A dairy farmer’s experiences in managing various levels of fertiliser nitrogen (N) inputs over the 1991–95 seasons is discussed and compared to previous years when very little N fertiliser was used. N requirements were assessed by regular herbage tests. Fertiliser N increased pasture growth in spring, early summer and autumn. Animal intakes were greater on N-boosted pasture. Higher rates of N fertilisers (450 kgN/ha/yr) generated large spring surpluses which were harvested as silage. Several changes in management were required to maintain pasture quality and effectively utilise these surpluses. Feed costs vs milk returns are compared for a number of seasons. Moderate fertiliser N usage (200– 300 kg N/ha/yr) is considered likely to give the most profitable balance. Keywords: clover, dairying, grazing management, milksolids, nitrogen, pasture growth, pasture quality
The current state of knowledge of white clover clonal growth processes and defoliation management is reviewed, and general recommendations on grazing principals made. Defoliation frequency determines herbage productivity through the manipulation of size/ density compensation between plant organ size (leaves) and numbers of growth units (growing point density). Hence large-leaved cultivars (Pitau, Kopu, Aran) are generally more productive under rotational grazing, whereas small-leaved cultivars are better suited to frequently grazed or set stocked conditions (Tahora, Prestige). The key to persistence is high growing point density, and the development of large-leaved densely branched cultivars should have superior performance over a wider range of grazing managements (Demand, Sustain). Grasses (perennial ryegrass, cocksfoot and tall fescue) grow by similar clonal processes to white clover and react in a similar manner to grazing management. Maintenance of pasture density (growing points/tillers) is crucial to persistence and is best achieved by rapid rotations or set stocking during spring/early summer. This provides protection against drought, and allows better exploitation of the genetic potential of species and cultivars through alternative grazing strategies over the remainder of the year. Keywords: clonal growth, cultivars, grazing management, morphology, populations, rotational grazing, seasonal growth patterns, set stocking, Trifolium repens L., white clover
The introduction of foreign genes into elite white clover (Trifolium repens L.) genotypes has resulted in the first field test of genetically modified white clover. We now require breeding strategies which efficiently deploy transgenes into commercial cultivars. Current white clover cultivars are synthetics, produced by randomly intermating selected parents or seed lines for up to 6 generations. Unfortunately, the uncontrolled nature of transgene insertion means each transformant has a different site of insertion and frequently has a variable number of inserts. This complicates breeding strategies because populations produced by intercrossing these transformants will contain multiple insertion sites, variable dosage at each insertion site, and be highly heterogeneous for expression level. A modified synthetic breeding method is proposed for crosspollinated crops such as white clover which overcomes these difficulties by identifying F2 progeny homozygous for a defined number of transgenes. These homozygotes are used as the parents to develop a synthetic with a specific genetic composition and high expression levels of the transgene in all progeny. The advantages of backcrossing into existing cultivars or directly transforming inbreds are also discussed. The initiation of new crossing programmes in successive years can be utilised to offset the initial lagphase until strategies which reduce the number of generations required to obtain commercial quantities are developed. Keywords: backcrossing, breeding methods, cross-pollinated, hybrids, inbreeding, plant breeding, transgenic plants, Trifolium repens L.
A brief history of how DSIR Grasslands operated as a plant breeding institute for New Zealand pastoral farming is presented, and this perspective shows how the present situation has been shaped whereby cultivars are now developed under contract to the forage division of AgResearch. A hypothetical cultivar development programme is detailed to show the mechanics of the Cultivar Development and Maintenance Unit (CDMU) operation. The role of CDMU in the future is discussed along with the continuing pressure for white clover seed production area in Canterbury. Keywords: buried seed, CDMU, cultivar development, plant variety rights, seed industry
During the early 1990s declining milk yields on coastal Bay of Plenty farms, against wider district trends, was attributed to pasture clover deficiency. To investigate possible causes pasture herbage yield, species composition, white clover growing point density and N-fixation activity were measured on two coastal Bay of Plenty dairy pastures over two years following nematicide treatment (Watson et al. 1994). Soil temperature was also monitored over most of this period. There was a marked decline in white clover growing point density of up to 90% from mid-December to mid- February in each year. This coincided with periods when surface (1 cm depth) daily maximum soil temperatures exceeded 30°C and soil moisture levels were below 30% Mw. Loss of clover was enhanced by clover cyst (Heterodera trifolii) and root knot (Meloidogyne spp.) nematodes which also delayed autumn recovery. Poor clover levels taken into the winter extended clover deficiency into a second season. Keywords: drought, grazing management, stolon density
White clover (Trifolium repens L.) genotypes of the cv. Grasslands Kopu which had differing numbers of vascular bundles within their stolons were tested for potential for resource sharing between shoot branches on either side of parent axis. Genotypes with a high (10–13) number of vascular bundles (H-genotypes) had larger leaves, thicker stolons but lower node appearance rates than genotypes with a low (8–9) number of vascular bundles (L-genotypes). In the first experiment all roots on one side of the parent axis were severed two days before plants were labelled with 32P (uptake period 24 h). In H-genotypes, distribution of radioactive phosphorus (32P) exported from a nodal root was restricted largely to near-side branches, i.e. branches which were on the same side of the parent axis as the source root, with only 4% allocated to far-side branches. In contrast about 20% of 32P exported from the source root was transported to far-side branches in L-genotypes. In the second experiment, where all far-side roots were severed three weeks before harvest, growth of far-side branches was similarly reduced in L-genotypes and Hgenotypes. When root formation along one side of the parent axis was prevented during the entire experimental period the mean ratio of total dry weight between nearand far-side branches was higher in H-genotypes compared to L-genotypes. Keywords: branch development, nutrient distribution, phosphorus, vascular bundle, white clover, Trifolium repens L.
