Spring Planting Date Research Articles

Influence of seed onion planting time on productivity and quality of bulb onion varieties

Vegetable crops play an important role in human nutrition. They contain the necessary organic acids, mineral salts, vitamins and other useful substances. The most popular among vegetables in the conditions of the Udmurt Republic are white cabbage, carrots and table beets, cucumbers, squash, tomatoes and various types of onions. Among onion crops, leeks and shallots are grown in small quantities; among perennial onions - welsh onions, chives and tree onions. The most common among the population is common onion grown mainly for bulbs, in small quantities - for greens. The study of the planting timing of onion varieties’ seeds is relevant. The studies’ results of the influence of the seed onion planting time on the yield and product quality of common onion varieties in the open ground of the Udmurt Republic are presented. Spicy varieties Stuttgarter Riesen and Shetana were selected for the study. Along with the early spring planting date adopted in Udmurtia, the fall seed onion planting was also studied (September 20, September 30, October 10, October 20). Phenological observations revealed that common onion plants of the standard variety Stuttgarter Riesen entered the leaf lodging and harvesting phases on average three days earlier than the studied variety Shetana. In terms of yield, Stuttgarter Riesen onion surpassed Shetana by 6.8 t/ha (28%) and had a higher content of dry matter, water-soluble sugars and ascorbic acid in the bulbs. Autumn planting dates led to a decrease in all the studied parameters of bulb onion.

Planting dates and seedling age of red cabbage during the spring season in Uzbekistan

The importance of red cabbage for expanding the range of vegetable crops in Uzbekistan is highlighted in this paper. The results of three-year (2018-2020) studies on the comparative assessment of the effectiveness of three spring planting dates (March 5-9, 13-16 and 25-27) at three seedling ages (70, 60 and 50 days) at each planting date were presented. It was revealed that the later the seeds are sown to obtain seedlings for spring culture, the faster the seedlings appear and the more the seedlings form leaves. With the postponement of the timing of planting seedlings, the survival rate of seedlings increases. It has been established that the later the seedlings are planted, the higher the temperatures are the growth of plants and the formation of heads. The most unfavorable temperature conditions are formed when the seedlings are planted on March 25-27, which causes a delay at the beginning of the formation of heads of cabbage, an increase in the number of leaves of a root rosette, a decrease in the setting and average weight of heads of cabbage and their marketability. The best indicators of head set-up, their average weight and marketability, yield per unit area are provided when planting on March 14-16, 70 and 60-day old seedlings. Planting seedlings on March 25-27, seedlings of any age, due to the formation of heads of cabbage at excessively high temperatures, delays the flow of products, reduces the setting, average weight and marketability of heads of cabbage and significantly reduces the yield per unit area. It is recommended for a spring culture to plant on March 14-16 with 70 and 60-day old seedlings and not allow planting at the end of March.

Dormant Sprigging of Bermudagrass and Zoysiagrass

Many bermudagrass (Cynodon sp.) and zoysiagrass (Zoysia sp.) cultivars are not available as seed and are commonly planted vegetatively using sprigs, especially for sod production or in sand-based systems. Sprig planting is typically done in late spring or early summer, but this can result in an extended grow-in period and delay the use of the turf in the first growing season. The objective of this study was to determine if sprigs of bermudagrass and zoysiagrass could be planted earlier in the year, during the dormancy phase, to hasten establishment. A field study was carried out in Fayetteville, AR, in 2014 and 2016 using ‘Tifway’ hybrid bermudagrass (Cynodon dactylon × Cynodon transvaalensis) and ‘Meyer’ zoysiagrass (Zoysia japonica), and in Guangzhou, China, in 2015, using ‘Tifway’ hybrid bermudagrass and ‘Lanyin III’ zoysiagrass (Z. japonica). Sprigs were planted in March (dormant), May (spring) and July (summer) in Fayetteville, and in January (dormant), March (spring) and May (summer) in Guangzhou. Sprigging rates of 30, 60, and 90 m3·ha−1 were tested at both locations and across all planting dates. Bermudagrass was less affected by planting date, with dormant, spring or summer plantings effectively establishing full cover in the first growing season. Zoysiagrass that was sprigged in the dormant season was successfully established by the end of the first growing season while a full zoysiagrass cover was not achieved with either spring or summer plantings in Arkansas. Dormant sprigging reached full coverage as fast or faster than traditional spring or summer planting dates at both locations, indicating that bermudagrass and zoysiagrass establishment can be achieved earlier in the growing season using dormant sprigging methods.

