How Do Rivers Make the Soil Fertile?

Soil fertility is a crucial factor to consider when it comes to growing crops and plants in a layer of land. The probability of growing crops and other plants as food and fodder depends heavily on the health of the soil and its fertility. And, rivers have an important role to play in making the soils fertile.

Rivers have a major influence on the rocks and soils over which they flow. So, when a river flows, it continues to erode the land and collect mud and silt as a result. With more and more rivers joining the main river along the way, the volume of silt increases. At this stage of a river’s path, it’s liable to flood the banks during periods of prolonged rainfall.

clay-soil-on-river

When a river overflows its banks, the nearby areas get flooded. During the flood, a thin layer of fine soil and silt gets deposited over the land, thereby forming rich alluvial soil which is highly fertile and nutrient-dense for the plants.

Now that the crucial link between soil fertility and rivers has been established, here’s moving on to the other aspects regarding fertile soil.

What Are The Factors That Make The Soil Fertile?

There are several factors that go into making a soil fertile, such as:

1. Soil pH

Soil pH determines the availability of nutrients in the soil. Thus, while testing the existing pH level of the soil, the nutrients present in it are also studied. The optimum pH range for the fertile soil is 5.5 to 7.

2. Organic Matter

Organic matter present in the soil has nutrients like phosphorus and nitrogen in them that get recycled before the next growing cycle. The organic matter gets mineralized and available to the plants.

3. Moisture Content

Soil fertility also gets influenced by the amount of moisture present in the soil. Nutrients present in the soil for being used by the plants are found in soil solutions instead of the solid matrix. Thus, the soil with high moisture content is usually highly fertile, as well.

4. Clay Content

The CEC (cation exchange capacity) of the soil is based on its clay content. More nutrients are present in soils that have a high CEC. On the other hand, a low CEC is an indication that the soil can easily lose nutrients by leaching.

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5. Bulk Density

Bulk density also determines soil fertility. The rule of thumb states that the soil to be utilized for plants shouldn’t be compacted because compaction will obstruct the penetration of roots. Thus, the roots will fail to source the nutrients that they need.

6. Mineral Composition

Mineral composition helps in predicting the soil’s ability to retain plant nutrients. Manures and fertilizers are applied to enhance the mineral composition of soils.

How to Make the Soil Fertile?

The extent of fertility in the soil is largely determined by the factors mentioned above. However, though soil fertility cannot be completely changed, it can be improved to some extent by following the techniques outlined below.

Addition of Fertilizers and Manures

The addition of fertilizers like phosphorus, potassium, and nitrogen in the soil helps to turn it fertile. Natural manures and chemical fertilizers are not only used in the extensive croplands, but also in the gardens and potted plants to help in their growth. 

Planting Leguminous Crops

Leguminous plants like soybeans, tamarind, peanuts, peas, and so on, contain nitrogen-fixing bacteria called Rhizobium in their root nodules. Plants are unable to take atmospheric nitrogen directly. Thus, rhizobium traps the atmospheric nitrogen to make it available to the plants as nitrogen compounds. The rest of the nitrogenous compounds get mixed in the soil and increase its fertility.

Using Compost on the Soil

Composting can help the soil in more ways than one. It increases the nutrient density of the soil, along with its physical condition. The soil that gets the right amount of compost on a regular basis is more aerated and better able to retain the moisture and nutrients for the plants.

Furthermore, it increases the microbial activity which aids in faster mineralization of soil nutrients, both natural and the ones received through chemical fertilizers.

Putting Animal Byproducts

Several animal byproducts are also effective in increasing soil fertility. For instance, feathers and waste material from poultries are rich in nitrogen. Besides, the features are such products that are slow in breaking down and releasing the nitrogen component in the soil. Similarly, waste products from slaughterhouses can also serve as good manure for the soil.

Using Plant Products and Seaweed

Alfalfa and soybean can be used in manure because they are rich in nitrogen and other crucial micronutrients. Seaweed fertilizers or manures usually contain kelp, though it makes for a pretty expensive option. Thus, kelp is generally used for gardens and horticultural crops.

