Anusha Satyal

Plants require essential elements (nutrients) for growth and development. They either acquire these nutrients from soil (e.g. nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca)) or from air (e.g. hydrogen (H), oxygen (O), and carbon (C)). However, nutrients available in the soil may not be always adequate for optimum plant growth and yield. The term nutrient management is defined as the efficient use of crop nutrient to increase the crop productivity with minimal damage to the environment. The key factor in the nutrient management is to balance the soil nutrient according to the plant requirement and in turn increase the crop production.

Inorganic Fertilizers

Inorganic fertilizers come in single-nutrient or multi-nutrient formulas. Multinutrient formulas include complete and balanced fertilizers. These contain basic nutrients, such as nitrogen, phosphorus and potassium. They may also contain secondary and micronutrients such as calcium, magnesium, boron and manganese.

On the package of the fertilizers are three numbers. The numbers indicate the percentage of nitrogen, phosphorus and potassium they contain. For example,NPK 5-10-5 contains 5% nitrogen, 10% phosphorus and 5% potassium. Balanced fertilizers are those that contain equal nutrient amounts, such as NPK 10-10-10

Other types of inorganic fertilizers include slow-release formulas. These formulas contain larger molecules that breaks down slowly in the soil. A typical slow-release fertilizer releases nutrients over a period of 50 days to a year. This reduces the chance of burning the plant or root system. These special formulas include plant foods for cocoa, azaleas, rhododendron or roses. Specially formulated fertilizers are usually highly acidic and used only on the plants for which they are indicated.

Inorganic Fertilizers

Nitrogen Fertilizers

Inorganic nitrogen fertilizers come in many different forms.Ammonium nitrate, potassium nitrate, calcium nitrate and urea. These fertilizers contain high levels of nitrogen. Nitrogen is one of the most vital nutrients for plant growth. However, these inorganic fertilizers tend to increase the pH of the soil when you apply them. They increase the chances of burn and damage to seedlings.Others pull moisture from the air. This makes it difficult to apply and store.

Potassium Fertilizers

Inorganic potassium fertilizers include potassium sulphate and potassium nitrate.  Also muriate of potash, also known as potassium chloride. Muriate of potash is the most commonly used potassium fertilizer. In some cases, plants may be sensitive to chloride. If a plant is sensitive to chloride, potassium sulphate, also known as sulphate of potash, is a better choice. It does not contain chloride. Potassium nitrate is easy to apply. This is because it does not pull moisture from the air. But it does slightly increase the pH of the soil upon application.

Inorganic Fertilizers

Phosphorus Fertilizers

Inorganic phosphorus fertilizers such as rock phosphate stay in the soil years after the first application. Rock phosphate works only in acidic soils. The nutrients do not break down for plants in neutral or alkaline soils.Super phosphate is another form of phosphorus fertilizer. This does not affect the pH of the soil upon application. Ammonium phosphates also come in water-soluble, granular forms

Organic Fertilizers

Organic fertilizers comprise a variety of plant-derived materials that range from fresh or dried plant material to animal manures and litters to agricultural by-products The nutrient content of organic fertilizers varies greatly among source materials, and readily biodegradable materials make better nutrient sources. Nitrogen and phosphorus content is lower, often substantially lower, in organic fertilizers compared to chemical fertilizers. Moisture content is another factor that reduces or dilutes the nitrogen and phosphorus concentrations of organic fertilizers. Thus, it can be cost ineffective to transport high-moisture organic fertilizer long distances. However, use of locally available sources is perfectly reasonable if its use is consistent with the production strategy.

Farm Yard Manure

Nutrient value of animal manures is more variable than that of agricultural by-products. The animal’s diet, the use and type of bedding material, manure age, and how it was stored are factors that affect manure nutrient value; these factors can vary seasonally on and among farms, and regionally or on a larger geographic scale. In contrast, nutrient content of agricultural by-products is less variable but can be affected by the industrial process used to produce the by-product. However, it always is advisable to analytically determine the nutrient content of the organic fertilizer.

In fact, the practice of incorporating organic as well as inorganic fertilizer in the soil can uplift health of both plants and soil as cons of one fertilizer is lowered by pros of another. An inorganic fertilizer is the one that is wholly or partially synthetic in nature and release only few number of nutrients in huge amount, whereas an organic fertilizer is completely derived from remains or by-products of living organism that releases multiple nutrients in trace amounts. The increased addition of synthetic fertilizer over a period can lead to decrease in organic matter as well as beneficial microorganisms of soil. In contrast, organic fertilizer adds life to soil, builds the soil structure as well as increase its water holding capacity. However, organic fertilizer lacks in releasing the nutrients instantly as compared to synthetics.

People Planting Rice In Nepal

Rice and Fertilizers scenario of Nepal

In Nepal, almost 50% of the cultivated land is under rice production. However, there lies a huge gap between demand and supply of rice in Nepalese market. Nepal has one of the highest rice per capita consumption (137.5 Kg) in the world. In 2019, Nepal imported 750 tons of rice. The import is expected to increase in 2020 as rice production has decreased by 1.7%. Likewise, Nepal imported approximately 39 lakhs metric ton of fertilizer in 2019 out of which 7.5 lakhs metric ton was supposed to be for rice cultivation. However, the allocation of fertilizer for rice decreased to 4.5 lakhs metric ton leading to scarce available of major fertilizer like urea and DAP. In this scenario, incorporating both organic and inorganic fertilizers in the rice fields can be worthy.

For healthy soil and increased production application of both fertilizers can be beneficial. Some of the basic method of applying both fertilizers are mentioned below.

Application of Organic fertilizer

  1. Farmyard manure, compost, and poultry manure can be applied to the field one month prior to transplantation or during land preparation. This helps in release of nutrients at crop stand and increase microbial activity, organic matter, and soil porosity.
  2. Green nitrogen rich plants such as Sesbania, Sun hemp, and Dhaicha can be incorporated in the fields either by growing them in the rice field or by collecting them from other fields. This process is called green manuring. It helps in improving soil structure, water holding capacity, reducing weed proliferation, reclaiming the alkalinity of soil, and feeding nutrients to the soil.
  3.  Biofertilizer like azolla can be intercropped with the rice after transplantation. However, the cons with azolla is that the field should be supplied with water continuously as azolla cannot withstand drying. Azolla in symbiotic relation with Anabena fixes atmospheric nitrogen and thus, nourish the soil.
  4. Oil cakes such as mustard oil cake, neem oil cake, and castor oil cake also benefit the soil.

Application of inorganic fertilizer:

Rice is a heavy nutrient-feeding crop. Thus, addition of chemical fertilizers becomes vital for the excellent performance of the crop. Especially, nitrogen (N), phosphorus (P) and potassium (K) are crucial for rice growth. It is recommended to add NPK in 100:30:30 kg per hectare. However, this is a blanket recommendation dose for all geographical regions. The best dose of fertilizer should be decided after proper soil nutrient analysis. In addition, 20-30 kg per hectare application of zinc phosphate in zinc deficient soil helps to prevent khaira disease of rice.

To obtain more production, the efficiency of the added nutrient should be more. The efficiency of nitrogen is less if applied at once as it is prone to leaching, denitrification, and volatilization. Hence, nitrogen should be applied in split doses: 25% as basal dose at time of transplantation, 50% during tillering stage, and remaining 25% during panicle formation.

To sum up, integrated fertilizer application could benefit not only the farmers and the nation in terms of production but can also enrich the soil, which otherwise may turn into desert with continuous application of synthetic fertilizer.

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