The effect of levels of calcium sulphate on the yield and composition of a grass and clover pasture

Summary 1. Gypsum was applied at various levels to a grass-clover association, and its effect noted on the yields and composition of both components.2. Both clover and grass responded markedly and a three-fold increase in dry matter and a four-fold increase in yield of N were noted.3. The extra nitrogen in the grass was shown to have been derived almost certainly by underground transference from the clover, the amount involved approximating to the amount of N retained in the aerial part of the clover.4. Whilst a high proportion of the S applied was recovered at rates up to 50 lb gypsum per acre, a low recovery was obtained from greater applications, and as residual SO₄ was very low, it is presumed that SO₄ was readily leached during one or two periods of heavy summer rainfall. The ease with which SO₄ is lost by leaching may merit attention to forms, times and rates of application of S.5. Nearly all the S in the clover was organic, whereas a big fraction of the S in the grass was SO₄-S. In regions where atmospheric returns of S are small and where no S is being made available from the weathering of S-containing minerals, S must be applied in some form or other to promote optimum N-fixation by legumes as grass may utilise almost all the mineral N and S made available from soil organic matter.6. Over large areas of the South Island of New Zealand it is doubtful if more than 1 lb S per acre is returned annually from the atmosphere and the application of S is of some considerable importance to promote N-fixation by clovers and hence high production from grass-clover associations.     

Nitrogen contribution from the soil for herbage growth

Summary and conclusions 1. Possible sources of free nitrogen are enumerated and evaluation has been attempted in respect of a West of Scotland soil.2. The total annual contribution of nitrogen to the soil from all free sources could be of the order 100–120 lb N per acre (=101–130 kg N per ha).3. Assuming that two thirds of this is harvestable in grassland then 66–80 lb N may be expected in the absence of added fertilizer nitrogen.4. The observed value for the nitrogen uptake by the grass component in a mixed sward (perennial ryegrass and white clover) in its third year (1965) amounted to 66 lb/N/acre.5. The uptake of nitrogen by perennial ryegrass grown alone without added fertilizer amounted to 89 and 65 lb in 1964 and 1965 respectively. These results corroborate the values for estimated nitrogen contribution outlined in (3) above and also agree well with the experimental findings of (4).6. Since the amount of nitrogen in the grass monoculture was similar to that obtained by the grass when grown in association with clover (1965 Data) it would therefore indicate that white clover did not materially affect the nitrogen uptake by perennial ryegrass.     

Investigations into nitrogen sources and supply in reclaimed colliery spoil

Summary Two trials were established to investigate the supply of nitrogen from ammonium and nitrate fertilizers, slow release nitrogen fertilizers, an organic nitrogen fertilizer and a legume, at two phosphate levels, to eight grass cultivars on colliery spoil. Spoil nitrogen supply and chemical characteristics and herbage dry matter and nitrogen yields were monitored for up to seven years. pH and conductivity fell at both sites. pH trends appeared to be independent of nitrogen treatment. Nitrogen in the ammonium form gave better yields than in the nitrate form when 125 kg N ha^–1 was supplied in a season but there was no difference when 62.5 kg N ha^–1 was applied. Slow release forms of nitrogen gave better yields more evenly distributed over the season than one application of ammonium sulphate per season. Once established white clover (Trifolium repens) plots had a more consistent nitrogen supply, more evenly distributed yield and better quality herbage than nitrogen fertilizer plots.Lolium perenne yielded poorly at low fertility.Festuca rubra andAgrostis castellana, although establishing slowly, yielded well under high and low fertility.     

Competition between Subterranean Clover and Rygrass for uptake of 15N-labeled fertilizer

Grasses and legumes are often grown together for improving quality of forage and for better yield when soil N availability is limiting. One compatible mixture is Trifolium subterranium L., subterranean clover and Lolium multiflorum Lam, ryegrass.Experiments were conducted with plants grown in a glasshouse and plant growth chambers to determine the competitive ability of these plants for fertilizer N. Fertilizer N was enriched with ¹⁵N to measure the contribution of dinitrogen fixation and fertilizer N to the growth of clover. In pure stands, with increased fertilizer N, the legume took up similar quantities of mineral N as the grass to make up for the deficit due to less dinitrogen fixation but in mixed stands the grass by far outcompeted the legume. The growth of clover suffered due to lack of N both from less dinitrogen fixation and the inability to compete with the grass for mineral N. Increasing levels of fertilizer N reduced dinitrogen fixation by the clover. When growing with the clover the grass did not receive N from the clover. A laboratory experiment using ¹⁵N label on pure stands of the two species indicated that the grass had an inherent capability of absorbing almost twice the amount of mineral N as the legume under the same conditions even when root weight and volume was not larger for the grass. The results of this research provide insight into the often observed phenomenon that growth of clover is reduced when grown with grass in proportion to the amount of mineral N provided. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Effect of Nitrogenous Fertilizer on the Photosynthesis and Growth of White Clover/Perennial Ryegrass Swards