Attaining a predictable and stable composition of white clover in pasture is affected by selective grazing and inter-species plant competition. This paper reports an experiment which demonstrates that when given a free choice between monocultures of ryegrass and white clover, cattle did not selectively graze only clover but chose a mixed diet. Ten young heifers were stocked for 3 weeks on 2 ha, comprised of adjacent 1-ha monocultures of each of ryegrass and white clover. Animals were given 1 week to adjust to the spatial separation and then on 2 consecutive days in each of 2 consecutive weeks, cattle were observed at 10-minute intervals during daylight hours. Behaviour (grazing or not) and location (ryegrass or white clover) were recorded. This procedure was conducted in December, February and May to assess seasonal variation in the species preference. At each occasion cattle choose a mixed diet by eating both ryegrass and white clover, but their preference for white clover changed with season. In February they exhibited a partial preference for white clover, by spending approximately 65% of grazing time on white clover and 35% on ryegrass. In December and May the partial preference for white clover was lower, with cattle allocating approximately 47% of grazing time to white clover and 53% to ryegrass. Results are discussed in relation to the extent of preference for white clover when limitations to selection are removed and how this information could be used to enhance white clover proportion in the diet to better match animal preference. Keywords: diet selection, grazing behaviour, perennial ryegrass, preference, Trifolium repens L.
The principal environmental impacts of nitrogen in pastoral agriculture are identified as: ammonia volatilisation, nitrous oxide emission, reduction of methane oxidation, and contamination of waters with organic nitrogen or inorganic nitrogen (nitrate, nitrite and ammonium). Each of these impacts is analysed in terms of its sensitivity to the form in which N enters the farming system, symbiotically or as fertiliser. Indirect effects that flow through from any changes in productivity are also examined. With the exception of organic N pollution of waters, all the impacts are shown to be directly affected by fertiliser N. Keywords: ammonia, leaching, methane, nitrate, nitrous oxide
An analysis is made of the main factors influencing nitrogen use in the European Union (EU). The Common Agricultural Policy (CAP) is identified as a major factor. A brief explanation is given of its functions and of recent reforms which are aimed at reducing overproduction. These reforms should favour more efficient use of nitrogen. The reasons why this is difficult to achieve are explained and the major factors influencing our ability to balance the nitrogen economies of food production are identified. The interrelationship between these factors is then used to predict the impact of CAP reforms on research, on fertiliser use and on the wider use of legumes. Keywords: Common Agricultural Policy, Europe, farm subsidies, legumes, nitrogen cycle, nitrogen fertiliser, nitrogen fixation, over-production, pollution, soil organic matter
White clover is important to New Zealand pastoral farming yet uptake of new agronomically superior cultivars by farmers is slower than expected. Three main areas which explain why this is occurring are: 1. The need to demonstrate economic benefits due to superior agronomic performance of new cultivars to overcome barriers such as price and farmers satisfaction with existing products. 2. Farmers are influenced by advice of seed retailers/extension personnel, their knowledge of white clover cultivars, local research, and their economic situation. 3. White clover seed quantity and quality has been adversely affected by poor weather conditions at flowering and harvest over the last 3 or 4 years. Seed availability is also being affected by the cultivar change regulations and the changing land use patterns of Canterbury. The problem is magnified by the increasing number of white clovers being grown on a decreasing land base. For greater uptake and use of new white clovers, strategies that deal with all three areas are required. Keywords: buying decision, economic benefit, farmer use, seed availability, white clover
Lines of white clover with higher and lower numbers of nodules were selected from a mutagenised Huia population, and seed was produced from a polycross of both lines. The progeny showed that the lines tended to have either more but smaller nodules, or fewer and larger nodules. In a further experiment, the line with fewer (larger average size) nodules, fixed more nitrogen (N) and grew bigger. Plants with fewer but larger nodules are a good model for efforts to increase the Nfixing capacity of white clover. An empirical screening method was used to obtain 15 genotypes that showed evidence of high mycotrophy. A second experiment confirmed that 5 of these genotypes gave abnormally high responses to mycorrhizal infection. Examination of the roots of these plants showed that the selections did not differ from their parent lines in terms of root length or root hair cylinder diameter. The results tend to confirm published work with spring wheat, which showed that land races and wild types respond more strongly to mycorrhizal infection than high yielding varieties do. Investigation of the mycorrhizal responses of clover ecotypes that are adapted to low phosphorus soils is a priority for future research. Keywords: mycorrhizas, nitrogen fixation, nodulation, symbioses, white clover
