and a negative nitrogen ± clover ± animal residues interaction in the second harvest year.
The results are discussed in relation to other published work and to their application in practice.     

EFFECT OF DEFOLIATION AND SOIL MOISTURE ON GRASSLAND RE-GROWTH

The results of field experiments with leys dominated by Festuca pratensis and Dactylis species appear to concur with the theories proposed by Kramer and Jäntti. Complete defoliation, while the soil moisture was at or near permanent wilting percentage down to about 40 cm. depth, arrested growth almost completely but the growth rate of plants with assimilating parts left was 70 to 90 per cent of the corresponding rate on moist soil. The interaction of defoliation and soil moisture, however, seemed to be confined to cases where defoliation was practically complete. When a 4 cm. stubble was left the effect of drought was relatively no more strong than in swards cut to only 12 cm. Defoliation alone causes heavy crop reductions even in moist soil, and these reductions are evidently more important quantitatively than those resulting from the interaction with soil moisture.     

A COMPARISON OF THE REACTION OF DIFFERENT GRASS SPECIES TO FERTILIZER NITROGEN AND TO GROWTH IN ASSOCIATION WITH WHITE CLOVER. II. YIELD OF NITROGEN

Seven species or varieties of grass, and a mixture of 3 of them, were sown in pure swards, treated with 4 levels of nitro-chalk (0, 17·5, 35, and 70 Ib N/ac/cut) and cut 4 or 5 times each year. Each species and the mixture were also sown with white clover, and the effect of fertilizer N on the yield of N in each grass was compared with the effect of clover on the yield of N harvested from the grass/clover swards.
The regression line for response in yield of N with increasing levels of fertilizer N showed slight, but significant, upward curvature. The grasses differed in their uptake of N from the soil, S37 cocksfoot and S48 timothy showing relatively high uptakes, and the ability of each grass to take up fertilizer N was usually related to its uptake of N from the soil. Differences in the yield of dry matter between the species, at a similar level of N, are discussed, and it was concluded that perennial ryegrasses were most efficient and Agrostis tenuis was least efficient in using the N taken up in the production of DM.
In general, there were no significant differences between the yields of N of the grass/clover mixtures; the N yields of the grass components were significantly different and tended to be inversely related to the N yields of clover.
Grasses which gave high yields of N with fertilizer were also high yielding when grown in association with clover. Pure grass swards required more than 200 Ib fertilizer N/ac/yr in order to yield the same amount of N as the grass/clover swards. The amount of N estimated to have been derived by grass from clover (indirect effect of clover) increased each year; it was highest with S37 cocksfoot and lowest with Irish perennial ryegrass, averaging 46 and 23 Ib N/ac/yr, respectively.     

THE EFFECT OF WHITE CLOVER AND NITROGENOUS FERTILIZER ON THE PRODUCTION OF A SWARD

Three-year leys of cocksfoot/white clover and cocksfoot alone were dressed with 0, 35, 105 and 210 lb N per acre every year to provide information on the effect of clover and N on production.
Data from the grass-alone swards allowed an estimate to be made of the effect of N on production at different cutting dates. This was compared with the effect of clover.
The effect of N was greater than that of clover in the mid- and late-season cuts. Clover made its greatest contribution, both directly and indirectly, at the first cut, taken in May.
Under very dry conditions (1959), N was more effective than clover in maintaining production and the proportional response was large in relation to that produced under moist conditions.
The results are discussed with reference to the present seasonal use of N on grassland and an argument is advanced for increasing its use in mid-season.     

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

A leafy strain of timothy and of perennial ryegrass showed no significant reductions in seed yields following grazing at different dates from October to January, when extra nitrogen was applied.
Spring and winter + spring grazing, together with extra nitrogen, significantly reduced the seed yield of S50 timothy for three successive harvest years.
Perennial ryegrass S101 showed no reduction after spring or winter + spring grazing when defoliation was made not later than mid-April, but when grazing was delayed until May and drought occurred there was a significant reduction in seed yield.     

