Using Grass, Hedges and Trees to protect soils
Modern farm machinery and cultural practices have enabled a wider range of steeper soils to be used for crops, resulting in a progressive increase in field size and the loss of native habitats including hedgerows.
Removing the vegetation breaks on longer slopes has increased the risk of erosion and runoff. The strategic use of grass, hedgerows and trees or woodlands offers opportunities to protect vulnerable farm soils from erosion, and to reduce runoff and water pollution.
Grass and other permanent vegetation can also act as a filter, preventing many of the chemicals and nutrients in runoff reaching watercourses.
Farmers with frequent or serious erosion problems have found that vulnerable areas, including valley bottoms, steep or long slopes and natural drainageways benefit from planting of permanent vegetation.
Erosion can be controlled, production maintained and off-farm effects reduced by judiciously combining grass and other vegetation cover with crops.
Grants are available for beetle banks, field margins and the reversion of arable land to grassland when they are managed to improve wildlife.
Re-establish or introduce hedges in conjunction with grass and woodland to break up vulnerable areas of arable land and reduce the length of slopes. Hedges should be aligned with the contour and associated with ditches or banks for maximum impact on runoff and soil erosion.
On long slopes where the soils are vulnerable to erosion and runoff, re-establish or introduce breaks using woodland in conjunction with grass and hedges. Farm Woodland grant schemes may provide aid and technical assistance.
Remember that a well-managed woodland can provide a source of income.
Crop protection is an essential part of ensuring good yields. However, recent experience has shown that using an integrated range of protective techniques is the most cost-effective approach in the long term.
Spending some time in reviewing the protection of your crops and seeking a site-specific balance of mechanical, chemical and biological controls often identifies opportunities to reduce labour costs and other inputs, whilst ensuring comparable yields and improving profits. It will also help to protect vital soil, water and wildlife resources.
In some cases it is possible to obtain grant aid e.g. for ‘beetle banks’ and field margin management, which will further reduce costs and improve product acceptability.
Use a farm advisor to help develop an integrated crop protection plan for the farm.
By carefully targeting use of chemicals, ensuring vigorous crop growth, and controlling damage from insects, diseases and weeds to acceptable levels, rather than trying to eliminate them altogether, a more balanced, productive system can be achieved.
There are three key elements to this strategy to protect your crops. The first line of defence is prevention, by using techniques such as crop rotation, variety selection and cultural measures. The next involves crop protection by forecasting, monitoring and controlling the impact of weeds, pests and diseases and by accurate targeting and applications of chemicals.
The third element encourages predators and parasites of pests by restoring or improving their habitats.
Crop varieties, rotation and cultivations
A diverse rotation can reduce the impact of weeds, pests and diseases by interrupting life cycles.
A four-year crop rotation is now considered by some farmers to be too short for the effective reduction of some pest problems. Where crops such as oilseed rape, potatoes and sugar beet are part of the rotation, pests and diseases can survive in the soil for several years.
Farmers are now selecting crop varieties with a high natural resistance based on assessment of the disease risk and cropping history of the farm.
Developing a stale seedbed and controlling weeds and volunteers between crops reduces the need for in-crop treatments and the weed seedbank.
Late drilling will help reduce weed competition and aphid attack but care must be taken to avoid damaging heavy soils in a wet autumn and causing soil erosion, because the crop does not have time to establish before winter.
Infestations by weeds and insects and infections of crops by diseases are commonly managed by applications of chemicals. However, some farmers are cutting costs by reducing inputs.
Chemicals are being used as little as possible but as much as necessary by quantifying incidence of weeds, pests and diseases and then comparing with treatment thresholds, followed by targeted use of chemicals. This helps to balance inputs to the optimum yield/cost ratio.
Encouraging predators of crop pests
In large arable fields, farmers can provide habitats such as grass strips and hedgerows to allow pest predators to migrate easily into the crop and help pest control.
Native tall tussock grasses such as Cocksfoot and Yorkshire Fog are suitable for ground beetles (hence the name ‘beetle banks’) and also provide an ideal habitat for small mammals. It may be possible to provide such grass areas in natural drainageways which could reduce the risk of soil erosion (see BFP 7) and attract grant aid for conservation (see BFP 12).