Between 1984 and 1990, the performance of ‘Tahora’, ‘Huia’, ‘Pitau’ and ‘Kopu’ white clover cultivars were evaluated in self-contained farmlets under rotational grazing and set stocking with sheep. A severe late spring-early summer drought in the third year from sowing (1986–87), caused a marked interaction between grazing management and cultivar performance. The drought caused no losses under set stocking, but large losses of stolon (75–90%) and a reduction in white clover content from 15% to 2% under rotational grazing. All cultivars were equally affected and recovery over the next 3 years was slow, although the small-leaved Tahora recovered faster than the large-leaved Pitau and Kopu. It was hypothesised that this would have caused differences in the preferential loss of genotypes with specific characteristics between grazing managements. Populations of white clover sampled from the field in 1989 and established from the original seedlines, were grown in common conditions for a year and compared for leaf size and cyanogenesis content. There had been a significant loss in mean leaf size in all cultivars with time, irrespective of drought or grazing management. It was shown that a general decline in stolon biomass commenced in all treatments 18 months after sowing, suggesting either, (1) a preferential loss of large-leaved genotypes with time irrespective of grazing management, or (2), a general change in per-formance of all genotypes, which may coincide with the change from dependence on seminal taproot of the seedling, to nodal rooting on free growing stolons. Keywords: cultivars, drought, genotypic change, grazing management, populations, Trifolium repens, white clover
White clover plants from a range of cultivars can now be routinely transformed with cloned foreign genes. However, before transgenic white clover cultivars can be developed, these inserted genes must be stably inherited and expressed at appropriate levels in progeny. Primary transgenic white clover plants containing a uidA (GUS) reporter transgene were outcrossed and the inheritance and expression of the uidA gene was examined over two generations, in several different cultivar backgrounds. Both Mendelian inheritance and consistent expression in different genetic backgrounds were obtained from strongly expressing primary transgenic plants. However, primary transgenic plants with weak or variable expression gave non-Mendelian inheritance and inconsistent expression of the transgene in progeny plants. Transgenic BC1 plants were also intercrossed to produce a segregating F2 population containing individuals heterozygous or homozygous for the transgene. In these populations heterozygous and homozygous plants had similar levels of uidA gene expression. These results indicate that F2 plants, homozygous for a transgene, might be used to develop a transgenic cultivar. However, both selection of a primary transgenic plant with stable, high level expression of the introduced gene and progeny testing, to determine the influence of genetic background, are prerequisites to such a development. Keywords: gene expression, inheritance, transgene, uidA reporter, white clover
During 1988/89 selected white clover (Trifolium repens L.) genotypes were studied to determine their inheritance of multifoliolate (mf) leaves in relation to the multifoliolate percentage of the parent material. Genotypes differing in multifoliolate frequency were crossed in an incomplete diallel with plants from three Grasslands white clover cultivars, Huia, Kopu and Tahora. Each cultivar was used in three separate pair crosses, with genotypes expressing multifoliolate leaf percentages of 25%, 50% and 75% respectively. These mf plants were also pair crossed and plants from within each cultivar were pair crossed 3 times. All plants in the total of 21 pair crosses were bee pollinated. Harvested seed from each genotype was sown and raised under glasshouse conditions, and after ninety days each young plant was evaluated for mf leaf production. Leaf count results showed that 31% of cultivar x mf genotypes expressed mf leaves, while in the mf x mf programme 90% of genotypes displayed mf leaves. A distinct increase in the percentage of multifoliolate leaves occurred in crosses between mf plants and the trifoliolate cultivars when the mf genotype was the maternal parent. It is apparent that the multifoliolate character is heritable and that the percentage of mf leaves can be increased through breeding and selection. Keywords: expression levels, inheritance, multifoliolate, white clover
Research into improving symbiotic nitrogen fixation of white clover in New Zealand pastures through the introduction of effective rhizobia is reviewed. Naturalised populations of rhizobia are usually highly diverse and of reduced effectiveness compared to inoculant strains, and large increases in nitrogen fixed have been found in situations where high nodule occupancy by an inoculant strain was obtained. The likelihood of an inoculant strain initially forming a high proportion of nodules is dependent on the size of the naturalised and inoculant populations, and the strain of rhizobia. Lack of persistence of the inoculant strain in competition with naturalised rhizobia also limits improvement of symbiotic nitrogen fixation in pasture through inoculation. Recent studies suggest that genetic instability of inoculant strains and exchange of symbiotic plasmids contribute to the diversity of naturalised populations and lack of inoculant persistence. Therefore, it is necessary to understand the ecology of naturalised populations, including their genetic interactions with inoculant strains, in order to develop strategies to improve the competitiveness and persistence of inoculant strains. Alternatively it may be possible to increase the effectiveness of indigenous populations through gene transfer from the inoculant strain. The possibility of breeding specific host cultivar/rhizobial strain combinations also merits further research. Keywords: competition, genetic stability, inoculation, nitrogen fixation, rhizobia, white clover
Leaf senescence is a programmed event where resources are mobilised from older tissues to the meristematic regions of the plant. In white clover (Trifolium repens L.), leaf and stolon senescence have an important impact on the persistence of the legume in pasture. As part of our investigation of leaf senescence, we have evidence for a central role for the plant hormone ethylene and have identified genes encoding ethylene biosynthetic enzymes. In this paper we include data showing some physiological changes as leaf tissue undergoes senescence and present evidence for the role of ethylene in regulating this process. Keywords: chlorophyll, ethylene, senescence, stolon, leaf, Trifolium repens L.
