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АРИДНЫЕ ЭКОСИСТЕМЫ, 2009, том 15, № 1 (37)
^ОТРАСЛЕВЫЕ ПРОБЛЕМЫ ОСВОЕНИЯ ЗАСУШЛИВЫХ ЗЕМЕЛЬ
УДК 581.132.52
ЗАВИСИМОСТЬ ПОКАЗАТЕЛЕЙ ПОДРОСТА ТОПОЛЯ ДЕЛЬТОВИДНОГО (POPULUSDELTOIDES) ОТ РАЗЛИЧНЫХ ТИПОВ И МЕТОДОВ БОРЬБЫ С СОРНЯКАМИ (ЦЕНТРАЛЬНЫЕ РАВНИНЫ США)
© 2009 г. В.А. Геер, С.Дж. Барден
Отделение лесоводства, Трокмортон Холл, Университет штата Канзас США, Манхеттен KS 66506, E-Mail: Wgeyer@ksu.edu
Реферат. Тополь дельтовидный (Populus deltoids Bartr. ex Marsh.) является массовым видом среди древесных насаждений на территории Центральных равнин США, используемых для берегоукрепительных и ветрозащитных посадок. Во время выращивания саженцев необходимо подавление сорняков, поскольку эти тополя чувствительны к конкуренции.
Общие стратегии борьбы с сорняками включают прополку, внесение гербицидов, укрывание грунтов (или мульчирование) создающее преграду для роста сорняков -пластмассой, листами полиэтилена, или геотекстилем (Appleton et al., 199G; Stevenson, 1994; Van Sambeek et al., 1995). Мульчирование имеет некоторые преимущества по сравнению с гербицидами и прополкой, оно не требует повторного применения, при этом сохраняется влажность почвы, уменьшается эрозия и выщелачивание питательных веществ (Stepanek et al., 2GG2; Truax, Gagnon, 1993). При редком использовании пластмассовых мульч в традиционном лесоводстве, ландшафтные мульчи широко используются в садоводстве (Green et al., 2GG3, Windell, Haywood, 1996).
В условиях эксперимента, поставленного на аллювиальных отложениях в условиях Центральных равнин США проведено сравнение эффективности различных методов борьбы с сорняками при выращивании Populus deltoides: прополки, использования дерна, применения гербицидов (изоксабен+оразалина и сульфометрон-метила), и мульчирования (голубым, светлым, желтым пластиком; черным, коричневым, серым полиэтиленом; тканевым полипропиленом). По окончании пятого вегетационного сезона в качестве показателя использовались: процент выживания, высота (м), диаметр ствола у основания (см), индекс биомассы, рассчитанный по формуле D2H где D - диаметр основания, и H -полная высота саженца (данный показатель имеет высокую корреляцию с объемом и весом дерева; Geyer, Walawender, 1997).
В работе обсуждаются результаты 3-х вариантов посадок с использованием различных приемов борьбы с сорняками. По истечении 5 лет показатели выживаемости саженцев тополя при использовании синтетической мульчи различных типов составили в среднем от 5G до 9G%, тогда как при использовании прополок и химических гербицидов выживаемость изменялась от 6G% до 76%. Показатели роста были наилучшими при использовании химических гербицидов, немного ниже при прополке, и практически одинаковые для всех пластиковых мульчей.
Применение синтетической пластмассовой и тканевой мульчи дали весьма положительные результаты. Хотя эти материалы первоначально кажутся очень дорогими для приобретения и применения, они практичны при использовании при посадках ограниченного размера и облегчают работу «под ключ», где землевладельцы не предполагают повторное применение гербицидов. Синтетические мульчи могут оказаться еще более ценными в областях с малым или ограниченным количеством осадков, по сравнению с результатами, полученными для данного региона. Использование дерна или изоксабен+оразалиновых гербицидов дали наихудшие результаты, поэтому их использование не желательно.
