Any farmer or gardener needs moisture in their garden or lawn to ensure optimal growth of plants and to guarantee healthy produce.
There is therefore need to know all about your garden soil moisture and how to deal with it to ensure the success of your plant growing venture.
Right levels of soil moisture
The required soil moisture levels are determined by factors such as the type of crops or plants you are already growing or wish to grow because different crops have different moisture needs.
For instance, most trees, shrubs and flowers require soil moisture levels that range anywhere between 21% to 40%, while all vegetables require soil moisture levels of between 41% to 80% for optimal performance and productivity.
Soil moisture levels are also determined by the type of soil you have because different soils have different water-holding capacities.
Types of soils and their moisture levels
Fine soils such as clay require moisture levels of between 80% to 100%. Their soil moisture levels should not go below 60%.
Medium-textured soils such as loamy soil require moisture levels of between 88% to 100%. Their soil moisture level should not go below 70%.
Coarse-textured soils such as sandy soil require soil moisture levels of between 90% to 100% and should not fall below 80%.
Below the allowable percentages, plants will die unless irrigation is incorporated.
When to apply irrigation to solve soil moisture
For fine soils such as clay, irrigation will be applied if soil moisture level ranges between 60% and 80%.
For loamy soils, irrigation must be applied if soil moisture levels range between 70% and 88% and for sandy soils, irrigation must be applied if moisture levels are between 80 to 90%.
Types of soil moisture
Soil is made up of organic matter, mineral matter, air and water. However, of these 4 soil components, soil water is the one component that does not remain constant but fluctuates every now and then.
Soil aeration also varies, but approximately inversely with the soil moisture content. Organic and mineral matter remains fairly constant in any given soil over a long period of time.
There are 4 different types of soil moisture, namely: gravitational moisture, capillary moisture, hygroscopic moisture, and moisture vapor.
- Gravitational moisture
Gravitational moisture is that moisture that drains away due to the force of gravity. It occupies the largest pore spaces in the soil and is known to cause damage to plants in cases of slow drainage.
- Capillary moisture
Capillary moisture is the moisture found in the micropores of the soil. It is held by surface forces as films around the soil particles, in capillary pores and in the angles between soil particles.
This moisture is the only important and most available moisture for plants as it is the one they utilize for growth and production.
- Hygroscopic moisture
Hygroscopic moisture is the soil moisture that is held by surface forces as very thin films on soil particles.
It moves only in the form of vapor due to its firm hold by surface forces. It is the moisture found in air-dry soil and is usually never utilized by plants.
- Moisture vapor
Moisture vapor is the water vapor that is found in the soil’s atmosphere and which occurs through water evaporation. It moves along vapor-pressure gradients.
How to know if my soil is dry
To determine whether your soil is dry, do the following:
1) Check the soil surface
If the surface of the soil has a lighter shade of brown, it is a clear indication of surface dryness.
Moist soil is almost always darker than dry soil no matter the soil type. However, this method is not the best for determining soil dryness when growing plants such as cactus.
2) Use a tensiometer
Use a device known as a tensiometer. This device is a sealed, water-filled tube that is inserted into the soil all the way to the depth of the plant root zone to measure soil moisture tension.
It has a ceramic tip at the bottom and a vacuum gauge at the top. It shows the moisture content of your soil, thus helping you to accurately determine whether it is dry or not.
3) Pay attention to your plants
Check your plants daily to help you observe any small changes like wilting or drying out of the soil. You can then water the soil as necessary.
4) Research on the needs of your plants
Doing research on the water needs of the type of plant you are growing will help you determine whether your soil is dry or not.
Plants in warm and dry areas will require more water than those plants grown in cold and wet regions due to loss of moisture through evaporation caused by the sun’s heat.
5) Poke your finger into the soil
This will give you a more accurate indication of the soil moisture content. Poke 2 or 3 inches into the soil to feel how dry or moist it is.
Be careful not to interfere with the root system of your plants, especially in cases where the plants are potted in small pots.
6) Lift the pots of your plants
This will help you to determine their weight and will help you to know how dry the soil of your potted plant is. This is particularly helpful in nurseries when watering your seedlings.
If the soil is dry, the pots will feel lighter than usual because water will always add weight. Water the pots and then lift them up to help determine their heaviest weight.
For larger pots, tilt them to one side to determine their weight as they may be too heavy to lift. Make a habit of lifting your pots occasionally to train yourself to determine when they need watering.
7) Check for wilting, dropping or drying leaves
If the leaves of your plants are wilting or dropping, it could be an indication that the soil is dry. Drying leaves are an indication of extremely dry soil.
Dropping can also be caused by other reasons such as overwatering, which leads to root rot, overfeeding, especially with fertilizers, overexposure to direct sunlight, disease, or pest invasion.