The application of nitrogenous fertilizer in March to a whiteclover (cv. Blanca) and perennial ryegrass (cv. S23) sward resultedin a rapid suppression of the clover, relative to clover ina treatment given no added nitrogen. Thereafter, the cloverin both treatments grew more rapidly than the grass and itsproportion of the total leaf area in the mixture increased,as the leaf area index rose to 8. After a second applicationof N in early July, clover was not suppressed to the same extentas in the first growth period. Overall, the photosynthetic capacities of newly expanded cloverlaminae were similar in the two treatments. Clover laminae hadhigher photosynthetic capacities than grass, even in the grass-dominant+ N treatment. Lamina area, petiole length, and the number of live leaves perstolon were similar in the two treatments, indicating that thedifferences in total leaf area were due to the presence of fewerstolon growing points in the + N treatment. Trifolium repens L., white clover, Lolium perenne L., perennial ryegrass, nitrogen, leaf area index, photosynthesis, growth     

Interactions between perennial ryegrass ( Lolium perenne L.) and white clover (Trifolium repens L.) under contrasting nitrogen availability: productivity,seasonal patterns of species composition,N2 fixation,N transfer and N recovery

Nitrogen (N) fertiliser and clover cultivar choice affect competition and productivity in grass-clover mixtures. Pure stands and mixtures of perennial ryegrass and white clover cultivars with contrasting growth habits were examined. The aim of this work was to study the effect of repetitive nitrogen (N) application and cultivar combination on competition and productivity, N yield in the harvested herbage, N₂ fixation in mixtures and pure stands, and transfer of N from clover to the companion grass. Large-leaved white clover cultivar Alice and small-leaved cv. Gwenda and perennial ryegrass cvs. Barlet (erect) and Heraut (prostrate) were sown in pure stands and as four binary grass-clover mixtures on a sandy soil in 1995. In the mixtures, two levels of N fertiliser were applied: 0 (-N) and 150 and 180 kg ha^-1 y^-1 N (+N) in 1996 and 1997, respectively, while the grass monocultures received three N levels (0, 140/180 and 280/360 kg ha^-1) in 1996 and 1997, respectively. No N was applied to pure clover. The plots were cut five times during 1996 and six times during 1997. Fertiliser N was applied in early spring and after every harvest. The treatments were continued until the summer of 1999. In pure grass, the applied N was effectively recovered. In mixtures, N application affected competition by enhancing grass growth and the overall effect of N application was 17 kg DM per kg N applied in 1996. However, there was no yield response to N fertilizer in 1997, because this was compensated for by a higher clover production in unfertilised mixtures. In 1997, -N mixtures yielded more N than +N mixtures, owing to the higher clover content and N₂ fixation. Large-leaved clover cv. Alice was better able to withstand the negative effect of repetitive N application on clover production in mixtures and increased its proportion during the growing season of the second harvest year. In 1997, mixtures with Alice yielded more N than mixtures with Gwenda, but in pure clover swards, there was no cultivar effect on N yield. Also, during the autumn of 1998 and the spring of 1999, the clover content was highest in mixtures with Alice. Harvested N and apparent N₂ fixation were almost twice as high in 1997 as in 1996. N yield and apparent N₂ fixation were higher in pure clover than in mixtures. In mixtures, the apparent N₂ fixation in 1996 was 142 kg N ha^-1, irrespective of cultivar or N treatment. In 1997, it was on average 337 kg N ha^-1, and higher in -N mixtures and in mixtures with Alice. For each tonne of clover DM in the harvested herbage, 65 and 57 kg N was harvested in 1996 and 1997 in -N mixtures, respectively. The apparent transfer of clover-derived N to grass was on average 29 and 70 kg N ha^-1 yr^-1 in 1996 and 1997, respectively. It was highest in +N mixtures and highest in mixtures with Gwenda in 1997. In contrast to clover, the grass cultivars were very similar in their productivity and seasonal patterns, despite their contrasting growth habits. Seasonal trends in N yield, N transfer and N recovery are discussed in relation to fertilizer application regimes and variation in production patterns in mixtures and pure stands. This revised version was published online in June 2006 with corrections to the Cover Date.     