Planting-date and cutting-time affect the growth and essential oil composition of Mentha × piperita and Mentha arvensis

Peppermint (Mentha × piperita L.) and Japanese mint (Mentha arvensis L.), as the prominent menthol bearing species are widely cultivated and have a considerable share in the global essential oil trade. In this research, the effects of two different planting dates (spring and autumn), diverse cutting time, and alluvial soil conditions were investigated on the growth and essential oil compounds of M. × piperita L. var. Black Mitcham and M. arvensis var. piperascens Holmes in Çukurova Region/Turkey, during 2011−2014. According to the results, despite the relative superiority of M. arvensis; no significant difference was recorded in the growth potential of two species. However, the content and yield of M. arvensis essential oil (4.8 % and 94 L ha−1) were substantially higher than M. × piperita (2.8 % and 43 L ha−1). In terms of plant height, dry biomass, leaf dry weight, and essential oil yield, the spring planting date was significantly superior to autumn. Among the six cuttings, the data of the first cuttings were significantly higher than the second cuttings for each year. The major essential oil constituents of M. × piperita were menthol (22.5–44.6 %) and menthone (13.8–37.4 %). Overall, menthol was more abundant in the spring cultivation of M. × piperita. In contrast, menthone amounts were higher in autumn cultivation. Menthol (53.6–70.5 %) was the major compound of M. arvensis. Isomenthone (4.5–17.7 %), menthone (3.3–14.5 %), and α- pinene (3.6–11.1 %) were the other major oil components of M. arvensis. Menthol content significantly decreased from the fourth cuttings. Although a declining trend in the yield of species was observed over time, the results were acceptable considering the restrictive conditions of the alluvial soils. All in all, without imposing the limits on the cultivation areas of the strategic agricultural crops; the cultivation of medicinal plants would be advisable with the plenty of alluvial lands.

Growth temperature and rhizome propagule characteristics affect rhizoma peanut shoot emergence and biomass partitioning

AbstractAdoption of rhizoma peanut (RP; Arachis glabrata Benth.) is limited by slow establishment. Understanding the factors affecting RP biomass partitioning during the shoot emergence period may aid in developing management practices that enhance establishment. A growth chamber study was conducted to determine shoot emergence and overall growth responses of two RP entries (germplasm Ecoturf and ‘UF Tito’) to day/night temperature (20/10 and 30/20 °C). A greenhouse study evaluated similar responses to rhizome propagule length (10‐ and 20‐cm fragments) and presence or absence of an apical shoot. Shoot emergence was greater (4.9 vs. 2.6 pot−1) at a day/night temperature of 30/20 than 20/10 °C. Root‐rhizome/shoot ratio was much less when RP was grown at 30/20 °C (1.4) than at 20/10 °C (8.5). Growth of more upright‐growing UF Tito was superior to Ecoturf at the greater temperature. In the greenhouse experiment, number of shoots emerged from rhizomes was generally greater with smaller rhizome fragments (10 cm) from which apical shoots were removed, especially for UF Tito. Root‐rhizome/shoot ratio decreased with presence of an apical shoot due to increased shoot biomass, especially for Ecoturf. We conclude that greater growth temperature after planting results in more rapid shoot emergence and greater growth during early establishment, likely favoring summer vs. early spring planting dates, especially for UF Tito. Although RP biomass partitioning responded to presence of an apical shoot on propagules, rhizome length did not affect partitioning and presence of an apical shoot did not consistently influence biomass responses, suggesting no particular requirement for rhizome fragmentation prior to planting.

