Clover Mixture Research Articles

Nitrogen balances in organic and conventional arable crop rotations and their relations to nitrogen yield and nitrate leaching losses

Nitrogen (N) flows in organic cropping systems differ considerably from those in conventional systems. The difference is particularly due to the N in organic materials in organic systems as opposed to the mineral N in fertilizer in conventional systems, which differently affect crop N supply and N losses. This implies different responses of conventional and organic cropping systems to N inputs and N management. Therefore, N flow dynamics were studied in a range of arable cropping systems with 4-year crop rotations at three different sites in Denmark varying in soil (coarse sand, loamy sand and sandy loam) and climatic conditions. The long-term field experiments included an incomplete factorial combination of (1) rotations with grass-clover in organic farming (OGC) or grain legumes in organic farming (OGL) or conventionally managed (CGL) systems, (2) with (+CC) and without (−CC) cover crops, and (3) with (+M) and without (−M) animal manure (in OGC and OGL), and with (+F) mineral fertilizer (in CGL). Cover crops in OGC and OGL included a mixture of perennial ryegrass and clover (at the sites with coarse sand and sandy loam soils) or winter rye, fodder radish and vetch (at the site with loamy sand soil), and cover crops in CGL included only perennial ryegrass at all the sites. Higher N input and N output was observed in CGL compared to OGC and OGL. The differences in annual N output in cash crops between CGL and OGL, and CGL and OGC after accounting for effects of differences in N inputs were 15 and 27 kg N ha−1, respectively. The N output was related to N input, with a higher response to mineral N in both fertilizer and manure than to biological N fixation (BNF). The N surplus (difference between N input and N output) was significantly lower in OGL/−M+CC compared with other treatments. The recycled N in above-ground plant residues was highest in OGC/−M+CC where grass-clover cuttings were left in the field, followed by +CC treatments in OGL and CGL. The response of nitrate-N leaching to N input depended on soil type and precipitation, and leaching was reduced by the use of cover crops. The nitrate-N leaching increased with increasing N input at rates of 0.13–0.22 kg N kg−1 N input, and it increased with increasing N surplus at rates of 0.21–0.27 kg N kg−1 N surplus.

Effects of mixture ratio and cutting time on forage yield and silage quality of intercropped berseem clover and italian ryegrass

The research was carried out to determine the effects of different mixture ratios and cutting times on dry-matter yield and silage quality of mixtures of bersem clover (Trifolium alexandrinum L.) with Italian ryegrass (Lolium multiflorum Lam.) in Adana province, Turkey. The experiment was laid out in split plot design with four replications during the years of 2011-2013. The mixture-ratios ( 80% BC + 20% IR, 60% BC + % 40 IR, 40% BC+ % 60 IR, 20% BC + 80 % IR, pure berseem clover (BC) and Italian ryegrass (IR) ) were main plots, and harvest times (beginning of the flowering, mid flowering and full flowering of BC) were sub-plots. From the result of the study, it was concluded that the mixture of 60 % BC +40 % IR harvested at full flowering of BC was superior in terms of dry matter yield and silage quality.

Grassland plant species and cultivar effects on nitrous oxide emissions after urine application

We tested whether plant species identity influenced emissions of nitrous oxide (N2O) in response to the addition of urine at a rate of 530 kg nitrogen (N) ha−1. The plants tested are all used in temperate pastoral agriculture and comprised 11 C3 grasses, 3 forbs and 2 legumes with controls of bare ground and a standard ryegrass/white clover mixture used in the region. Total N2O emitted over 6 weeks after the application of cattle urine was highest in the bare ground. Plant identity was important with emissions ranging from an average of 0.67 kg N2O-N ha−1 for the Italian ryegrass Grasslands Moata (Lolium multiflorum) to 3.20 kg N2O-N ha−1 for the upland brome Grasslands Gala (Bromus stamineus). The 4 perennial ryegrass (Lolium perenne) cultivars had generally low emissions (average of 1.02 kg N2O-N ha−1) and the white clover (Trifolium repens) cultivars high emissions (average of 2.86 kg N2O-N ha−1). Plants with high N uptake rates had low N2O emissions. However, this was not always due to a high N uptake rate per se as during the first 2 weeks after urine was applied, when N2O emissions were at their highest, soil mineral N was in excess of plant N demand. It seems that some traits related to a high plant N uptake, such as low soil nitrification potential, might be important in driving differences in emissions associated with different plant species.