THE EFFECTS OF DIFFERENT LEVELS OF NITROGEN FERTILIZER ON THE YIELDS OF VARIETIES OF PERENNIAL RYEGRASS AND COCKSFOOT

Little is known about the possible differential responses to Nitrogen fertilizer in varieties within grass species. Two trials were conducted to study interactions between varieties and level of N. The dry-matter yields of 3 varieties of perennial ryegrass were compared in 4 cuts/yr at 3 levels of N fertilizer. Four cocksfoot varieties under the same cutting management were compared at 2 levels of N. In a total of 20 comparisons, the variety effect was significant on 10 occasions, and the N effect significant in all 20 sets of data. The interaction of variety and N level was significant in only one case suggesting that all varieties in each trial responded similarly to increasing levels of N fertilizer.     

氮源对马铃薯微型薯的影响

本文报道不同氮素来源对马铃薯微型薯形成的影响。结果表明:NO_3~-—N 浓度与成薯指数呈直线负相关关系;NH_4~+—N 浓度与成薯指数呈二次抛物线形式;NO_3~-—N/NH_4~+—N 比值对微型薯形成的影响呈双曲线形式;当总氮浓度在30～40m 时,成薯指数有较大值;降低 NO_3~-—N/NH_4~+—N 比值或总氮含量有利于微型薯的形成。NO_3~-—N 与 NH_4~+—N 的最佳组合为[NO_3—N]=17.325mM,[NH_4~+—N]=16.612mM。     

THE EFFECT OF SHEEP EXCRETA AND NITROGENOUS FERTILIZER ON THE BOTANICAL COMPOSITION AND PRODUCTION OF A LEY

Results are presented for the final two years of a previously described experiment.
The return of dung and urine by sheep to a ryegrass/white-clover ley was controlled by suitable harnesses to give four treatments (no dung or urine, dung, urine, dung and urine) which were combined in a replicated factorial design with four levels of nitrogenous fertilizer application (0, 52, 182, 312 1b. N per acre).
Applied nitrogen and urine were the dominant factors affecting botanical composition. The percentage of ryegrass increased and that of clover decreased with the progressive increases in nitrogen application. Volunteer species (mainly Poa spp.) contributed up to 20 per cent by the final year, the maximum occurring under the medium-high nitrogen treatment.
Urine restricted the incursion of weed grasses.
Combined with urine or the full return of excreta, high levels of applied nitrogen increased herbage production by up to 120 per cent. There was little response to dung except at the highest nitrogen level.
The yield response to applied nitrogen was almost linear. In the absence of animal returns response was poor, partly due to shortage of potash. When both excreta were withheld the light nitrogen dressing depressed the annual production compared with the control; where both excreta were returned together with this dressing no reduction occurred in annual yield and the spring yield was improved (p <0.05).     

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.     

THE EFFECT OF FERTILIZER AND GRAZING ON THE BOTANICAL COMPOSITION AND OUTPUT OF AN AGROSTIS/FESTUCA SWARD

The results are reported of the effects of fertilizer and grazing or cutting for hay over a period of 6 years on the composition of an Agrostis/Festuca permanent pasture on low-lying land at Beghroke Hill. Applications of N up to 264 units/ac each year associated with frequent defoliation every 21 days produced only small changes in sward composition; Agrostis spp. declined and Poa trivialis increased. Lolium perenne did not increase from a small initial presence. Records of animal performance and hay yield showed that the mean output from the experiment as a whole was 530 Ib liveweight gain/ac and 0·5 ton hay/ac.     

整薯播种对马铃薯生育及产量的影响

1979～1984年,在黑龙江省北部黑土地区气象条件、生产水平和栽培条件下,通过田间试验,研究了整薯播种对马铃薯生育和产量的影响。结果表明:整薯播种与传统习惯的切块播种相比,6年期间平产出现频率为2次,一般年份整薯播种比切块播种增产9～12%,在春旱严重的1980年,整薯播种表现出非常突出的抗旱保苗效果。在群体叶面积发展进程上,整薯播种表现早发早衰,切块播种晚发晚表,一般年份光合势前者比后者高9.6%,春旱严重的1980年高82.8%。块茎商品率以112.5克为准时,6年平均整薯播种为74.1%,切块播种为80.0%,两者相差5.9%;以50克为准时,整薯播种为97.3%,切块播种为98.2%,两者相差0.9%。