Влияние способов полива и приемов окучивания на урожайность картофеля

The article considers three ways of watering potatoessprinkling, furrowing, drip and two methods of hilling – ridge and ridge at early spring and summer planting times. The use of drip irrigation systems in the cultivation of potatoes in the subzone of light-chestnut soils of the Lower Volga region leads to an increase in yield of 63 % compared with sprinkler irrigation, at 31 % compared to irrigation furrows in the spring planting time and by 34 % compared to sprinkler irrigation, by 28 % compared to irrigation furrows on the options for summer planting time. Ridge hilling technique led to an increase in potato yield compared to the ridge technique by 8.5…13.3 % at early spring planting times and by 6.6…13.5 % at summer planting times. The analysis of yield of the main production shows that potatoes of spring term of landing formed mass of tubers to 57,4 t/ha, and at summer plantings to 62,6 t/ha. On average, the yield of potatoes at summer planting dates was higher than the yield of potatoes at spring planting dates by 13 %.

Feed productivity of sainfoin in the conditions of the right-bank Forest-Steppe

The purpose of the research was to study the effect of planting time on the formation of productivity of Hungarian sainfoin when grown for green forage. Methods are field, laboratory, statistical, correlation and regression relationships. Research results. It is established that under uneven humidity and high temperature regime in the year of sowing, Hungarian sainfoin formed two yields under spring planting date and one yield under summer planting date. In the second and third years of growth, no significant effect of the planting date on the stages of organogenesis of Hungarian sainfoin was found, where the maturity of the herbage was reached simultaneously. Productivity of Hungarian sainfoin was only conditioned by hydrothermal conditions, where the yield of green mass averaged 45.9—49.6 t/ha with crude protein content of 1.58—1.73 t/ha. At the same time, the highest dry matter yield of 10.25 t/ha and crude protein of 1.73 t/ha was provided by agrophytocenosis when sown on April 12. The productivity index of Hungarian sainfoin in the first year of life was determined, where the highest indicator was obtained during the early spring sowing period (29.04) – 7.85 kg/ha of dry matter per 1 hour of light day, whereas for the recommended summer sowing period was 1.13 kg/ha, or 6.9 times lower. The correlation equation between dry matter output, duration of daylight and the sum of precipitation from full shoots to the beginning of flowering in the first year of life is described. It is found that with increase of precipitation by 1 mm the dry matter output increases by 1.53 % and there is a tendency increase with increasing the length of daylight by 1 minute. Conclusions. It has been established that on gray forest soils of the right-bank Forest-Steppe, over two years of intensive use of the grass stand, regardless of hydrothermal conditions, Hungarian saifoin provided a stable forage productivity when sown in spring. Thus, dry matter yield was 9.38—10.25 t/ha with crude protein content of 1.58—1.73 t/ha. In particular, as for summer planting date, July 20 appeared to be the most effective planting date, which provided dry matter yield of 9.78 t/ha with crude protein content of 1.61 t/ha.

How Much Are Planting Dates for Maize Affected by the Climate Trend? Lessons for Scenario Analysis Using Land Surface Models

Process-based land surface models are important tools to study the historical and future effects of climate change and land use change. The planting date has a considerable effect on crop growth and consequently on dynamic parameters used in land surface models, for example albedo and actual evapotranspiration. If planting dates can be related to climate, scenarios can use this relation to estimate planting dates. Such a relation is expected to differ according to agro-ecological zone. In this study, spring and summer maize planting date observations at 188 agricultural meteorological experiment stations of China, as well as monthly weather records, over the years 1992–2010 were used as the data source. In order to quantify the relation between planting dates and climate parameters, growing season monthly average minimum temperature (Tmin), mean temperature (T), and precipitation (P) were used. The time trend analysis of planting dates and weather data, principal component analysis (PCA) of weather data, and multivariate regression of planting dates as affected by weather data were used. Both Tmin and T increased during this period in most zones, whereas precipitation showed no trend. In southwest and northwest China, maize planting dates advanced significantly for both spring and summer maize. However, in the north China plain (summer maize) and northeast China (spring maize), the planting date was significantly delayed. Ordinary least squares multivariate regression models were able to explain 33% and 59% of the variance of planting dates in the southwest China (i.e., the humid subtropics zone) for spring and summer maize, respectively. However, only 3% could be explained in the Loess Plateau. Thus, adjusting planting dates in scenario analysis using land surface models is indicated for some zones, but not others, where socioeconomic factors are dominant.

