In order to assess and compare the potential forage production of CRIMSONCLOVER with other CLOVER species in different planting dates, an experiment was carried out in split plot arranged in a randomized complete block design with 12 treatments in four replications in Karaj during 2003-2005. In this study pkanting dates were considerd as main plot in four levels (d1: 23 Aug., d2: 6 Sep., d3: 23 Sep. and d4: 7 Oct.) and CLOVER cultivars as subplot in three levels (v1: CRIMSON CLOVER, v2: Berseem CLOVER and v3: Persian CLOVER). The results of combined analysis of the experiment demonstrated that effects of year, planting date, year × planting date, species, year × species, planting date × species and year × planting date × species (except dry matter yield) were significantly different for fresh and dry matter yield. Mean comparison of planting dates and CLOVERspecies showed that planting date d1 with 70.20 tha-1 fresh yield, 13.23 tha-1 dry matter yield, and Persian CLOVER with 83.40 tha-1 fresh yields (the same group with Berseem CLOVER), 15.23 tha-1 dry matter yields were the best treatments. Meanwhile, mean comparison of the interaction of planting date × species showed that d3v3 with 90.21 and 18.82 tha-1 fresh and dry matters was the best treatment.

Scince 1990 research on CLOVER has been commenced in Karaj and other field stations of Seed and Plant Improvement Institute, Iran. One of the achievements of this initiative is selection, improvement and release of Alborz 1 CRIMSON CLOVER cultivar. New CRIMSON CLOVER cultivar, Alborz 1 was primarily selected from CLOVER germplasm received from Food and Agriculture Organization (FAO), The United Nations, in Seed and Plant Improvement Institute, Karaj, Iran. Agronomic and yield trials were carried out in Karaj, Dezfoul, Arak, Mazandaran and Esfahan. Demonstration plots and research-extension verifications were performed in Karaj, Golpayegan and Shahr-e-Kord. The important agronomic characteristics of Alborz 1 cultivar are: earliness, high fresh forage yield in early spring season, suitability for being grown as second and third crop in cropping systems as well as tolerant to diseases and pests. Alborz 1 is also tolerant to deficit irrigation and cold, therefore, it is also suitable to be grown in cold and foothills areas. This cultivar is a reliable substitute for Berseem CLOVER in paddy cropping systems. Alborz 1 cultivar had very good performance in agronomy and yield trails with 30-35 t ha-1 fresh forage and 5-5.5 t ha-1 dry forage yields of 16% protein content, 60% digestibility and 70-80% platability.

To investigation the management of winter cover crops on weed control in corn, an experiment was carried out as split-plot in randomized complete block design with three replications at the Agricultural and Natural Resources Research Center of Moghan, Iran, during 2016-2017. Cover plants (wheat + CRIMSON CLOVER mixed culture, wheat single culture and rye + wheat mixed culture) were considered as the main factor and their management methods (removing residues from the soil surface and remaining residues on the soil surface as mulch) as the sub-factor together with a control treatment (without cover plants). The results showed that the lowest total dry weight of weeds was obtained from rye + wheat treatment with mulch management. In general, total dry weight of weeds was reduced by 65% under mulch conditions and 35% under removing residues conditions compared to control treatment. The highest grain yield (4 t. ha-1), biological yield (15. 1 t. ha-1), number of rows per ear (14 rows) and number of grains per row (26 grains) was obtained from CLOVER + wheat mixed culture in the management of removing residues. The results showed that dry fodder produced by wheat single culture, rye + wheat mixture and wheat + CRIMSON CLOVER mixture was 1960 kg. ha-1, 1933 kg. ha-1 and 1800 kg. ha-1, respectively. In total, the results of this research indicated that the accurate management of cover plants, in addition to more efficient use of resources and livestock nutrition, can be considered as an important component of the sustainable weed management strategy.

To assess required growing degree days (GDD) for phenological stages of four CLOVER species in different planting dates a field experiment was conducted in 2010-11 and 2011-12 cropping seasons in Seed and Plant Improvement Institute in Karaj, Iran. Three planting dates (14 September, 28 September and 13 October) and six CLOVER varieties were assigned to main plots and sub-plots, respectively, as split plot arrangement in randomized complete blocks design with four replications. Results showed that delaying planting date decreased the required growing degree days for forage production in CLOVER species by 8.2% and 14.7% in second and third planting dates, respectively. Average growing degree days showed that for three cutting of forage in Karaj region about 2437 GDDs are required. Result also revealed that the greatest GDDs (612.7) was required from emergence to vegetative growth stage and the least GDDs (82.1) belonged to from emergence to the appearance of first simple leaf stage. Comparison of CLOVER species showed that red CLOVER with 2994.9 GDDs and CRIMSON CLOVER with 1107.7 GDDs had the greatest and least thermal requirements for forage production, respectively.