Forbs differentially affect soil microbial community composition and functions in unfertilized ryegrass-red clover leys

Increasing plant diversity in agroecosystems is proposed to enhance multiple ecosystem services. Adding selected forbs such as caraway (Carum carvi L.) and plantain (Plantago lanceolata L.) to productive grass-clover mixtures can further enhance forage yields, root biomass, uptake of mineral nutrients and improve animal performance. Yet, it remains unclear whether and how adding these forbs to grass-clover mixtures can influence soil microbial communities and associated soil carbon (C) and nitrogen (N) cycling. Based on a three-year grassland experiment varying in species diversity and composition with and without fertilizer application, we determined soil microbial community composition and functions related to C and N cycling under laboratory incubations. Results showed that inclusion of caraway modified soil microbial community composition by enhancing fungal-to-bacterial phospholipid fatty acids of the ryegrass-red clover mixture. Adding plantain to the ryegrass-red clover mixture increased the relative decomposition rate of the labile C pool, but not of the recalcitrant C pool. Yet, β-glucosidase activity and net N mineralization were unchanged due to inclusion of either forb. Moreover, fertilization with cattle slurry generally weakened these forb-induced changes in soil microbial properties. These findings demonstrate that adding selected forbs to unfertilized grass-clover leys can modify soil microbial community composition and associated C and N cycling, implying a potential for promoting long-term soil C sequestration through enhanced fungi-to-bacteria ratio, but a limited role in improving soil N fertility.

Of macropores and tillage: influence of biomass incorporation on cover crop decomposition and soil respiration

AbstractCarbon sequestration in agricultural soils may help to reduce global greenhouse gas concentrations, but building up soil carbon levels requires accumulating organic matter faster than it is lost via heterotrophic respiration. Using field and laboratory studies, this study sought to elucidate how tillage, the below‐ground incorporation of cover crop residue, and soil macroporosity affect soil respiration and residue decomposition rates. In the field, residue from a cover crop mixture of barley (Hordeum vulgare) and crimson clover (Trifolium incarnatum) was placed into litter bags that were left on the surface versus incorporated into the soil at three depths (4, 8 or 12 cm), while the laboratory study compared surface‐placed versus incorporated litter (8 cm depth). To assess tillage effects on cover crop decomposition, the field study simulated no‐till and conventional tillage treatments, while the laboratory and field studies both included treatments in which artificial soil macropores were created. The field study showed that conventional tillage and the presence of macropores enhanced soil respiration, while in the laboratory study, incorporating cover crop residue resulted in higher soil respiration and faster litter decomposition rates. Additionally, the laboratory measurements showed that macropores increased soil respiration in wet conditions, likely by enhancing oxygen diffusion. Thus, organic matter incorporation and macropores may represent important factors that affect soil respiration and carbon dynamics.

Implications of Cereal Rye/Crimson Clover Management for Conventional and Organic Cotton Producers