Ta Ta for now: Thlapsi arvense (pennycress), an emerging model for genetic analyses.

Ta Ta for now: Thlapsi arvense (pennycress), an emerging model for genetic analyses.

Agro-Climate Projections for a Warming Alaska

Abstract Climate warming is expected to disproportionately affect crop yields in the southern United States due to excessive heat stress, while presenting new farming opportunities through a longer growing season farther north. Few studies have investigated the impact of this warming on agro-climate indices that link meteorological data with important field dates in northern regions. This study employs regional dynamical downscaling using the Weather Research and Forecasting (WRF) Model to assess changes in growing season length (GSL), spring planting dates, and occurrences of plant heat stress (PHS) for five regions in Alaska. Differences between future representative concentration pathway 8.5 (RCP8.5; 2011–40, 2041–70, 2071–2100) and historical (1981–2010) periods are obtained using boundary forcing from the Geophysical Fluid Dynamics Laboratory Climate Model, version 3, and the NCAR Community Climate System Model, version 4. The model output is bias corrected using ERA-Interim. Median GSL shows increases of 48–87 days by 2071–2100, with the largest changes in northern Alaska. Similarly, by 2071–2100, planting dates advance 2–4 weeks, and PHS days increase from near 0 to 5–10 instances per summer in the hottest areas. The largest GSL changes occur in the mid- (2041–70) and late century (2071–2100), when a warming signal emerges from the historical interannual variability. These periods coincide with the greatest divergence of the RCPs, suggesting that near-term decision-making may affect substantial future changes. Early-century (2011–40) projections show median GSL increases of 8–27 days, which is close to the historical standard deviation of GSL. Thus, internal variability will remain an important source of uncertainty into the midcentury, despite a trend for longer growing seasons.

Examining grain and oil yields of different safflower cultivars affected by irrigation withholding treatment in two planting dates

Safflower is a native plant to Iran, resistant to arid environment that will be used as an oil seed for future hopefully. The experiment was a split plot based on complete randomized block design with four replications. Main plot includes two spring and summer plantings and sub-plots include three irrigation withholdings (control, irrigation withholding at the start of flowering and irrigation withholding at the start of grain filling period) and ten safflower cultivars including Soffe, Goldasht, Sina, Faraman, Golmehr and Mexican cultivars, Mec117, Mec295, Mec184, Mec11, Mec7, were located in main plot as sub-plots. The results indicated that delaying in plantings reduced biologic yield, grain yield, harvest index and oil yield in Safflower cultivars, significantly. At the start of flowering, irrigation withholding reduced grain and oil yield significantly. Irrigation withholding treatments and safflower cultivars did not affect on oil percentage. However, Mexican cultivars had suitable yields in spring planting date, but it reduced during summer planting date, extremely; while, Iranian cultivars had higher grain and oil yields during both planting dates. Among the cultivars, Soffe and Goldasht had the highest grain and oil yield.

اثرات تاریخ کاشت، زمان آبیاری و کاربرد گیاهان پوششی بر رشد و عملکرد زعفران (Crocus sativus L.)