Most healthy plants drop off older leaves as a way of renewing their foliage. It is therefore advisable to consider the amount and pattern of leaf-drop to determine if it is abnormal or not.
8) Check for yellow or brown leaves
If the color of your plant leaves changes from green to yellow or brown, it could be an indication of incorrect watering. However, sometimes it is caused by overexposure to the sun or the presence of a disease.
9) Use a skewer or stick
Sometimes the appearance of the soil surface deceives because thou it may appear wet, the soil underneath may be dry.
Use a skewer to help determine how dry the soil is. Insert it several inches into the soil, depending on the type of plant but avoiding the roots.
Mark how far you have inserted the stick to properly assess the depth of the soil’s moisture level. You can use a pen to do this or you can hold the stick at the surface level of the soil to indicate the depth.
Leave the skewer or stick in the soil for 1 or 2 minutes so that the soil moisture can get to stick on the skewer. Remove it and look for a wet mark on its side. How deep the wet mark is will help you determine the dryness of the soil.
Tools to measure soil moisture
There are several tools or instruments used to measure soil moisture, and this article has already mentioned the most common one, which is a tensiometer.
However, there are other tools which include gypsum block, neutron probe, pressure plate and pressure membrane apparatus.
Frequently asked questions regarding soil moisture
- Which soil has lowest moisture?
The soil with the lowest moisture content is sandy soil. This is because sandy soils contain very little amounts of clay and silt, causing them to hold much less water as compared to other types of soil.
In actual fact they do not hold any water, making them unfit for growth of crops. The space between sand particles is very large, allowing for water to drain through to the deeper layers of the soil.
- What happens if soil moisture is too high?
Too much soil moisture is known to cause problems such a soil erosion, root rot, fungal challenges, leaching of nutrients and little to no growth of plants.
When soil becomes water-logged, the roots of plants rot, leading to smothering of plants. Some plants develop fungal problems, especially when water lying on top of leaves causes spores and bacterial cells to penetrate and infect the plants.
Leaching of nutrients also occurs when soil moisture proves to be excess. Soil nutrients drain to the lower soil horizons beneath the top soil, thus denying plants of necessary nutrients for optimal growth and productivity.
Too much moisture also leads to soil erosion as most of that water runs off the garden/farm, carrying with it the top soil which is critical for plant growth.
How to fix moisture in soil?
Soil needs to be kept moist in order to grow healthy plants. There are a number of ways to fix moisture into the soil. Below are some of them:
1) Water the soil regularly
You can do this by use of a garden hose or by way of irrigation. Sometimes, rainfall is not sufficient for growth of crops. Again, you may want to grow certain crops outside or beyond the rainy season. Watering your lawns will therefore be ideal and will help fix moisture in the soil.
2) Prevent water evaporation
Water evaporation can be prevented through weeding, tillage, installing water absorbent mats beneath potted plants, and moving potted plants to a shaded area. These measures will fix moisture into the soil.
Why is my soil still dry after watering?
One of the reasons why your soil may still be dry after watering it is that it could be hydrophobic.
Hydrophobic soil does not absorb water. Instead the water glides over its surface and runs off, or, remains on the soil surface until evaporation occurs. This type of soil occurs when waxy residue builds up on the soil particles, preventing absorption.
It is common in soils containing organic matter that has not decayed. It is also common in dried-out potting mix and sandy soils. Another reason why soil may remain dry after watering is compactness.
Compact soils such as clay cannot absorb water, and this leads to water runoff. To cure this problem, you may start by sieving the soil and repeatedly sprinkle water on the soil surface lightly to give the soil time to absorb the water.
Keep repeating the process until the soil becomes sufficiently soaked. You could also mulch your soil to allow it time to slowly absorb the water without the risk of water runoff.
Is clay soil moist or dry?
Clay soil is usually heavy, often moist and very rarely dry. The reason for this is that it tends to hold water for longer periods of time.
If your garden soil is made of clay, you will not need to water it often. It consists of very tiny mineral particles that cling tightly together, and because they are abundant, they create a large surface area that holds onto water and nutrients.
Why won’t my soil absorb water?
- Any soil with enough water will fail to absorb more, leading to runoff.
- Old depleted soil that has lost all organic matter and nutrients will fail to absorb water.
- Your soil will also fail to absorb water if it is hydrophobic as already aforementioned.
- The roots of your plants may have taken over, totally depleting the soil that should be absorbing water.
- Frequent tilling. Excessive tillage disrupts the natural structure of the soil, making it unable to absorb water.
- Too much clay hinders absorption, particularly when it is compact.
- Use of too much peat moss. This leads to the soil becoming hydrophobic.