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VEGETABLE GARDEN: IRRIGATING THE GARDEN
[continued]

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  MG Manual Reference
Ch.10, pp. 21 - 24
[Irrigating the Garden: irrigating | rooting depths ]

Table 10.7

ROOTING DEPTHS


PLANT FEEDER ROOT DEPTHS*Top


CROP FEEDER ROOT DEPTH CROP FEEDER ROOT DEPTH
ALFALFA 3 to 6 feet NUTS 3 to 6 feet
BEANS 2 feet ONIONS 1 1/2 feet
BEETS 2 to 3 feet ORCHARD 3 to 5 feet
BERRIES (Cane) 3 feet PASTURE (Grasses) 1 1/2 feet
CABBAGE 1 1/2 to 3 feet PASTURE (w/Clover) 2 feet
CARROTS "1 1/2" to 2 feet PEANUTS 2 feet
CORN 2 1/2 feet PEAS 2 1/2 feet
COTTON 4 feet POTATOES 2 feet
CUCUMBERS 1 1/2 feet SOY BEANS 2 feet
GRAIN 2 to 2 1/2 feet STRAWBERRIES 1 to 1 1/2 feet
GRAIN, SORGHUM 2 1/2 feet SWEET POTATOES 3 feet
GRAPES 3 to 6 feet TOBACCO 2 1/2 feet
LETTUCE 1 foot TOMATOES 3 to 4 feet
MELONS 2 1/2 to 3 feet    
*Majority of Feeder Roots

**All information in this fact-sheet regarding soils, their classifications, water holding capacity, available moisture and infiltration rate; crops, as to feeder root depth, water use, etc.; climate, as to irrigation efficiency is general or for average conditions. This information is to be used only as a guide; local conditions must govern each individual design.
Table 10.8

NET AMOUNT OF MOISTURE TO APPLY TO VARIOUS SOILS UNDER DIFFERENT
MOISTURE RETENTION CONDITIONS
Top


Soil Type Root
Zone

Depth
Field
Capacity
Amount Held at
Wilting Point
Available
Moisture
Plant Uses
Net Inches to Apply per
Irrigation with Various
Percent
  FEET INCHES PERCENT INCHES INCHES 67% 50% 33%
LIGHT
SANDY
1 1.25 20% 0.25 1.00 0.33 0.50 0.67
1 1/2 1.88 0.38 1.50 0.50 0.75 1.00
2 2.50 0.50 2.00 0.66 1.00 1.33
2 1/2 3.13 0.63 2.50 0.83 1.25 1.67
3 3.75 0.75 3.00 0.99 1.50 2.00
4 5.00 1.00 4.00 1.32 2.00 2.66
MEDIUM 1 2.25 25% 0.56 1.69 0.57 0.85 1.13
1 1/2 3.38 0.85 2.53 0.84 1.26 1.70
2 4.50 1.12 3.38 1.11 1.69 2.26
2 1/2 5.62 1.41 4.21 1.39 2.11 2.82
3 6.75 1.69 5.06 1.67 2.53 3.38
4 9.00 2.25 6.75 2.23 3.38 4.52
HEAVY 1 3.67 35% 1.28 2.39 0.79 1.20 1.59
1 1/2 5.50 1.92 3.58 1.18 1.79 2.38
2 7.34 2.56 4.78 1.58 2.39 3.25
2 1/2 9.17 3.20 5.97 1.97 2.98 3.97
3 11.0 3.84 7.17 2.36 3.58 4.77
4 14.68 5.12 9.56 3.15 4.78 6.37
NOTE: For optimum yield of high valued shallow rooted crops maintain 67% available moisture. For lower valued deeper rooted crops maintain 50% available moisture. For low value deep rooted crops maintain 33% available moisture.
Some basic techniques and principles for watering:
1. Adjust the flow or rate of water application to about 1/2 inch per hour. Much faster than this will cause run-off, unless the soil has exceptionally good drainage. To determine the rate for a sprinkler, place small tin cans at various places within the sprinkler's reach, and check the level of water in the cans at 15 minute intervals.
2. When using the oscillating type of lawn sprinklers, place the sprinkler on a platform higher than the crop to prevent water from being diverted by plant leaves and try to keep the watering pattern even by frequently moving the sprinkler, overlapping about 1/2 of each pattern.
3. Do not get foliage wet in the evening; this can encourage diseases. Morning watering is preferred.
4. Perforated plastic hoses or soaker hoses should be placed with holes down (if there are holes) along one side of the crop row or underneath mulch. Water is allowed to soak or seep into the soil slowly.
5. It is best to add enough water to soak the soil to a depth of at least 12 inches once plants have become established. It takes approximately .65 to 1.3 gallons of water for each square foot or 65 to 130 gallons for 100 square feet of garden area. This varies with the nature of the soil. Frequent, light waterings will only encourage shallow rooting which will cause plants to suffer more quickly during drought periods, especially if mulches are not used. On the other hand, too much water, especially in poorly drained soils, can be as damaging to plant growth as too little water.
6. By knowing the critical watering periods for selected vegetables, you can reduce the amount of supplemental water you add. This can be important where water supplies are limited. In general, water is most needed during the first few weeks of development, immediately after transplant, and during development of edible storage organs.
Specifically, the critical watering periods for selected vegetables are:
Asparagus Spear production, fern development
Broccoli Head development
Cabbage Head development
Cauliflower Head development
Beans Pod filling
Carrot Seed emergence, root development
Corn Silking, tasseling, ear development
Cucumber Flowering, fruit development
Eggplant Flowering, fruiting
Lettuce Head development; moisture should be constant
Melons Flowering, fruit development
Peas Pod filling
Tomato Flowering, fruiting
7. In areas prone to repeated drought, look for drought-resistant varieties when buying seed or plants.
8. If water supplies are short in your area and you wish to use grey water (water from household uses) on your vegetable garden, a few rules should be observed:
  • Do not use "black water" (any water run through the toilet) because of the possibility of contamination from fecal organisms.
  • It is preferable not to use kitchen waste water that contains grease or harsh cleaners, ammonia, bleach, softeners, or non-biodegradable detergents
  • If using water from the bathtub or washing machine, use only mild, biodegradable soaps. Omit softeners and bleaches. Allow wash and rinse water to mix, if possible, to dilute the soap content. Never use a borax-containing product (such as washing soda) in water to be used on a garden because of the danger of applying plant-toxic levels of boron.
  • Apply greywater to the soil, not to plant leaves. Some county health departments require that grey water be discharged below ground, through a drip system or similar mechanism.




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