Гербицид сульфометрон-метил обеспечил наилучшие экологические условия для роста. Пришли к выводу, что в условиях Центральных равнин США синтетическое мульчирование может с успехом использоваться для выращивания саженцев деревьев.
Ключевые слова: тополь дельтовидный (Populus deltoids), биомасса, выживаемость, полиэтиленовые, полипропиленовые, пластиковые мульчи, контроль сорняков, гербициды.
GROWTH OF YOUNG POPULUS DELTOIDS AS EFFECTED BY VARIOUS WEED-CONTROL TECHNIQUES IN THE CENTRAL PLAINS OF THE UNITED STATES
© 2009. W.A. Geyer, C.J. Barden
Forestry Division, Throckmorton Hall, Kansas State University USA, Manhattan KS 66506, E-Mail: Wgeyer@ksu.edu
Abstract. Various synthetic mulches were tested on an alluvial site in three studies to examine survival and growth of cottonwood and hybrid poplar seedlings. Blue, clear, and yellow waste plastics; black, brown, and gray/black polyethylene; and polypropylene fabric weed barrier were compared with cultivation; sod; or isoxaben + orazalin (Gallery + Surflan) or sulfometron methyl (Oust) herbicide weed control treatments. After five years, cottonwood seedling survival was moderately high (50-91%) for all synthetic mulch types, whereas seedling survival with cultivation and Oust treatments ranged from 60 to 76%. Seedling growth was best with Oust herbicide, slightly less for cultivation, and nearly the same for all plastics. Planting in sod or use of Gallery + Surflan is not advisable, as these treatments yielded the poorest results. Oust provided the best environmental conditions for growth. Synthetic mulches seem to be practical for use in tree establishment under environmental conditions found in the central Great Plains.
Keywords: Populus deltoides, biomass, survival, height, plastic mulches, weed control, polyethylene, polypropylene, herbicide.
Introduction
Cottonwood (Populus deltoides Bartr. ex Marsh.) is an important tree species in the central plains of the United States for riparian and wind-barrier plantings. Weed suppression is necessary during establishment as cottonwoods are sensitive to competition. Common weed-control strategies include cultivation, application of herbicides, ground covers, or weed barrier mulches including plastic, polyethylene sheets, and woven landscape fabrics or geotextiles (Appleton et al., 1990; Stevenson, 1994; Van Sambeek et al., 1995). Mulches have several advantages over herbicides and cultivation. Mulches do not require repeated application, can conserve soil moisture, and reduce soil erosion and nutrient leaching (Stepanek et al., 2002; Truax, Gagnon, 1993). Although there is scant use of plastic mulches in traditional forestry, landscape mulches are used widely in horticulture. Various new types of plastics and fibers appear frequently on the market and are continually being evaluated (Green et al., 2003; Windell, Haywood, 1996).
Early studies with weed barrier materials were done with 1.5- to 6- mil black polyethylene films that were impermeable to water. Woven polypropylene weed barrier fabrics are now widely available including Sunbelt, manufactured by the DeWitt Company in Sikeston, MO. Sunbelt was one of the first permeable weed barrier fabrics developed. Sunbelt weighs 110.2 g m-2, has an infiltration rate 491 L m-2 min-1, is durable, and contains carbon black as a UV light stablilizer. The objective of this study was to investigate the effects of weed-barrier fabric and various plastic mulches versus conventional herbicides and cultivation for controlling competing vegetation under newly planted cottonwood and hybrid poplar seedlings in the central Great Plains of the USA.