به منظور بررسی اثرات زمان‌های کاشت بهاره، تابستانه و پاییزه و نیز مدیریت آبیاری و استفاده از گیاهان پوششی، بر ویژگی‌های رشد و عملکرد گیاه دارویی زعفران (Crocus sativus L.) آزمایشی در مزرعه تحقیقاتی دانشکده کشاورزی دانشگاه فردوسی مشهد در سال‌های زراعی 89-1388 و 90-1389، به صورت کرت‌های دوبار خرد شده در قالب طرح پایه بلوک‌های کامل تصادفی با سه تکرار اجرا شد. فاکتورهای آزمایشی عبارت بودند از: تاریخ کاشت بهاره، تابستانه و پاییزه زعفران به عنوان فاکتور اصلی (اول خرداد ماه، اول مرداد ماه و اول مهر ماه)، مدیریت آبیاری به عنوان فاکتور فرعی (انجام آبیاری و عدم انجام آبیاری پس از هر تاریخ کاشت) و کاربرد گیاهان همراه در سال دوم آزمایش به عنوان فاکتور فرعی فرعی [شبدر ایرانی (Trifolium resopinatum L.)، خلر (Lathyrus sativus L.) و شاهد]. نتایج نشان داد که با تأخیر در کاشت بنه‌ها از اول خرداد به اول مهر، شاخص‌های کمی زعفران به طور قابل ملاحظه‌ای کاهش پیدا کرد و شدت کاهش در سال دوم آزمایش به مراتب بیشتر بود. بیشترین عملکرد گل در تاریخ کاشت مرداد ماه (به ترتیب 28 و 98 کیلوگرم در هکتار برای سال‌های اول و دوم آزمایش) و کمترین آن در تاریخ کاشت مهر ماه (به ترتیب 18 و 34 کیلوگرم در هکتار برای سال‌های اول و دوم آزمایش) به دست آمد. کاشت زعفران در تاریخ اول مرداد ماه موجب بهبود سرعت گل‌دهی و کاهش نسبی سرعت ظهور برگ گردید. عدم آبیاری پس از کاشت باعث افزایش شاخص‌های کمی زعفران شد؛ به طوری‌که عملکرد گل در تیمار انجام آبیاری پس از کاشت در سال اول نه و در سال دوم 43 کیلوگرم در هکتار و برای تیمار عدم انجام آبیاری در سال‌های اول و دوم به ترتیب 37 و 78 کیلوگرم در هکتار بود. بیشترین تعداد گل در هکتار (480000 گل در هکتار) و نیز بیشترین درصد بنه‌های گل‌دهنده (100 درصد) در سال دوم آزمایش و در تیمار تاریخ کاشت خرداد ماه و عدم انجام آبیاری پس از کاشت به دست آمد. کاربرد گیاهان پوششی به خصوص خلر تا حدودی باعث بهبود ویژگی‌های رشد و عملکرد زعفران گردید؛ به طوری‌که استفاده از این گیاه پوششی، عملکرد گل و کلاله را در مقایسه با شاهد حدود دو درصد افزایش داد. همچنین بیشترین سرعت گل‌دهی و کمترین سرعت ظهور برگ در تیمارهای تاریخ کاشت خرداد ماه، عدم انجام آبیاری پس از کاشت و کاربرد گیاه پوششی خلر مشاهده شد.

Cover Crop Impact on Weed Dynamics in an Organic Dry Bean System

Weed suppression is one possible benefit of including cover crops in crop rotations. The late spring planting date of dry beans allows for more growth of cover crops in the spring. We assessed the influence of cover crops on weed dynamics in organic dry beans and weed seed persistence. Medium red clover, oilseed radish, and cereal rye were planted the year before dry beans; a no-cover-crop control was also included. After cover-crop incorporation, common lambsquarters, giant foxtail, and velvetleaf seeds were buried in the red clover, cereal rye, and no-cover control treatments and then retrieved 0, 1, 2, 4, 6, and 12 mo after cover-crop incorporation. Dry beans were planted in June and weed emergence and biomass measured. Eleven or more site-years of data were collected for each cover-crop treatment between 2011 and 2013, allowing for structural equation modeling (SEM), in addition to traditional analyses. Cereal rye residue increased giant foxtail and velvetleaf seed persistence by up to 12%; red clover decreased common lambsquarters seed persistence by 22% in 1 of 2 yr relative to the no-cover-crop control. Oilseed radish and incorporated cereal rye rarely reduced weed densities. When red clover biomass exceeded 5 Mg ha−1, soil inorganic N was often higher (5 of 6 site-years), as were weed density and biomass (5 and 4 of 12 main site sample times, respectively). Using SEM, we identified one causal relationship between cover-crop N content and weed biomass at the first flower stage (R1), as mediated through soil N at the time of dry bean planting and at the stage with two fully expanded trifoliates. Increasing cover-crop C : N ratios directly reduced weed biomass at R1, not mediated through changes in soil N. Cover crops that make a significant contribution to soil N may also stimulate weed emergence and growth.

