Avoidance of degradation of alpine pasture through grazing management: Investigations of change in vegetation nutrition characteristics as a consequence of sheep grazing at different periods of the growing season

The maintenance of animal husbandry in mountain areas can prevent the general degradation of the landscape due to the disuse of pastures and meadows. This study investigated the changes over the productive season of the nutritional characteristics of an Alpine pasture with the objective of maintaining grazing sheep fed only on the available herbage. Four homogeneous areas of an Alpine pasture located in northeast Italy were cut at the end of June, July, August, and September, simulating different grazing periods by the animals. the herbage was sampled to estimate the botanical and chemical composition and fed to four Lamon breed wethers (76-5 kg average bodyweight) measuring voluntary intake, digestibility and energy value. the botanical composition of the pasture changed as the vegetative season advanced, with a progressive increase in grass species. the protein content decreased from 16-3 per cent dry matter in the first grazing period, to 9-6, 9-9 and 7-9 per cent, respectively, in the following, while the neutral detergent fibre increased from 62-1 per cent in the first period to 78-4, 77-7 and 79-4 per cent in July, August, and September, respectively. The nutritional evaluation of the forage material was carried out using four Lamon wethers housed in single metabolic cages. the voluntary intake of herbage was 1151 g d⁻¹ at the end of June, decreasing significantly to values below the recommended requirement for maintenance in the subsequent periods of the study. No selectivity was observed for specific botanical species. the in vivo digestibility of the herbage was lowered by the delay in the use of the pasture and the resulting energy intake met the recommended maintenance requirements for grazing only in the earlier period of pasture consumption. the late use of the pasture and the corresponding underfeeding of the animals would necessitate a feed supplementation to limit excessive loss of bodyweight. the conclusion is that the objective of maintaining grazing animals in mountain areas without any supplementation can be carried out exclusively by adopting an efficient grazing management able to provide good quality pasture throughout the vegetative season.     

BIG BLUESTEM RESPONSE TO FERTILIZER AND DEFOLIATION ON THE LOUISIANA COASTAL PLAIN

Although big bluestem (Andropogon gerardii Vitman) is used for forage and conservation in the Great Plains, potentially useful Louisiana ecotypes have received little attention. Cloned plants from a robust big bluestem plant collected near Rosepine, LA were assessed for responses to fertilizer and defoliation in a field evaluation of potential forage value. Annual application of nitrogen fertilizer at 50 kg ha^?1 did not increase herbage yield until the third year. Clipping twice annually decreased productivity compared to once annually after the second year. Fertilizer effects on forage nutritive value were small. Clipping improved late-season nutritive value largely due to greater stem development of previously undefoliated plants. Limited responsiveness to fertilization and detrimental effects of repeated defoliation on productivity indicate that even this robust local big bluestem ecotype provides little potential as a pasture plant. Potential is indicated for other uses including wildlife habitat and grassland ecosystems managed for conservation purposes.     

Seasonal variation of selenium,crude protein,and in vitro organic matter digestibility of Brachiaria humidicola from marajó island,brazil

Abstract

Nutritional content of Brachiaria humidicola grass in relation to crude protein (CP), in vitro organic matter digestibility (IVOMD), and selenium (Se) as related to wet and dry seasons in the Amazon region of Marajó Island, Brazil, was determined. Twenty‐four samples, 12 from the dry and 12 from the wet season, were analyzed. Grass selenium concentrations were not influenced by season and the means were above the minimal requirement for beef cattle in both seasons (0.14 or 0.15 ppm). Factors other than rainfall may be involved. Crude protein concentrations were lower (P<.05) in the dry (3.5%) than in the rainy season (4.8%) and in both seasons were lower than the critical level for cattle (<7.0%). The IVOMD means were extremely low, 33.5% in the wet season and 33.6% in the dry season. These analytical values indicate that Brachiaria humidicola grown at Marajó Island has nutritional limitations for grazing buffalo and cattle production.     