Grass strips on arable field margins can increase the range and number of beneficial insects, prevent ingress of aggressive weeds and improve wildlife on the farm.
Uncropped field margins can also be used as no-spray buffer zones next to watercourses.
1. General description of the soils in Haskovo region
1.1. Physico-geographical characteristics of the region
Haskovo District is located in the southeastern part of Bulgaria and occupies 5% of the country’s territory with an area of 5,543 km2. The area includes the southwestern part of Sakar Mountain, part of the Eastern Rhodopes and part of the Thracian Lowland.
1.1.2. Geological features
In terms of geology and tectonics, most of the Haskovo region is attached to the structures of the Eastern Rhodope block and the Sakaro-Strandzha tectonic zone, which contact with the Marishka fault.
The lithological diversity is represented by pre-Paleozoic and Paleozoic metamorphites and phylitoids, Paleogene volcanic-sedimentary rocks (rhyolites, andesitite, tuffites, tuff-breccias, etc.). The lithological diversity is represented by pre-Paleozoic and Paleozoic metamorphites and phylitoids, Paleogene volcanic-sedimentary rocks (rhyolites, andesitite, tuffites, tuff-breccias, etc.). The Sakar anticline is filled with gneisses, amphibolites, gneiss-shales, metamorphosed granitoids, etc., covered by carbonate sediments. Neogene-Quaternary materials are represented by gravels, sands, clays, coal seams, poorly welded sandstones and core limestones. Ore minerals are associated with lead-zinc, copper-iron, copper-zinc, copper-polymetallic, and non-metallic – with trace, perlite, bentonite, zeolite and others. A small part of the region falls into the Upper Thracian Depression, which is characterized by the presence of conglomerates, sandstones, andesites, tuffs, limestones, alumina, sands, clays, gravels and others (Nam, 2003).
The study area is dominated by hilly-ridge and lowland relief, divided by differently configured river valleys, valley extensions and gorges. The horizontal segmentation of the terrain varies from 1.5 to 3.5 km / km2 and the vertical segmentation is between 50 and 200 m / km2. About 62% of the territory of Haskovo region is occupied by lands with a slope over 3°. The lands with a slope of 3-9° are 49% of the territory of the region, those with a slope over 9° occupy 2% of the area of the region (Ruseva et al., 2010). As a result of exogenesis, river-valley, volcanogenic and karst landforms have formed (Nam, 2003).
Haskovo district falls in the Continental-Mediterranean climatic region, characterized by hot summers and mild winters, two maximum rainfall, pronounced summer-autumn drought, episodic and volatile snow cover. (Topliiski, 2006). The average annual temperatures are between 12 °C and 13 °C. The average annual air temperature in the warmest month of July varies between 22.8 °C and 23.7 °C. The average annual air temperature in the coldest month of January is between 0.5 °C and 1.5 °C. The average annual amount of precipitation is about 650 – 700 mm (Topliyski, 2006). The Mediterranean influence affects the amounts and annual distribution of precipitation, which are concentrated mainly in the autumn-winter period and spring and are very limited in summer. Rainfall conditions are intense and torrential in nature to a significant extent which causes floods and intensification of erosion processes, especially in hilly and low-mountainous areas (Velev, 1974). Nearly 14% of heavy rains are erosive. About 12% of the territory of the district, located mainly in the Eastern Rhodopes, is characterized by 4th class rain erosion, and 82% of the territory is characterized by low rain erosion. (Ruseva et al., 2010).
The largest rivers in the region are Maritsa, Arda and Sazliyka. Surface runoff depends on the rains and snowfalls during the year. The annual distribution of precipitation predetermines the presence of two distinct phases of the river outflow – the phase of high water in April and the phase of low water in September. It is common for smaller rivers to dry up. A typical example is the Byala River, which in the high water phase can generate 60.1 m3/s, and in the low water phase the amount of river runoff is only 1.2 m3/s. This nature of the outflow is typical for the rivers of the Mediterranean (Nam, 2003; Yordanova, 1972).
