Topping stage of tobacco is a key time for development of agriculture measures to promote the quality of leaves. In order to investigating influence of topping timing and suckericide content on tobacco leaf, a factorial experiment on the basis of RCB design with 3 replications was conducted in 2011 at the Tobacco Research Farm of Isfahan. Treatments were including topping time (T1: topping at early button and T2: at early flowering), Prim+content (A1: 8, A2: 10, A3: 12, A4: 14 ml/per plant) and Prime+concentration (C1: 1.35%, C2: 1.5%) are first, second and third factors, respectively. Results showed that, effects of topping timing and Prim+content were significant for number of suckers, fresh and dry weight of suckers and leaf area of tobacco. Dry weight and leaf length of tobacco were significantly affected by different Prim+ concentrations. Topping at early button resulted in deduction of suckers in tobacco, consequently caused to production of lower sucker weight and higher tobacco leaf area. Moreover, application of higher concentration of Prim+at early button stage had considerably better effects on sucker growth control and tobacco leaf quality. This result clearly indicated that topping at early growth stage and controlling sucker growth with using suckericide enhanced tobacco leaf quality in the field.

To study response of cotton (Gossypium hirsutum L.) cultivars to topping and pix as a plant growth regulator an experiment was conducted in Parsabad, Moghan region of Iran with four cultivars included Sahel, Varamin, Bakhteghan and Mehr and topping at 30 days after flowering (DAF), pix spraying at 15 and 30 DAF, and a treatment with neither pix nor topping as control. Results indicated that Sahel had good response to pix spraying at 30 DAF and could increase lint yield up to 210 kg ha-1 when compared to the control. For Sahel cultivar that was sprayed and topped at 30 DAF, cotton plants matured earlier, but other treatments especially control plots matured later. Pix sprayings and topping had no-significant effect on plant height of Varamin, and there was not significant difference among treatments for earliness. Bakhteghan sprayed with pix at 30 DAF was earlier by 78%. Response of Mehr to spraying was better than topping, and after treatment its yield improved (1015 kg ha-1) as compared to the control. Mehr in topping at 30 DAF with 78% earliness was earlier than other cultivars. It is concluded that cotton stem topping of 10-15 cm and pix spraying may decrease plant height and increase earliness and yield of Sahel, Bakhteghan and Mehr cotton cultivars.

Evening Primrose (Oenothera biennis) is the herbaceous plant; biennial fuchsia belongs to the family Onagraceae. The yellow flowers of this plant are bisexual. The seeds contain non saturated oils as γ-linolenic acid, Linolenic acid and Oleic acid. In this research toping height (without toping and toping on 20, 30, 50 cm of plant) and irrigation type (drip, furrow) treatments on length and width of leaf, node distance, number and length of flowering stems per plant; and in complete ripening the characters of weight of seed per capsule and per plant, weight of 1000 seed, number of capsule per stem and per plant, weight of fresh/ dry shoot material and oil extracted from seeds were measured. The results showed that by increasing of toping, width of leaf, internode distance, length of lateral stems were decreased. In drip irrigation internode distance, length and number of lateral stem increased. The most of number capsule per stem and plant, weight of seed per plant, weight of 1000 seed, oil percentage of seed were obtained in toping of 30cm and drip irrigation. This research is primary investigation about toping height and irrigation type in Primrose and more studies for complete results are necessary.

To study the effects of plant density and source limitation on grain yield, yield components and dry matter and nitrogen remobilization in corn (Zea mays L.), a field experiment was conducted at Seed and Plant Improvement Institute in 1998. A strip plot design based on randomaized complete blocks with 4 replications was used. In this study maize hybrids (KSC704 and KSC711) were sown in vertical plots. Density (65, 70, 75, 80, 85, 90 thousand plant ha-1) and topping levels, T1 (control) and T2 (Removing tassel and all leaves above the ear) were assigned as factorial to horizontal plots. Results revealed that toppng at two weeks after anthesis did not have any adverse effect on grain yield. Therefore, a considerable quantity of forage could be harvested without any reduction in grain yield. The highest yield of green fodder (5.45 tha-1) was obtained from 90 thousand plant ha-1. Although topping caused an increase in 1000 kernel weight by 7 percent compared to control, but there was no significant difference in their grain yield. Remobilization of dry matter and nitrogen from different parts of th shoot (leaves and stem) to the grain responded differently and among them stem contributed more. Maximum remobilization of dry matter from stem (58%) was recorded in 80 thousand . plant ha-1 which had significantand positive correlation with grain yield.

