1/5/2009 DMA: Chapter 6 Hartmann's Plant Science, 4th edition ١ LAND PREPARATION Tilth is a subjective term for the physical condition of the soil with respect to its capability to provide a good environment—aeration and porosity—for optimizing crop production); For most crop plants, such a seedbed is one in which the surface soil is loose and free of clods (Fig. 6-18). Major purposes of land preparation are to: (1) Level the land where needed. (2) Incorporate crop residues, green manure, and cover crops. (3) Prepare and maintain a seedbed in good tilth. (4) Help control weeds, diseases, and insects. (5) Improve the physical condition of the soil. (6) Help control erosion where needed.
Tilth is a subjective term for the physical condition of the soil with respect to its capability to provide a good environment—aeration and porosity—for optimizing crop production);
For most crop plants, such a seedbed is one in which the surface soil is loose and free of clods (Fig. 6-18).
Major purposes of land preparation are to:(1) Level the land where needed. (2) Incorporate crop residues, green manure, and cover crops. (3) Prepare and maintain a seedbed in good tilth.(4) Help control weeds, diseases, and insects.(5) Improve the physical condition of the soil. (6) Help control erosion where needed.
• Tillage is defined as the mechanical manipulation of soil to provide a favorable environment for crop growth.
• Soil moisture condition is a factor in the effectiveness of tillage. Unfavorable soil conditions—too dry, too wet—will result in ineffective tillage and will damage soil structure.
• The subsoil is permeable to air and water and has adequate drainage and aeration.
Plowing• Often, the first step in seedbed preparation is to plow
the land. However, when large amounts of crop residues are left on the field from a preceding crop, they are often chopped with a disk or a rotary stalk cutter before plowing.
reduce further the size of soil clods left after disking, to smooth the soil surface, and to do small-scale leveling.
• Frequently, farmers attach a harrow behind the disk and do both operations simultaneously.
• This is a final touch to seedbed preparation, unless beds are to be formed for irrigated row crops (Fig. 6-24).
• Harrowing is becoming less common and necessary, particularly for agronomic crops, as new planters become more capable of operating in uneven seedbeds.
• In some areas, row crops are planted on ridges formed by listers.
• A lister is a plow equipped with two moldboards that cuts a furrow slice two ways—half to the right and half to the left. This forms a ridge of soil commonly about 20 to 25 cm (8 to 10 in.) high and of variable width at the base.
• Listers can be equipped with attachments to list, plant, and fertilize in one operation.
• The main reason for cultivating is to control weeds, but other benefits are improved water infiltration and soil aeration on soils that crust, the conservation of soil mois-ture, loosening compacted soils (Fig. 6-25), and in some cases help with insect control.
Deep Tillage• Deep tillage (60-180 cm) is used to improve problem soils. It shatters
the soil profile and breaks any deep, hard, cemented layers (Fig. 6-28).
• Unfortunately, some soils become recompacted and the operation needs to be repeated every three to seven years, depending on the nature of the compacted layer.
• In the alluvial desert of the southwest United States, deep ripping is used instead of deep plowing to keep the accumulated soil salts buried.
Conservation Tillage Systems• Conservation tillage systems often involve one pass with a
chisel plow, disk harrow, or field cultivator, followed by planting, and spraying to control weeds (Fig. 6-30).
• The ultimate form of conservation tillage is no-till, a practice in which no tillage is performed prior to planting and the maximum amount of residue is left on the soil surface prior to planting.
• Reducing the intensity of or eliminating tillage can protect the soil from1. Erosion; by leaving a blanket of crop residue on the surface,
thus protecting it from wind and rain.2. Compaction.
Land Leveling• Irrigated land generally benefits from being level,
especially if flood (Fig. 6-31 & 6-32) or furrow irrigation is used and row crops are grown.
• Land is leveled to permit water to flow and spread evenly over the soil surface without causing erosion.
• Features that render a site unsuitable for leveling:(1) Excessively permeable soil, (2) Soil that is very shallow, and (3) Rough topography (excessive grading will be needed).
• Land should not be leveled in the rainy season because leveling of wet soil subjects it to compaction.
Soil Fumigation• For some crops, the soil must be fumigated before seedbed
preparation. These usually are high-value crops where the potential for pest damage is severe enough to justify treatment.
• Certain chemicals are used to fumigate soil and destroy harmful bacteria, fungi, and nematodes as well as many weed seeds.
• Nursery employees often prefer to use steam instead of chemicals to partially sterilize, or pasteurize, their soil. Thetemperature at the center of the soil mass is brought to above 71°C (160°F) for thirty minutes to destroy disease-causing organisms.
Artificial Soils• Most are utilized for production of greenhouse and
nursery crops in pots.
• Most are designed to facilitate rapid seedling emergence, rooting, and early plant development, and allow for relatively easy management of water and fertilization.
• Most are usually prepared to hold significant amounts of plant-available water after irrigation but also to drain readily and thus avoid water logging that can damage or kill roots.
• Most contain a blend of many different components, such as organic soil, sand, peat moss, and expanded vermiculite.
