DAUGĖLIENĖ, N.1, ŽEKONIENĖ, V.1, GAVENAUSKAS, A.1
Key words: ph1ytocenotic charakteristic, yield, grassland.
Abstract
Legumes play an important role in organic farming, as they enable farmers to reduce the use of nitrogen fertilizer. In an eleven years plot experiment in Lithuania, legumes were the most variable part of the fl oristic component. Their variation was usually cyclic and depended on diff erent factors. Composition of herbage phytocenoses varied depending on their biological properties and ability to adjust to meteorological
conditions. Legumes amount in the sward varied from 13.2 to 43.6%. They spread best (34.4–43.6%) when
summer was rainy. The spread of legumes in herbage is also aff ected by mineral fertilisers. Having fertilised the sward with P60K60 and having calculated the relationship between legumes and fertilisers used it was found that phosphorus fertilisers had a greater eff ect on the spread of white clover. A medium strong
correlation (r = 0.52) was determined between these indicators. Grasses occupied from 32 % to 63.1 % of
the sward area. With sward senescence the content of forbs (mainly Taraxacum offi cinale L.) increased.
Dry matter yield varied within 2.3–5.1 t ha-1 range. It was determined by legumes. The eff ect of legumes on
herbage dry matter yield was very strong (r = 0.786**l), and that of grasses moderate (r = 0.619*l).
Introduction
Species composition of herbs is largely dependent on soil type, natural conditions, sward fertilisation, management, utilisation and other factors. Between grasses and legumes there exist biotic relations that are benefi cial for both populations. Legumes accumulate nitrogen in the soil which can be used by grasses too. Mutalism is specifi c to legume and grass populations, which manifests itself between legume plants and nitrogen fi xing Rhizobium bacteria. The bacteria are able to turn free molecular nitrogen that has passed with air into nodule’s intercells into available nitrogen for legumes and for themselves (Lapinskas, 1998; Stravinskienė 2003). Legumes are the most variable part of the fl oristic component. Its variation is usually cyclic and depends on diff erent factors (Gutauskas, 2003). Natural conditions also have a great impact, however, a proper choice of perennial grass species and mixtures for specifi c natural zones could eliminate this factor. The yield diff erence depends on soil potential fertility. Water defi cit infl uences the basic processes connected with grass productivity (Assuero et al., 2002; Jones, 1998). The portion of legumes and grasses in dry matter yield is in the relationship of cyclic fl uctuation. The duration of cyclic fl uctuation in legumes spread varied between 5–7 years (Daugėlienė, 2002; Gutauskas, 2003). Some literature sources indicate that 25–35 % of legumes in pasture swards can supply grasses with nitrogen (Breazu et al., 2002). Under such conditions the number of species of herbs also declines (Golinska et al, 2005).
Materials and Methods
The experiments were conducted in Western Lithuania. The soil of the experimental site was a sod podzolic Hapli-Endohypogleyic Luvisols (IDg4-p) light loam on medium loam with top soil pH KCl 5,2, available P2O5 of 108 mg kg-1 and K
2O of 142 mg kg
-1. The liming was done before pasture sowing. Grass mixture, containing 35%Trifolium repens L., 40%Phleum pratense L. and 25%Poa pratensis L. were sown. The sward was fertilized annually in spring with 60 kg ha-1 of both P
2O5 and K2O. Treatments were replicated 4 times and grazed 4 times with a herd of dairy cows. The botanical composition (grasses, clovers, forbs) of the samples was measured after separation as dry matter weight. DM yield was determined on the basis of total DM amount per plot and calculated as DM yield ha-1. Analysis of variance and correlation-regression methods were used for experimental data processing. Variation coeffi cient (V %) was calculated (Tarakanovas et al., 2003).
Results and Discussion
The spread of legumes in a pasture sward is also aff ected by mineral fertilisers. Having fertilised the sward with P60K60 and having calculated the relationship between white clover and fertilisers used it was found that phosphorus fertilisers had a greater eff ect on the spread of white clover. A medium strong correlation (r = 0.52) was determined between these indicators. Grasses occupied on average half of the long-term sward’s area and their variation was the least (Table 1). During the eleven years of use the content of grasses either increased or declined depending on the weather conditions under the eff ect of which the share of legumes varied. A marked reduction in the content of grasses was identifi ed in the fi fth year of sward use when only 366 mm of rainfall fell during the growing season. Although the amount of rainfall in July only inappreciably exceeded the monthly mean, the torrential rains that resulted in this amount of rainfall did not have any decisive eff ect on grasses. The share of grasses declined by 9 % in the fi nal year compared with the fi rst year of sward use.
Tab. 1: The variation of fl oristic composition of grassland (% of the DM), averaged data from 1992–2003.
Botanical
composition Mean Standard error Minimum Maximum
Coeffi cient of variation %
Legumes 26,55 3,02 13,00 44,00 37,76
Grasses 47,64 2,91 32,00 63,10 20,29
Forbs 30,57 4,04 15,70 61,50 43,88
With the senescence of swards the competitive power of the good legumes and grasses diminishes and weeds spread rapidly, of which dandelion accounts for the largest share. In the long-term trial forbs occupied on average one third of the sward area (Table 1). Variation coeffi cient suggests that distribution in diff erent years was very high. With the sward growing older the content of forbs consistently increased. During the 11 years of use the content of forbs in the sward increased from 19.8 to 33.28%. The highest content of forbs (61.5%) was identifi ed in the ninth year of sward use. Taraxacum offi cinale L. was the dominant forbs species.
In our experiment having fertilised with P60K60 in a drier year it was possible to obtain both a low (2.05–2.62 t ha-1) and optimal (3.04–3.6 t ha-1) dry matter yield best utilised by cattle. In wet years dry matter yield reached 4.69–5.05 t ha-1. Such great yield variation is refl ected by a high coeffi cient of variation (29%).
The results of correlation analysis indicate that herbage dry matter yield of the long-term sward was mostly dependent on the content of legumes in the sward (Table 2). A strong linear correlation of 99% probability level was identifi ed between these characteristics.
Tab. 2: The infl uence of dry matter yield from yield fl oristic composition t ha-1,
averaged data from 1992–2003.
Indices Linear correlation Linear regression
x grasses y yield r Sr t05 Y = A+ Bx
Grasses 1,46 0.619*l ± 0.262 0,261 2,002
Legumes 0,87 0.786**l ±0 .206 1,911 1,464
Forbs 0,85 0.72*l ± 0.231 2,042 1,341
Conclusions
The amount of legumes in the sward ranged from 13.2 to 43.6%. It spread best (34.4–43.6%) when the summer was rainy. Grasses accounted for 32% to 63.1% of the total sward area. With sward senescence the content of forbs increased.
Dry matter yield of herbage varied within the 2.3–5.05 t ha-1 range. The amount of rainfall in July had the greatest eff ect on the yield. A strong correlation (r=0.75) was identifi ed between the dry matter yield of herbage and the amount of rainfall. The eff ect of legumes on the dry matter yield was also very strong (r=0.786**l) and that of grasses moderate (r=0.619*l).
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