基于划区轮牧理论的祁连山北麓牧区动态草畜平衡研究

为了恢复和保护祁连山北麓草地生态系统,建设生态畜牧业,该文以肃南县祁连山北麓牧区为研究对象,基于划区轮牧理论模拟不同降水情景下轮牧区理论载畜量并分析现状牧区草畜平衡状况,分析理论载畜量下轮牧牧区产草需草过程,进行牧区动态草畜平衡分析,并与传统方法和基于关键场理论方法进行对比。结果表明:肃南县祁连山北麓牧区降水量极大地影响着牧区理论载畜量,宜将平水年理论载畜量100.9万标准羊单位作为今后牧区畜牧业管理的主要参考指标;2015年牧区同时存在牲畜超载和欠载并且冷暖草场理论载畜量差异较大,应在后期发展中注重调整当前的畜牧业发展结构和合理配置冷暖草地资源。通过3种方法的草畜平衡动态对比分析,基于划区轮牧理论方法不仅能保证不同轮牧区的草畜动态平衡,且能保持饲草的高效利用,在轮牧区草畜平衡分析计算中具有一定的优越性。     

Specific polyphenol oxidase activity of red clover (Trifolium pratense) and its relation with forage quality in field experiments

Abstract

In feeding studies, red clover (RC) influenced positively the N utilization by ruminants. A relationship between polyphenol oxidase (PPO) activity and forage quality has not been established. Our objective was to investigate seasonal, site, genotype, and management effects on specific PPO activity in RC in three experiments under field conditions, and relate the activity to forage-quality parameters. In Experiment 1, six RC genotypes at two study sites were submitted to a 3-cut system. Specific PPO activity, forage quality, and vegetation stage were determined. PPO activity varied between harvest and study sites, with genotypes differing up to 3-fold in PPO activity within harvests. The specific PPO activity, forage quality, and vegetation stage in RC subjected to 5-cut system and grazing (Experiment 2) were determined. Additionally, in Experiment 3, cutting frequency in RC swards including mechanical stress (rolling) was investigated. The induction of PPO activity in RC by grazing or mechanical stress (Experiments 2 and 3) increased the activity up to 2.5-fold compared with RC at similar vegetation stage submitted to the 5-cut system. Mechanical stress induced by grazing or rolling, and seasonal differences, seem to have a larger influence on specific PPO activity than does the genotype effect observed in Experiment 1. For forage quality, an increased specific PPO activity explained 29–46% of the reduction in protein fraction ‘A’ content (non-protein N) in the cutting systems in Experiments 2 and 3. Other CP fractions achieved a lower relation. Furthermore, the precipitation-to-temperature ratio preceeding a harvest explained 63% of the variation in the specific PPO activity. In conclusion, the PPO activity in RC is induced by grazing and rolling. Whereas weather conditions preceeding a harvest showed a large influence, genotype influence had only minor relevance. These results may have implications for regional harvest management towards efficient N utilization by ruminants.     

Soil aluminium availability in Andisols of southern Chile and its effect on forage production and animal metabolism

Soil acidification limits livestock production in many parts of the world. Two experiments were carried out to investigate the effect of aluminium (Al) on pasture yield and animal production. In experiment 1, the effect of raising soil pH (in water) from 5.1 (acid soil, A) to 5.6 (corrected soil, C) was tested on forage and animal production. In experiment 2, Friesian calves were individually fed either silage with or without the addition of 2000 mg kg^?1 of Al as aluminium sulphate. Al, P, Ca and Mg concentrations were measured in forage, and in animal blood and faeces. Live weight gain (LWG) was also measured. Soil acidification resulted in a 36% overall reduction in pasture yield in the A treatment (9.4 ± 0.31 and 14.7 ± 0.47 t ha^?1 year^?1 for the A and C treatments respectively) and in 15% reduction of the protein concentration in the herbage. No significant differences were found for the individual daily LWG (P > 0.05). Direct Al intake reduced animals daily LWG by 14% (P ≤ 0.05). The correction of soil acidification increased livestock production by 125% when stocking rate was strictly adjusted to grassland production.     

Management options to decrease phosphorus and sediment losses from irrigated cropland grazed by cattle and sheep

