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How Is Over-Irrigation Damaging to Soil?

The damage over-irrigation does to plants might be relatively easy to notice. The soil, however, suffers severely from overwatering too.

Soil contains various substances including organic matter, minerals, water, and air. These substances are typically present in fairly constant percentages.

While water is naturally in soil, it is normally present in limited amounts. Even when irrigation is done within normal limits, the percentage content of water in the soil eventually normalizes.

So, how is over-irrigation damaging to soil? When one over-irrigates, excess water accumulates in the soil. If this water remains in the ground long enough, it upsets the balance of the content of the earth.

Why Soil Gets Over-Irrigated


To beat the adverse effects of drought on plant life, some flower growers increase their irrigation rate and volume. Normally, these measures would increase irrigation costs.

But some growers create their irrigation systems using a solar-powered water pump for irrigation, so, they do not incur extra running costs when they increase the irrigation rate.

In trying to beat drought by raising the rate of irrigation, people sometimes go overboard. This leads to over-irrigation.

When the water in the ground exceeds the water storage capacity of the plant (field capacity), it starts leaking into the root zone, where most of the damage to plants and to the soil happens.

How Does Over-Irrigation Damage the Soil?


One of the ways over-irrigation damages the soil is by raising salinity. Under normal conditions, the salt content of the soil is located in the deeper parts of the earth (around the root zone).

As water starts leaking into the root zone due to over-irrigation, however, the excess water will push the salt in the root zone upward. Consequently, the salinity of the soil increases.

With too much water in the ground, the space available for air exchange reduces. As a result, aeration drops, and plants and beneficial organic material (microorganisms) eventually die off.

Also, when the accumulation of excess water persists, most of the nutrients are eventually leached or washed away. Consequently, soil fertility drops. When soil fertility falls, you may have to get fertilizers to restore the leached nutrients.

Waterlogging caused by unlimited irrigation may also alter soil structure and lead to compaction by spreading clay particles. As these particles spread and we apply weight on the soil, the ground becomes more compact.

Of course, root penetration, water penetration and aeration are limited in compacted soil. So, plant life typically does not thrive in it.

The Consequences of Over-Irrigating the Soil


adult and child watering cans - how is over-irrigation damaging to the soil

Increased Weed Pressure

Increased weed pressure basically means having more weeds per unit area of the soil surface. Now you may be wondering why weeds will grow in a compacted soil that contains too much water. Well, weeds are generally able to survive certain extreme conditions.

Some thrive in arid lands, some do well in acidic lands, while some will do just fine in soggy soil.

You can expect weeds like dock, sedge, and chickweed to do well in waterlogged grounds. Also, the growth of weeds like knotweed and chicory is promoted in compacted land.

Water Logging

Water logging is one of the most direct consequences of overwatering the soil. With the ground saturated/oversaturated with water, the normal equilibrium of its composition is lost. Everything becomes either diluted or washed away from its usual position in the ground.

Nutrient Leaching

With waterlogging comes nutrient leaching. The excess water that comes with over-irrigation either washes nutrients away or washes them down to layers where the roots of plants cannot reach them.

With essential nutrients like nitrogen, phosphorus and potassium washed away, plants will not survive on these grounds. Ultimately, if plants cannot grow, the soil becomes functionless.

Reduced Plant Yield

It goes without saying that if nutrients (like nitrogen) are lost from loam, plants will not survive and yield will drop. Also, if aeration drops due to waterlogging, the plants will not get enough oxygen for respiration and they will die. Of course, as plants die, yield will drop.

Then, if the increased moisture in the ground promotes weed growth, the weeds will compete with plants for space, nutrients and oxygen. Therefore, the chances of plant survival drop even further.

Impaired Soil Aeration

Plant roots need dissolved oxygen for aerobic respiration, but as the moisture levels in the ground become excessive, the circulation of oxygen becomes impaired.

The excess water that accumulates in the ground following over-irrigation blocks pores meant for aeration. Consequently, oxygen will not get to roots and beneficial microorganisms as needed.

Besides the effect of the excess water, the compaction that results from watering the ground too much causes the blockage of the aforementioned pores.

Altered Soil pH

Since waterlogging blocks aeration, many microorganisms may die, and as they decay, they release CO2. The CO2 emitted from the decay reacts with water to form carbonic acid, which contributes to increased acidity.

Besides that, as the surplus water leaches basic minerals like calcium, sodium and potassium way, acidic minerals become predominant.

How to Prevent Over-Irrigation


Getting an automatic irrigation system is perhaps the easiest way to prevent over-irrigation. With an automatic system, your flowers are watered as required and when required—there is no going overboard.

Another way to avoid over-irrigation is to put a proper drainage system in place. With proper drainage, the ground effectively removes surplus water as you irrigate.

You could also determine the water storage available to your flowers in the root zone and try to reconcile it with the watering rate of your irrigation system. If you know the water storage available, you can determine how long the soil can be irrigated before it starts to get leached.

Instead of worrying about the effects of drought on your plants, you could start a greenhouse. With greenhouse farming, water loss is minimized. Therefore, drought will not readily affect your plants.

Conclusion


The effects of over-irrigation are not so easy to correct when they get really bad. The best solution is to avoid over-irrigating your land at all. If you have started seeing early signs of over-irrigation, however, you should work on correcting the situation now. Later might be too late.

Feature image: JEREMY MORRIS; Image 1: RODNAE Productions

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