Preplant Cultivation Techniques and Planting Date Effects on White Clover Establishment into an Existing Cool-season Turfgrass Sward

Managed turfgrass species require frequent inputs to maintain an acceptable level of density and appearance. Among these inputs, the N supply is often the most limiting input in terms of growth and development of the turfgrass stand. However, N fertilization has been linked to nonpoint source (NPS) pollution of groundwater and natural water bodies. White clover (WC), which would provide N in mixed turfgrass swards, could help reduce NPS pollution from N fertilization of turf. To test the feasibility of introducing WC into existing turf, a field study was designed to determine the best method of incorporating WC in mature stands of two cool-season grasses. Two varieties of WC, ‘Dutch White’ (DW), and ‘Microclover’ (MC), were sown (24.4 kg·ha−1) into existing stands of kentucky bluegrass (KBG) (Poa pratensis L.) and tall fescue (TF) (Festuca arundinacea Schreb.). Establishment techniques tested included core aeration (CA), scalping (SC), and vertical mowing (VM) compared with direct sowing into the turfgrass stand. Establishment treatments were performed in April, July, and October of 2012–13 to examine for any seasonal timing effect on establishment. No significant difference in plant numbers (individual clover plants per square meter) was found between WC varieties among planting dates and techniques. The SC treatment resulted in the highest individual clover plant numbers. However, turfgrass recovery was significantly slower from the SC treatment than all other treatments. The summer planting date yielded the highest WC plant numbers. Recovery of the turfgrass from all preplanting treatments was also highest at the spring and summer planting dates.

Valerian roots (Valeriana officinalis L.): Produced in autumn and spring planting date

This paper examines the influence of agro-ecological conditions and plantation periods on the occurrence of planting dates of flower stalks, offering fresh and dried valerian root. The aim of this paper is to solve one of the technological unknowns in primary production of valerian roots, where one group of manufacturers base their production on fall plantation, whereas the other group applies spring plantation. The experiments were established in a randomized block design with four replications in the period of tree years from 2013 to 2015, on the soil of marshy black type. The medicinal plant species of valerian (variety “Vojvodinian”) was used, as the plant material planted in autumn and spring. In the first year of experiment there was a significantly lower number of flower stalks than in the second year. The number of flower stalks were lower when planting was done in spring. Primary reasons for such results were a shorter vegetation period and a larger number of warm days. The higher yield of fresh roots was realized in the first year (2013) due to the lower number of flower stalks, better distribution and larger amounts of rainfall. Overall, twice the yield of fresh valerian roots was recorded in the autumn plantation (14.91 kg ha-1) compared to the spring plantation (6.72 kg ha-1). The result of our research has confirmed some of the benefits of establishing an autumn crop of valerian. Obtained roots with rhizomes from autumn planting dates were bigger and brighter compared to those from spring planting dates.

Common Smut Reduces Sweet Corn Yield and Ear Processing Quality

The impact of natural infection of Ustilago maydis (causal agent of common smut) on processing characteristics of three F1 hybrid sweet corn (Zea mays L.) cultivars was evaluated in a 2-year study with early and late spring planting dates. At harvest maturity, size and location of galls were recorded and quality characteristics measured. Galls on the lower stalk, upper stalk, and tassel reduced fresh weight and diameter of husked ears, whereas galls on the base of the stalk reduced fresh weight only. Ear length was reduced by galls on the upper stalk. As gall size increased from 0 to greater than 10.2 cm in diameter, ear fresh weight and diameter decreased. The presence of galls greater than 10.2 cm in diameter reduced ear length. Kernel depth was unaffected by size or location of gall. Additional ears of the same three cultivars were sampled from commercial fields planted in midseason near Walla Walla and Patterson, WA. Galls located on the upper and lower stalk reduced fresh weight, length, and diameter, whereas galls on the base of the stalk reduced fresh weight only. As gall size increased, fresh weight, length, diameter, and kernel depth decreased.

Effects of seed source and pre-planting treatment on emergence of Juniperus scopulorum Sarg. in a Great Plains nursery

Reliable propagation of Rocky Mountain juniper (<i>Juniperus scopulorum</i> Sarg. [Cupressaceae]) for use as an evergreen shelterbelt species in the southern Great Plains is hindered by inconsistent seedling emergence and establishment. We evaluated a series of pre-planting treatments as well as 2 planting depths for both fall and spring planting dates using a single seed source. We then tested 6 seed sources using the 3 best treatments. The best treatment was 13 wk at 22 °C (72 °F) followed by 13 wk at 4 °C (39 °F; 23% emergence for fall and spring planting combined). Fall planting resulted in greater success for differing pre-planting treatments. Planting depth did not affect emergence. Only one of 6 seed sources produced seedlings in response to cold-only treatment while combining warm and cold treatments was generally successful for all seed sources.