In southern New Zealand, grazing of forage crops is common practice to satisfy feed requirements of animals in winter when pasture growth is limited. This practice has been shown to cause soil physical damage and increased loss of surface water contaminants sediment and phosphorus (P) to water bodies. Strategies to mitigate the loss of sediment and P were trialled on a Pallic soil type (Aeric Fragiaquept) in the North Otago Rolling Downlands of New Zealand. All sites were irrigated and measurements were made of losses in overland and sub‐surface flow from intensive cattle or sheep grazed, winter forage crops, and sheep grazed pasture. Two mitigations (restricted grazing of crop to three hours and the application of aluminium sulphate) were assessed for their potential to decrease contaminant loss from cropland. Volumes of surface runoff and loss of total P, filterable reactive P and sediment showed significant differences (P < 0.05) between the control treatments (i.e. no mitigation) with cattle crop (88 mm surface runoff) > sheep crop (67 mm) > sheep pasture (33 mm). The contribution of irrigation water to overland flow water, as a result of saturation‐excess conditions, varied between treatments with more loss under cattle crop (20% of total) compared with sheep crop (15%) and sheep pasture (11%). These differences are probably an effect of soil physical condition and highlight the importance of accurate irrigation scheduling to keep soil moisture below field capacity. Restricted winter grazing and alum application after grazing significantly (P < 0.05) decreased P losses in surface runoff under cattle (from 1.4 to 0.9 kg P/ha) and sheep (from 1.0 to 0.7 kg/P/ha) grazed crop plots by about 30%. In cattle grazed plots, restricted grazing also decreased suspended sediments (SS) by 60%. The use of restricted grazing is suggested as a means of decreasing P and SS loss from grazed winter forage crops. The use of alum shows some promise for decreasing P losses, but requires further work to determine its long‐term effectiveness and use in other soils and management regimes.     

Nitrogen and mineral composition of autumn‐grazed pasture

Abstract

Grazing management in autumn can influence the botanical composition and productivity of a sward. Cycling of nutrients as a result of grazing livestock activity and variable canopy growth rates may influence mineral nutrient supply and demand in a dynamic canopy. An experiment was conducted to determine the influence of autumn grazing practices on the growth and composition, including minerals in terms of ruminant requirements, of a grass/legume sward. Paddocks were established and three replicates grazed by growing lambs for 30‐, 60‐, or 90‐d intervals beginning in late summer. Herbage samples were collected at the beginning of the grazing interval and at the end of each interval (closing date). Herbage mass, and nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), and sulfur (S), as well as copper (Cu) and zinc (Zn) were examined in terms of the influence of sampling date, closing date, year, and the interaction of these factors from stockpiled and grazed canopies. Soil mineral composition was determined as well. Concentrations of all minerals declined with increasing soil depth and P, Na, Mg, and Ca increased in soil over the course of the experiment. Soil N concentration was reflected in the pattern of herbage growth in autumn. In general, closing date had no influence on herbage mineral composition and concentrations were within the recommended levels for a range of livestock. Phosphorus was the exception and concentrations in herbage were low in terms of requirements for high producing livestock such as lactating dairy cattle. Uptake or mineral reallocation within the plant remained constant during the autumn growth interval, since mineral yields were stable as growth rates declined in 1991 and increased when growth rates were stable in 1992. Mineral related nutritional problems in grazed mixed‐species pasture, would most likely be a function of mineral bioavailability or interactions, rather than low concentrations in the herbage.     

Long-Term Residual Value of Zinc Fertilizer for Pasture Legumes Using Yield of Dried Herbage and Critical Concentration of Zinc in Young Tissue

The zinc (Zn) requirements of subterranean clover (Trifolium subteraneaum L.) are well known for the predominantly marginally acidic to neutral sandy soils of southwestern Australia, but the Zn requirements of French serradella (Ornithopus sativus Brot.) and biserrula (Biserrula pelecinus L.), now also grown on these soils, is not known and were investigated in a glasshouse pot experiment. Soil was collected from field plots never treated with Zn or treated once only with 0.5 and 1.0 kg Zn/ha as Zn oxide either in 1983, 1984, 1986, 1990, 1992, 1996, 1997, or 2000. In the pot experiment, six levels of Zn were freshly-applied to samples of soil collected from each Zn treatment of the field experiment, and pots were sown either with subterranean clover cv. ‘Dalkeith’, French serradella cv. ‘Margurita’, or biserrula cv. ‘Casbah’. The pasture species were defoliated by cutting pasture herbage 3 cm above the soil surface for up to 4 consecutive defoliations. The approximate linear relationship between the level of freshly-applied Zn in the pot experiment required to produce 90% of the maximum yield of dried defoliated herbage (y-axis) and the number of years since Zn was applied in the field (x-axis) was used to project the number of years it took for the 0.5 or 1.0 kg Zn/ha treatments applied in the field to require the same level of freshly-applied Zn to produce 90% of the maximum yield of the nil-Zn treatment in the field. This was 18–19 years for the 0.5 kg Zn/ha treatment and 32–35 years for the 1.0 kg Zn/ha treatment. The range in values was due to differences between legume species and the defoliation treatments, which were not significant. When yields were measured, samples of young growth (YG) were separated from the rest of the defoliated herbage (ROH) and the concentration of Zn in YG and ROH was measured. The concentration of Zn in YG that was related to 90% of the maximum yield of defoliated dried herbage (critical tissue test value) was (mg/kg) 13 for subterranean clover, 17 for French serradella, and 19 for biserrula; respective critical tissue test values for ROH were 19, 24, and 21 mg/kg. The approximate linear relationship between critical Zn concentration in YG (y-axis) and the number of years since Zn was applied in the field (x-axis) was used to project the number of years it took for the 0.5 and 1.0 kg Zn/ha levels applied in the field to reach the same critical tissue test value as the nil-Zn treatment of the field experiment. This was 17–20 years for the 0.5 kg Zn/ha treatment and 31–37 years for the 1.0 kg/ha treatment, which was similar to the 18–19 and 32–35 years projected using yield data. Before sowing the legumes in the pot study soil samples were collected to measure soil test Zn using the DTPA procedure. The critical DTPA soil test Zn, the soil test value that was related to 90% of the maximum yield of defoliated dried herbage, was about 0.20 mg Zn/kg for the 3 pasture legume species and all Zn treatments in the field and pot studies.     