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Do Plants Grow Easily in Fertile Soil?

Plants need nutrients to survive and thrive just as people do. And, fertile soil has all the important nutrients needed for basic plant nutrition. Thus, plants can easily grow in fertile soil.

Fertile soil is rich in potassium, phosphorus, and nitrogen, along with other trace nutrients required in small quantities. These trace nutrients are magnesium, calcium, iron, sulfur, copper, zinc, molybdenum, boron, and nickel.

Usually, fertile soils also have organic matter, moisture retention capacity, and nutrient retention ability that improves soil structure and quality. However, all kinds of soil do not have the right levels of required plant nutrients or suitable pH balance for growing crops.

Does High pH Improve Soil Fertility?

High pH makes the soil alkaline and that does not improve soil fertility. Let’s explain this aspect further to give you a clear idea about it.

Soil pH is the feature that denotes the relative alkalinity or acidity of the soil. So, the soil that has a pH of <5 is acidic and extremely acidic when it hits <4. Similarly, soils are alkaline when the pH is >7.5 and extremely alkaline when the pH goes >8.

The reason why pH is so important is that it is one of the determinants of the availability of major nutrients in the soil.

The ideal pH for soils is almost neutral. Neutral soils usually fall within the range that is a tad bit acidic with a pH of 6.5 to a bit alkaline with a pH of 7.5. Most of the crucial plant nutrients are available optimally to the plants when the soil pH ranges from 6.5 to 7.5. Also, this pH range is also conducive to the growth of plant roots.

Nitrogen, sulfur, and potassium are the important plant nutrients that are not as directly affected by soil pH as most others. However, another crucial nutrient i.e. phosphorus gets directly affected.

When the soil pH is alkaline, i.e. greater than 7.5, phosphate ions start reacting quickly with magnesium and calcium to create less soluble compounds. As the soil pH turns acidic, the same ions start reacting with iron and aluminum to create less soluble compounds.

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Most of the micronutrients are less available when the soil pH is above 7.5. In fact, slightly acidic soil pH of 6.5 to 6.8 has optimal availability of most micronutrients. The only exception to this scenario is molybdenum, which is usually less available in acidic soil and readily found in slightly alkaline soils.

Does Deforestation Impact the Soil Fertility?

Deforestation refers to the decrease in plant cover due to land uses like urbanization, agriculture, and mining. It is ironic that deforestation negatively impacts soil fertility, even though agriculture is one of the main causes of deforestation. Let’s take a closer look at how deforestation reduces soil fertility.

Felling trees and harvesting trees removes crucial nutrients such as phosphates from the system. Furthermore, removing the plants is like taking away the protective cover from the soil.  The soil gets exposed to wind velocity, raindrop impact, and strong winds, thereby, causing rapid erosion of the fertile topsoil. Removal of the topsoil also leads to a decrease in the nutrient content of the soil.

The accelerated soil erosion from rain splash and wind has further consequences. Reduced humus content makes the soil loose and infiltration reduces. Plant roots also help in binding the soil and hold the soil structure together. Thus, the rate of erosion goes on increasing and the soil keeps getting washed off as runoff after heavy rains.

That’s not all! Deforestation also makes its impact felt in the form of a reduction in the evapotranspiration rate. It leads to a decrease in humidity and the regional rainfall goes down. Thus, the area goes through increasing desertification because the rainfall is less and less each year. All these factors cumulate into a reduction in soil nutrient content as the depth of the layer of fertile topsoil keeps decreasing continuously.

Conclusion

As you can understand, soil fertility is a result of several factors, which are both natural and dependent on us. Though we cannot completely reverse the qualities of infertile or semi-fertile soil, the least we can do is to ensure that fertility hasn’t dwindled any further through deforestation or improper land use.

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Sonia Madaan is a writer and founding editor of the science education blog EarthEclipse. She loves writing on topics related to space, environment, chemistry, biology, geology and geography. When she is not writing, she loves watching sci-fi movies on Netflix.