Agronomy - Land Preparation

This lesson will teach the reader how to prepare samples of soil: coarse samples of large clods, pulverized soil samples, and compacted soil samples. It also teaches about water movement through soils and erosion, and how to set up an erosion chamber. The lesson also includes teaching aids, such as a poster of a production unit with crop sections that includes a ditch for irrigation and drainage.

Objective:

Minimize land preparation costs and increase crop production through better land management.

Lesson Preparation 1. Prepare samples of soil: a) coarse sample of large clods. b) pulverized soil sample.

  1. Compacted soil.

  2. Water movement through soils and erosion.

  3. Set up erosion chamber.

  4. Teaching aids: Poster of production unit with crop sections, including ditch for irrigation and drainage.

Concepts to be Taught

  1. Purpose of land management.

  2. How should land be prepared?

  3. Best time for seedbed preparation.

Click on the magnifying glass of any image for enlargement.

Introduction:

Worn out soil that has been cropped for 1000's of years or soil where water and wind have washed or blown away, is not replaced overnight (#1). In fact, it takes nature more than 100 years to form 1/4 inch of new top-soil. Therefore, despite a lifetime of good farming practices, a farmer will not increase his topsoil. However, with farming practices, which encourage soil loss to water or wind, one person can reduce topsoil by many inches during a lifetime. Through wise management, the farmer can produce crops in the abundance required to feed his family and, at the same time, conserve and improve soils and the environment, thus providing a priceless inheritance for his children and their children (#2). Tillage (land preparation) is one of the important management practices used in agriculture.

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Concept 1:

Purpose of land preparation.

Group Discussion: Why do we need to prepare & conserve the land?

Preparing the land for crop production serves many purposes, including: a) the creation of a seedbed, where planted seeds are in contact with the soil moisture so they will germinate to become established quickly (#3-4). b) Weed control. Removal of weeds is necessary because they successfully compete with crops for moisture, nutrients and light. In addition, some weeds secrete chemicals from their roots into the soil that inhibit crop seeds from germinating. c) The incorporation of crop residues and fertilizer materials into the soil, when plowed into the soil, helps buildup organic matter and nutrients for the crop (#5). d) Also, plowing breaks the soil crust and hardpans, improving water penetration and aeration. e) Shapes the soil for irrigation and erosion control.

Because of the possible damage to soil structure from overworking the soil, one modern approach to soil conservation is to use only as much tillage as is required to produce a good crop. The kind and amount of tillage is determined according to crop, soil and field conditions. No one set of guiding standards is appropriate for all situations. Tillage must be done in a way that will assure adequate protection of soil and water resources. A good soil surface will prevent crust formation and allow rapid rainfall penetration.

Other management practices such as contouring, strip planting, cover cropping, alley cropping,reduced tillage, terracing and leaving some crop residue on the land help to eliminate or minimize the loss of soil from water and wind erosion (#6). Using good erosion control practices not only preserves the soil, but also many nutritional elements needed for plant growth. In addition to these practices, a good fertilizer program promotes greater crop growth. Crops, in turn, contribute to soil improvement by protecting the soil against the impact of falling rain, by holding the soil in place with extensive plant root systems, and by providing soil nutrients from organic matter of decomposing plant residues. (For more ideas on fertilizer program, refer to lesson 1.5)

 

Concept 2:

Methods of Land Preparation.

Equipment: Tractor and plowing implements, animal traction and hand operations.

There are things that need to be considered, other than weed control, in selecting the right tillage practices (#7-9). Farmers probably already know that plowing is the most effective method for weed control. Before planting, plowing completely cuts off perennial weed shoots and exposes many root stocks to sunlight so they dry out and die. Also,the plow leaves the surface rough and porous, increasing the amount of water that enters the soil and helping to control erosion. Soil runoff can also be reduced if furrows are plowed opposite to the way water would flow. Good contact between the seed and soil is needed in order for the seed to take on enough water to swell and germinate.

A soil with good tilth can be described as one that has good aeration, takes water readily, drains well, and works down to a good, loose, seedbed. This is one of the functions of tillage seedbed preparation (#10). Tillage to prepare a seedbed after the land has been plowed is accomplished with disks, harrows or field cultivators. The best depth to plow is a much-discussed subject. Although research shows that 8 inches (20 centimeters) is usually deep enough, deeper plowing has sometimes produced slightly higher yields. Disk plows should be used in soils that have been plowed and left with rough surfaces, in preparation of a good seedbed. There is little reason why disking should not replace completely plowing in soils that have relatively little or fine crop residues. If you go once over with a disk plow it nearly completes seedbed preparation. At this time, most of the trash and residues are worked into the soil. Overworking a field with a disk can be disastrous as it leaves the soil surface fine, and loose. Overworked soil easily looses moisture and the lower half of the plowed soil layer may end up as hard as before it was plowed because it gets compacted with the machinery. It needs to be considered that the disk does not function well in fields with large stones, it could be damaged.

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While tillage of some kind is desirable, there are many small farmers who, because of steep land and/or lack of access to equipment, plant without tilling the soil first. In these cases the farmer clears the land with a machete (may do manual plowing, as well) and plants using a planting stick (#11).

Group Discussion: How should land be prepared?

 

Concept 3:

Best time for Seedbed preparation.

Marginal moisture supply is critical at plowing time because the soil must be dry enough for tillage without causing excessive compaction or creating clods in fine-textured soils (#12-15). As soon as the crop has been taken out, the land can be tilled and preparations can be started for next cropping season. In areas where there are more than one cropping season per year, land can be prepared once a year, using the same crop furrows for subsequent crops. The best time to work the land will be just before planting time making sure the land is not too wet or too dry. Under most conditions, a smooth, finely pulverized seedbed should not be prepared until just before a crop is to be planted.

Group Discussion: When should we start preparing our production unit?

Activity: Participants decide if their production units meet the criteria just discussed. What can be done to better prepared their land.

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List of figures for lesson 1.3

(Click on the numbered links below to view and print full-sized figures)

1. Drawing of eroded soil and/or of soil conservation practices.

2. Drawing of soil profile showing different horizons.

3. Drawing of good and poor seedbed preparation.

4. Drawing of field being cultivated.

5. Drawing of field with crust and other with crop residues on top.

6. Drawing of field with terracing and contour farming.

7. Same as number 4.

8. Drawing of a tractor or team of horses tilling the land.

9. Drawing of farmers with hoes working the field.

10. Same as number 8.

11. Drawing of a farmer planting with a stick.

12. Drawing showing good tilth vs. poor tilth.

13. Drawing of a tractor or team of horses tilling the land.

14. Drawing of relative sizes of soil grains.

15. Drawing of plant showing root depth in good vs. poor soil.

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