Plant root morphology and soil biological indicators under primary development of various swards

Plant nutrition conditions are limited in naturally acidic soil due to harmful hydrogen and aluminium ions. More favourable conditions for plant nutrition (soil liming) will affect root qualitative and quantitative parameters and influence ecosystem stability. Four legume–grass swards were cultivated. The swards were a combination of one species of legume and two species of grasses: Trifolium pratense L., Trifolium repens L., Trifolium hybridum L., Medicago sativa L. (each of 50%) with Phleum pratense L. (35%) and Poa pratensis L. (15%). The aim of this study is to evaluate the root morphological and soil biological indicators of legume–grass swards under the first two years of development in soils with different pH levels.

Sward ecosystem development depends on the pH of the soil, sward species composition and soil biota. During the first year of sward development, soil pH had a significant influence on the morphology of root system. Sward‘s root mass and total root length was 2.4 and 2.2 times bigger in naturally acidic soil. This resulted in a change of biological parameters.

In the second year of sward development, soil pH had no significant influence on sward‘s root mass. However, under the impact of different soil pH, various sward‘s root systems were formed and the root C:N ratio had changed. It is observed that, regardless of the sward species composition and the year of development, at higher root C:N ratio soil microbial biomass was higher and CO₂ emissions were lower in swards in naturally acidic soils.

Regardless of soil pH, different types of clover–grass swards promoted organic carbon immobilization in microbial biomass and, at the same time, stabilized the sward ecosystem in the top soil layer (soil respiration in 0–10 and 10–20?cm layers was lower) more effectively than the alfalfa–grass sward.     

Reduced grazing and the decline of Pulsatilla vulgaris Mill. (Ranunculaceae) in England, UK

In England Pulsatilla vulgaris is a threatened herb that declined from 130 to 33 sites between 1750 and the 1960s due to ploughing-up of calcareous grassland. We examined the subsequent fate of these populations using documentary evidence and field survey. Demographic trends were related to changes in grassland composition, structure and management and responses to increased above-ground competition (caused by reduced grazing) were simulated in a 10-year shading experiment. Since 1968 P. vulgaris has been lost from 16 sites and gradually declined on four others. However, the total population size increased by 258% due to the reintroduction of winter grazing on three sites. This produced a significantly shorter, more herb-rich sward, with a lower cover of Bromopsis erecta (c. 10%), than on sites where populations remained stable or declined. Experimental shading had a significant negative effect on plant survival and flowering performance. These results confirmed that reduced grazing is now one of the major threats to species dependent on short swards, especially on isolated sites where livestock farming is no longer economically viable. That many of these declines took place on nature reserves highlights the difficulties of managing isolated grasslands, and the urgent need to re-instate grazing on reserves supporting populations of threatened species in otherwise intensively managed lowland landscapes.     