Core Ideas Cereal rye/crimson clover cover crop mixtures can be used for weed suppression and soil moisture conservation in cotton production.Cover crop management at cotton planting can influence cotton emergence, weed suppression, and soil moisture dynamics.Cotton emergence declined when cotton was planted directly into standing cover crop and without row cleaners engaged, but this reduction did not affect cotton lint yield.Soil temperature was reduced and soil moisture was increased by the presence of a cover crop mulch regardless of cover crop residue management strategy at cotton planting.Cover crop residue management did not affect cotton lint yield when herbicides were used, indicating that conventional producers have flexibility in terminating cover crops and residue management at cotton planting. Cover crop residue management can affect performance of the subsequent crop. This experiment was conducted in five environments in North Carolina from 2014 to 2016 to determine the effect of a cereal rye (Secale cereale)/crimson clover (Trifolium incarnatum) mulch on cotton (Gossypium hirsutum L.) emergence, soil temperature, soil moisture, weed suppression, and cotton yield under a conventional and organic weed control context. The cereal rye and crimson clover mixture was planted in mid‐October and terminated 1 wk prior to cotton planting using a roller‐crimper or herbicide application. Cover crop residue management included fertilized, rolled cover crop with row cleaners engaged at planting (Roll+F+RC), rolled cover crop with row cleaners engaged at planting (Roll+RC), rolled cover crop (Roll), standing cover crop with row cleaners engaged at planting (Stand+RC), and no cover crop (BARE). Weed treatments included with and without herbicides. Cover crop dry biomass ranged from 3820 to 6610 kg ha−1 across environments. Fertilizing the cover crop enhanced cover crop dry biomass production by 250 to 1860 kg ha−1. Cotton emergence declined when cotton was planted directly into standing cover crop and without row cleaners engaged. Soil temperature was reduced and soil moisture was increased by the presence of a cover crop. Cover crop residue management did not affect late‐season weed biomass at four of the five environments. Cover crop residue management did not affect cotton lint yield when herbicides were used, indicating that conventional producers have flexibility in terminating cover crops and residue management at cotton planting.

Nutrient quantification in fresh and dried mixtures of ryegrass and clover leaves using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is an analytical technique that can be used to facilitate variable rate fertilizer application, potentially increasing yield, reducing costs and reducing environmental side effects of nutrient loss. LIBS can give real-time information about macro and micro nutrients with little to no sample preparation. The study reported in this paper investigated whether LIBS can predict nutrient levels of fresh and dried pelletized pasture and what the limitations are. Spectra were acquired in air and under argon. Partial least square regression was used to build models for each macro and micro nutrient. The best results were for potassium, sodium and manganese with root mean square errors of cross-validation of 0.20, 0.029 and 0.0008 wt%, respectively, coefficient of determination of 0.92, 0.93 and 0.90, limits of detection of 0.99, 0.11 and 0.0027 wt%, and precisions of 0.30, 0.042 and 0.0012 wt%. LIBS can be used to assess nutrient levels of fresh pasture. Reducing the shot-to-shot variation will lead to improved calibrations.

Enhanced biological nitrogen fixation and competitive advantage of legumes in mixed pastures diminish with biochar aging

Soil amendment with biochar can increase biological nitrogen fixation (BNF) and improve growing conditions for legumes, while such effects may alter when biochar properties change with time (biochar aging). We examined BNF and competitiveness of legumes in a mixed pasture (dominated by clover, Trifolium repens) after 26 months of biochar amendment (field aged biochar) and in a pot study with grass (Lolium perenne) and clover mixture using fresh and chemically aged biochars. In both studies, the fraction of N derived from symbiotic fixation (%Ndfa) was not affected by aged biochar treatments, while it reduced from 73% in the control to 68% with fresh biochar addition in the pot study. However, this reduction in %Ndfa was compensated with greater biomass production resulting in the largest amount of N fixed with fresh biochar application. The amount of N fixed was reduced by field aged biochar, although it was not affected by chemically aged biochars. Moreover, in the field study grasses became more competitive than legumes with biochar, while such an advantage by grasses was not observed in the pot study. Aging of biochar can reduce BNF and competitiveness of legumes in mixed pastures with significant implications for pasture management.

Effects of including forbs on N2-fixation and N yield in red clover-ryegrass mixtures

Legume biological nitrogen (N2)-fixation is stimulated by neighbouring non-fixing species, but studies of legume N2-fixation in temporary grasslands including non-leguminous forage herb (forb) species are rare. We investigated N2-fixation, N yield, and total herbage production in a range of species mixtures consisting of three forb species—chicory (Cichorium intybus L.), ribwort plantain (Plantago lanceolata L.), and caraway (Carum carvi L.)—mixed into a traditional red clover (Trifolium pratense L.) and perennial ryegrass (Lolium perenne L.) mixture at two fertilisation levels. The percentage of red clover N derived from the atmosphere (%Ndfa) was higher in mixtures containing non-legumes than in pure stand but, did not increase with inclusion of forbs. On a whole-seasonal basis, red clover in mixtures derived 90% or more of its N from fixation even when fertilised with 216 kg total N ha−1. Forbs, in particular chicory, reduced the amount of N2-fixation and total N yields by affecting the red clover proportion in the harvested biomass. Generally, inclusion of forbs in red clover-ryegrass mixtures had no negative effect on total herbage production and percentage of legume N2-fixation. However, to maintain a high total N and N2-fixation yields, mixtures should not include a high seeding proportion of chicory.

