Soil Science Agricultural Chemistry

The bacteria like Nitrosomonas, Nitrosospira, Nitrosococcus, and Nitrosolobus are involved in the conversion of ammonia to nitrite in the nitrogen cycle.

Fertilizers can be applied to crops using various methods to supply nutrients efficiently and improve crop yield.
These methods are broadly classified into broadcasting, placement, and foliar application.
1. Broadcasting: In this method, fertilizers are uniformly spread over the entire field, either before sowing (basal application) or as a top dressing during crop growth.
It is simple and suitable for crops grown densely like rice or wheat. However, it may lead to uneven nutrient distribution and higher losses.
2. Placement: Here, fertilizers are placed close to the plant roots in bands, rows, or pockets.
Common placement methods include side dressing, band placement, and drilling.
Placement reduces nutrient losses, increases use efficiency, and ensures better availability to plants.
3. Foliar application: In this method, fertilizers (usually micronutrients) are dissolved in water and sprayed directly on the crop foliage.
It provides quick correction of deficiencies during critical growth stages.
4. Fertigation: This modern method involves applying fertilizers through irrigation water, especially in drip or sprinkler systems.
Fertigation ensures uniform application, saves labor, and improves nutrient use efficiency.
Choosing the right method depends on the crop type, soil conditions, nutrient requirements, and available equipment.

Soil fertility is the ability of soil to supply essential nutrients to crops in adequate amounts for healthy growth and optimum yield.
There are various methods to evaluate soil fertility. Three important ones are:
1. Soil testing: This is the most scientific method to assess the nutrient status of soil.
Soil samples are collected from different parts of a field and analyzed in a laboratory for macro and micronutrients, pH, and organic carbon.
Based on the results, farmers receive fertilizer recommendations to correct deficiencies and maintain soil health.
2. Observation of crop growth: Farmers and extension workers observe visual symptoms of nutrient deficiencies in crops.
Yellowing of leaves, stunted growth, poor flowering, or fruiting are signs that indicate specific nutrient problems.
Although this method is simple, it requires good knowledge to correctly identify deficiency symptoms.
3. Plant tissue analysis: This involves sampling plant parts like leaves or stems during the growing season to measure nutrient content.
It helps detect hidden hunger — a condition where crops appear normal but yield is reduced due to sub-optimal nutrient levels.
Tissue analysis complements soil testing and ensures timely corrective action through foliar sprays or top dressing.
Combining these methods provides a complete picture of soil fertility and helps farmers make informed nutrient management decisions.

Broadcasting is a common method of applying fertilizers by spreading them uniformly over the soil surface.
However, it has some notable disadvantages:
1. Low nutrient use efficiency: When fertilizers are broadcasted, a significant portion may be lost due to surface runoff, volatilization, or leaching.
This leads to wastage of fertilizers and increases the cost of cultivation without proportionate benefits to crops.
2. Uneven distribution: Broadcasting may not ensure uniform placement of nutrients near the plant root zone.
As a result, some plants may receive excess nutrients while others get insufficient amounts, leading to uneven crop growth.
Due to these disadvantages, placement methods like banding or side-dressing are often preferred for better efficiency.

Farm Yard Manure (FYM) is an important organic source of plant nutrients used in agriculture to maintain soil fertility.
On average, FYM contains about 0.5% to 0.8% phosphorus (P2O5) by weight.
The exact content can vary depending on the type of livestock, feed, bedding material, and how the manure is stored and composted.
Phosphorus in FYM is released slowly and improves the availability of this vital nutrient to crops.
Besides phosphorus, FYM also provides nitrogen, potassium, micronutrients, and organic matter, which enhance soil structure and microbial activity.
Regular application of FYM reduces dependence on chemical fertilizers and promotes sustainable farming.

One common challenge faced during soil sampling is obtaining a truly representative sample of the entire field or plot.
Soil properties can vary greatly within a small area due to differences in soil texture, moisture, crop residues, or previous fertilizer applications.
If samples are not collected systematically from different spots and depths, the test results may not reflect the actual soil fertility status.
Poor sampling can lead to incorrect fertilizer recommendations and poor crop performance.
Therefore, it is important to use proper sampling tools and follow a zig-zag or grid pattern to cover the entire area uniformly.

There are a total of 17 essential plant nutrients required for the normal growth and development of plants.
These nutrients are divided into two main groups: macronutrients and micronutrients, based on the quantity needed by plants.
Macronutrients include primary nutrients like nitrogen, phosphorus, and potassium, as well as secondary nutrients like calcium, magnesium, and sulfur.
Micronutrients include elements such as iron, manganese, zinc, copper, boron, molybdenum, chlorine, and nickel.
Each nutrient plays a unique role in plant physiological processes such as photosynthesis, enzyme activation, and protein synthesis.
Deficiency or excess of any essential nutrient can adversely affect plant health and yield.

Soil testing is an essential practice in modern agriculture for evaluating soil fertility and guiding nutrient management.
The main objectives of soil testing are to determine the nutrient status and pH of the soil.
It helps in recommending the right type and amount of fertilizers and soil amendments for optimal crop production.
Soil testing also identifies nutrient deficiencies or toxicities, which can affect plant health and yield.
Another key goal is to prevent overuse of fertilizers, thereby reducing environmental pollution and saving costs for farmers.
By understanding soil characteristics, farmers can adopt site-specific nutrient management and sustainable farming practices.
Regular soil testing improves soil health and supports long-term agricultural productivity.

The fertilizer that contains 46% of available nitrogen is Urea.
Urea is the most widely used nitrogenous fertilizer in agriculture around the world due to its high nitrogen content and ease of application.
It is a white crystalline organic compound that dissolves easily in water and is quickly converted to ammonium and then nitrate in the soil.
Farmers use urea to promote vegetative growth, increase leaf area, and boost overall crop yields.
However, proper management is essential because nitrogen losses can occur through volatilization and leaching if not applied correctly.
Using urea in split doses and incorporating it into the soil helps improve nitrogen use efficiency.

The criteria of essentiality for plant nutrients were given by two well-known scientists: Arnon and Stout in 1939.
They proposed three fundamental conditions to classify an element as essential for plant growth and development.
First, the element must be necessary for the completion of the plant’s life cycle.
Second, its function must not be replaceable by any other element.
Third, it must be directly involved in the plant’s metabolism, for example, as a component of essential molecules or enzymes.
These criteria helped botanists and agronomists identify and categorize macro and micronutrients required for healthy plant growth.
Their work laid the foundation for modern soil fertility management and plant nutrition research.