IV. WATERING

- Joshua Machinga


Water is very important for both soil and crops. Water is a cooling agent, carries nutrients in solution in the soil, and keeps plants turgid and erect.

The retention of water in soil depends on:
Soil type
Structure and texture of soil
Climate and air temperature
Humidity and wind characteristics
Plants themselves

BIA’s emphasis on healthy soil should not be overlooked when examining your beds’ capacity to absorb and retain moisture to the benefit of the plants. The deep soil preparation and the addition of good compost allow the soil to hold its moisture longer. Compost has a sponge-like ability to retain water. Other aspects of the Bio-Intensive method further increase water efficiency. Due to the living mulch of Bio-Intensive spacing, evaporation can be reduced by 13%-63%. Since a high level of soil fertility is maintained, transpiration by a plant can be reduced by 10%-75%. We should all know that plants lacking nutrients use more water to try to get the necessary elements.

Water your garden approximately 2 hours before sunset, when water has over half a day to sink down to the root zone before the hot sun appears again. This saves considerable water otherwise lost to evaporation. The water is available and percolates into the soil the whole night, which is critical since plants do a significant amount of their growing at night.

Immature plants and seedlings in flats may have to be watered in the morning and again in the afternoon if there will be sun the whole day. As the living mulch effect develops due to their leaves growing close together, less water will be required.

When watering a new bed, the shiny layer should stay for 2-3 seconds. On older beds it will stay for 5-15 seconds. If the shiny layer disappears sooner, continue watering. If the water is not being absorbed well at all, it may be that the bed is so dry that it is acting like a barrier to the water. Try to wet the soil under the surface to allow water to be absorbed.

It is wise to check the soil moisture before starting to water, to determine at what depth the soil is moist and how much water is needed. A soil can look very dry and be wet just under the surface, or appear damp when it is very dry. Also check how deeply water is going into the soil when you irrigate.

Climate considerations that indicate the amount of watering that will be needed are:
rainfall
amount per day
distribution per day
intensity per hour
temperature- mean monthly and extremes
evaporation rate

Points to remember when watering:

Different stages of a plant’s growth require different amounts of moisture
Being near to the soil surface small seeds dry out easily. Water them well but carefully- too much water or pressure can wash them right off the bed
Carelessness with a watering-can or hose can break stems, damage leaves, remove flowers, and bruise fruits - be gentle
Pay attention to a bed’s corners and edges as they dry out easier
Frequent, light watering encourages roots to grow near the soil surface making them prone to drying out and less capable of surviving drought conditions - it also reduces a plants ability to absorb minerals from deep in the soil
Does a plant wilting mean its time to water? Midday wilting on a hot day is normal for most plants. They lose water through transpiration quicker than their roots can pull it from the soil, and will usually recover overnight - if they are wilting in the morning they should be given water quickly
Salty conditions interfere with a plants ability to absorb water because the mineral competes for available moisture
Be careful of using large amounts of poultry or feedlot manure. Both of these are mixed with urine which has a high salt content. Certain crops are more tolerant of salty conditions. These are beets, spinach, lettuce, broccoli, and tomatoes. The salt sensitive crops are beans, carrots, onions and radishes
Potassium affects the rate of a plant’s water retention by regulating the opening and closing of its stomata. Thus the availability of this major nutrient determines how rapidly photosynthesis takes place
Fruiting crops and crops in the tomato family, ie. tomatoes and eggplant, dislike overhead watering. For this same reason they are bad crops for rainy season - they need their soil, but not their leaves and fruit, to be watered
Letting your spray of water travel high through the air before hitting the crops oxygenates the water, to the benefit of your plants

Under- and Over-watering:

Under-watering:
Slows down photosynthesis, reducing amount of food manufactured by a plant
Harmful wilting
Prevents adequate transport of nutrients
Over-watering:
Compacts soil / can suffocate roots
Creates environment for damping off
Prevents proper transport of nutrients, interfering with plant growth
Leaches nutrients from soil

Both under-watering and over-watering weaken plants by making them more vulnerable to insect infestation, and less resistant to disease and harsh environmental conditions.

TERMS USED:
Soil Pore space: portion occupied by air and water. In sandy soil pore spaces are large, and in clay soils pore spaces are numerous and smaller.
Soil Texture: different sized particles a soil has in it. There are stones, gravel, sand, and silt and clay particles. The water holding capacity of a soil depends largely on its texture –the amount of sand, silt and clay in the soil.
Soil Structure: grouping together of the particles in a soil into larger pieces or granules. The structure has a large influence on the retention and release of water.
The addition of organic matter to your soil will significantly improve its water holding and drainage capacity; compost is the best material for this.
Capillary water: water held in between soil particles.
Gravity water: percolates through soil under the force of gravity.
Infiltration: rate at which water moves into the soil, measured in millimeters per hour.
Field Capacity: moisture holding capacity of the soil after gravity water has been removed. Water added beyond field capacity will not be held in the soil’s pore spaces. The field capacity of light soils is les than that of heavy soils. Light soils need much light irrigation, and heavy soils can take fewer, heavier waterings.
Permanent Wilting Point: level of moisture at which plants are not able to extract any more water and from which they do not recover but wilt and die. Structure, texture and organic material affect the permanent wilting point.
Plant Root Zones: (deep rooted or shallow rooted plants) determine the frequency and the amount of watering required. Deep rooted plants need heavy, infrequent watering. Shallow rooted plants want light, shallow watering frequently. Plants make most use of water from the upper area of their root zones.
Evaporation is high in initial plant growth. As the plant matures its larger leaves shade the soil. Transpiration is a larger factor of water loss than evaporation.
The Hydrologic Cycle: movement of water from the earth’s surface and back.