Prinos travno-detelinske smeše na kiselom zemljištu u trećoj godini nakon kalcizacije

Soil acidity is one of the most common reasons for low yields of forage crops. This paper analyzes the long-term effect of liming (control - without CaO; 3 t*ha-1 CaO; 6 t*ha-1 CaO) applied to an acid soil (pHH2O 4.8) before stand establishment on the productivity of a mixture of red clover (Trifolium pratense L.) and tall oat grass (Arrhenatherum elatius L.) during the third year of production. Soil liming significantly increased hay yields in the first and second cuts by 17-25% and 46%, respectively, which resulted from an increase in the total yield and dry matter content of forage. In the third cut, soil liming had no effect on forage and hay yields due to the lower amount of precipitation in the second part of the growing season. Both lime application rates led to a significant reduction in the percentage of red clover in the first and second cuts, thus favoring the percentage of tall oat grass. In the third cut, only the percentage of weeds was lower in both lime treatments, as it decreased by more than 55% compared to the control.

Forage Accumulation and Nutritive Value of Italian Ryegrass–Kura Clover Mixture in Central Europe

ABSTRACTThe quest to reduce importation of plant protein for livestock feed and to reduce expense and environmental consequences of nitrogen fertilizer use have resulted in renewed interest in forage legumes in EU countries. The objectives of this study were: (i) to assess forage accumulation and nutritive value of mixtures of Italian ryegrass (IRG, Lolium multiflorum Lam.) and kura clover (KC, Trifolium ambiguum M. Bieb.), and (ii) to model milk production potential of this mixture, relative to IRG and KC monocultures in northern Poland. Italian ryegrass and KC were grown in monocultures or intercropped (IRG‐KC mixture) and harvested three times per year in two consecutive years. Italian ryegrass had greatest accumulated forage in harvest 1 and 2, followed by IRG‐KC and the KC monoculture. In harvest 3, IRG‐KC accumulated more forage than KC or IRG. Crude protein, neutral detergent fiber digestibility, and in vitro true digestibility across harvests followed the trend KC > IRG‐KC > IRG. The KC monoculture had the greatest calculated milk per megagram dry matter but the least milk per hectare, whereas IRG monoculture had least milk per megagram dry matter and greatest milk per hectare, with intermediate values for the IRG‐KC mix. Although forage accumulation of the mixture was less than that of nitrogen fertilized IRG, greater crude protein concentration and no nitrogen fertilizer application make it an intriguing opportunity for EU countries striving to reduce feed protein imports and use of fertilizer nitrogen.

Effect of wood ash and crushed rock soil amendments on red clover growth and dinitrogen fixation

The fertiliser effect of adding wood ash or crushed rock to a low-fertility soil, compared with an unamended control, was assessed in a pot experiment with a perennial ryegrass-red clover mixture. Dinitrogen (N2) fixation by the clover and translocation of fixed N to the grass were determined using 15N natural abundance. The wood ash produced the highest accumulated clover biomass over two cuts, followed by the crushed rock. Chemical analyses suggested that the increase was due to K supply by the amendments. The wood ash also led to larger amounts of fixed N compared with the control. However, N2 fixation was not increased as much as biomass amount, leading to dilution of plant N. There were minor or no treatment effects on mineralisation from soil N pools. This indicates that good-quality wood ash can be successfully used as a multi-element soil amendment to enhance clover growth on low-fertility soils.

