Land preparation encompasses several separate activities, namely - clearing often combined with burning, pre-plant spraying and ripping. Land preparation is an important part of establishment with the aim of achieving high survival and rapid early growth of the planted trees.
The type and method of land preparation will determine planting material survival, initial plant growth rates and final yield of biomas. It is critical that land preparation operations are related to prevailing site conditions and are done in a cost-effective way since these initial costs are compounded over an extended period until the time of harvesting. Incorrectly applied or careless operations particularly on sensitive soils may result in long-term damage to the site.
Objectives of land preparation are mainly to:
Improve ease of planting
Reduce competition from unwanted vegetation
Encourage rapid root development
Improve water holding capacity
Initial clearing is the removal of the vegetation that occurs on the site to be planted. It is an operation that has to be done before any cultivation of the land is done. This can be done mechanically or manually or chemically. Where there is dense grass, burning is recommended before cultivation is done.
Land clearing can be done in a number of ways depending on the nature of the vegetation e.g:
Manual cutting and/or slashing.
Spraying with herbicide
Mechanical means such as bulldozers.
Combinations of two or more of the above methods can be used. Mechanical land clearing can be very cost-effective if well planned.
Good initial land clearing reduces subsequent weeding operations. Where there is a lot of slash from the land clearing operation, the best option is to have a controlled, cool burn. The burn will be more successful if the cut vegetation has dried out for a period following cutting. Burning must be done when conditions are favourable. Do not burn when the fire danger index is high and especially on windy days. There should be sufficient numbers of people with suitable fire fighting equipment on standby during the burning.
The importance of good timing of land preparation
The timing of land preparation is crucial for its success. Manual clearing can be very labour intensive, and it can take a long time to clear a small area. Whatever method of land clearing is used, it is important to allow enough time ahead of planting so that the vegetation can be cut, piled, dried and burnt. Where pre-plant spraying with Glyphosate (Round up) is planned, time must also be allowed for a flush of weeds to grow so that they can be sprayed with the herbicide just before planting.
Topography Survey and Water Management Planning:
After land clearing, a topographical survey work is the be undertaken as a prerequisite for detailed planning for land leveling operations, irrigation and drainage planning and making overall master plan for the farm.
Then land leveling and removal of rock outcrops are to be started. The study of topographical survey work will reveal the suitable places of drainage channels. All cultivable area should have smooth slope towards the drainage channels. There should not be any “basin” within the farming area without any channel for water drainage. The steeper slopes are to be smoothed down to minimize high-speed surface water runoff and erosion. For two steep and too long slopes, terrace farming may be considered.
Manual leveling and countering of the lands are often very time consuming. Hence heavy earthmoving equipments are generally employed.
The main drainage channels and their lateral gullies are to be excavated preferably with earth moving equipment with a regular slope towards the catchment basin. Drainage is accomplished by two methods — open-ditch systems designed to provide primarily surface drainage (surface runoff) (Figure 6) or underground systems comprised of drain tile or tubing designed to lower the water table by subsurface flow. A surface drainage system typically consist of 3- to 5-foot deep, open ditches installed on 300- to 600-foot intervals. Surface runoff develops when the rate of rainfall exceeds the soil’s capacity to absorb water, thereby resulting in surface ponding. Shallow surface drains (hoe drains) are often utilized to effectively convey stagnated surface water to ditches. Vegetated field borders and drop inlet pipes are used to stabilize ditch banks and minimize erosion while conveying surface runoff from the surface drains into the ditch. Subsurface drainage is obtained by buried tile or tubing (4- to 6-inch diameter) that is placed 3 to 5 feet deep and 50 to 200 feet apart. A subsurface system provides drainage when the water table rises above the drain depth and water flows toward and into the drain. The drainage process whereby water infiltrates into the soil and moves within the soil profile is referred to as subsurface drainage, shallow ground water flow, or sometimes interflow
The ploughing method is dependent on prevailing soil type, texture and previous systems of cultivations practices on the land. For farming on virgin land – without any previous history of cultivation, a rigorous systematic approach is to be undertaken. The process is described below –
1. Chisel ploughing
The land is first prepared with deep chisel ploughing. The chisel plough is a common tool to get deep tillage (prepared land) with limited soil disruption. The main function of this plough is to loosen and aerate the soils while leaving crop residue at the top of the soil. This plough can be used to reduce the effects of compaction and to help break up ploughpan and hardpan. The chisel will not invert or turn the soil.
The chisel plough is typically set to run up to a depth of eight to twelve inches (200 to 300 mm). However some models may run much deeper. Each of the individual ploughs, or shanks, are typically set from nine inches (229 mm) to twelve inches (305 mm) apart. Such a plough can encounter significant soil drag, consequently a tractor of sufficient power and good traction is required. When planning to plough with a chisel plough it is important to bear in mind that 10 to 15 horsepower (7 to 11 kW) per shank will be required.
2. Rock windrowing
After the chisel plow loosens the surface and sub-surface soil and raises up subsurface rocks, the rocks are collected by a rock windrower and deposited in rows on the surface. The rocks, depending on the quantity, can be removed later manually or truck and a front end loader.
3. Disk Harrowing
In the next step, primary heavy duty disc harrows of 265 to 1000 lbs per disc are mainly used to break up virgin land, to chop material/residue, and to incorporate it into the top soil. Lighter secondary disc harrows help completely incorporate residue left by a primary disc harrow, eliminate clumps, and loosen the remaining soil packed soil. The notched disc blades chop up stover left from a previous crops, such as cornstalks. Disc harrows incorporate remaining residue into the top soil, promoting rapid the decay of the dead plant material.
After disk harrowing, especially in clayey or in any other hard to work with soils, Rotavetor is used to produce a fine tilth. For Stevia grown as row crop, fine tilth is required to ensure quick establishment, good root growth and smooth bed top. Rotavetor works on the soil by means of rotating blades. It is a tractor-operated implement attached to a three point linkage of the tractor and are driven by a power take off shaft. Unlike tractor drawn implements, the power is directly transmitted from engine, so it pulverizes the soil with minimum draft. Generally it is considered as a secondary tillage implement.
All the unit operation described for soil preparation may not be required for all situations. In some cases some unit operations may have to be done more than once. The decision is to be taken by a farming expert so that optimal soil preparation can be done with minimal investment. Otherwise, there may be sub-optimal soil preparation or over-expenditure.