Disposal of debris by windrowing consists of linear heaping or piling of woody debris so it can be burnt or left to rot. Windrowing may not-be necessary in areas where the woody material can be disposed of as fuel or by other means. A mechanized windrowing operation can be accomplished by equipping the same crawler tractors used for felling with front mounted rakes; 4 x 4 rubber-tyred tractors fitted with similar equipment can also be used.
- To get rid of debris created through felling or vegetation clearing which can be the source of subsequent problems.
- To clean littering debris from the planting site in order to aid soil cultivation and provide the necessary space for an improved plantation growth.
- On sites where there is debris after a felling operation.
- On sloping land where the control of run-off and erosion is necessary (the operation should be carried out along the contours).
The windrowing operation should be carried out during the dry season. The windrows should be built about 50 m apart by lowering the front mounted rake to ground level and pushing all debris over a pass 25 m long and at right angles to the windrow line. In degraded forests and coppice, the raking process should be repeated after a reverse pass over a 25 m-long path.
A similar operation should be carried out on the other side of the windrow leaving a 50 m-wide cleaned area between the piling lines. Passageways 5 m-wide should be left at intervals of 100 to 200 m along the linear heaps. The distance between windrows may vary from 25 m to 50 m depending upon the terrain conditions and the amount of debris. Raking in windrowing operations should be done with care in order to minimize the disturbance and displacement of top soil. Afterwards, the debris should be left to rot or disposed of by burning.
The efficient disposal of debris after felling or any other landclearing operation provides a variety of ecological benefits. It eliminates competition from the existing vegetation for nutrients, moisture, air and light. As a result, there is more space for the planted seedlings which leads, in turn, to better growth. When choosing the equipment, soil characteristics, and the type of debris and terrain should be taken into account in order to minimize the displacement of top soil during raking. On sloping land, windrowing must be done on the contour lines where there are the necessary soil and water conservation measures. If burning is carried out, it is important to follow the appropriate smoke management principles and procedures. It should be borne in mind that after a controlled burning operation, nutrient cycling is interrupted, the soil environment is altered and a layer of ash is deposited on the soil surface. Furthermore, under certain conditions, burning removes about one-third of the nitrogen in the organic horizon lying on the mineral soil surface (DeByle, 1974).
Soil cultivation, prior to planting, is becoming an increasingly important practice in afforestation operations throughout the world. The cultivation takes place after eliminating or reducing previous vegetation on the site. The trend towards cultivation in afforestation is due to the need to reduce early weeding costs, and enhance the survival, growth and uniformity of the established stands. The practice usually promotes favourable site conditions by improving the soil's physical properties, infiltration capacity and moisture conditions. The cultivation techniques in use vary greatly and depend upon the nature of the terrain, the existing vegetation and the physical characteristics of the soil. The mechanized cultivation of soils will be treated under two general headings: strip cultivation of land; and clean cultivation or the cultivation of the entire site. Both these cultivation techniques can be modified to suit particular needs.
This is the cultivation of a relatively narrow strip of land along the planting line on contours. In such cases, the survival, growth and development of the planted seedlings depends entirely upon the local soil preparation and weeding. On sites where there is a steep topography and erodible soils, the method can assume the role of a soil and water conservation measure. In this case, it should consist of contour ploughing on a narrow band of sloping land.
- To improve physical and hydrological properties of soils. This, in turn, helps boost the growth and development of planted stock by providing better aeration and moisture conditions for root development.
- To improve soil tilth during subsequent disking and harrowing which helps weed control and survival of planted seedlings (Tolay et al, 1982).
- On sites where there is a high risk of erosion because of the terrain and soil conditions.
- Where ploughing and soil tilth along a strip of land may suffice to control weeds and improve the survival and growth of the planted stocks.
- Where economic considerations are a pressing factor. (Strip cultivation method is more cost-effective than cultivation over an entire area.) The latter method is used almost exclusively on flat land for high-value crops.
- As far as the terrain is concerned, slope is the most critical factor. Tractor clearing can be carried out on slopes of up to 35 degrees but cultivation equipment has lower limits. Ploughing along contour strips using wheeled tractors, fitted with single or double discs and a ripper tine, is possible across gradients of 15 to 18 degrees if the slope is even. Crawler tractors with rippers, on the other hand, can operate on slopes of up to 20 - 25 degrees. (Brown, 1971).
Mechanized strip cultivation can be achieved by the harrowing effect of a mechanical tree planting machine on sites where mechanized planting is planned. On sloping lands, strip ploughing along contour lines should be carried out by a reversible disc plough attached to a 4 x 4 rubber-tyred tractor. Harrowing after an initial cultivation to a depth of 30 cm usually results in a good soil tillage.