Rehabilitation of degraded Calluna vulgaris (L.) Hull-dominated wet heath by controlled sheep grazing

Many upland areas of the British Isles have seen declines in the area and condition of heather (Calluna vulgaris)-dominated heathland vegetation. To reverse this decline, management regimes must be designed to rehabilitate areas that have seen this decline. As most of this heathland vegetation is primarily managed by grazing, such management has to determine what stocking levels can maintain the vegetation in a desired state. This paper describes how to reverse this decline through suitable grazing management.A degraded ‘wet-heath’ system, previously grazed at 2.1 sheep ha⁻¹, was subject to a range of grazing treatments over a 5-year period. Treatments varied in intensity (0-1.4 sheep ha⁻¹) and timing (summer only, winter only, or year round) of grazing. Grazing levels were maintained at 2.1 sheep ha⁻¹ outside the fenced areas. Vegetation composition remained stable outside the fenced treatments. All the fenced treatments showed an increase in the relative frequency of the evergreen Calluna vulgaris, with the greatest increase being in the ungrazed treatment, and the least in the year round 1.4 sheep ha⁻¹ treatment. This increase was in line with a reduction in heather utilisation to relatively low and sustainable levels. Other species that benefited from reduced grazing included Carex nigra, Deschampsia flexuosa and to a lesser extent Galium saxatile and Erica tetralix, whereas a range of moss species including Hypnum jutlandicum and Rhytidiadelphus loreus were more frequent at higher grazing levels. Though the recovery of heather was similar in the two seasonally grazed treatments, the vegetation showed different overall trajectories. Winter only grazed allowed a substantial increase in the cover of the deciduous Molinia caerulea, whereas this species was kept in check by summer only grazing. A stocking level of between 0.7 and 1.4 sheep ha⁻¹ appears to be appropriate to maintain and even enhance the cover of heather on degraded wet heath. Complete removal is not necessary. Grazing restricted to the winter period is inappropriate in areas where M. caerulea occurs. Setting appropriate stocking levels to maintain the condition of the vegetation must take into account site conditions, especially the presence of species that can affect the utilisation of heather.     

Forage nitrogen yield and soil nitrogen in artificial grasslands with varied Medicago seedling proportion

ABSTRACT

This study aimed to understand the effects of Medicago spp proportion on symbiotic and non-symbiotic nitrogen (N) utilization of plants, and subsequent forage production and soil N status in an artificial Leymus chinensis grassland. By a two-year field experiment conducted in semi-arid northern China, it was found that the corresponding biomass proportions of legume in swards were 0, 39, 63, 83 and 98% when legume seedling proportions at sowing were 0, 25, 50, 75 and 100%, respectively. Increased Medicago seedling proportion (from 25 to 100%) decreased legume N₂ fixation capacity from 53 to 21%, as a consequence, this reduced total symbiotic N₂ fixation and its contribution to forage production with Medicago seedling proportion increasing from 50 to 75% or more. However, as increased Medicago seedling proportion enhanced legume biomass and sward uptake to soil mineral N, higher legume stands still led to the greater biomass and N yield. The cultures with 50% seedling of legume had 4–13% greater soil N concentration than the cultures with 0, 25, 75 and 100% seedling of legume. We concluded that pure Medicago stands led to the greatest forage yield, while medium Medicago stands could lead to the greater symbiotic N fixation and soil N concentration.     

Pasture renovation practices of farmers in the neotropical savannahs

Degradation of sown pastures in the neotropics is a well known but poorly documented phenomenon. The paper reports the results of a survey conducted in the eastern savannahs of Colombia to quantify farmers' reactions to perceived pasture degradation. The survey was conducted in an area of 23 644 km². The sample consisted of 46 farms, which had 19 012 ha of Brachiaria decumbens pastures distributed in 374 paddocks. Of these paddocks, 196 had been sown with vegetative seed, and 281 had received modest rates of P fertilization at planting. Pastures sown on flat lands had younger modal ages (three years) and were renovated more frequently than those sown on hilly or dissected savannahs (10 years). These differences were probably a result of variations in infrastructure and relative stage of development of the two topographies, but slight differences in inherent soil fertility may also have played a role. We found no relationship between grazing management and frequency of pasture renovation. Implications for future research on pasture reclamation are discussed. © 1998 John Wiley & Sons, Ltd.     