Previous work found that white clover (Trifolium repens L.) yield initially decreased, but subsequently increased following a pastoral fallow. The objective of this research was to quantify the response in herbage production and stolon characteristics of white clover up to 4 years after fallowing. Four treatments were used: fallowed 1990/91 (F4), fallowed 1991/92 (F3), fallowed 1993/94 (F1) and non-fallowed (F0). The fallowing period was between September and May. White clover dry matter yield (between 15/12/94 and 18/5/95) was significantly greater for the treatment F4 than F0 (P<0.05). Total herbage and grass production showed no statistical difference between treatments. The total stolon length (98.1 m/m2) of F4 was significantly greater than that of F3 (45.9 m/m2) and F0 (39.3 m/m2). Total stolon weight and growing point density also increased significantly during the 4 year post-fallow period (P<0.05). The average internode length remained greater until 6 months after fallowing (2.8 mm) and declined thereafter (1.9–2.3 mm). It is concluded that the increase in white clover postfallowing was attributed to its ability to disperse through the pasture during fallowing and re-establish in gaps in the pasture where it had previously not been present. Keywords: hill country, pastoral fallow, stolon, Trifolium repens
The value of white clover as a component of New Zealand pastures is undeniable, but it is also widely recognised that clover has limitations as a pasture plant and that these can lead to inefficiencies in the performance of grass/clover associations. This paper identifies some of the limitations to optimising the contribution of clover in complex soil/pasture/animal systems, within the context of the expectations commonly held of clover. Limitations to exploiting the greater digestive efficiency and short-term intake rate of clover compared to grass when they are grown in a mixture include animal behaviour responses that sometimes impose a restriction on total daily intake of nutrients, and the fact that clover often constitutes less than 20% of the pasture. Nitrogen inputs and yield advantages are also restricted by the low clover content of pastures. A simulation model is used to analyse the co-existence of grass and clover as influenced by N dynamics. This model explains the basis for selfregulation by grass/clover mixtures of the amount of mineral N in the soil. Self-regulation minimises N losses from mixtures, but the dynamic response of grass and clover to N availability also means that there may only be limited scope for increasing the overall clover content, or decreasing the spatial heterogeneity in clover distribution, of a mixture. Managing grass/clover associations to realise the benefits of white clover therefore means manipulating a complex system, where the outcomes of manipulation depend as much on the response of the companion grass as on the response of the clover itself. Opportunities for attaining a higher clover content in pastures include: manipulating the preferences of animals for clover versus grass; spatially separating grass and clover within fields; increasing the metabolic efficiency of N fixation in clover; uncoupling the apparent link between rhizobium symbiosis and the N content of clover leaves; and modifying the stolon morphology of clover as a way of increasing clover presence in favourable microsites within the pasture. Keywords: genetic improvement, grass/clover competition, grazing behaviour, intake, models, N fixation, nitrogen dynamics, nutritive value
The causes of low seed set per floret in white clover (Trifolium repens L.) are reviewed. Three stages of flower head development are distinguished as important for a high level of seed set: a pre-fertilisation stage, a stage of anthesis leading to pollination, and a postfertilisation stage in which seed provisioning occurs. In sunny conditions the percentage seed set is limited at the pre-fertilisation stage by up to 20–30% ovule sterility. Relatively low light intensities during the postfertilisation stage can lead to abortion of a high proportion of fertilised ovules and developing seeds. Experimental results suggest that seed yields under optimal growing conditions can be limited solely by the level of pre-fertilisation ovule sterility and probably cannot be bettered, but further understanding of the seed-provisioning requirements for photosynthate could lead to improved management practices for seed production under conditions of lower light intensities. Keywords: abortion, light intensity, ovule, seed provisioning, sterility, white clover
Effects of high N fertiliser rates on white clover content in the sward and clover plant morphology were monitored over two years (June1993–June 1995) at the DRC, Hamilton. The clover study was part of a farmlet trial aimed at increasing milksolids (MS) production to 1750 kg MS/ha using urea (0, 200 or 400 kg N/ha/yr) to increase pasture production at low (3.2 cows/ha) or high (4.5 cows/ha) stocking rates. On low stocked farmlets clover contents declined to 10.6% (200 kg N/ ha/yr) and 2.2% (400 kg N/ha/yr) by June 1995 compared with 16.8% under no N. Decreased clover content was a result of increased competition from N-boosted ryegrass. At the high stocking rate, N application resulted in clover contents of 14.9% (200 kg N/ha/yr) and 6.8% (400 kg N/ha/yr) compared with 15.4% under no N. Pasture utilisation was better on these farmlets, suggesting the improved utilisation and control of additional feed, particularly during spring, was responsible for the higher clover content. Measurements of clover plant density supported the clover content observations. By June 1995 there were 438, 227 and 26 plants/m2 under 0, 200 and 400 kg N/ha/yr respectively. High N rates also affected clover plant morphology; plants developed fewer axillary buds and stolons, and had lower stolon dry weights under 400 kg N/ha/yr. Keywords: clover content, dairying, morphology, nitrogen, plant density, Trifolium repens, white clover