In heavy clay soils, the cleared strips should be prepared for cultivation by ripping the soil with sweep-mounted tines fitted to a crawler tractor. The operation should be done at gradients of 0-40 percent on sites where the existing vegetation has previously been uprooted by raking. On sloping lands, operation should take place on the cleared strips along the contour lines. The ripped area can be disked, along the contour lines, by heavy-duty trailed disc harrows attached to 4 x 4 rubber-tyred tractors. This method is recommended by Donmez (1985) for "entire area" soil preparation in Turkey. The operation should be confined to areas where gradients do not exceed 20 percent because of the potential erosion hazard.
However, in coarse-textured soils, the cleared strips can be cultivated by discing and harrowing at gradients of 0-20 percent. In semi-arid and arid regions of the Mediterranean basin, gradoni-type ditches are built on contours of sloping land by ploughing the soil at gradients of 20-40 percent. This technique helps to conserve soil and water. On sites where the soil profile includes hard-pan formation at lower depths, the subsoil can be ripped along the contour lines in the strips by using subsoilers or thin ripper tines.
Strip cultivation carried out in conjunction with soil and water conservation measures has the following benefits:
- it increases infiltration and conservation of rain water falling prior to and immediately after planting;
- it increases the amount of nutrients, especially nitrogen, by breaking down and incorporating organic matter in the soil;
- it reduces weed growth which impairs the development of young planted stock by competing with them for soil moisture, nutrients and light.
Strip cultivation, as compared to entire area cultivation is a more economical and environmentally sound technique. It also prevents erosion and sediment discharge on plantation sites. By removing obstacles such as smaller tree stumps and logs, it facilitates mechanization of subsequent operations such as planting, tending, thinning and harvesting.
Root raking in strip clearing operation prior to cultivation has the the following shortcomings:
- considerable nutritious top soil ends up in the windrows;
- a large amount of non-productive time is spent backing away from windrows;
- the extra traffic compacts the soil.
On slopes exceeding 10 percent or where soils are highly erodible, and low in nutrients, the adverse effects of root rakes and bulldozers may well outweigh any advantages (William and et al, 1976). It is, therefore, important to carry out this cultivation method on suitable terrain using the correct equipment and skilled operators.
Entire area cultivation or clean cultivation is a pre-planting soil preparation which usually consists of two consecutive stages: pioneer ploughing; and disking and harrowing prior to planting (or top soil tillage using a disc harrow).
Pioneer ploughing is an initial mechanized operation which turns over the soil with a plough or heavy-duty offset disc on a previously cleared planting site. Following this initial stage, top soil tillage is carried out by harrowing (Photo 4).
- To break in or turn over the soil, and to plough in all weeds and minor vegetation. This initial stage of soil preparation is aimed at achieving better growth of the planted stock.
- To break up clods to create a level soil surface and a good tilth before planting.
- To increase the infiltration capacity of surface soil, and improve permeability, non-capillary porosity and aeration. This leads to better soil moisture relations which facilitate growth and development.
- On sites where the terrain is not characterized by steep slopes and easily erodible soils.
- In arid and semi-arid regions where clean weeding is required to control the competitition for soil moisture and nutrients posed by herbaceous weeds. The method gives better results on sites with deep and medium-textured soils.
- Where labour is expensive, the necessary machinery and equipment are available and the mechanized operation proves time and cost effective.
There are several techniques and practices used in entire area cultivation. They vary considerably, according to terrain conditions, soil profile characteristics, the existing type of vegetation and that to be established, socio-economic conditions and environmental considerations. The cleared land usually needs to be cultivated prior to planting to improve the soil's workability. This cultivation can be achieved by any type of ploughing method and should be done when the soil is sufficiently moist. Heavy-duty disc harrow ploughs with steel discs of over 75 cm diameter attached to a crawler tractor are often used for this type of soil cultivation. Where site conditions permit, the soil can be effectively ploughed down to a depth of 30 cm. In certain cases, this type of heavy duty harrow can be used to plough unstumped lands (Chapman and Allan, 1978).
In different regions of Turkey, several methods or combinations of methods have been used. In degraded coppice areas, subsoiling by raking along the contour lines after an uprooting operation using a front-end mounted rake, gave satisfactory results. M. Bul(1985)
reports that a top soil tillage, using heavy-duty disc harrows, improved site conditions in the following ways: by increasing soil infiltration capacity and permeability rate; by reducing thermal conductivity of soil; and by ensuring a subsequent economic mechanized weeding.
