Establishment of Grass Strips for Maintaining Biodiversity in Agroecosystems

Main principle of the common agricultural policy of European Union is achievement of high results with the least possible negative impact on the environment, land protection and efficient use of natural resources. For that purpose, a number of studies are carried out, related to the improvement of biodiversity and protection of the pollinators in the areas of production. Two type of grass mixes were observed: “Laitamag” (Hungary) composed of White mustard (Sinapis alba L.), White clover (Trifolium repens L.), Phacelia (Phacelia tanacetifolia Bentham), Crimson clover (Trifolium incarnatum L.), Egyptian clover (Trifolium alexandrinum L.), Red clover (Trifolium pretense L.), Wild oats (Avena sativa L.), Alfalfa (Medicago sativa L.), Buckwheat (Fagopyrum esculentum Moench) and Sainfoin (Onobrychis viciifolia Scop.) and a mix, proposed by the Agrarian University: White mustard (Sinapis alba L.), White clover (Trifolium repens L.), Phacelia (Phacelia tanacetifolia Bentham), Buckwheat (Fagopyrum esculentum Moench), Coriander (Coriandrum sativum L.). The vegetation of the autumn crops began in March, as the blossoming lasts for 60-63 days, from the beginning of April until 24 June. For the spring sowing (18 March), the flowering of the mixes occurred later, in the second 10-day period of May and ended at the end of June. As a result of the low temperatures during winter, the white mustard, buckwheat and sainfoin plants perished. White clover proves to be the most resilient species.


Introduction
The intensive use of agricultural areas for solving the food provision issues, the ever growing global population and the climate changes often result in a loss of the natural habitats of organisms (Pollinators and Agriculture, 2013;Pesticides and Biodiversity, 2011).This results in brakage of the balance in the ecosystems and cause favourable conditions for episodic amplification of certain insect species, which possess economic significance as pests.
In the agricultural ecosystems in Europe, approximately 80% of all crops are pollinated by insects, such as bumblebees, honeybees, butterflies etc.Yields of certain fruit-tree species and plants decrease by over 90% in the absence of insects-pollinators (Klein et al., 2007).In the period 1985-2005 the bee colonies decreased by an average of 16%, and in certain European countries, such as United Kongdom, Germany, the Czech Republic and Sweden, the percentage is reported to be much higher.The number of wild bee colonies also decreased as a result of the effect of a number of factors (STEP, 2007).Some authors reported for decline in pollinators but they focus on the improvement of the available habitats, which is in line with EU's common agricultural policy (Westphal еt al., 2003).
agrocenoses with rich species diversity of living organisms.This is also the main objective for the sustainable development of agricultural areas in Bulgaria and corresponds to European Union's common agricultural policy.
In order to improve the biodiversity in agricultural areas, it is necessary to establish new habitats for pollinators at the perimeter of agricultural land.Flower meadows, strips of blossoming plants, field-protection belts, buffer strips have been established in some European countries to provide sources of food and habitats for the living organisms, as well as a depot for the multiplication of pollinators and for attracting honey bees, ensuring high economic results of the production.
There are developped some international initiatives to reinstate the natural habitats and to provide essential food for pollinators, like "Operation Pollinator" (Syngenta global project).It demonstates that environmental management and intensive agriculture can co-exist in the same field.In this way, agricultural producers in Europe and around the world establish and maintain habitats for pollinators in agricultural areas (Isaacs et al., 2010).Operation Pollinator helps growers across Europe in successfully establishment and management of essential habitat for pollinating insects on commercial farms.The initiative was realized with the involvement of more than 2500 farmers from countries, such as: Belgium, the United Kingdom, France, Germany, Greece, Hungary, Ireland, Spain, Portugal, Sweden, Switzerland, Bulgaria etc.
Main objective of the study is to test the germination and development of different grass mixtures to establisg flowering strips, attracting pollinators near production areas.

Mehods
This study was conducted in the period 2013-2015 at the Educational Experimental and Implementation Facility of the Agrarian University, Plovdiv.Two types of grass mixes were chosen for the trials: comersial mixture of Laitamag (Hungary) and locally developed by Agrarian University, Plovdiv.Both mixes were tested with two types of sowing (autumn and spring).
The sowing rate for both mixtures was 20 kg/ha, and the depth of sowing was 1.0-1.5 cm.The test area was 420 m 2 (6 × 70 m).The autumn sowing was performed on October 29, 2013, and the spring on March 18, 2014.Before and after sowing, the terrain was rolled.The sowing density and species ratios was recorded per m 2 , based on a sampling plot.
The plot-test plots, applied for the sowing of the studied grass mixes were as follows: The germination, wintering of the plants (in the case of autumn sowing), their development, species distribution and density of the strands was monitored.

Results and Discussion
The favourable weather conditions in the autumn of 2013 and the spring of 2014 enabled good garnished stands of the crops, in accordance with the sown species and the grass mix ratios.
Although mild, with temperatures around 0 °С, but without any snow cover, winter had an adverse effect on some species, reducing their number/m 2 and changing the original plant ratio in the sown areas.White mustard manifested itself as being very sensitive to low temperatures, and therefore it was destroyed by frost in Plot ІІ.The stand densities in the spring showed that of all plants, included in both mixes, the white clover was the most resistant to cold.
As a result of the respective plasticity, competitiveness and ratios of the species in the composition of both mixes (Laitamag and Agrarian University), different strand density was reported in the spring of 2014.For the Laitamag grass mix it was 59.8 plants/m 2 , and in the Agrarian University mix-228.4pcs./m 2 (Tables 1 and 2).The reduced density in the first plot as a result of the winter conditions are most apparent, if compared to the spring sowing-Plot ІІІ.The reported strand density was 263.5 pcs/m 2 , and 272.4 pcs/m 2 in Plot ІV.The values for Plot ІІ and IV (Agrarian University-autumn, spring sowing) were relatively close, showing that the commercialized mix (Hungary) is sensitive to the low winter temperatures in the Plovdiv region (Tables 3 and  4).For the autumn (second decade of October) and spring sowing (the middle of March) the most suitable plant species for grass mixes are alfalfa, phacelia, wild oats, coriander and various clover species (crimson, Egyptian and white).As a result of the low winter temperatures, the following species were destroyed by frost: white mustard, buckwheat and sainfoin.

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The blossoming in the case of autumn sowing lasted for 60-63 days, beginning from the April and lasting until the beginning of June.In the case of the spring sowing, the duration was 40 days, starting from the second decade of May and until the end of June.

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The plant species phacelia and coriander formed the top level in the grass mix, which was purple-and white-coloured.White mustard, crimson, Egyptian and white clover formed the bottom level-yellow, red and white.

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The summer mowing after the white mustard, coriander, phacelia and white clover reached complete maturity, maintained the grass stand for multiple vegetation cycles.

Table 2 .
Plot II: Agrarian University grass mix, autumn sowing in 2013