To assess agronomic and economical aspects of mixed cropping of alfalfa and annual forage crops a filed experiment was carried out using split plot arrangement in randomized complete block design with three replications, in research field of Seed and Plant Improvement Institute, Karaj, Iran in 2007 and 2008 growing seasons. Experimental treatments included mixed ratio of alfalfa seed with other forage crops (Pesian CLOVER, CRIMSON CLOVER and Forage rape). These ratios were 100:0, 75:25, 50:50 and 0:100 (alfalfa: forage crop). For agronomic traits, fresh and dry forage yield, analysis of variance and mean comparison were preformed. For economical assessment partial budgeting and breakeven analysis were used. Results showed that there were significant differences among mixed cropping treatments for fresh and dry forage yield. Substitution of 75% Alfalfa + 25% CRIMSON CLOVER by other mixed cropping treatment was not profitable. Application of 75% Alfalfa + 25% CRIMSON CLOVER had 14.94 million Iranian rials per hectare net profil which was greater than the other treatments. Breakeven point for selected treatment (75% Alfalfa + 25% CRIMSON CLOVER) in comparison with sole crop of alfalfa (Second priority treatment) and 75% Alfalfa + 25% Forage rape (Third priority treatment) were estimated 22.8 and 24.8 million Iranian Rials, respectively. Breakeven points of gross income of selected (75% Alfalfa + 25% CRIMSON CLOVER) in comparison to sole crop of Alfalfa and 75% Alfalfa + 25% Forage rape were 34.6 and 32.7 million Iranian Rials, respectively.

Trifolium incarnatum L. is reported for the first time for the flora of Iran. It has been collected from Marivan area in Kurdistan province. This species belongs to the section Trifoilium and distinguished from T. sylvaticum Gerard ex Loisel by the following characters: Dense, large head (about twice as much as the later one) and red flowers. Also it differs from T. stellatum L. by possessing larger leaflets, oblong heads (about two times longer than the later) and red flowers.

In order to evaluate freezing tolerance of some CLOVER species as well as planting date and acclimation period effects on plant tolerance, an experiment was conducted in 2012-13 in Faculty of agriculture, Ferdowsi University of Mashhad in completely Randomized Design with factorial arrangement and four replications. Experimental factors included two planting dates (late September and late October), four CLOVER species (red CLOVER T. pratense, white CLOVER T. repense, Persian CLOVER T. resupinatum (autumn species) and CRIMSON CLOVER T. incarnatum (spring spieces) and eight freezing temperatures (0 (control),-3,-6,-9,-12,-15,-18,-21º C). Electrolyte leakage percentage of leaf and crown was measured and used to determine lethal temperature for 50% of plants (LT50el(l) and LT50el(c) for leaf and crown, respectively). Results indicated that interaction of planting dates, species and freezing temperatures on electrolyte leakage of leaf was significant in a way that a lower mean of this parameter was observed in autumn species in first planting date compared to the second planting date but the reverse was found in spring species. Decreasing temperature to less than-12 and-15 ˚ C resulted in an increase in electrolyte leakage of crown in red and Persian CLOVERs, and white and CRIMSON CLOVERs, respectively). The least LT50el(l) in first planting date was found in red and Persian species and the highest in CRIMSON species while in the second planting date, the lowest mean was observed in Persian and CRIMSON and the highest in red species. Also, plant dry weight decreased as freezing temperature dropped to-9 ˚ C.

Given prevalence of CLOVER cultivation in Iran, it is likely to face with environmental stresses, such as cold stress for this plant. Therefore, the present study was done to investigate the relationship of carbohydrate concentration and morphological characteristics of roots with cold stress tolerance in CLOVER genotypes using a split-plot design in time. Planting date at three levels as the main factor, 10 CLOVER genotypes as a sub-factor, and also cutting time at three levels as a sub-factor were all considered in a randomized complete block design with four replications in two crop years. With delay in planting, root length, root weight, crown diameter, and crown weight were decreased in CLOVER genotypes and root –to- shoot ratio was increased. Red CLOVER and Persian CLOVER (late maturity) had higher concentrations of soluble carbohydrate, fructose, glucose, and starch in the roots, while Persian CLOVER (one cutting) and CRIMSON CLOVER showed the lowest concentrations. Delay in planting caused a 13% decrease in total soluble carbohydrate concentration and glucose, fructose, and starch concentration was decreased by 20, 21, and 9%, respectively. Slope of the sugar storage curve between the two stages of winter dormancy and spring regrowth was milder in the red, berseem, Persian (one cutting), and CRIMSON CLOVER, respectively and root sugar storage curve was used less. Slope of carbohydrate storage curve was higher in berseem and CRIMSON CLOVER from regrowth until the first cutting, and because of this rapid growth, these genotypes can be used in the areas with low-stress temperatures within this time range.