White clover (Trifolium repens L.) is the key to the international competitive advantage of New Zealand’s pastoral industries, which are reliant on a cheap, high quality feed source. White clover benefits pastoral agriculture through its ability to fix nitrogen, its high nutritive value, its seasonal complementarity with grasses, and its ability to improve animal feed intake and utilisation rates. The annual financial contribution of white clover through fixed nitrogen, forage yield, seed production and honey production is estimated as $3.095 billion. The impact of white clover has resulted from understanding how it grows, and then developing appropriate management systems, fertiliser strategies, and improved cultivars. While the future of white clover as the legume base of our pasture is secure there are challenges and opportunities ahead. These include the increasing use of mineral nitrogen, competitiveness with high endophyte ryegrasses, filling gaps in our knowledge base, responding to industry signals, the advent of transgenic technologies, the removal of anti-quality characters particularly those associated with the incidence of bloat, and assuring that nitrogen fixation rates, in grazed pastures, increase as the yield potential of white clover is itself increased. Keywords: economic value, nitrogen fixation, nutritive quality, pastoral agriculture, white clover
Seed yield in white clover depends largely on the number of ripe inflorescences per unit area, and the plant growth regulator paclobutrazol has been used in an attempt to both increase and concentrate inflorescence production, and hence increase seed yield. However results reported from both New Zealand and Europe have been inconsistent, with seed yield responses ranging from highly significant increases to no effects. The current high cost of the chemical ($1280/ha) requires a seed increase of over 300 kg/ha to ensure an economic return. Similarly no consistent effects of paclobutrazol on white clover vegetative and reproductive growth and development have been established. Possible reasons for this variable response of white clover to paclobutrazol application are presented and discussed. Keywords: inflorescence production, Parlay, reproductive growth, seed yield components, Trifolium repens, vegetative growth
Increased taproot diameter is an important component in maintaining white clover (Trifolium repens L.) growth, nitrogen fixation and persistence during short-term moisture stress. Previous reports indicated selection for large taproot diameter would result in commensurate increases in leaf size and poorer growth habit. The current research investigates the response to selection for taproot diameter and the association between taproot diameter and leaf size in large-leaved clovers suited to dairy grazing systems. Taproot diameter increased by 2.4% per cycle while leaf size and growth habit were not significantly altered. Furthermore, while taproot diameter did not increase between cycle 2 and 3, the root index which measures the ratio of taproot diameter to leaf size increased linearly across all three cycles. These results suggest it is possible to select white clovers for dairying which have larger taproot diameter while maintaining a suitable growth habit. Keywords: dairying, drought, genetic improvement, root morphology, Trifolium repens L., white clover,
Insect pests and their predators were sampled in Canterbury white clover crops during the 1994–95 season. Bluegreen aphid and potato mirids occurred early (late October to mid-November) during the season and were a potential cause of major injury to developing flowerheads. Australian crop mirid, wheat bug, brown shield bug, and spittle bugs occurred later in the season during January and were more likely to affect seed fill and resultant seed quality. Bluegreen aphids reached an overall maximum number of 800 per m2 during early December, while potato mirid nymphs and adults were found in significantly (P<0.001) higher numbers in the field edges reaching maximum numbers of 40 and 5.7 per m2 in early December and mid-December, respectively. Of the five species of arthropod predators collected, lacewing larvae and ladybird adult and larvae numbers were positively (P<0.01, 0.001, 0.05, respectively) correlated to bluegreen aphid numbers. Selective insecticides should be applied to conserve arthropod predator populations, while controlling hemipteran pest numbers. Keywords: bluegreen aphid, hemipteran, lacewing, ladybird, pests, potato mirid, predators, seed production, white clover
For the last five years an average 14,761 ha of white clover has been grown for seed, with 77%, 8% and 15% sown in public cultivars, New Zealand and overseas proprietary cultivars, respectively. The area presently contaminated by proprietaries is estimated at 20,000 ha. New Zealand requirements for cultivar-change are more effective than OECD requirements. The five-year break period enables successful cultivar change in 90% of cases and is improved further when buried seed counts were used prior to sowing to indicate paddocks with unacceptable buried seed load. Current isolation distances appear adequate with virtually all foreign pollen deposition occurring within 24m of the pollen source. Capture of additional public cultivar area (77%) by proprietary cultivars will rely on increasing the seed yields of proprietary cultivars by approximately 25%. This is realisable through greater attention to the environmental requirements of each cultivar and through better technology transfer between head licencees and growers. Keywords: buried seed, crop areas, cultivar-change requirements, public cultivars, proprietary cultivars, seed production, Trifolium repens L., white clover
