Regulation of Urtica dioica L. on grasslands Vozár Ľ., Jančovič J. and Bačová S. Slovak Agricultural University in Nitra, Faculty of Agrobiology and Food Resources, Department of Grassland Ecosystems and Forage Crops, Nitra, Slovakia E-mail: [email protected] Abstract We studied some possibilities for the biological and mechanical control of the ground cover of Galio-Urticetea Passarge ex Kopecký 1969, with the association of Urtica dioica L., in a place which belongs to the village of Chvojnica in the Strážov Hills in the middle of Slovakia. The place was used as a corral for cattle in the past. Cattle had a great influence on the eutrophication of the soil. The floristic composition changed there. We examined 4 variants in our experiment: 1st – control, without cutting; 2nd – cutting every 5th week with biomass being taken away; 3rd – cutting every 5th week with mulch- ing; 4th –Dactylis glomerata L. and Trifolium repens L. reseeding, cutting four times a year. According to the five-year results of the different types of regulation it seems that the best way of regulation is reseeding with the strong competitive species Dactylis glomerata L. and Trifolium repens L. Keywords: regulation of weed infestation, Urtica dioica L., stand eutrophication, corral for cattle Introduction Livestock numbers have decreased to 1/3 of their original level in Slovakia since the year 1989 (Green Report, 2007). The area of grassland utilisation has been reduced. Inaccessible areas have been abandoned and degraded and have become covered by weeds. These stands have low or toxic forage value and these weeds also have negative influences on the en- vironment and formation of the countryside. One way to destroy undesirable species in grasslands is mechanical treatment. The ground cover is removed when it is at the maximum expansion of the leaves and the root and rhizome carbohydrate reserve matter is depleted (Vozár et al., 2007). Frame (1992) has a similar opinion. He writes that many weeds can be effectively controlled by cultural or mechanical measures, especially when dealt with at the correct stage in their life cycle. Another possibility for the biological control of weeds is reseeding with strong competitive species. Vozár et al. (2006) found out a way through the biyearly monitoring of different types of regulation. They state that the best treatments were reseeding with powerful competitive species and tillage with the subsequent sowing of the powerful competitive species. The aim of this study was to investigate some possibilities for the biological and mechani- cal control of Urtica dioica L. in grasslands overgrown with weeds. Materials and methods The site is situated at an altitude of 640 m a.s.l. in the locality of Chvojnica in the Strážov Hills (48°53'N, 18°33'E). Climatically it is a mildly temperate region, a mildly dry re- Alternative functions of grasslands 559 gion with prevailing cold winters. According to year-long measurements, the average year temperature is 7.5 °C and that within the growing season is 11.1°C. The long-term average of the whole year sum of precipitation is 848 mm and that of the growing season 431 mm. The soil-forming substrate is formed by crystalline rocks with a predominance of granite and crystalline slates on which a brown, acidic, sandy-loam soil (Cambisol) has developed. The original grassland is represented by the Lolio-Cynosuretum Tx. 1937 association. The place was used as a corral for cattle in the past. Cattle have had a great influence on the soil eutrophication in the corral, which changed the floristic composition. An association of Galio-Urticetea Passarge ex Kopecký 1969 was created there, within an Urtica dioica L. association. We monitored four variants in our experiment: 1st – control, without cutting; 2nd – cutting every 5th week, harvesting of above-ground phytomass; 3rd – cutting every 5th week, mulching with above-ground phytomass; 4th – Dactylis glomerata L. and Trifolium repens L. reseeding, cutting every 5th weeks. The first cut of the 2nd, 3rd, and 4th variants took place when