The same report indicated that in areas covered with maquis vegetation, including deep-rooted species such as Quercus cocciferus, the chopping operation should be supplemented by raining in order to remove roots. It has been reported that pioneer ploughing using a medium-wheeled tractor with a mounted disc plough can also be done to a shallower depth than with the harrow plough (Chapman and Allan, 1978).
In certain regions of Turkey covered with maquis or/and degraded coppice vegetation, pioneer ploughing on contour lines of sloping lands has been carried out as an initial sub-soiling operation over the entire area. Double ripper tines mounted on a crawler tractor were used for the operation. The top-soil tillage over the entire area should be undertaken by double passes at right angles to each other using a Pettit heavy disc harrow. Alternatively, gradoni are made by single passes of a doublefurrow tine plough mounted on a MB TRAC tractor (Bul, 1985).
The following conclusions were reached after examining various clearing and soil preparation techniques used in afforestation projects in Turkey:
- vegetation clearing by dozer blade results in an excessive removal of nutrient~rich topsoil and is, therefore, not recommended.
- the best method for afforestation projects in Turkey is the macerating of the existing vegetation using chopping machines. In the areas in question, travertine layers in the subsoil can easily be broken down by ripping and tine ploughing operations where the correct moisture conditions exist. Deep subsoiling and following top soil tillage generally give better results (Bul, 1985).
Following the ploughing of an entire area, a pre-planting harrowing is recommended in order to break-up soil clods and create a good tilth. It also helps to clean the soil from weeds. The harrowing operation is carried out by a wheeled tractor, with a mounted dic harrow, which moves in the same direction as the ploughing.
Entire-area cultivation on plantation sites should be practiced with care and must take into account the potential environmental effects of such an operation. The soil erodibility index together with the gradient of sloping lands should be the main points considered. Complete ploughing should not be carried out in environmentally-vulnerable areas, such as sloping lands adjacent to stream channels, lakes or reservoirs. This is in order to minimize the erosion hazard and sediment discharge from the operation sites, which would, impair the water quality. On sloping lands, a complete ploughing operation should be carried out along with soil and water conservation measures such as contour ploughing, trenching or terracing. These measures help control erosion and improve soil moisture conditions which in turn, result in better survival and growth rates.
Compaction of soils on afforestation sites which impairs its infiltration capacity and aeration, is becoming a more serious problem with the increased use of heavy, mechanized equipment. It should be borne in mind that the more porous the soil initially, the greater the degree and depth of the subsequent compaction. The choice of mechanzied equipment and cultivation techniques should be aimed at minimizing soil compaction by taking into account beforehand, the soil texture and moisture conditions.
Subsoiling or ripping involves tillage of the subsoil using heavy-duty rippers attached to a crawler or 4 x 4 wheeled tractor. The operation is usually undertaken by either a single-tooth subsoiler or multiple-tooth types which rip the subsoil to depths of at least one metre. On sites with shallow soils it should be done to a depth of not more than 60 to 70 cm.
- To facilitate the percolation of rain water and root penetration by ripping the subsoil of a compacted soil profile or subsoil suffering from a hard-pan formation.
- To increase the effectiveness of top soil cultivation by ripping and improving the impermeable or heavy subsoil, resulting in better survival and growth of the established plantation.
- On sites where extremely arid conditions prevail and a hard-pan formation, or a heavy-textured and compacted subsoil limits root development and water penetration.
- On terrain where the operation does not pose the risk of a subsequent erosion problem or the formation of sediment.
The subsoiling operation is usually carried out by rippers or specially adapted tines, mounted behind a crawler tractor. Either single-tooth or multiple-tooth subsoilers attached behind an appropriate tractor can rip the subsoil to a depth varying from 60 cm to 1 metre. In certain cases, special shoes are attached to the subsoilers in order to break up the hard-pan formation in the soil profile. This practice proves effective when used in deep soils but is not recommended for soils possessing a resistant calcareous formation in the subsoil. The angle between the subsoiling and/or ploughing equipment and the soil surface should be adjusted in order to achieve the best results. On sloping lands, the subsoiling should be carried out on contour lines to provide better infiltration and soil moisture conditions.
A subsoiling operation is an efficient way of improving percolation of rain water and root penetration to deeper zones of soil profiles which improve the growth of the planted trees. Special care should be taken to follow the contour lines on sloping lands, in order to minimize sediment accumulation and erosion which may harm the water quality of nearby streams, reservoirs and lakes. In some cases incorrect subsoiling methods may lead to soil erosion.
A subsoiling operation which is carried out properly opens up the ground, helping the moisture to penetrate down into the subsoil reservoirs to be stored for later use. By opening up the ground in this way, it enables planted tree roots to reach into the subsoil stores of moisture and essential nutrients.