Implications of grass–clover interactions in dairy pastures for forage value indexing systems. 1. Context and rationale

ABSTRACTThe development of economic indexing systems for ranking cultivars of forage species requires new knowledge of factors that may influence the scaling of agronomic data collected in controlled, small-plot evaluation trials to whole farm systems. In the case of perennial ryegrass indexing, one such knowledge gap is the effect of growing clover with ryegrass on the relative rankings of different ryegrass cultivars. The objective of the investigation reported in this series was to test whether the relative yield rankings of perennial ryegrass (Lolium perenne L.) cultivars representing the range in phenotypes now available to New Zealand farmers as a result of recent breeding differed when those cultivars were grown in monocultures (as per standard protocols for cultivar yield trialling systems such as the National Forage Variety Trials) versus mixtures of grass and clover. This paper presents the rationale for the investigation by reviewing developments in perennial ryegrass breeding and evaluation in the context of grass–clover relationships in grazed pasture systems. The papers that follow report results from a multi-year, multi-site investigation comparing the yield, nutritive value and other productivity-related variables of eight perennial ryegrass cultivars grown with or without white clover (monoculture versus mixture respectively) at two levels of nitrogen fertiliser. Key considerations in the design of the experiment on which the investigation was based are discussed.

Impact of sulfur applications on the agronomic performance of rapeseed–clover mixtures

AbstractRapeseed (Brassica napus L.) is a crop requiring high levels of nitrogen (N) fertilizer for growth and to optimize yield and seed quality. To limit the environmental pollution associated with intensive N fertilizer use, rapeseed–clover (Trititcum incarnatum L.) mixtures were grown in lysimeters under low N conditions (100 kg N ha−1). Considering the high sulfur (S) requirements of both rapeseed and clover, two inputs of S fertilizer (30 and 60 kg S ha−1) were applied. The effects S input on the agronomic performance of rapeseed in mixture and monocrops considered as reference, the N2‐fixing capacity of clover, and the leaching of nitrate and sulfate were monitored. This study showed that the N2‐fixing capacity (%Ndfa) of clover was improved (1.3‐fold) when it was grown in mixture with rapeseed at S60. However, irrespective of the type of cropping (monocrops or mixtures) and S application level (30 or 60 kg S ha−1), the biomasses and total N and S contents of both plants were not significantly different, nor was the rapeseed seed quality. Moreover, the yield of rapeseed grown in mixture at S60 was significantly lower than the yield of rapeseed grown as a monocrop (331.5 ± 9.8 versus 380.8 ± 3.5 g DW m−2, respectively). The results demonstrate that, in our field conditions, rapeseed mixed with clover required only 30 kg S ha−1 to maintain yield and seed quality, despite the high S needs of both plants. More surprisingly, compared to the rapeseed monocrop, the rapeseed–clover mixture led to an increase in N (‐N) and S (‐S) leaching during the early winter period of cultivation.

Red clover varieties of Mattenklee type have higher production, protein yield and persistence than Ackerklee types in grass–clover mixtures

AbstractDairy farmers have increased interest in multiyear red clover–ryegrass ley pasture swards because of their high productivity and protein concentration but the adoption of such mixtures has been restricted because of poor persistency of many red clover cultivars currently used. We aimed (i) to assess dry‐matter yield (DMY), persistence and nutritive value of four Mattenklee and four Ackerklee cultivars and (ii) to investigate the underlying plant morphological traits. We conducted a 4‐year field experiment with red clover–ryegrass mixtures, in combination with a short‐term pot experiment in which the red clover cultivars were grown both in monoculture and in mixture with Lolium perenne L. In the field, Mattenklees showed higher production (on average 42% higher) and clover content (on average 34% higher) in the third and fourth year of production compared to Ackerklees. In the fourth year, Mattenklees had slightly lower digestibility and lower protein concentration compared to Ackerklees cultivars; however, the digestible DMY and the protein yield were higher for Mattenklees. Both persistence and nutritive value of the different red clover cultivars were closely correlated with plant morphological traits. For stem length, there was close correlation (r > .77) between the results from the pot experiment and the field experiment, suggesting that stem length may be an important trait for plant breeding.

