Weyrich's Knotweed

Economic Significance

Weyrich's knotweed (buckwheat) regrows early, making it possible to obtain the first cut in early summer and the second in early autumn. The green mass is used fresh and preserved for silage, haylage, and vitamin-rich feed.

The green mass of Weyrich's knotweed is characterized by a high content of protein and ascorbic acid. It is well suited for ensiling alone, but silage is of higher quality when ensiled in combination with crops high in carbohydrates. 100 kg of silage contains 12–16 feed units and 1.5–2.4 kg of digestible protein. The palatability of silage, especially combined silage, by animals is good — up to 35 kg per cow per day.

100 kg of green mass corresponds to 13.5 feed units and contains 2.4 kg of digestible protein.

Besides Weyrich's knotweed, attempts are being made to introduce other species into cultivation, for example, mountain knotweed, tannin knotweed, Transbaikal knotweed, Sakhalin knotweed, and fragrant knotweed.

History of Cultivation

Weyrich's knotweed was first sown in Russia at the end of the 19th century in the Botanical Garden of St. Petersburg.

Cultivation Areas

In natural phytocenoses, Weyrich's knotweed occurs in Sakhalin and the Kuril Islands, as well as in Japan.

It is promising for cultivation in areas of sufficient moisture in Russia, as well as in Belarus, the Baltic states, and Ukraine.

Yield

Green mass yield during the growing season reaches 35–75 t/ha.

Botanical Description

Weyrich's knotweed (Polygonum weyrichii Fr. Schmidt) is a perennial plant of the buckwheat family (Polygonaceae). The plant is a large, well-leafed bush.

The root system includes a well-developed main root (rhizome, stem-root); with age it thickens and produces more overwintering buds and adventitious roots.

The stem is erect, slightly curved at the nodes, hollow, grooved, weakly branching, up to 150–250 cm high.

The leaves are large, broadly ovate, pubescent beneath.

The inflorescence is a loose, branched panicle. The flowers are whitish-pink or red. Cross-pollinated.

The fruit is a three-angled brown achene. The weight of 1000 fruits is 2.0–3.0 g.

Biological Characteristics

Weyrich's knotweed is a cold-hardy and winter-hardy plant. Rhizomes can withstand frosts down to −35 °C (Institute of Biology of Komi). Leaves are partially damaged by spring and autumn frosts of −5…−6 °C.

It requires moisture but is drought-resistant. Plants are most sensitive to moisture deficiency in the first year of life, especially during emergence and post-emergence development, when the root system is formed. With age, sensitivity to moisture deficiency decreases; plants make good use of autumn-winter precipitation.

Shade-tolerant; belongs to long-day plants.

Not demanding as to soils. Medium loamy and sandy loam soils with acidity pH 5.5–6.0 (according to other data, pH 5.5–7.0) are considered optimal.

Plant Nutrition

From 1 t of green mass, 4–5 kg of nitrogen, 0.9–1.0 kg of phosphorus, 5–6 kg of potassium, and 1.9–2.3 kg of calcium are removed from the soil.

Vegetation

Weyrich's knotweed is characterized by rapid growth, regrowth capacity, ecological plasticity, and undemandingness to cultivation conditions. Plant lifespan is 10–15 years.

Development type is spring.

In the first year it grows slowly and is strongly suppressed by weeds. In the second and subsequent years, it begins to regrow immediately after snow melt. It produces the greatest increments of aboveground mass during budding–flowering.

Regrowth after mowing depends on moisture and is observed after 1–2 weeks. Shoots emerge from buds located on the rhizome and lower uncut stem nodes.

Maximum productivity of stands is observed in the 3rd–4th year and persists in subsequent years of life.

Crop Rotation

For perennial plantations of Weyrich's knotweed, a weed-free out-of-rotation plot near livestock farms is allocated, on which seeds are sown or rhizome cuttings (seedlings) are planted.

Good preceding crops include row crops and grain legumes.

Fertilization

According to research by the MAA named after K. A. Timiryazev and the Institute of Biology of Komi, it is recommended to apply 60–90 t/ha of manure, 4–6 t/ha of lime, and 60–90 kg/ha of a.i. of mineral fertilizers to the soil under plowing. Lime fertilizers are best applied with manure.

However, greater efficiency is achieved by applying organic and mineral fertilizers calculated for the planned yield based on nutrient removal with the harvest, taking into account effective soil fertility and coefficients of utilization of nutrients from soil and fertilizer. Thus, in experiments of the MAA named after K. A. Timiryazev, on average over four years, when applying fertilizer rates calculated for the planned yield, the yield of Weyrich's knotweed by fresh mass was 60.5 t/ha and by dry mass 10.5 t/ha, whereas with recommended rates (60 t of manure and N₆₀P₆₀K₆₀) it was 52.4 t/ha and 9.1 t/ha, respectively; the yield in the unfertilized control was 44.0 t/ha and 7.7 t/ha.