The potential of legumes as a nitrogen source for the reclamation of derelicht land

Summary White clover (Trifolium repens) growing in association with grasses on colliery spoil amended with lime and complete fertilizer proved to be an effective nitrogen source for the developing ecosystem. Nitrogen transfer from the clover to an associated grass became aparent within 22 months of sowing.     

Effects of white clover (Trifolium repens L.) on plant and soil nitrogen and soil organic matter in mixtures with perennial ryegrass (Lolium perenne L.)

To increase our insight into the above- and belowground N flows in grass and grass-clover swards relations between crop and soil parameters were studied in a cutting trial with perennial ryegrass (Lolium perenne) monocultures and ryegrass–white clover (Trifolium repens) mixtures. The effects of clover cultivar on herbage yield, the amount of clover-derived nitrogen, apparent N transfer to companion grass, dynamics of N and organic matter in the soil were estimated.The grass monocultures had very low DM yields (<2.1 t ha^-1) and a low N concentration in the harvested herbage. During 1992–1995 the annual herbage DM yield in the mixtures ranged from 7.0 to 14.3 t ha^-1, the white clover DM yield from 2.4 to 11.2 t ha^-1 and the mean annual clover content in the herbage DM harvested from 34 to 78%. Mixtures with the large-leaved clover cv. Alice yielded significantly more herbage and clover DM and had a higher clover content than mixtures with small/medium-leaved cvs. Gwenda and Retor. Grass cultivar did not consistently affect yield, botanical composition or soil characteristics.The apparent N₂ fixation was very high, ranging from 150 to 545 kg N ha^-1 in the different mixtures. For each tonne of clover DM in the harvested herbage 49 to 63 kg N was harvested, while the apparent N transfer from clover to grass varied between 55 and 113 kg N ha^-1 year^-1.The net N mineralization rate was lower under monocultures than under mixtures. The C mineralization and the amounts of C and N in active soil organic matter fractions were similar for monocultures and mixtures, but the C:N ratio of the active soil organic matter fractions were higher under grass than under mixtures. This explains the lower N mineralization under grass.     

Nitrogen fixation by white clover when competing with grasses at moderately low temperatures

It was the aim of this study to determine the way in which low temperature modifies the effect of a competing grass on nitrogen fixation of a forage legume. White clover (Trifolium repens L.) was grown in monoculture or in different planting ratios with timothy (Phleum pratense L.) or perennial ryegress (Lolium perenne L.) in growth chambers at either 7.5/5°C (LoT) or 15/10°C (HiT) average day/night temperatures, and with 2.5 or 7.5 mM ¹⁵N-labelled nitrate in the nutrient solution.Competition with grass led to a marked increase in the proportion of clover nitrogen derived from symbiosis (% N_sym). This increase was slower at LoT where % N_sym was reduced considerably; it was closely related to the reduction in the amount of available nitrate as a result of its being utilized by the grass.Nitrogen concentration in white clover herbage and dry matter yield per clover plant were reduced, for the most part, when a competing grass was present. The amount of nitrogen fixed per plant of white clover decreased markedly with temperature. Low temperature consequently accentuated competition for nitrate. The capacity of white clover to compete successfully was limited by its slower growth and nitrogen accumulation.     

The composition of the leachate through cropped and uncropped soils in lysimeters compared with that of the rain

Summary The composition of the leachate from undisturbed monolith lysimeters cropped with white clover or meadow fescue or maintained bare was compared with that of the rain falling on them. No nitrogen fertilizer was applied only an initial dressing of phosphorus and potassium. The grass received much more nitrogen from the rain than it lost by leaching whereas the clover lost more than it received. Most of the leached nitrogen was NO₃-N - 92 per cent on the bare soil and 90 per cent on the clover. About 27lb nitrogen per acre (30 kg/ha) per year was drained from the actively growing clover sward rising to about 117lb N/acre/year (131 kg/ha) when the clover died or was removed. Only 2.3lb/ac (2.5 kg/ha) was drained from the actively growing grass sward. It was estimated that the clover fixed at least 270lb N/ac/year (303 kg/ha/year. The rates of leaching of potassium from a grass sward was about 1.7lb/ac/year (1.9 kg/ha) and 0.8 lb (0.9 kg) phosphorus. The quantities were similar for clover. The grass received from the rain more phosphorus and potassium than was leached but only 60 per cent of the calcium and 13 per cent of the magnesium, similar results being obtained with white clover. During the year of establishment of the grass sward there was evidence of loss of gaseous nitrogen (elemental and/or compound) from the soil: subsequently the nitrogen content of the soil slowly increased. Calcium loss from the bare soil with an average rainfall of 26″ (650 mm) was about 100 lb Ca/ac/year (112 kg/ha).     