Cover type of on–farm storages has an important role in reducing the freezing damage and respiration of beet roots in the pile. This experiment was conducted in 2006 in Karaj region in order to evaluate the effects of cover types of storage on the mass and sugar losses of both topped and untopped beets. The experimental design was a split plot factorial in RCBD with three replications. The main plots consisted of: a1- a layer of wheat straw with 10-15 cm depth, a2- a layer of sugar beet top with 10-15 cm depth, a3 - propylene cover with 0.55 mm diameter and a4- without cover as a check. The sub plots consisted of a combination of two storage durations: b1- 30 days and b2- 60 days with two types of beet topping: c1- topped and c2- untopped. The size of pile was 2 meters width, 1.5 meters height and 3 meters length in the N-S direction. Air temperature inside and outside the pile was recorded daily using a max- min thermometer. Weight and technical quality of beet samples were determined before and after storage. The results showed that mean air temperature under all covers were greater than uncovered treatments. Mass losses of sugar beet under covers were significantly less than those of uncovered treatment. Molassed sugar of beet under both straw and propylene covers were significantly less than other cover treatments. Mean sugar loss in the first 30 and 60 days were 489 and 279 g/t/d that may be related to greater respiration rate of sugar beet in 30- day storage. Sugar loss of untopped beet was 88 g/t/d less than that of topped beet. In conclusion, under conditions of this experiment, covering sugar beet with both propylene and straw covers under on-form storage had less molassed sugar and maybe considered as suitable pile covers. Sugar losses of untopped beets lacking any petiole were less than that of topped beets. Thus, untopped beets maybe recommended, for storing sugar beet in on-farm storage

Growth analysis is a valuable method to quantify crop growth, development and production. Because, parameters of nonlinear regression models have significant physiological meanings, it was decided to study the effect of topping and variety on crop growth indices by using a logistic nonlinear regression model in a factorial experiment, based on randomized complete block design with 3 replications, at the Research Farm of Gonbad University during 2014-2015. The first factor consisted of five faba bean verities (Zohreh, Shami, Sheshband, Sarazeri and Barkat) and the second factor of two levels, topping and control. Results showed that using this molel described well the variation pattern of dry matter accumulation and LAI by time. It was also revealel that the difference between verities for the time to reach maximum leaf area index and the time required to reach 50 percent of maximum dry matter were not significant. The effect of variety on leaf area index was significant at the 5% level. The maximum and minimum leaf area index, total dry matter and crop growth rate of Barkat, Zohre and the Saraziri were higher than Shami and Sheshband varieties, and thus this was resulted in higher yield. Leaf area index in all varieties was the critical leaf area index. The average critical leaf area index in varieties was 1.37. The maximum and minimum relative growth rate at the beginning of the growing season belonged to the Saraziri and Barkat with 0.066 and 0.055 g/g.day, respectively.

Leaves are one of the most important organs of plants where food (starch and sugar) are produced. These materials are used to maintain plant tissues, growth and production of new leaves. In order to evaluate the commercial fall growing cultivars of sugar beet, their potential to produce new leaves, a factorial experiment based on randomized complete block design was conducted with three replications at Varsan Agricultural Research Station (Gorgan), during 2018 growing season. The first factor consisted of 6 commercial sugar beet cultivars (5 foreign cultivars and Sharif, domestic) and the second factor of two times at toppings in May (middle stage of growth) and June (final stage of growth). Sugar beet root yield and some important quality characteristics were measured after harvesting. The results showed that the commercial cultivars showed significant differences in terms of yield and percentage of sugar (grade) at the one percent level of probability. Highest root yield was obtained from Jrakavas and lowest from veles cultivar. The highest percentage of sugar was due to veles and lowest to Rosagold cultivars. Topping reduced borb quantity and quality of sugar beet root, while May and June toppings reduced quality and yield of sugar beet root by 8. 8% and 10. 2% respectively as compared to the control treatment. The interaction effect of cultivar × topping was significant in all studied traits except root dry matter.