Soil Tillage

When establishing a plantation by seed, pre-sowing soil tillage should be more thorough, since this is a small-seeded crop whose cotyledons are carried to the surface during germination.

After plowing, disking and leveling of the soil are carried out. Before sowing, rolling is done.

Sowing

Seeds of Weyrich's knotweed are sown in late autumn before frosts. When sown in spring, seedling density sharply decreases. Vegetable seeders SO-4.2 are used for sowing. The sowing method is wide-row with row spacing of 60–70 cm. Seeding rate is 6–8 kg/ha, seeding depth 1–2 cm. A square-cluster sowing method is also possible.

Seeds store poorly and sharply lose germination after a year, so freshly harvested seeds of the current year are recommended for sowing. For spring sowing, seeds are stratified for 20–25 days.

Planting with seedlings is also possible; it is carried out with seedling-planting machines in early spring when shoots begin to grow. The planting method is also wide-row with row spacing of 60–70 cm and in-row spacing of 40–60 cm. Seedlings are prepared on ridges by sowing seeds before winter using a vegetable seeder. Row spacing is 20 cm, and the seeding rate is 30 kg/ha. 100 m² of seedling bed is sufficient to establish 1 ha of plantation.

The main advantage of the seedling method is significantly less concern about keeping plantings clean of weeds.

Crop Care

Weyrich's knotweed develops slowly in the first year, so the main task in crop care is weed control. For this, 2–4 inter-row cultivations are performed; herbicides are used if necessary.

In the second and subsequent years, in early spring and after the first harvest, inter-row cultivation is carried out using KRN-4.2 cultivators. At the same time, fertilizing with mineral fertilizers N_60-90P_60-90K_60-90 is done.

Periodically, every 2–3 years, rotted manure is applied to the plantation in autumn or early spring at 15–20 t/ha. After 4–5 years, surface liming of the soil is carried out.

Harvesting

Harvesting of the green mass of Weyrich's knotweed in the first year is usually not carried out, since the yield is low and mowing weakens the plants. An exception is the seedling method of planting, in which it is possible in the first year of plantation life to obtain a small cut of 15–20 t/ha without harming the plants for overwintering.

From the second and subsequent years, harvesting for green fodder and grass meal is carried out in the budding phase, and for silage and haylage in the phase of mass flowering. For harvesting, forage harvesters KS-2.6A, E-281, KSK-100, KPKU-75 are used. The second cut forms by late August–early September.

According to data from the MAA named after K. A. Timiryazev, in the central regions of the Non-Chernozem Zone, harvesting is recommended in late June–early July. Thus, when harvested in the flowering phase, yields of fresh and dry mass were respectively: June 20 — 71.6 t/ha and 10.5 t/ha; June 30 — 74.8 t/ha and 12.2 t/ha; July 10 — 56.5 t/ha and 12.5 t/ha. It is advisable to alternate two-cut harvesting of plantations every 2–3 years with single-cut harvesting.

Seed Production

Weyrich's knotweed is capable of producing seeds in almost all regions of Russia, except the northern ones.

Fruit ripening is greatly extended. Ordinary forage crops can be allocated for seed production, alternating them by years of use for fodder or seed purposes.

Harvesting for seed begins when 70% of seeds in the panicle reach the wax ripeness phase. For seed harvesting, semi-mounted sorghum harvesters can be used, for example SM-2.6, which allows cutting panicles at a height of 140–250 cm. Cut panicles are dried under a canopy, and threshing is carried out on a threshing floor. Seed yield with this harvesting method reaches 300 kg/ha with high sowing qualities.

After seed collection is finished, the green aboveground mass can be harvested with silage harvesters.

Varieties

Syktyvkarets (1979). The variety was developed by the Institute of Biology of Komi and the MAA named after K. A. Timiryazev.

Kormovik (2001). A variety of Transbaikal knotweed.

List of Sources

1. Vavilov P. P., Gritsenko V. V., Kuznetsov V. S. et al. (1986). Plant Growing. Edited by Vavilov P. P. 5th ed., revised and enlarged. Moscow: Agropromizdat.
2. Kolomeichenko V. V. (2007). Plant Growing/Textbook. Moscow: Agrobiznescentr.
3. Niklyaev V. S. (2000). Fundamentals of Agricultural Production Technology. Agriculture and Plant Growing. Moscow: Bylina.