Effects of coexistence on the performance of white clover-perennial ryegrass mixtures

Summary Yields from five white clover/perennial ryegrass mixtures, each based on coexisting components, were compared with those produced by ten mixtures whose constituents had no previous history of coexistence. The former group consisted of five paired clover/ryegrass populations, four collected from natural pastures and one from a sown pasture, whilst the latter group comprised the same five clover populations grown in turn with each of two ryegrass companions.In the first harvest year, when artificial fertilizer plus soil mineralization supplied most of the nitrogen to this experiment, the grasses were generally favoured at the expense of the clovers. Although those mixtures based on coexisting populations had significantly lower yields the clover within these mixtures made a significantly higher contribution to their productivity. This advantage was retained into the second harvest year when it was accompanied by a correlated response in the grasses, which by then may have become dependent upon the clover for their nitrogen supply. Consequently, by the end of the second harvest year those mixtures based on coexisting populations yielded over 20% more on average, due mainly to improved early season growth. Despite considerable differences in productivity, all five clover populations gave their highest yields when grown with their matching grass.     

Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization

Simulated mixed swards of Perennial Ryegrass (Lolium perenneL.) cv. S23 and White clover (Trifolium repens L.) cv. S100were grown from seed under a constant 20 °C day/15 °Cnight temperature regime and their growth and carbon economyexamined. The swards received a nutrient solution daily, whichcontained either High (220 mg l^–1) or Low (10 mg l^–1)nitrate N. Rates of canopy photosynthesis and respiration, and final drymatter yields were similar in the two treatments although theproportions of grass and clover differed greatly. The Low-Nswards were made up largely of clover. The grass plants in theseswards had high root: shoot ratios and low relative photosyntheticrates – both signs of N deficiency – and were clearlyunable to compete with the vigorously growing Low-N clover plants.These had higher relative growth rates and dry matter yieldsthan their High-N counterparts. In the High-N swards clovercontributed around 50 per cent to the sward dry weight throughoutthe measurement period despite having a smaller proportion ofits dry weight in photosynthetic tissue (laminae) than grassover much of it. The latter was compensated for, initially bya higher specific leaf area than grass, and later by a higherphotosynthetic rate per unit leaf weight. The results are discussedin relation to observed declines in the clover content of swardsafter the addition of nitrogen fertilizer in the field. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, nitrogen, photosynthesis, carbon balance     

不同包膜控释尿素对农田土壤氨挥发的影响

为了探索包膜控释尿素土壤氨挥发损失规律特征和提高肥料氮素利用率,采用小麦玉米轮作田间试验,通过与普通尿素进行对比,运用土壤氨挥发原位测定方法——通气法系统研究了硫包膜和树脂包膜控释尿素的施用对小麦玉米轮作农田土壤氨挥发的影响.研究结果表明:在两种施氮量水平下(210 kg/hm2和300 kg/hm2),与普通尿素相比,硫包膜和树脂包膜控释尿素在小麦基肥期、小麦追肥期和玉米施肥期的施用均减少了土壤氨挥发的累积损失量,分别达35.1％-54.3％、59.6％-75.2％、65.6％-98.1％;有效降低了土壤氨挥发通量峰值且延迟其出现时间3-8 d,并能延缓土壤氨挥发主要阶段的时间分别为4-12 d、5-12 d.在小麦玉米轮作周年中,控释尿素土壤氨挥发累积损失量为28.39-43.35 kg/hm2,土壤氨挥发损失率为4.48％-5.63％,控释尿素时段土壤氨挥发通量比普通尿素降低了51.0％-70.8％;且树脂包膜控释尿素的施用降低小麦玉米轮作农田土壤氨挥发的效果优于硫包膜控释尿素.     