1.2. Basic soil types
The territory of Haskovo region falls in the Rhodope-Strandzha province of the South Bulgarian xerothermal soil zone (Koinov et al., 1974). The soil diversity of the area is presented in figure 2. The main soil types in the district are Chromic luvisols, Eroded chromic cambisols, Cambisols, Fluvisols, Mollic fluvisols and Vertisols soils.
Cambisols are the main and most widespread bioclimatic soil type in Central and Southern Bulgaria. They are formed under dry forests and shrubs in Mediterranean, semi-Mediterranean or similar in nature warmer and wetter climates. In fact, cinnamon forest soils in our country are a more northern version of the brown and red-brown Mediterranean soils, which, however, in Bulgaria have a number of specific features due to the transitional Mediterranean conditions. These are more or less clayey, reddish-brown forest soils with well-defined textural differentiation. They occupy the low hilly and foothill areas and the foothills of almost all the mountains in Central Southern Bulgaria. In the valley fields and lowlands they are deep and well developed, formed mainly on Pliocene and Old Quaternary sediments. In the hilly and foothill areas this soils are mostly shallow in a complex with incompletely developed soils formed on various hard rocks.
The area of Cambisols in terms of climate can be generally referred to the transitional-continental area with a Mediterranean climate. Unlike the typical Mediterranean regions, the climate is cooler and wetter, and compared to Northern Bulgaria the winter is warmer. In addition, the area of cambisols is characterized by alternating wet with dry hydrothermal periods – wetter and cooler autumn, milder winter with light rainfall, spring drought with later rainy months and dry and hot summers. The main features and peculiarities of cinnamon forest soils should be sought in the conditions that existed at the beginning of their formation – during the Pliocene and the Old Quaternary, when the formation of most of the chromic cambisols in Bulgaria began.
In the hilly and foothill parts of the country Cambisols are formed on various hard rocks – marble, limestone, marl and sandy limestone, sandstone, granite, rhyolite, diorite, andesite and others. In the valley fields and lowland areas, they are formed mainly on Pliocene and Old Quaternary sediments, which are in fact redeposited weathering and soil products from the upper rocks.
The vegetation under the influence of which the Cambisols were formed in Bulgaria is represented mainly by relatively rare dry forests of the southern hairy oak type, with the participation of cera, winter oak and hornbeam and shrubs from sub-Mediterranean communities.
Both forest and herbaceous vegetation, especially in the fields, have been destroyed in many places and Cambisols are intensively used in agriculture.
They are most typically expressed on old weathering products and deposits in the geochemically accumulative now drained areas and in the softer relief forms.
In general, in the plain regions they occupy genetically the old relief forms, the old terraces and the Pliocene plateaus.
The climatic geomorphological and plant conditions highlighted above indicate of the important and essential role of the time factor, which defines these soils as genetically old, having a heavy mechanical composition and bright reddish coloration. As genetically old, these soils have undergone a long process of soil formation, the manifestation of which is favored by its more intensive course during most of the year and by the alternation of the different wetter hydrothermal periods.
Cambisols, Eroded Choromic cambisols and Chromic luvisols have been identified within the study area.
1.2.2. Choromic cambisols
The leached Choromic cambisols within the boundaries of the studied site are characterized by a medium-strength profile, the depth of which is usually in the range of 1 to 1.6 m moderately and strongly eroded. The thickness of the humus horizon is about 20 – 25 cm. The mechanical composition is quite clayey and depends on the soil-forming rocks and the nature of the relief. The heaviest (slightly to medium clay) soils are formed in the low and flat areas. Lighter (heavy sandy-clayey) are those formed on larger partial materials and on more sloping terrain. A characteristic feature here is the weak differentiation of the clay along the depth of the soil profile. Inside, the soil clay covers the entire profile, but is better expressed in the metamorphic horizon, due to which the amount of clay in it is greater. The clayier is the soil, the greater the participation of montmorillonite in the silt fraction. Red iron hydroxides are also available.