In recent years there has been an increase in the number of white clover seed crops taken for a second harvest. Traditionally yields from second year crops are substantially lower than first year crops. A trial was established investigating techniques to increase yields in second year crops. The trial was located in a dryland crop of white clover (cv. Grasslands Demand) 4 km east of Methven, mid Canterbury. It involved 10 herbicide treatments and 8 ‘inter-row’ treatments arranged in a split block design. Number of mature flower heads were recorded on all treatments at harvest as an indirect estimate of yield. Additionally, selected treatments were cut and collected using a rotary type mower, threshed, and machine dressed for direct estimates of seed yield. Flower number and machine dressed seed yield were significantly (P<0.01) higher on treatments with late winter applications of Paraquat and Gardoprim (terbuthylazine) at 400 g + 1000 g ai.ha-1 (640 flowers.m-2, 311 kg.ha-1) and 400 g + 1500 g ai.ha-1 (710 flowers.m-2, 326 kg.ha-1), compared to an untreated control (490 flowers.m-2, 209 kg.ha-1). Flower number was significantly (P<0.01) decreased by late winter applications of Glean (Chlorosulfuron 5.5 g and 11.0 g ai.ha-1) and a spring application of Harmony (Thifensulfuron-methyl 15 g ai. ha-1). Flower number and machine dressed seed yield were significantly (P<0.01) increased by a light cultivation followed by grazing in mid winter (650 flowers.m2, 395 kg.ha-1) compared to no mechanical disturbance (500 flowers.m-2, 305 kg.ha-1). ‘Creating’ new rows at right angles to the original (first harvest rows) by inter-row spraying in winter (Glyphosate and Dicamba 30, 45 and 60 cm row spacing) and spring (Buster – Glufosinate ammonium – 30 cm row spacing) did not significantly affect seed yield or flower number. The significant yield increases are associated with increased space for stolons to run, and effective residual weed control. On this dryland site which experienced early summer moisture stress, inter-row spraying appeared to be too ‘severe’ in terms of creating space, and the stolons did not run to fill the whole area. Light cultivation and grazing was considered a less severe treatment, leaving more plants, and appeared a more suitable treatment on this dryland site in a dry season. Keywords: inter-row spraying, residual weed control, second harvest, white clover, seed production
The breeding history of 10 white clover cultivars bred in New Zealand is described. The cultivars are compared for leaf size, cyanogenesis and stolon growing point density. Leaf size and stolon growing point density were negatively associated although more recent cultivars (Prestige, Demand, Sustain and Challenge) had higher stolon growing point densities than older cultivars of similar leaf size. Both leaf size and peak flowering period, and leaf size and cyanogenesis level were positively associated among the 10 New Zealand cultivars. The agronomic performance of cultivars is summarised on the basis of preferred management, key seasonal performance, disease tolerance, and climatic and edaphic adaptation. Keywords: adaptation, breeding, cultivars, cyanogenesis, flowering, leaf size, white clover
Ten years experience from trial-and-error plus some advice, has led to the development of successful base management systems for white clover cultivar-change. These systems are capable of modification according to site and season to maximise seed returns and have reached the point where white clover is now my safest crop. This paper considers crop management requirements necessary from the ‘change’ decision, some years before inception, through to harvested seed yield. Keywords: crop management, cultivar-change requirements, harvest, seed production, sowing technology, Trifolium repens L., white clover
Two populations of white clover, selected for long (L) and short (S) root hairs from the cultivar Tamar, were used to determine the root hair response curve to a range of aluminium (Al) concentrations similar to those found under field conditions. Seeds from the L and S populations were germinated and grown in low ionic strength hydroponic culture. Al was added to give final concentrations of 0, 2.5, 5, 7.5 and 10 ìM Al in solution. After 4 weeks plants were harvested and subsampled for root hair analysis. Mean root hair length, root hair number and total root hair length were recorded. Mean root hair length decreased by about 30% at 2.5 ìM Al, and by 70% at 10 ìM Al, but the most Al sensitive parameter was root hair number. Root hair numbers decreased by 70% at only 2.5 ìM Al, and at 10 ìM Al, had decreased by 99%. This pruning effect on total root hair length and number has major implications for the root hair functions of nutrient acquisition, preserving the moisture film, anchorage and nodulation. These are discussed in relation to New Zealand pastoral systems. Keywords: aluminium tolerance, nodulation, root hairs, root pulling, Trifolium repens L., white clover