Materials and methods
Three plantings were established in the central Great Plains Region of the United States near Manhattan, Kansas (39.62° N 96.62° W), at 366 m above sea level. Precipitation averages about 760 mm per year, with 75% coming during the growing season. The planting site was on a flat, alluvial, old field site. The soil was
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classified in the Eudora silt loam series (coarse-silty, mixed, mesic, fluventic Hapudolls) and consisted of 25 cm of silt loam underlain by very fine sandy loam. In all three plantings, tall fescue sod was treated with 2% glyphosate (Roundup T.M.) and later cultivated in 1.8 m wide rows spaced 3.6 m apart. The sod and Gallery + Surflan treatments were not cultivated, but the Oust treatment was cultivated each spring before application of the herbicide. Herbicide plots were treated for three years. Grass strips were left between the rows. Cottonwood seedlings (1-0) were used in the first (1996) and third study (1998) and hybrid poplar (NE clone unknown) seedlings were used in the second study (1997). Trees were hand planted with a KBC planting bar in the spring at 1.2 m (1996 and 1998 plantings) or 0.6 m (1997 planting) apart in four 120 m long rows, for a total of 394 trees or 800 trees, respectively. The films (1.8 m wide) were manually laid and the edges were trenched and covered with soil to hold the material in place. The area between the plots was mowed often during the growing season for accessibility.
Each row was divided into eight 1.8 m by 15 m plots with 12 or 24 trees each. A randomized complete-block planting design was used, with each row considered a block. Weed control treatments for all three studies were as follows: 1) solid and punctured 3-mil black plastic polyethylene mulch (Tredegar Film Products); 2) solid and punctured 3-mil gray/black plastic polyethylene mulch (Edison Plastics); 3) brown 2-mil plastic polyethylene mulch; 4) yellow 3.5-mil yellow commercial waste plastic (silicon coated on one side); 5) blue 3.5-mil commercial waste plastic (silicon coated on one side); 6) clear 3.5-mil plastic commercial waste plastic (silicon coated on one side); 7) sunbelt woven polypropylene fabric (DeWitt); 8) tall fescue sod; 9) Bi-monthly cultivation only; 10) commercial application of Gallery (2.24 kg ai/ha) and Surflan (0.84 kg ai/ha) each spring over the top of dormant seedlings; 11) Application of Oust at 36.6 ml/ha each spring after shallow cultivation.
Variables Studied. Weed control treatments were tested for their effects on survival and growth. Percent survival, height in m, and stem diameter at the ground line in cm of the cottonwood trees were recorded at the end of the fifth growing season. Biomass index was evaluated with the D2H expression which is highly correlated to tree volume or weight (Geyer, Walawender, 1997), where D is ground diameter, and H is total height. Data were analyzed by analysis of variance by using SAS General Linear Model procedure (Stastical ..., 2003). Duncan's procedure (Duncan, 1955) was used to separate treatment means when significantly different at the p=0.05 level. Survival differences were determined with the chi-square test.
Results and discussion
Significant differences existed after five growing seasons among weed control treatments for survival, height, stem diameter, and biomass in all three studies (Table 1). In the 1996 planting, survival of the seedlings was very poor when planted in the sod (33%, confirming previous observations that weed control is usually required for successful establishment (Boysen, Strobl, 1991). Seedling survival was less with the use of Gallery + Surflan herbicide (52%) than with weed barrier treatments or cultivation (67-89%). The best individual tree growth was with bi-monthly cultivation to control herbaceous competition (Table 1). Although not significantly different, the average height for the trees with the three polyethylene or polypropylene mulches was about 90% of the height of the trees in the cultivated treatment. Height was the shortest in tall fescue sod or herbicide weed control treatments. Stem diameter followed a similar pattern to height; but diameter for trees grown with the three polyethylene or polypropylene mulches was about 80% of the diameter of the saplings in the cultivated treatment. The D2H biomass index showed that Populus grown with plastic mulches had about 50% of the biomass of the trees in the cultivated treatment. In contrast, the trees in the tall fescue sod and herbicide weed control treatments had only 19% of the biomass compared to those under the cultivated treatment. Use of herbicides to control herbaceous competition was less effective than expected. As is often true in field application, the herbicides were applied later in the spring than desired. Late spring application to dry soils in the Great Plains resulted in heavy weed competition and reduced height of the seedlings.