The humus content in these soils under virgin conditions for the humus-accumulative horizon is high 3-4% and gradually decreases downwards. In the case of arable soils in arable land, it has significantly decreased and is on average 2-2.5%. In the presence of carbonates in the arable land, the soils are poorly stocked with comparable forms of iron, zinc, boron and manganese, and well stocked with molybdenum, moderately stocked with copper. Leached ones, where the carbonates are relatively deep, are better stored with mobile forms of trace elements. The reaction is neutral in both the humus and metamorphic horizons. CEC (cation exchange capacity) is completely saturated with basic cations (calcium and magnesium). The sorption capacity is relatively high throughout the soil profile 35-50 mequ / 100g soil (for soil profile see Annex 1). Under virgin conditions, these soils have a relatively well-defined structure in the humus-accumulative horizon – water-resistant aggregates larger than 0.25 mm are about 70%. In the arable land, however, the structure is significantly destroyed. Due to the more clayey mechanical composition and the significant destructuring, these soils do not have very good physico-mechanical properties. The plow lyer became sticky when it rains, and when it dries it can form a crust. When cultivate in a drier state, it is crushed into large hard lumps. In the wet state, these soils show great plasticity, stickiness and strongly swell, and when dry they shrink strongly and some of them, like vermisols, crack. Therefore, when cultivate them in both wet and dry conditions, they show a high resistance of 0.7 – 0.9 kg / cm2. The interval of favorable humidity for cultivation (physical maturity) is short. In accordance with the clay mechanical composition and the values of the main hydrological indicators are high. Thus, the coefficient of wilting varies from 18-24%, and WHC (water holding capacity) 32-34%. The water permeability is too low 0.09 m / 24h. They have an unfavorable water regime. Here the summer droughts are well expressed and a lot of moisture is lost by evaporation from the soil, due to which the cultivation of much later spring crops without irrigation is inefficient. This is especially true for shallower and eroded soils.
1.2.3. Chromic luvisols
The Chromic luvisols within the region are weakly deep, moderately and strongly eroded. The morphology of the soil profile (see annex 1) is typical for the Chromic luvisols in the region. The surface horizon is eluvial bright. Its thickness varies from 0 to about 15-18 cm. The transitional B (t) iluvial-metamorphic horizon is yellow-red in color and has a thickness of 40-70 cm. It has a heavy texture and is significantly compacted. The shallowest profiles of the Chromic luvisols are found in the high convex parts of the terrain, where the soil is very strongly eroded and the illuvial-metamorphic, red-colored transitional horizon is established on the surface.
The structure of the surface horizon is highly diperesed, and in the alluvial-metamorphic horizon it is interspersed with carbonate-free skeletal materials, the granulometry of which is characterized by rock fragments with sizes usually in the range of 10 to 50 mm. In the zone of the most active accumulation of clay in the illuvial-metamorphic horizon, the appearance of yellow-red spots of iron oxides is established. The texture of these soils varies depending on the soil-forming materials. The soils formed on Pliocene and Old Quaternary sediments are heavier, and the soils formed on coarser deposited weathering products obtained from granites, granite gneisses and sandstones are significantly lighter. The soils formed on younger river terraces (low valleys) are also relatively lighter in mechanical composition. Shallow soils formed on hard rocks or deposited products thereof have a significantly lighter texture. A sharp profile differentiation is observed along the depth of the profile.
The humus content is generally low, under natural conditions it is 2-3% in the humus-eluvial horizon, and in arable land it has greatly decreased and is about 1%. In more acidic soils (as a result of long-term use of physiologically acidic mineral fertilizers) the quality of humus is even worse (the amount of humic acids is reduced, the participation of the aggressive fraction of fulvic acids and free humic acids is increased, i.e. humus becomes acidic, unsaturated). The reaction in the arable land is usually moderately acidic (pH in water 5-5.5), and in the alluvial horizon below 5. The plow layer of old arable soils is quite highly dusty, water-resistant aggregates are reduced to 30-35%. The deteriorating quality of the humus also reduces the possibilities for structuring. Due to the destructuring and acidification of these soils, they do not have very favorable physical and mechanical properties. In the rain, the plow became sticky and compacted, when it dries, it hardens, a crust is formed and if it is cultivated in such a state, it is crushed into large lumps. The water balance is not very favorable – precipitation is unevenly distributed and due to destructuring much of the moisture evaporates unproductively during the warm dry months.