Biological nitrogen fixation in grass–clover affected by animal excreta

Aiming at estimating the average N2-fixation in a pasture, ap preciating the great variability due to patchy urine and dung deposition, the in fluence of dairy cow excreta on biological N2-fixation in a perennial ryegrass–white clover mixture was studied using natural urine and dung. Application of urine as well as dung affected the N2-fixation by promoting the growth of grass and thereby the proportion of clover was significantly reduced. Also the proportion of clover-N derived from the atmosphere (pNdfa) was significantly reduced. In control plots clover dry matter constituted between 40 and 50% of the total dry matter production and the pNdfa ranged between 0.8 and 0.9. Addition of urine caused a significant increase in the grass growth rates, which was the primary reason for a decrease in proportion of clover. At the same time pNdfa decreased to 0.2–0.4 followed by an increase resulting in a total reduction of 45% in the N2-fixation in urine affected areas over a period of four months. The dung only affected the N2-fixation for a distance of up to 10 cm from the edge of the dung pats. In this border area the pNdfa decreased from 0.85 to 0.75 during one month after application followed by an increase, so that after three months there was no difference between pNdfa at 0–10 and 10–20 cm distance from the dung hill. The proportion of clover was lower in the 0–10 cm than in the 10–20 cm distance, which totally resulted in a total reduction of 20% in the N2-fixation over a period of four months in the 0–10 cm area around the dung pats. Considering the proportion of a pasture which may by affected by excreta at a stocking density of 4–6 cows ha-1, the length of the grazing period, the frequency of excretion and the area covered by individual patches, it was estimated that the N2-fixation in a grass-clover pasture would be reduced by 10–15% compared to the N2-fixation in a grass-clover sward not exposed to animal excreta.     

Effect of Temperature and Nitrogen Supply on the Growth of Perennial Ryegrass and White Clover. 2. A Comparison of Monocultures and Mixed Swards

White clover (Trifolium repens L.) and Perennial ryegrass (Loliumperenne L.) plants were grown, in Perlite, in simulated swardsas either monocultures or mixtures of equal plant numbers. Theywere supplied with a nutrient solution either high (220 µgg^–1) or low (40 µg g^–1) in ¹⁵N-labelled nitrateand grown to ceiling yield at either high (20°C day/15°Cnight) or low (10°C day/8°C night) temperature. Temperature had little effect on the maximum rates of grosscanopy photosynthesis which were similar in High-N grass andHigh-N and Low-N clover monocultures. However these maxima werereached more slowly in clover than grass, and more slowly atlow rather than high temperature. Nitrogen supply increasedphotosynthesis in grass but not in clover. Clover had higherN contents than grass in all four treatments, although in anygiven treatment its N content was lower, and contribution ofN₂-fixation relative to nitrate uptake higher, in mixture thanin monoculture. Conversely, grass had higher N contents in mixturethan monoculture, because more nitrate was available per plantand not because of transfer of biologically fixed N from clover. Under Low-N, clover outyielded grass in mixture, particularlyat high temperature. The grass plants in the Low-N mixtureshad higher N contents and higher SLA, LAR and shoot: root ratiosthan those in monoculture. It is proposed that competition forlight is the cause of the low relative yield and negative aggressivityof grass in these swards. Under High-N, grass outyielded cloverin monoculture and mixture, at both temperatures but particularlyat low temperature when grass had a high aggressivity. Nitrogenand yield component analyses shed no light on clover's apparentlylow competitive ability and evidence is drawn from the previouspaper to demonstrate that grass grew faster than clover onlyas spaced individuals during non-com petitive growth. The relativemerits of measures of competitive ability based on final harvestdata and physiological data taken over a growth period are discussed. Trifolium repens L., white clover, Lolium perenne, perennial ryegrass, competition, temperature, nitrogen     

THE MUTUAL EFFECT OF RYEGRASS AND CLOVER WHEN GROWN TOGETHER

Italian ryegrass and a late-flowering red clover were grown together, with abundance of water and nutrients for both. It was found that even a small number of ryegrass plants reduced the growth of clover by 30%. This effect varied very little with increasing density of the clover crop.
The presence of clover reduced the ryegrass crop by an amount diminishing as the density of the ryegrass was increased. In a sparse crop of ryegrass, clover reduced the growth of the grass considerably more than did barley under comparable conditions.
There is no evidence of any specific effect of the roots of one plant on the other. When ample nitrogen is available the clover tends to take some that would otherwise be available for the grass and does not provide the grass with additional nitrogen.     