White clover in New Zealand fixes nitrogen equivalent to 4.5 million tonnes of urea annually. Experiments on the tactical use of about 50 kg N ha-1 yr-1 to stimulate grass growth when clovers are less active indicate that it is generally profitable, but much heavier dressings have rarely been shown to pay at current cost/price structures. The significance of biological nitrogen fixation (BNF) cannot be measured solely by dry matter yields as the quality of herbage is influenced by the contribution of clover and affects yields of animal products and health. Our dependence on BNF gives us a relatively low energycost system of pastoral farming because of the high energy cost of producing fertiliser-N and is therefore more sustainable. The heavy use of fertiliser-N suppresses clover growth and N-fixation, increases losses of ammonia and nitrous oxide to the air and nitrate in drainage water. The extra stock carried leads to greater emission of methane. Reliance on clovers may give lower production but lessens damage to the environment. Keywords: biological nitrogen fixation, energy costs, environment, fertiliser nitrogen, pastoral agriculture, sustainability
Root-knot nematode (Meloidogyne sp.) reduces growth and nutrition of white clover (Trifolium repens L.) in New Zealand, and breeding resistant cultivars (with low galls per gram of root) is the preferred control method. Resistant and susceptible selections were bred from a wide range of white clover lines for three generations. In the third generation there were significant differences between seed lines from the selections for number of galls, root dry weight, visual growth score and galls/gram of root dry weight. Resistant selections had 43% of the susceptible selections’ galls per gram, and 50% of the number of galls. Germplasm showing resistance to Meloidogyne spp. in the USA showed partial resistance to the local Meloidogyne sp. Two resistant and two susceptible genotypes were also compared for nematode egg production; resistant genotypes had a mean of 3,460 eggs/plant, compared to 25,030 for susceptible genotypes. Keywords: breeding, Meloidogyne sp., resistance, rootknot nematode, screening, selection, Trifolium repens, white clover
White clover (Trifolium repens L.) is the dominant legume of temperate pastures, having been improved by breeding since the 1930s. The 1994 OECD Register lists 93 cultivars, with a further 25–30 cultivars also known to commerce. Therefore, in excess of 100 cultivars are available to fulfil a world annual market of 8500–10,500 MT. Globally, New Zealand is the major white clover production region, providing 50– 55% of the seed. Other key production regions are Denmark, USA and South America. Consumption of white clover has been relatively static for some time, ranging from 8000–10,000 MT per annum. Between 55–60% of the seed is used in the northern hemisphere (approx. 40% by Western Europe – UK, France, Germany). USA, South America and New Zealand all consume similar tonnages annually (approx. 1000–2000 MT each) with smaller tonnages used in Australia. One cultivar, Grasslands Huia, has dominated the world white clover seed market for many years and it still remains the world’s major cultivar by volume. However, in the last 10 years its position has come under increasing pressure from New Zealand and international proprietary cultivars. Eventually proprietary cultivars with improved agronomic performance will supersede the consumption of commodity/public white clovers in those countries where national listing is required to obtain release and recommended listing is need to ensure successful marketing. Despite this, Grasslands Huia will continue for many years to play a major role in supplying markets where national listing is not a prerequisite to release and price is a major factor in purchase decisions. Keywords: commodity cultivar, global market, Grasslands Huia, leaf size, market share, production trends, proprietary cultivar, seed industry, Trifolium repens L., white clover
The Gardyne Family farm a 710 hectare property at Chatton near Gore in Southland. The property is intensively farmed with 9,375 stock units, sheep and beef being carried at rates of 17.5 su/ha on the cropping property and 12.5 su/ha on the Pyramid Hill grazing property. White clover is the key to animal, crop and herbage production supplying nitrogen for highly productive pastures, building organic matter levels for the cropping rotation, and providing very high quality feed for finishing young stock. Management techniques to maximise clover production are essential and include: (i) use of adequate P, K and S fertiliser to ensure Olsen P levels above 20, (ii) set stocking the grazing block from lambing to weaning to generate maximum clover yields, (iii) returning older grass dominant pastures to cropping to harvest the fertility build up and restore a clover-dominant pasture, and (iv) maintaining adequate pasture cover to allow the pasture plants to express their potential. The Gardyne family use and experience the benefits of the regionally bred Grasslands Demand white clover on their property. Establishment of new cultivars is discussed, and suggestions made for further research. Keywords: beef, cropping, fertiliser, Grasslands Demand, pasture establishment, pasture management, sheep, Southland, stocking rates, white clover