Dynamics of reproductive growth of lesquerella ( Physaria fendleri) over different planting dates

Vegetative and reproductive growth information of lesquerella ( Physaria fendleri), a new oilseed crop targeted for bio-products, is important to understand especially in the early commercialization stage of this new crop. The objective of this study was to determine the effect of fall, winter, and spring planting dates over three years on the ontogeny of the crop including biomass, floral buds, flowers, and siliques. Fall plantings always produced more than the other plantings due to the extended season. Winter and spring plantings had less biomass and produced fewer buds, flowers, and siliques. The compensation of lower crop management costs and a shorter growing season could make winter a viable option for planting in the southwest. Spring planting could become viable if seed shatter due to summer rains could be reduced. The information will help decide growing regions suitable for crop production and determine what reproductive stages could be manipulated to improve seed yields.

Chemical Composition of the Essential Oils from Foliages and Seeds of Ajowan (Trachyspermum ammi (L.) Sprague) in two planting dates (spring and summer)

The seeds (at ripening) and foliage (before flowering) of ajowan were collected from field in Esfahan province (central region of Iran) where two planting dates (spring and summer) were conducted. In the spring planting date, fourteen and eleven components were identified in the seed and foliage oils of ajowan, respectively with thymol 44.5 % in seed and 20 % in foliage as main constituent. Other components in seed and foliage oils were: γ-terpinene (26.6 % and 21 %), p-cymene (21.6 % and 10.8 %), limonene (1.1 % and 0.3 %) and carvacrol (0.3 % and 3.6 %). Sum of these components were 94.2 % and 55.7 % in the seed and foliage oils, respectively. In the summer planting date, twelve and eleven components were identified in seed and foliage oils, respectively and the most important constituents were: Thymol (55.5 % and 56.2 %), γ-terpinene (22.5 % and 26.9 %), p-cymene (14.2 % and 11.2 %), limonene (1.9 % and 0.5 %) and carvacrol (0.3 % and 1.4 %), respectively. Sum of these components were 94.4 % and 96.2 % in the seed and foliage oils, respectively.

Plant population, planting date, and germplasm effects on guayule latex, rubber, and resin yields

Guayule ( Parthenium argentatum Gray) is a perennial shrub native to the Chihuahuan Desert. While guayule traditionally has been cultivated for rubber, more recently it is being cultivated for its hypoallergenic latex. Other uses including termite resistant wood products and an energy source have also been identified. However, the effects of various agronomic practices, such as planting and harvesting dates, plant spacing, cutting height and frequency, irrigation frequency, and herbicide application, on latex concentration and yield of newly developed germplasm have not been reported. The objectives of this study were to determine the yield and concentration of latex, rubber, and resin of four guayule lines planted at two populations and two planting dates. Four guayule lines (AZ-1, AZ-3, AZ-5, and 11591) were transplanted at two dates (28 November 2000 and 7 June 2001) and two plant populations (27,000 and 54,000 plants ha −1). Treatments were replicated four times. Each treatment plot was subdivided into six subplots for harvesting at 6-month intervals beginning 1 year after transplanting. Results showed that transplanting date did not affect plant size or latex concentration or yield consistently. Instead, it appeared that the time of harvest (fall vs. spring) was more important. The sixth (last harvest) in the fall planting date and the fifth harvest date in the spring planting date were the optimum for plant biomass and latex, rubber, and resin concentrations and yields. The lines AZ-1 and AZ-3 were larger, whereas AZ-5 had higher latex and rubber concentrations than the control, 11591. The greater plant population (54,000 plants ha −1) had higher biomass, rubber, and resin yields than the lower population (27,000 plants ha −1) at the early harvest dates, but not at the later harvest dates (5 and 6). More studies must to be conducted to determine the optimum plant population and transplanting date for other newly developed guayule germplasm lines.