Introduction: In Iran, CLOVER is the second most important forage crop after alfalfa (Medicago sativa) and is cultivated on a surface of about 70, 000 hectares. Yield improvement of this plant could be achieved through autumn cultivation. Iran is still one of the main centers for the diversity of CLOVER species, there is not much information about freezing tolerance of native species of this important plant. Since freezing stress is one of the most important winter stresses which causes severe damage to the plant cells and tissues and ultimately plant death, evaluation of freezing tolerance of this crop could help to determination of the best planting date in order to achieve the highest yield. The aim of this study was to evaluate the freezing tolerance of four CLOVER species through assessment of plant survival and re-growth after freezing stress. Materials and Methods: In order to study growth criteria of four CLOVER species after freezing stress in controlled conditions, an experiment was conducted in 2012-13 in Faculty of agriculture, Ferdowsi University of Mashhad. Treatments were arranged as factorial based on Completely Randomized Design with four replications. Factors were included of planting dates (late September and late October), CLOVER species (red CLOVER T. pratense, white CLOVER T. repense, Persian CLOVER T. resupinatum (autumn species) and CRIMSON CLOVER T. incarnatum (spring species) and freezing temperatures (0 (control),-3,-6,-9,-12,-15,-18,-21º, C). Survival percentage, LT50 according to Survival (LT50su), leaf area, Reduced 50% Leaf Area Temperature (RLAT50), dry weight and Reduced Dry Matter Temperature 50 (RDMT50) were measured after three weeks re-growth. Results and Discussion: Results indicated that survival percentage was significantly affected by interaction of planting date, species and freezing temperatures. In both planting dates, CRIMSON and white species showed a good survival till-15°, C while they were killed as temperature was more decreased to-18°, C. In first planting date, two species of red and Persian CLOVER had 50 and 42% survival, but were killed in this temperature in the second planting date. The lowest LT50su in autumn (red, white and Persian) and spring (CRIMSON) species was found in first and second planting dates, respectively indicating higher freezing tolerance in CRIMSON species at second planting date and a better acclimation of autumn species at first planting date which led to a higher survival compared to spring species. Leaf area was significantly affected by planting date, species and freezing temperatures at the end of the recovery period. In first planting date, decreasing temperature from zero to-18°, C caused reduction of 98 and 48% of leaf area in red and Persian species while no plant of white and CRIMSON species was survived in this condition. In second planting date, leaf area was decreased about 6, 33 and 2% as temperature decreased from zero to-15°, C while leaf area of Persian species, not only was not decreased, but also increased by about 12%. The lowest and highest RLAT50 were observed in Persian and red species. Interaction of planting date and species on RDMT50 was significant in a way that in delayed planting date, RDMT50 was increased in red, Persian and CRIMSON species while it was decreased in white species. Conclusions: Red and Persian species showed higher freezing tolerance according to indices of survival percentage and LT50su. The highest recovery ability of plants based on leaf area per plant, RLAT50, plant dry matter and RDMT50 was found for second planting date. Also annual species of Persian and CRIMSON had lower RLAT50 and RDMT50 and higher freezing tolerance compared to perennial species of red and white CLOVER.

The use of cover crops before planting the main plant along with selecting the type of tillage can be considered as one of the effective methods in sustainable agriculture. In order to show the efficacy of this system, an experiment was conducted in a no-tillage system and with six treatments, barely (Hordeum vulgare L. ), rye (Secale cereal L. ), rape (Brassica napus L. ), vetch (Vicia villosa L. ), CRIMSON CLOVER (Trifolium incarnatum L. ) and control, in a randomized complete block design with three replications, at the farms of agriculture and education research center and natural resources of Ardabil Province (Moghan) during the 2015-2017. Variance analysis showed that the effect of the treatments on the total weed density was significant. On average, in four sampling stages, total control of winter and spring weed at barley, rye, rape, vetch and CLOVER treatments were 83. 5, 77. 25, 66, 25, 51, and 26. 25 respectively. The results also showed that the soil cover percentage was significantly affected by the treatments. Decrease in weed density increased biomass of cover crops and their soil coverage. Barley, rye, rape, and CLOVER had the highest biomass. Effect of cover crops on maize yield was significant. Corn grain yield were 9. 12, 8. 45, 7. 92, 6. 93, 6. 52 and 6. 31 ton/ha in barley, rye, rape, vetch, CLOVER, and control treatments, respectively. According to the results of this experiment, cereals can be used in combination with conservative tillage system to achieve the desired yield while controlling weeds and reducing chemical inputs.