Nitrogen Accumulation in Soybean Following Defoliation

The effects of defoliation on soybean [Glycine max (L.) Merr.] growth and yield have been well studied, but relatively little is known about its nitrogen (N) accumulation after defoliation. An experiment was conducted to examine soybean recovery and N accumulation following defoliation. The indeterminate cultivar (‘Tousan 69’) was planted in a greenhouse, and two defoliation treatments (no defoliation and 67% defoliation) were imposed at the R₂ stage when plants had at least one flower in the two uppermost nodes. At 0, 15, 30 and 45 days after defoliation (DAD), plants were destructively sampled to measure dry mass production, nitrogen accumulation and nitrogen fixation. Seed yield and N concentration also were measured at maturity. Neither the seed yield nor its N concentration was affected by defoliation. Although defoliation temporarily reduced soybean dry weight and N accumulation during 15 DAD, defoliated plants completely recovered their dry weight and N accumulation 30 DAD. There was little difference in N concentration between defoliated and non defoliated plants, indicating that N acquisition was restored during the recovery process. Recovery of N accumulation in defoliated plant was due to complete recovery of N₂-fixing ability and maybe related to improvement in N absorption after defoliation.     

The mineralisation and fate of nitrogen following ploughing of grass and grass-clover swards

This project aimed to investigate the release of mineral N following the ploughing of clover-rich and grass-dominated swards, previously subject either to cutting or grazing regimes. The hypotheses tested were firstly that N mineralisation and losses following incorporation of grass-clover swards are greater than from grass swards, and secondly that N mineralisation and losses following incorporation of previously grazed swards are greater than from previously cut swards. Following ploughing of previously grazed swards in 1992 and swards that had been subjected to an unfertilised, ungrazed regime in 1993, N uptake, N leaching losses (measured by soil solution samplers with drainage estimation from a nearby experiment) and N₂O losses (measured by the closed chamber method) were determined on both resown and fallow plots. Results showed: (1) higher N release after ploughing from the grass-fallow treatment (449 kg N ha^-1) than from the grass-clover fallow treatment (244 kg N ha^-1) over 18 months; (2) the net release of N after ploughing and reseeding, compared with a continued unfertilised sward, was about 85 kg ha^-1 for the grass-clover plots and 140 kg ha^-1 for the grass-only plots, over the following 18 months. Of this, the net releases in the second cropping season after incorporation were 19 and 25 kg N ha^-1 on the resown grass-clover and grass-only plots, respectively; (3) the net release of mineral N after ploughing in 1993/1994, when swards had not been grazed for over a year, was only about 40 kg ha^-1 and no effect of the previous sward was evident; (4) in the 7 weeks after the 1992 ploughing, there was a considerable short-term input of N₂O to the atmosphere (1.5-3.7 kg N ha^-1), due to the supply of readily available C. Leaving swards ungrazed and unfertilised over winter before ploughing in spring has the potential to reduce such emissions considerably. We conclude that N release following cultivation of grazed swards is more a function of grazing intensity and history prior to ploughing rather than of sward composition.     

Sowing a winter catch crop can reduce nitrate leaching losses from winter‐applied urine under simulated forage grazing: a lysimeter study

Grazing of winter forage crops is a common management option used in the dairy industry of New Zealand, particularly in the South Island, where they are used to feed nonlactating, pregnant dairy cows prior to calving. However, there is concern that the large crop yields per hectare grazed, combined with a high stocking density of cows, lead to large amounts of urinary nitrogen (N) deposited on bare, wet soil that, in turn, could lead to large nitrate leaching losses. We report the results of a simulated winter forage grazing event using field lysimeters planted with a kale (Brassica oleracea L.) crop. The effect of sowing a ‘catch crop’ of oat (Avena sativa L.) following the simulated winter forage grazing on nitrate leaching losses from urine applied at different times throughout the winter was measured. A catch crop sown between 1 and 63 days after the urine deposition in early winter reduced N leaching losses from urine patches by ~34% on average (range: 19–49%) over the winter–spring period compared with no catch crop. Generally, the sooner the catch crop was sown following the crop harvest, the greater the uptake of N by the catch crop and the greater the reduction in nitrate leaching losses. The results indicate that sowing of a catch crop following winter crop grazing could be an effective management strategy to reduce nitrate leaching as well as increase the N‐use efficiency of dairy winter forage grazing systems.     