In the second and third studies, similar tree growth results were found. Survival was high (85%) in all treatments of the 1997 planting. Oust herbicide resulted in the best individual tree growth (Table 1). Bimonthly cultivation provided good height and diameter growth results were statistically equivalent to the Oust herbicide. No significant differences were found among the synthetic mulches for biomass, but Oust and cultivation were clearly superior. In the third study (1998 planting), Oust herbicide was again the best treatment also (all parameters significant at p=0.01). Growth with bi-monthly cultivation and with black or
Table 1. Fifth-year survival and growth in a Populus planting using six-eight weed control methods (1996-1998 study) *. Таблица 1. Выживаемость после 5 лет и рост посадок Populus при использовании 6-8 видов борьбы с сорняками (опытные исследования 1996-1998 гг.)*.
Treatment / Тип мульчи Survival, % / Выживаемость,% Height, m / Высота, м Diam, cm/ Диаметр, см Biomass index (D2H)/ Индекс биомассы
study 1996 / исследование 1996 г.
Plastic / Пластиковые мульчи
Black / Черная 89a 7.2a 9.7ab 422b
Grey-black /Серая-черная 67b 6.7a 8.4b 318b
Sunbel fabric / Тканевая 81a 6.5a 8.1b 332ab
Other / Другое
Bi-monthly cultivation / 77a 7.7a 10.7a 671a
Прополка 2 раза в месяц
Gallery and Surflan / 52b 4.7b 5.6 c 115d
Изоксабен+оразалин
Tall fescue sod / 33 c 4.6b 5.1 c 140d
Дерн высокой овсяницы
Mean / Среднее значение 67 6.2 7.9 333
Sign. / Значимость 1% 1% 1% 1%
study 1997 / исследование 1997 г.
Plastics / Пластик
Black / Черный 94a 10.1c 9.4b 515c
Blue waste / Синий 90a 9.5de 8.9bc 460c
Clear / Светлый 75b 9.2e 8.4c 407c
Gray—black / Серая—черная 80b 10.0cd 9.1cb 475c
Yellow waste / Желтый 87a 10.2c 9.4b 495c
Sunbelt fabric / тканевый 91a 10.1c 9.1cb 486c
Other / Другое:
Bi-monthly cultivation / 86a 10.8b 10.4a 666b
Прополка 2 раза в месяц
Oust/Гербицид вытеснитель 84ab 11.5a 11.2a 788a
Mean / Среднее значение 85 10.2 9.4 533
Sign. / Значимость 1% 1% 1% 1%
study 1998 / исследование 1998 г.
Plastics / Пластик
Black / Черный 50b 9.4ab 11.9ab 783ab
Blue waste / Синий 75a 9.6ab 10.7bc 606bc
Brown / Коричневый 50b 9.4ab 10.4bc 633bc
Gray-black / Серая—черная 71ab 9.1b 9.7cd 463cd
Yellow waste / Желтый 60ab 7.9c 8.4d 360d
Sunbelt fabric / тканевый 60ab 9.2b 10.4bc 553cd
Other / Другие:
Bi-monthly cultivation / 60a 9.3b 9.9a 620Ьс
Прополка2 раза в месяц
Oust/Гербицид вытеснитель 76ab 10.3a 12.4a 923a
Mean / Среднее значение 63 9.3 10.7 619
Sign. / Значимость 1% 1% 1% 1%
Annotation: * - In the Table 1 values followed by the same letter are not significantly different at the p=0.01 level. Примечание: * — В таблице 1 величины, сопровождаемые одними и теми же буквами, различаются незначительно, на уровне p=0,01.
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brown plastics ranked high (Table 1). Height and diameter growth differed little between the mulches, except for the yellow plastic, for which growth results were was much smaller.
The biomass index on an area basis (individual tree D2H x survival) of each treatment for all three studies combined was expressed as percent of cultivation and shown is in Figure. The Oust herbicide treatment was 140% of the cultivation yield. All the synthetic mulches ranged from 58 to 84%. Sod and Gallery + Surflan were very poor (<10% of cultivation). Mean survival of all three studies was 69% over all treatments , with 75% for the synthetic mulches; 33% for sod, 80% for Oust.