1.2.4. Eroded Chromic Cambisols
Regarding the susceptibility of these soils to erosion, it was found that 80% of the territory of the region is covered with soils with medium and medium to strong susceptibility to erosion; 6% – from soils with strong susceptibility to erosion and 10% – from soils with very weak and low susceptibility to erosion. (Ruseva et al., 2010). Soils with strong susceptibility to erosion are concentrated in the foothills of the Eastern Rhodopes and Sakar, at the transition to the Upper Thracian Lowland.
Erosion changes the morphological and hence the physico-chemical properties of soils. Thus, the carbonates in the Eroded chromic cambisols are washed at an average depth between 70 and 130 cm. The thickness of the humus horizon varies widely between 5 and 35 cm. The thickness of the compacted horizon compared to the non-eroded ones can be reduced to zero or covers the soil layer between 0 and 120 cm. In addition, the compacted horizon due to the humus horizon is mostly started from the surface itself.
These are heavy textured soils, forming in the summer wide cracks with a depth of up to 50 cm from the surface. Vertisols contain more than 60% physical clay. They occupy the plains and are often in a complex with Cambisols. They have a “gilgay” relief. It is characteristic for them that they have wavy contact with the soil-forming materials and are mulched on the surface (Boyadzhiev, 1994a, b).
Despite the not very high content of organic matter in Vertisols (about 3.5% evenly distributed on the profile) the color of these soils is usually dark, often black, which is related to the quality of this very well evolved organic matter. The minerals montmorillonite in these soils are often mixed with a small amount of silt and represent 40 to 60% of the total soil mass, determining the physico-chemical properties of the profile. The cation exchange capacity is usually very high – 40 to 80 meq / 100 g. This is due to the predominance of montmorillonite.
The essential characteristic of Vertisols is their homogeneity, associated with constant stirring through circular motions. The differentiation is very weak – 80 to 100 cm. In some cases, when less evolved organic matter is abundant, a structure coarser than that of the rest of the profile is formed on the surface. In summer, small clay aggregates are formed, which form surface mulch, protecting the lower part of the profile from drying out. Horizon B is characterized by the presence of cracks that are more or less wide and distinguish large prisms.
According to the classification of soils adopted in Bulgaria, soils with circular motions are separated into a separate type – vertisols, and four subtypes are defined – carbonate, typical, leached. The most widespread are the leached resins (Atanasov, 1987).
In the soil classification of the international organization FAO Vertisols are divided into a separate category of the highest order and are divided into two groups – Pellic Vertilols (dark colored) and Chromic Vertisols (light colored).
The thickness of the soils in the region of Haskovo exceeds 2 m. The soil is characterized by a very heavy texture, the clay varies from 56.9 to 65.7%, unfavorable general physical properties (bulk density 1.38 to 1.45 g / cm3, low porosity – less than 50%), a small amount of air (6.9 to 12.0%), large water capacity and good to satisfactory water drainage.
These soils are rich in organic matter. The amount of humus in the humus-accumulating horizon is 2.9 to 4.5%, they contain a large amount of alkaline hydrolyzable nitrogen, a sufficient amount of available forms of phosphorus, potassium and iron.
The carbonates in the soil are washed to a depth of less than 60 cm and do not exceed 6-7%. The reaction of the soil is from neutral to slightly alkaline.
The data indicate that these soils have a very good water capacity (WHC is from 24.7 to 28.0%), which is important for a number of crops that can be grown without irrigation.
The exchangeable cations (calcium Ca2+ and magnesium Mg2+) and the absorbed iron are sufficient for the normal rate of chlorophyll photosynthesis in plants.
The heavy texture of the vertisols determines their unfavorable physical and mechanical properties – high plasticity, stickiness and bonding in the wet state and high hardness in the dry state. Therefore, they are difficult to be cultivated. They have high resistance during cultivation. The texture also determines high values of the main hydrological indicators – high WHC (water holding capacity) 36-38%, high percentage of wilting humidity 20-25%, due to which from 60 to 65% of the water supply is dead (unavailable water).
Despite some not very favorable properties, vertisols also have very good qualities that create great potential for high fertility of these soils.