Short‐term residual N unaffected by forbs in grass‐clover mixtures

AbstractWe determined the effect on residual nitrogen (N) of including forbs (chicory, ribwort plantain and caraway) in perennial ryegrass‐red clover mixtures. Although soil N inputs during the grassland phase differed markedly between mixtures, in a pot experiment we found no differences in the potentially mineralizable N of the soil or in the dry matter production and N content of the spring barley test crop. The fertilizer value of the grassland mixtures corresponded to 10 g N/m2, irrespective of forb inclusion. Thus, the inclusion of nonlegume forbs did not negatively affect short‐term residual N fertility of legume‐based grasslands.

Biological nitrogen fixation in three long-term organic and conventional arable crop rotation experiments in Denmark

Abstract Biological nitrogen (N) fixation (BNF) by legumes in organic cropping systems has been perceived as a strategy to substitute N import from conventional sources. However, the N contribution by legumes varies considerably depending on legumes species, as well as local soil and climatic conditions. There is a lack of knowledge on whether the N contribution of legumes estimated using short-term experiments reflects the long-term effects in organic systems varying in fertility building measures. There is also limited information on how fertilizer management practices in organic crop rotations affect BNF of legumes. Therefore, this study aimed to estimate BNF in long-term experiments with a range of organic and conventional arable crop rotations at three sites in Denmark varying in climate and soils (coarse sand, loamy sand and sandy loam) and to identify possible causes of differences in the amount of BNF. The experiment included 4-year crop rotations with three treatment factors in a factorial design: (i) rotations, i.e. organic with a year of grass-clover (OGC), organic with a year of grain legumes (OGL), and conventional with a year of grain legumes (CGL), (ii) with (+CC) and without (−CC) cover crops, and (iii) with (+M) and without (−M) animal manure in OGC and OGL, and with (+F) mineral fertilizer in CGL. Cover crops consisted of a mixture of perennial ryegrass and clover (at the sites with coarse sand and sandy loam soils) or winter rye, fodder radish and vetch (at the site with loamy sand soil) in OGC and OGL, and only perennial ryegrass in CGL at all sites. The BNF was measured using the N difference method. The proportion of N derived from the atmosphere (%Ndfa) in aboveground biomass of clover grown for an entire year in a mixture with perennial ryegrass and harvested three times during the growing season in OGC was close to 100% at all three sites. The Ndfa of grain legumes in both OGL and CGL rotations ranged between 61% and 95% depending on location with mostly no significant difference in Ndfa between treatments. Cover crops had more than 92% Ndfa at all sites. The total BNF per rotation cycle was higher in OGC than in OGL and CGL, mostly irrespective of manure/fertilizer or cover crop treatments. There was no significant difference in total BNF between OGL and CGL rotations, but large differences were observed between sites. The lowest cumulated BNF by all the legume species over the 4-year rotation cycle was obtained at the location with sandy loam soil, i.e. 224–244, 96–128, and 144–156 kg N ha−1 in OGC, OGL and CGL, respectively, whereas it was higher at the locations with coarse sand and loamy sand soil, i.e. 320–376, 168–264, and 200–220 kg N ha−1 in OGC, OGL and CGL, respectively. The study shows that legumes in organic crop rotations can maintain N2 fixation without being significantly affected by long-term fertilizer regimes or fertility building measures.

Forbs enhance productivity of unfertilised grass-clover leys and support low-carbon bioenergy

Intensively managed grasslands are dominated by highly productive grass-clover mixtures. Increasing crop diversity by inclusion of competitive forbs may enhance biomass production and sustainable biofuel production. Here we examined if one or all of three forbs (chicory, Cichorium intybus L.; caraway, Carum carvi L.; plantain, Plantago lanceolata L.) included in ryegrass-red clover mixtures enhanced above- and below-ground productivity, and assessed their biofuel potentials, based on a three-year experiment with and without fertilisation as cattle slurry. We determined herbage yield, standing root biomass, and estimated methane energy output and greenhouse gas (GHG) emissions per energy unit using life cycle assessment. Results showed that plantain-containing grass-clover mixtures significantly increased herbage yield, while chicory- or caraway-containing mixtures maintained similar yields to the grass-clover mixture. Standing root biomass of the grass-clover mixture was enhanced by inclusion of caraway and plantain, with that of plantain further enhanced by fertilisation. The highest methane energy output was achieved in plantain-containing grass-clover mixtures. All unfertilised mixtures achieved the 60% reduction in GHG emissions compared to fossil fuel, whereas all fertilised mixtures did not meet the 60% reduction target. These findings suggest that including competitive forbs such as plantain in grass-clover mixtures enhances productivity, supporting low-carbon footprint bioenergy production.