Treatment
Fig. Biomass index yields (D2H) indexed to the cultivation treatment set at 100%, over all three sites. Рис. Индекс биомассы (D2H) для трех опытов (за 100% берется показатель, полученный при прополке).
Durability of the plastic mulches exceeded the life expectancy normally expected under full sunlight because they became covered by tree leaf litter and grassy vegetation at the barrier edge. The clear plastic deteriorated within a year, whereas the blue and yellow waste plastics lasted about two years where they were not covered by debris. The Sunbelt polypropylene is the most durable and is expected to last for at least 10 years. The Sunbelt fabric did not girdle the base of the tree, but it is advisable to slit the fabric after 5 years to prevent bark and cambium compression. Rodents didn't seem to damage the tree trunks, which have been reported as a concern when using mulches.
Summary and conclusions
Weed control is necessary for cottonwood and hybrid poplar tree seedling establishment in the Plains States for both soil moisture and shade reduction (Table 2). Proper selection and application of a herbicide is worthwhile if conditions are favorable. Often in field applications, herbicides are applied later in the spring than desired or receive less than adequate amounts of moisture for activation. In typical plantings, Sunbelt fabric or plastic sheet weed barriers may yield better results than herbicides. Mulches can be installed over weeds that may have already germinated, and the opaque fabrics will exclude light, killing existing vegetation and minimizing subsequent germination of weed seeds. Even with the use of weed barrier fabrics, some weeding may be necessary within the planting hole around the tree.
In this study, five-year growth was best when Oust herbicide was used. Bi-monthly cultivation is highly desirable as the next-best alternative, but requires more labor. Synthetic mulch weed barrier plastic sheets and fabrics have many positive attributes. Although these UV-resistant materials initially are very expensive to purchase and apply, they are practical to use in limited size plantings and facilitate turn-key operations where landowners are not inclined to repeatedly cultivate and apply herbicides. The commercial landscape materials, black or gray /black plastic polyethylene, and polypropylene fabric weed barriers worked well and were the durable for a long period of time. Synthetic mulches may prove even more valuable in areas of more limited precipitation than found at our study site.
Table 2. First and second year soil temperature and moisture values at the 6 in (15 cm) and 12 in (30 cm) levels under various mulch types*. Таблица 2. Температура и влажность почвы в первый и второй годы опыта на глубине 15 см и 30 см под различными типами мульчи*.
Treatment / Тип мульчи Temperature, °C/ Температура, °C Moisture, %/ Влажность, %
15 cm 30 cm 15 cm 30 cm
1st year 2nd year 2nd year 1st year 2nd year 2nd year
Clear plastic / Светлый пластик 27.2 a 24.8 а 24.1 b 15.1a 27.4a 27.5b
Blue waste / Синий 27.7 a 24.4 b 23.9 bc 12.2b 25.3bc 26.8b
Gray—black plastic / Серый—черный пластик 24.8 bc 24.4 b 23.9 bc 15.3a 24.9ab 26.1b
Black plastic/Черный 27.6 a 25.3 b 24.8 a 16.5a 26.6ab 29.9a
Sunbelt fabric / тканевый 25.6 b 24.4 b 23.9 bc 16.8a 26.2abc 27.9ab
Yellow waste /Желтый 26.9 a 24.5 b 23.9 bc 15.4 a 24.5cd 25.8b
Bi-monthly cultivation/ Прополка 2раза в месяц 25.6 b 24.3 b 23.8 bc 11.3b 22.8d 25.6b
Sulfometron Methyl / Сульфометрол Метил 23.6 c 23.4 c 23.0d 25.8b
Sign. / Значимость 1% 1% 1% 1% 1% 1%
Annotation: * — In the Table 4 values followed by the same letter are not significantly different at the p=0.05 level. Примечание: * — В таблице 4 величины, сопровождаемые одними и теми же буквами, различаются незначительно, на уровне p=0,05.
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