Fluvisols soils are referred to as river sediments (alluvium) or alluvial-meadow soils. In the FAO international soil classification, the name Fluvisols is adopted, which means river soils. Occupy parts of the flood terrace (arch) of the larger rivers. They are located on both sides of the riverbed. These soils are very young. They are in the early stages of development.
Contemporary soils in the area are formed on powerful sediments of Neogene-clays, sands, incompletely weathered sandstones, with high quartz content. In some places, in the northeastern parts of the terrains, infiltration limestones have been established, in a complex with marls and calcareous conglomerates and alluvial sediments on the high terraces of the Maritsa River. The Maritsa alluvial deposits are mainly the Quaternary terraces, and in the studied area they are mainly of sandy-clay composition. The underlying base of the Maritsa terraces is represented exclusively by alternating layers of Pliocene gravel, sand and clay. Due to the differences in the temporal nature of sediment erosion, caused mainly by changes in the bed of the Maritsa River, the water saturation of the indicated Pliocene deposits is not the same. The maximum water content in the region is manifested in the areas close to the Maritsa River, near the eroded waterproof deposits, in contact with the Maritsa terrace deposits.
These soils have not formed genetic horizons, but there are only separate layers or the primary humus horizon (A) is barely outlined, followed by different layers of sediments – most often sandy. From the upper flow of the river to its estuary, the sediments become finer.
As the riverbed moves away to the first non-flooding terrace in the area of the middle part of the arch, the water moves more slowly when the river overflows and deposits smaller particles. This creates conditions for sustainable development of meadow vegetation and the transition of alluvial soils to alluvial-meadow. In the farthest part of the riverbed near the non-flooded terrace the finest materials are rarely deposited. The terrain is the lowest (groundwater is close to the surface). Meadow-swamp and swamp vegetation develops well here and the soils turn into meadow-swamp and peat-swamp. When the terrace remains high and the soils are no longer flooded, they gradually turn into the zonal soils typical of the area.
The farther these soils are from the riverbed and closer to the estuary, thir texture is heavier. In terms of profile depth, the soil texture is also very heterogeneous. The soils are sandy to sandy-clayey in dept. The humus content is low 1-2%. The physico-chemical properties of these soils depend on the content of carbonates and clay. In carbonate soils the reaction is slightly alkaline, and in others it is neutral to slightly acidic. In the case of intensive fertilization of weakly acid soils with physiologically acidic nitrogen fertilizers, there is a danger of their further acidification. Fluvisols have good physical and mechanical properties, they are loose, do not sticky and crack, do not form crusts. They can be lightly cultivated at any time. In terms of water properties, they are characterized by good water permeability, but not high moisture content.
Fluvisols have good natural fertility and are used intensively in agriculture. Many agricultural crops are successfully grown on the more widespread clayey-sandy and sandy-clayey Fluvisols – cereals, legumes, all major vegetable crops, vineyards and fruit species. Areas with shalow groundwater can be used as meadows.
1.2.7. Mollic Fluvisols
Mollic Fluvisols are similar to the Fluvisols described above. They differ in that they are further away from the riverbed, due to which the sediments are finer in part, the groundwater is closer to surfase (about 1.5 m). They are flooded infrequently and for a short time, during which very fine sediments are deposited. This allows the development of moisture-loving meadow vegetation from cereals and legumes grasses and sedges, under the influence of which a well-defined humus horizon is formed. The grassy vegetation here is considered to be secondary. The primary vegetation was moisture-loving forest – field ashl, elm, willow, poplar and others. Now it is largely destroyed and the soils are cultivated or used as meadows. The soils are young, representing the next stage in the development of Mollic Fluvisols. Soil formation is characterized by accumulation of mature humus. The conditions for the formation of humus are favorable. Here the meadow vegetation develops well and the large amount of plant residues (mainly as roots) is intensively humified, many humic acids are formed. They bind to calcium and remain in the soil as calcium humate. Depending on the change of the hydrological regime of the territory, when the level of the groundwater approaches the surface, they pass into meadow-swamps. When the level of the groundwater decreases, they gradually pass into the zonal soils for the region. Their texture is heavier than the Fluvisols ones. They are medium sandy-clayey. They are layered and finer in depth. The humus content in virgin soils is 2-4%, and in arable 1-2%.