The yield advantage and inter-specific completion were studied in corn-soybean mixtures. Species monocultures and all combinations of 3 corn densities (5.5, 7.5 and 9.5 plant/m2) and 3 soybean densities (23, 33 and 43 plant/m2) were plants in a complete randomized block design with factorial arrangement and 3 replicates. Topping treatment on corn was conducted at soft dough stage and data analysed as a split plot design where topping were allocated to main plots. Ignoring the soybean density, increase in corn density to 9.5 plant/m2 led to an increased corn grain yield in mixture. The highest grain and biological yield of soybean was obtained in mixture with medium corn and low soybean densities (7.5 and 23 plant/m2, respectively). Corn topping led to a increase in corn grain no. per row and 500 grain weight of soybean. However, the other yield components of species were not significantly affected by this treatment. Reciprocal yield models showed that in corn intra-specific competition and in soybean inter-specific competition were the main determinates of grain and biological yield. That is corn was the dominant species of mixture. When corn topping was conducted the effect of each corn plant on grain and biological yield of soybean was respectively, equivalent to 9.37 and 9.14 soybean plant. However, this equivalency in control treatment was increased to 11 and 13 soybean plant, respectively. That is, corn competitive ability decreased after topping. This result was confirmed according to completion indices. Land Equivalent Ratio (LER) of mixtures increased with increasing spices density in mixture. Corn topping was also led to an increase in LER so that the highest LER in topping and non-topping treatments were 1.215 and 1.078, respectively.

Milk thistle is used traditionally as a hepaprotective agent and supportive treatment of liver disorders. The most problems in Milk thistle harvest are tall height, seed shedding and being spinous. In this trial, effects of 3 native populations (p1: Isfahan violet flower, p 2: Ahvaz white flower and p3: Ahvaz violet flower) and 3 topping levels (t1: control, t2: topping in 7 leaves stage and t3: cutting back in first capitulum appearance stage) on qualitative and quantitative properties of Silymarin, Silybin, Isosilybin, Silychristin, Silydianin, Taxifolin , seed, tall height and days until blooming was studied. Experimental design was factorial and conducted as a randomized complete block design with 3 replications in experimental field of Ramin Agricultural and Natural Resources University (2006-2007). The results indicated that, seed yield in topping and native populations had not significant difference. Effect of topping on decrease of tall height was significant but population’s was't. Topping moreover creation stress caused delay in blooming and synchrony seed filling with high heat, thereupon, thermal stress increased medicinal active substances. Amount of medicinal active substances among popoulations were very difference. In p1 amount of silymarin was 2.81 and 2.09, silychristin 2.30 and 4.64 and isosilybin 3.63 and 4.90 fold p2 and p3 respectively. P2 had not silydianin. Amount of silybin in p 3 was 2 and 6.09 fold of p1 and P2 respectively. The results showed that effects of populations on medicinal active substances were much more than topping. P1 was 26 days more serotine than p2 and p3.

To study the effect of the intensity and timing of topping on maize grain yield, an experiment was conducted for two years during 2002-2003 cropping seasons at Safiabad Agriculture Research Center (SARC) using KSC 704 maize hybrid. The experiment was carried out in factorial experiment using a Randomized Complete Block Design with four replications. Treatments were three levels of topping above the ear after anthesis (complete topping, one leaf left and two leaves left) and four topping dates (immediately after anthesis and three topping dates following anthesis with 10 days interval) and control treatment without topping. Results indicated that, there were significant differences among treatments for grain yield and 1000 kernels weight. Topping decreased grain yield and 1000 kernels weight. Control treatment had the highest grain yield (9.94 t/ha) and 1000 kernels weight (327.4 g), and complete topping treatment at anthesis had the lowest grain yield (8.15 t/ha) and 1000 kernels weight (269.79 g). Therefore, topping can decrease grain yield and 1000 kernels weight about 18 percent. There were no significant differences for protein content among treatments. The effect of topping and topping dates for forage yield was also significant. Complete topping with (6.57 t/ha) forge yield had the highest and two leaves with (2.63 t/ha) had the lowest level. Therefore, although topping produced about (6.57 t/ha) forage yield, however, reduced grain yields about (1.79 t/ha) or 18 percent, hence it is not recommended.