Improved per hectare production in a lamb finishing system using mixtures of red and white clover with plantain and chicory compared to ryegrass and white clover

Over a three year period the performance of lambs being finished on three sward treatments were compared. The three treatments included (i) ‘Grass-clover mixture’; perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens) (ii) ‘Plantain-clover mixture’; plantain (Plantago lanceolata), white clover and red clover (Trifolium pratense) (iii) ‘Chicory-plantain-clover mixture’; plantain, chicory (Cichorium intybus L.), white- and red-clover. Each year was divided into five grazing periods namely; winter, early spring, late-spring, summer and autumn with only the Grass-clover mixture being utilised in the winter due to the growth profile and management requirements of the herb species. Over the three year period, a total of 3353kg live weight per ha was produced on the Grass-clover mixture, which was less (P<0.05) than the 3838kg/ha produced with the Plantain-clover mixture or 3768kg/ha on the Chicory-plantain-clover mixture. Similarly over the three year period, 1270kg of carcass weight gain per ha was produced on the Grass-clover mixture, which was less (P<0.05) than the 1706kg/ha produced with the Plantain-clover mixture or 1732kg/ha with the Chicory-plantain-clover. This indicates that farmers aimed at lamb finishing can have some confidence that when utilising these herb-clovers mixtures they can increase lamb and meat productivity for at least three years.

Contribution of subterranean clover (Trifolium subterraneum) to changes in morphological and physiological parameters raised alone and with birdsfoot trefoil (Lotus corniculatus)

Changes in some morphological and physiological parameters (leaves/stems ratio, total plastid pigments content, fixed amount nitrogen) of birdsfoot trefoil (Lotus corniculatus L.) (cv. Targovishte 1) and three subterranean clover subspecies, i.e. Trifolium subterraneum ssp. brachycalicinum (cv. Antas), Trifolium subterraneum ssp. yaninicum (cv. Trikkala) and Trifolium subterraneum ssp. subterraneum (cv. Denmark) were studied in a field trial in the Institute of Forage Crops, Pleven, Bulgaria (2012-15). Crops were grown alone (100%) and in mixtures as follows: birdsfoot trefoil + Trifolium subterraneum ssp. brachycalicinum (50:50%); birdsfoot trefoil + Trifolium subterraneum ssp. yaninicum (50:50%); birdsfoot trefoil + Trifolium subterraneum ssp. subterraneum (50:50%). Leaves/stems ratio for alone grown crops was found: birdsfoot trefoil (1.33), Trifolium subterraneum ssp. brachycalicinum (1.02), Trifolium subterraneum ssp. yaninicum (0.93) and Trifolium subterraneum ssp. subterraneum (0.93). Leaves/stems ratio for birdsfoot trefoil in all mixtures was found be higher as compared to alone grown birdsfoot trefoil - by 13.0% for the mixture with Trifolium subterraneum ssp. yaninicum, by 16.3% for that with Trifolium subterraneum ssp. brachycalicinum and by 20.1% for the mixture with Trifolium subterraneum ssp. subterraneum. Total plastid pigments in birdsfoot trefoil increased in all mixtures: with Trifolium subterraneum ssp. brachycalicinum by 7.4%, with Trifolium subterraneum ssp. subterraneum by 8.1% and with Trifolium subterraneum ssp. yaninicum by 15.6%. From mixtures of birdsfoot trefoil were obtained more fixed amount of nitrogen - from 1.71 kg N/da (with Trifolium subterraneum ssp. subterraneum) to 4.84 kg N/da (with Trifolium subterraneum ssp. brachycalicinum) as compared to alone grown birdsfoot trefoil. Birdsfoot trefoil and subterranean clover in mixtures showed good tolerance, morphological and physiological status.