Cover Image
close this bookSoils, Crops and Fertilizer Use: A Field Manual for Development Workers (Peace Corps, 1986, 338 p.)
View the document(introduction...)
View the documentAbout this manual
View the documentAcknowledgements
close this folderChapter 1: Down to earth - Some Important Soil Basics
View the documentWhat is soil, anyway?
View the documentWhy do soils vary so much?
View the documentTopsoil vs. subsoil
View the documentThe mineral side of soil: sand, silt, and clay
View the documentDistinguishing ''tropical'' soils from ''temperate'' soils
View the documentOrganic matter - a soil's best friend
View the documentThe role of soil microorganisms
close this folderChapter 2: Trouble-shooting soil physical problems
View the document(introduction...)
View the documentGetting to know the soils in your area
View the documentSoil color
View the documentSoil texture
View the documentSoil tilth
View the documentSoil water-holding capacity
View the documentSoil drainage
View the documentSoil depth
View the documentSoil slope
close this folderChapter 3: Basic soil conservation practices
View the document(introduction...)
View the documentRainfall erosion
View the documentWind erosion
close this folderChapter 4: Seedbed preparation
View the document(introduction...)
View the documentThe what and why of tillage
View the documentCommon tillage equipment
View the documentThe abuses of tillage and how to avoid them
View the documentMaking the right seedbed for the crop, soil, and climate
View the documentHow deep should land be tilled?
View the documentHow fine a seedbed?
View the documentSome handy seedbed skills for intensive vegetable production
close this folderChapter 5: Watering vegetables: When? How Often? How Much?
View the document(introduction...)
View the documentIt pays to use water wisely
View the documentSome common watering mistakes and their effects
View the documentFactors influencing plant water needs
View the documentOk, so get to the point! how much water do plants need and how often?
View the documentSome methods for improving water use efficiency
close this folderChapter 6: Soil fertility and plant nutrition simplified
View the document(introduction...)
View the documentLet's Make a Deal
View the documentHow plants grow
View the documentAvailable vs. unavailable forms of mineral nutrients
View the documentSoil negative charge and nutrient holding ability
View the documentSoil pH and how it affects crops growth
View the documentImportant facts on the plant nutrients
close this folderChapter 7: Evaluating a soil's fertility
View the document(introduction...)
View the documentSoil testing
View the documentPlant tissue testing
View the documentFertilizer trials
View the documentUsing visual ''hunger signs''
close this folderChapter 8: Using organic fertilizers and soil conditioners
View the documentWhat are organic fertilizers?
View the documentOrganic vs. chemical fertilizers: which are best?
View the documentSome examples of successful farming using organic fertilizers
View the documentHow to use organic fertilizers and soil conditioners
close this folderChapter 9: Using chemical fertilizers
View the document(introduction...)
View the documentWhat are chemical fertilizers?
View the documentAre chemical fertilizers appropriate for limited-resource farmers?
View the documentAn introduction to chemical fertilizers
View the documentCommon chemical fertilizers and their characteristics
View the documentThe effect of fertilizers on soil pH
View the documentFertilizer salt index and ''burn'' potential
View the documentBasic application principles for N, P, and K
View the documentFertilizer application methods explained and compared
View the documentTroubleshooting faulty fertilizer practices
View the documentGetting the most out of fertilizer use: crop management as an integrated system
View the documentUnderstanding fertilizer math
close this folderChapter 10: Fertilizer guidelines for specific crops
View the document(introduction...)
View the documentCereals
View the documentPulses (grain legumes)
View the documentRoot crops
View the documentVegetables
View the documentTropical fruit crops
View the documentTropical pastures
close this folderChapter 11: Liming soils
View the document(introduction...)
View the documentThe purpose of liming
View the documentWhen is liming needed?
View the documentHow to measure soil pH
View the documentHow to calculate the actual amount of lime needed
View the documentHow and when to lime
View the documentDon't overlime!
close this folderChapter 12: Salinity and alkalinity problems
View the document(introduction...)
View the documentHow salinity and alkalinity harm crop growth
View the documentLab diagnosis of salinity and alkalinity
close this folderAppendixes
View the documentAppendix A: Useful measurements and conversions
View the documentAppendix B: How to determine soil moisture content
View the documentAppendix C: Spacing guide for contour ditches and other erosion barriers*
View the documentAppendix D: Composition of common chemical fertilizers
View the documentAppendix E: Hunger signs in common crops
View the documentAppendix F: Legumes for green manuring and cover-cropping in tropical and subtropical regions
View the documentAppendix G: Some sources of technical support
View the documentAppendix H: A bibliography of useful references

Some methods for improving water use efficiency

In much of the Third World, water is scarce during the dry season, yet irrigated crop production requires tremendous quantities. Below are some suggestions for helping farmers use water more efficiently. While each of them will help conserve water, using several of these methods together will be the most effective.