Acetylene reduction assay on white clover genotypes and on grass/clover swards

Acetylene reduction assay was used to measure the nitrogenase activity of white clover genotypes in pots and of grass/clover swards in situ. Much of the variation in nitrogenase activity of single genotypes and hybrid populations was associated with plant dry weight. After adjustment for plant dry weight it was concluded that there was limited scope for selection for increased nitrogenase activity. In plant breeding this technique would seem to have greatest application in the selection for continued nitrogen fixation activity in the presence of inhibitory factors such as high levels of mineral nitrogen. The in situ studies revealed differences in nitrogenase activity of grass/clover swards based on contrasting cultivars of white clover. These differences were due to variation in clover density and also to variation in activity per unit clover dry weight. It was concluded that the variation in nitrogenase activity per unit dry weight reflected differences in growth pattern of the cultivars in the autumn when these assays were made. The in situ studies offer a means whereby the nitrogenase activity of cultivars and selected families can be monitored under varying levels of mineral nitrogen and other husbandry treatments without disruption of the sward.     

Soil fertility management as a factor in weed control: the effect of crimson clover residue,synthetic nitrogen fertilizer,and their interaction on emergence and early growth of lambsquarters and sweet corn

Previous experiments have shown that crimson clover (Trifolium incarnatum L.) used as a green manure may supply weed control benefits as well as nitrogen (N) to a subsequent crop of corn (Zea mays L.). In contrast to use of synthetic N fertilizer, use of fresh, incorporated crimson clover residue as an N source has been found to suppress lambsquarters (Chenopodium album L.) aboveground drymatter accumulation but to only temporarily reduce that of sweet corn. One possible cause of the clover's suppressive effect is the initial low availability of N that may occur after residue incorporation in the soil. A factorial treatment combination of +/– crimson clover residue and four rates of N fertilizer was used in two field experiments to further document the clover's influence on early plant growth and development and to test the hypothesis that low initial N availability is responsible for the clover's previously observed suppressive effects. The presence of crimson clover residue was found to reduce total emergence of lambsquarters by 27%, while application of N fertilizer increased lambsquarters emergence by almost 75%. Lambsquarters emergence was also delayed by the residue treatment. Addition of N did not alleviate the clover's suppressive effect on total emergence or emergence rate of lambsquarters. Sweet corn emergence and emergence rate differed by less than 5% in 0 N/+residue and 0 N/–residue treatments. Applications of N to residue plots suppressed rather than enanced sweet corn emergence. Lambsquarters aboveground biomass accumulation was 46% tower in the residue than nonresidue treatments at 23 days after planting (DAP) and remained 26% lower at 53 DAP. Addition of N did not alleviate the suppressive effect of the clover residue on lambsquarters aboveground drymatter accumulation. Sweet corn aboveground biomass accumulation was not affected by the presence of the clover residue. The results of the experiments indicate that the suppressive effect of crimson clover residue on lambsquarters emergence and growth is not attributable to initial low availability of N. However, given the stimulatory effect of N fertilizer on lambsquarters development, use of crimson clover as an N source would appear to provide weed control benefits both as a direct suppressant of weed emergence and growth and as a substitute for fertilizer N.     

Nitrogen leaching losses from conventional and new nitrogenous fertilizers in low-land rice culture

Summary A pot-culture experiment was conducted to assess the leaching losses of N from the conventional and new nitrogen fertilizers under low-land rice culture. Leaching losses of N were generally less than 20% of applied N with sources other than sodium nitrate and these could be reduced by blending urea with nitrification inhibitor N-Serve or coating withneem cake or by using urea super granules or slow-release N fertilizer sulphur coated urea. These new nitrogen fertilizers were more effective than urea for rice.     

Competition between grass and clover in spring as affected by nitrogen fertiliser

Detailed measurements of irrigated ryegrass/white clover swards growing without interruption, with or without nitrogen fertiliser in spring, showed that the relative growth rate of clover was as great as that of grass, in the + N sward, and considerably greater than grass, in the – N sward. Clover leaves were not overtopped by grass leaves. Indeed, in both swards, clover had a greater proportion of its leaf lamina area in the upper, well lit, layers of the canopy than grass did. Consequently, clover had a greater mean rate of leaf photosynthesis in situ in the sward than grass. Clover's advantage in photosynthetic rate per leaf area was offset to some extent by its smaller ratio of leaf area to total above-ground dry weight than grass. The consequences of these results for our understanding of competition between grass and clover in mixed swards are discussed.