the ground cover was 250–300 mm high. The dominance of the botanical groups and individual species was determined in accord- ance with Regal (1956). This was done each spring and autumn. Results and discussion The botanical composition of the association Galio-Urticetea Passarge ex Kopecký 1969 over the period investigated (2004–2008) is given in Table 3. The community consisted mainly of nettles (Urtica dioica L., from 90.0 to 95.3%) before the regulative interven- tions were applied. The changes came after their application. We found only a minimal change in the portion of Urtica dioica L. in variant 1, which represented the original association Galio-Urticetea Passarge ex Kopecký 1969. Its pro- portion did not drop to less than 83.3%. Table 1. Agrochemical soil properties of the original site. Depth N P K pH/KCl tot C (g kg–1) (mm) (mg.kg–1) ox 100 5.4 1,735.0 28.0 717.0 21.0 200 5.6 4,080.0 84.0 590.0 34.0 600 3.7 2,512.0 6.0 150.0 22.0 Table 2. Dates of reseeding and cutting in the first year of the investigation (2004). Variants Reseeding 1st cut 2nd cut 3rd cut 4th cut 1st – – – – – 2nd – 12.5. 16.6. 21.7. 25.8. 3rd 20.4. 12.5. 16.6. 21.7. 25.8. 4th - 12.5. 16.6. 21.7. 25.8. 560 Grassland Science in Europe Vol 14 Table 3. Botanical composition of the association Galio-Urticetea Passarge ex Kopecký 1969 im- pacted by different management (%) (average of replicates) Variants 1st 2nd 3rd 4th Year groups Botanical spring autumn spring autumn spring autumn spring autumn 2004 – – – 1.3 0.7 15.0 - 21.7 2005 – – 5.0 3.3 17.0 23.3 13.3 84.0 2006 0.3 - 9. 7 3.7 24.0 10.0 68.3 89.3 2007 4.3 0.3 13.0 16.0 23.3 22.7 79.7 91.7 Grasses 2008 6.0 - 41.7 42.7 43.0 21.0 88.7 89.0 s2 8.00 0.0 265.7 301.7 231.5 32.8 1639.1 901.1 2004 – – – 1.7 – – – 51.7 2005 – – 0.7 0.0 + + 48.0 9.3 2006 – – 1.7 1.7 1 + 12.3 0.3 2007 – – 3.7 6.7 2.3 2.0 + - Legumes 2008 – – 4.0 10.3 1.0 11.7 0.3 2.3 s2 – – 3.2 18.5 0.9 38.9 512.1 488.0 2004 97.7 100.0 91.7 64.3 95.3 48.3 91.7 13.3 2005 100.0 100.0 60.0 95.0 44.7 58.7 21.0 5.7 2006 96.3 100.0 88.7 94.7 66.7 90.0 17.7 6.0 Herbs 2007 95.7 99. 7 81.0 75.0 68.7 75.3 17.0 8.3 2008 91.0 100.0 51.7 47.0 55.3 65.7 10.3 7.7 s2 11.0 0.0 317.3 421.1 359.1 254.1 1145.1 9.5 2004 90.0 100.0 91.7 45.0 95.3 29.0 91.0 8.3 L. 2005 96.0 91.7 15.0 8.3 23.0 4.7 8.7 0.3 2006 90.7 94.7 2.7 1.3 22.3 7.3 1.3 + 2007 88.0 97.0 1.7 0.7 10.7 6.3 0.3 0.3 2008 83.3 92.7 1.3 1.7 6.0 1.3 + + Urtica dioica s2 21.0 11.4 1529.0 362.4 1328.7 121.2 1930.4 21.3 2004 2.3 – 8.3 32.7 4.0 36.7 8.3 13.3 2005 – – 34.3 1.7 38.3 18.0 16.7 1.0 2006 3.3 – + – 8.3 – 1.7 4.3 2007 – – 2.3 2.3 5.7 – 3.3 – Blank places 2008 3.0 – 2.7 + 0.7 1.7 0.7 1.0 s2 2.6 – 230.9 246.6 234.4 259.2 43.7 30.3 s2 – variance, + rarely, – without presence The share of grasses rose to 42.7% (autumn 2008) with cutting every fifth week with phytomass harvesting (variant 2). It was attended by the dominance of Poa trivialis L. (34.3%). The portion of Urtica dioica L. fell to approximately 1%. The negative effect Alternative functions of grasslands 561 was the substitution of Urtica dioica L. by Rumex obtusifolius L. (44.3%, autumn 2008). The positive effect was the increasing of the leguminous part (to 10.3%, autumn 2008). A similar tendency to that in variant 2 was observed in variant 3 (cutting + mulching). There Urtica dioica L. was also replaced by Rumex obtusifoilius L. Its portion increased to 54.3% (autumn 2008). The most positive effect in the botanical composition from the animal feeding viewpoint was found in variant 4. There Urtica dioica L. was substituted by reseeded Dactylis glomerata L. Its share of the ground cover stabilised at a level around 80.0% from the 3rd year of the investigation. The development of the reseeded Trifolium repens L. was also very interesting. Its portion increased from 0.0% to 51.7% in the 1st year of the observa- tion. However, a rapid reduction in its ground cover, to 9.3% (autumn 2005), was found the next year. The portion of blank places of the exploitation variants (variant 2–4) rose noticeably from the beginning of our observation.