· Draw up a watering quantity and frequency schedule tailored to the specific soil, weather, and crop. Remember to consider the water supply and labor factors mentioned above. For example, it might be possible to water older tomatoes just once very 4-5 days on a clayey soil, yet the well may not be able to supply the large quantity needed all at once.

Use the bed-and-alley system for small scale vegetable production (see Chapter 4). By allowing much closer spacing of plants and reducing soil compaction, it usually results in higher yields than using a conventional wide-row spacing system. The higher plant populations and yields per sq. meter of bed actually require little or no extra water, because the closely-spaced plants shade the soil surface more effectively, thus acting as a living mulch. Due to higher yields, water needs per kg of production are usually much less.

Use windbreaks where hot, drying winds are a problem. They'll cut down water losses from evapo-transpiration as well as protect from wind damage itself. Staggered rows of fast-growing trees around the windward portion of a garden can be very effective and also provide fruit, animal feed, and firewood. (Refer to Chapter 3 for further details on windbreaks.)

Mulching the soil surface with peanut hulls, rice hulls, straw, or dried grass will greatly reduce water evaporation losses. Mulching has several other benefits (see Chapter 8) but may attract crickets, ants, termites, slugs, and other harmful insects. Consider both preemergence and post-emergence mulching.

Choice of seedbed: Raised beds (if not mulched) dry out more quickly than sunken or flat beds. Under very dry conditions, sunken beds are usually the best choice, especially since they prevent water from running off. (See Chapter 4 for seedbed styles).

Microcatchments are shallow "bowls" from about 30 cm to several meters in diameter made in the soil with a plant or tree placed in the center. They are very effective at collecting water from the surrounding area and concentrating it around the roots. In rainy conditions, however, they may promote poor drainage and encourage soil-borne diseases.

Various kinds of macrocatchments can be used which collect water from larger areas that have moderate slopes. One technique is contour damming where soil barriers are run across the slope to collect water runoff.

Soil conservation measures like contouring and terracing will markedly improve water retention by lessening runoff from rainfall or watering. See Chapter 3.

Rainwater can be collected off roofs and used for gardening. Each sq. meter of roof will provide 1 liter of water per I mm of rainfall.

Good weed control will also reduce water losses, because weeds can use up considerable amounts of water.

Where soils are very clayey and compacted, double-digging the plots and adding organic matter to the subsoil will improve rooting depth and allow greater intervals between watering. (See Chapter 4).

Adding compost or manure to sandy soils will increase their water-holding capacity.

Use partial shade on less heat tolerant crops like lettuce and the Crucifer family (cabbage, broccoli, cauliflower, etc.).

The "double transplant" ("double nursery") method of raising vegie transplants is worth trying. When transplants are big enough to be set in the field, they are instead transplanted to a larger nursery seedbed where they can be spaced about 15 cm apart. This allows them to be kept in a confined area much longer, thus saving water as well as labor. This method works well with tomatoes, since they have good tolerance to delayed field-setting. (They should be "deep set" when transplanted so that most of the stem is buried underground where it will generate new roots; most other vegies lack this ability.)

Choose drought-resistant varieties: This applies more to field crops like maize where more work has been done on selection and breeding for drought resistance. For example, even though maize isn't very drought tolerant, there is considerable variation among varieties. However, choosing drought tolerance at the expense of needed disease resistance or other desirable traits may not be a good tradeoff.

Balanced fertilization, whether chemical or organic, helps improve water use efficiency by stimulating more extensive root growth. Note, however, that crops can't utilize as much fertilizer when moisture is limiting.

Soil nematode control: When present, root-feeding nematodes can seriously inhibit water (and fertilizer) uptake by plant roots.

Drip irrigation is a method of supplying water to plants by running small diameter plastic tubing down the row. Porous tubing (trickle tubing) is used for closely-spaced crops like carrots; for crops wider-spaced crops such as tomatoes, small individual emitters are used to concentrate the water around the plants. Water is provided at low volume and pressure, and plants are watered about once every day or two.

Drip irrigation can save water by delivering it close to the plants and by reducing water runoff and the amount of wetted soil surface prone to evaporation. However, water use efficiency is highest when the system is used with widely-spaced plants like tomatoes and squash since less area needs to be wetted. Orip irrigation is relatively inexpensive and, except for the micro-tubing, most components can be fabricated from in-country materials. Fertilizer can also be distributed through the system, though special soluble types are needed. The main problem with drip irrigation is its tendency to clog, even when fiItering is used. Improved tubing and emitter designs have overcome this problem somewhat. With care, the microtubing may be used for several seasons.