Rehabilitation of degraded dry heather [Calluna vulgaris (L.) Hull] moorland by controlled sheep grazing

Many areas of heathland in Europe have seen a decline in the area and condition of Calluna vulgaris (heather)-dominated vegetation, with subsequent declines in the associated faunal interest. Grazing, alongside burning, is still the predominant means of managing heathland vegetation, and, therefore, it is by manipulating this management that cost-effective improvements in vegetation condition can be made. This paper investigates the suitability of different grazing treatments for rehabilitating degraded ‘dry heath’. Treatments varied in the intensity (0-1.9 sheep ha⁻¹ year⁻¹) and timing (summer vs. winter) of sheep grazing. These treatments were compared with the behaviour of vegetation outside the fenced area kept under the previous management (open access all year round). As rabbits were common on the site, fences were erected to prevent access to the sheep grazed plots. Vegetation composition remained stable outside the fenced area, whilst all the fenced treatments showed a decrease in heather utilisation and an increase in the relative frequency of heather over the 5 years of the experiment. The increase was in proportion to the reduction in stocking rate, with only slow increases in relative frequency observed in the high grazing treatments (winter and summer). Other species that benefited from reducing grazing included Empetrum nigrum and Vaccinium myrtillus, whilst declines were observed for Agrostis capillaris and total monocotyledonous species. Only small overall differences were observed between the winter low, summer low and no sheep grazing treatments. However, a difference in response was present between the sheep exclosures and the sheep+rabbit exclosures, indicating that rabbits were having a noticeable effect on heather recovery at this site. On this degraded ‘dry heath’ system, imposing a reduction in stocking density improved the condition of the dwarf shrubs present and reduced the grass component of the vegetation. There was little effect of the timing of grazing, such that a reduction in sheep numbers to 0.8/0.9 sheep ha⁻¹ year⁻¹, to give utilisation levels of below 20%, can achieve the desired result of improving vegetation condition whilst still achieving some economic return from grazing. However, the wide range of ‘sustainable’ stocking densities for different heathland systems highlights the need to base effective management on measured utilisation rather than on stock numbers.     

Application of Water-stress Models to estimate the Herbage Dry Matter Yield of a Permanent Grassland Pasture Sward Regrowth

This study proposed the concepts of water availability and the related growth support factor and defined them quantitatively. Based on these concepts, the water-stress-dependent effective temperature and global solar radiation accumulation were defined and used as regression variables in statistical modelling of herbage regrowth dry matter (DM) yield of a permanent grassland pasture sward under varying degrees of water shortage. It was found that the proposed method greatly improved the DM yield model accuracy when the influence of water stress on grass growth was prevalent. An effective model was obtained and is recommended for herbage yield prediction under such water-stress conditions. The recommended model predicted DM yield with a coefficient of determination of 0·92 and a mean square error of 0·21 t ha⁻¹. The model can be used for similar herbage regrowth of 3 weeks and beyond. Evaluation using an independent data set confirmed that the recommended model is robust and accurate. The methodology proposed can also be adapted to modelling the herbage growth of different sward types and different (re)growths under the influence of water stress.     

Adaptive attributes of tropical forage species to acid soils II. Differences in shoot and root growth responses to varying phosphorus supply and soil type

Identification of plant attributes that improve the performance of tropical forage ecotypes when grown as monocultures or as grass+legume associations in low fertility acid soils will assist the development of improved forage plants and pasture management technology. The present work compared the shoot and root growth responses of four tropical forages: one grass and three legumes. The forages were grown in monoculture or in grass+legume associations at different levels of soil phosphate. Two infertile acid soils, both Oxisols, were used: one sandy loam and one clay loam. They were amended with soluble phosphate at rates ranging from 0 to 50 kg ha^‐1. The forages, Brachiaria dictyoneura (grass), Arachis pintoi, Stylosanthes capitata and Centrosema acutifolium (legumes), were grown in large plastic containers (40 kg of soil per container) in the glasshouse. After 80 days of growth, shoot and root biomass production, dry matter partitioning, leaf area production, total chlorophyll content in leaves, soluble protein in leaves, root length, and proportion of legume roots in grass+legume associations were determined. The grass, grown either in monoculture or in association responded more to phosphorus supply than did the three legumes in terms of both shoot and root production. At 50 kg ha^‐1 of phosphorus, the grass's yield per plant in association was greatly enhanced, compared with that of grass in monoculture. The increase in size of grass plants in association compared with that in monoculture may have been caused by reduced competition from the legumes. These differences in shoot and root growth responses to phosphorus supply in acid soils between the grass and the three legumes may have important implications for improving legume persistence in grass+legume associations.