Ten cultivars of white clover were grown in a glasshouse at three levels of soil moisture. Leaf productivity was greatly reduced by moisture stress. The productivity of cultivars was found to be significantly different under well-watered conditions. Larger-leaved cultivars tended to be more productive than those with smaller leaves, but this difference was lost at high moisture stress creating a significant cultivar by moisture treatment interaction. Water use efficiency (WUE) increased with increasing moisture stress, but within any one moisture level there were no significant differences between the cultivars. An integrated measure of WUE is captured by the level of discrimination against 13C in plants tissue (Ä). Over the range of moisture levels used, a strong negative correlation was found between Ä and WUE. A strong positive correlation was found between productivity and Ä over the range of moisture treatments, however, within any one moisture level no significant relationship was established. Keywords: carbon isotope discrimination, cultivars, moisture stress, Trifolium repens, water use efficiency
Despite the potential value of white clover for Australian pastures in the high rainfall zone, there is a lack of adapted cultivars, especially for dryland environments where hot dry conditions in summer limit persistence. A joint NZ AgResearch – NSW Agriculture breeding project is evaluating key groups of world-sourced white clover germplasm characterised by specific criteria; medium leaf/early flowering, high nodal root frequency, taprootedness, stoloniferous/medium leaf and drought tolerance. Results in the first growth cycle indicated that plant spread and herbage yield were associated with these criteria. Results over three growth cycles will be used to identify elite parent genotypes for polycrossing and testing in target dryland environments. Keywords: breeding, drought tolerance, dryland pastures, persistence, Trifolium repens, white clover
An ecotype collection of 98 populations of white clover (Trifolium repens L.) from pastures in the eastern USA together with five USA Ladino and five New Zealand cultivars were grown in grass swards at Raleigh, North Carolina; Palmerston North and Lincoln, New Zealand. The material was compared for leaf size, cyanogenesis, seasonal growth, % clover cover and persistence. When examined as a single group, the USA ecotypes consisted of a wide range of plant types from small-leaved acyanogenic to large-leaved cyanogenic types. This contrasted with the uniformly large-leaved acyanogenic USA Ladino cultivars which have been the principal cultivars sown in eastern USA. Various selection pressures over time together with introgression between Ladino and resident wild clover types has resulted in a wide array of plant types. At the North Carolina site, USA ecotype material generally demonstrated better growth and persistence compared to the USA Ladino and New Zealand cultivars. The best ecotype plots from the Piedmont (inland region) had 55% clover cover by the third spring compared to 12% cover from the USA cultivar, SRVR and 2% cover from the NZ cultivar, Huia. Selective pressures such as hot summers, viruses, root-feeding pests and other stresses on the local clover types have resulted in ecotype material with improved adaptive features. The USA ecotype collection is an important source of germplasm for development of improved white clovers for the eastern USA. At the New Zealand sites, the USA material demonstrated pooraverage yields compared to NZ cultivars. However, a small set of USA ecotypes showed good recovery following the dry 1995 summer at Lincoln and this material warrants closer examination to determine the adaptive mechanisms involved. As the USA ecotypes show a general lack of adaptation to New Zealand pastures, any desirable features such as heat tolerance, deeper nodal roots or virus resistance uncovered in this material will require hybridisation and backcrossing with selected elite New Zealand material to capture the benefits. Keywords: adaptation, eastern USA, ecotype populations,
Annual production in New Zealand dairy pastures is limited by nitrogen supply and therefore requires nitrogen fertiliser to increase annual pasture production. This paper summarises the advantages and disadvantages of clover nitrogen and fertiliser nitrogen including the effects of both nitrogen sources on feed quantity and quality, factors limiting nitrogen fixation and nitrogen fertiliser response, defoliation effects on white clover (Trifolium repens L.), animal health problems associated with clover and nitrogen fertiliser, and environmental effects. UDDER, a dairy farm simulation model, is used to predict the nitrogen fertiliser rate and white clover content in pasture necessary for optimum pasture production and feed quality. Maximum gross margins per ha and a high level of milksolids production per ha and per cow can be best achieved by combining nitrogen inputs from white clover and nitrogen fertiliser. The model predicts best results would be achieved with clover contents of 30–40% and nitrogen fertiliser rates of 100–200kgN/ha/yr. Keywords: dairying, feed quality, nitrogen fertiliser, nitrogen fixation, Trifolium repens
A large proportion of clover stolon in the field (20– 95%) is found below the soil surface (Hay 1983, Sackville Hamilton & Harper 1989). The proportion increases dramatically through the autumn and is reduced in spring. This pattern of burial has been attributed to earthworm casting and livestock trampling (Hay et al. 1987). In greenhouse experiments we observed that stolons were often held tightly to the soil surface and some nodes on mature stolons were beneath the surface. Three experiments designed to measure downward movement of stolons relative to the soil surface in controlled conditions without trampling or earthworm casting are described. Keywords: roots, stolon burial, Trifolium repens L.