Agriculture Fertilizers - Overview, Types, uses

The organic fertilizers are prepared in the following ways:

• Manure - This is prepared from cow dung and other animal wastage.

• Compost This is an organic matter decomposed through composting.

• Rock phosphate

• Chicken Litter

• Bone meal 

• Vermicompost

The fertilizers are also classified into following types. They are:

1) Single nutrient: These are also known as straight fertilizers. That is the type of fertilizers that contains only a single element either nitrogen or phosphorus and it serves the purpose of fertilizers. Examples of single nutrient fertilizers are ammonium nitrate, superphosphates, phosphogypsum, muriate of potash(MOP), etc.

2) Multinutrient: Multinutrient fertilizers are those that contain the combination of two or more elements. These are further classified into following types.

• Binary fertilizers: Binary fertilizers contain the combination of nitrogen or potassium, nitrogen or phosphorus and potassium or phosphorus. The common binary fertilizers are monoammonium and Diammonium phosphate.

• N-P-K fertilizers: These fertilizers provide the combination of nitrogen, potassium and phosphorus to the plants. These are represented by three numbers separated by dashes which indicates the percentages of these three components.

The use of fertilizers affects the environment in the following ways.

• Production of fertilizers may cause global warming

• Water pollution

• Degradation of soil microbes

• Accumulation of toxins in ecosystem

• Leads to climate change

Different crops have varying nutrient requirements based on their growth habits, yield potential, and physiological needs. For example, leafy vegetables often require more nitrogen for foliage growth, while fruiting plants may need more phosphorus and potassium for flower and fruit development. Understanding these differences is crucial for developing effective fertilization strategies for different crops.

Soil pH greatly influences nutrient availability to plants. Most nutrients are most readily available to plants when the soil pH is between 6.0 and 7.5. In highly acidic or alkaline soils, certain nutrients become less available or even toxic to plants. For example, phosphorus becomes less available in very acidic soils, while iron becomes less available in alkaline soils.

Nutrient use efficiency (NUE) refers to the ability of plants to utilize available nutrients effectively for growth and yield production. It's calculated as the ratio of crop yield to the amount of nutrient applied or available. Improving NUE is crucial for sustainable agriculture as it helps reduce fertilizer waste, minimize environmental impact, and increase crop productivity.

The three primary macronutrients found in most fertilizers are nitrogen (N), phosphorus (P), and potassium (K). These are often referred to as NPK. Nitrogen promotes leaf growth, phosphorus supports root and flower development, and potassium enhances overall plant health and disease resistance.

Legumes, such as beans, peas, and clover, have a symbiotic relationship with nitrogen-fixing bacteria in their root nodules. These bacteria can convert atmospheric nitrogen into a form that plants can use. When legumes die or are plowed under, they release this fixed nitrogen into the soil, naturally improving soil fertility and reducing the need for nitrogen fertilizers.

Organic fertilizers are derived from natural sources like animal manure, compost, or plant residues. They release nutrients slowly and improve soil structure. Inorganic fertilizers, also called synthetic or chemical fertilizers, are manufactured and contain specific nutrient ratios. They provide nutrients more quickly but don't improve soil structure as much as organic fertilizers.

Biofertilizers contain living microorganisms that enhance plant nutrition by various mechanisms, such as nitrogen fixation, phosphorus solubilization, or improving nutrient uptake. Unlike traditional fertilizers that directly supply nutrients, biofertilizers work by increasing the availability or uptake of existing nutrients in the soil. They are considered more environmentally friendly and can improve long-term soil health.

Base fertilizers are applied before or at planting time and are incorporated into the soil to provide a foundation of nutrients for the entire growing season. Top dressings are additional fertilizer applications made during the growing season, usually to the soil surface around growing plants, to supplement nutrients as needed based on plant growth stage or observed deficiencies.

The NPK ratio on fertilizer labels indicates the proportion of nitrogen (N), phosphorus (P), and potassium (K) in the fertilizer. For example, a 10-5-5 fertilizer contains 10% nitrogen, 5% phosphorus (as P2O5), and 5% potassium (as K2O) by weight. This information helps users choose the right fertilizer for their specific crop and soil needs.

Over-fertilization can harm plants by causing nutrient burn, which damages roots and leaves. It can also lead to excessive vegetative growth at the expense of fruit or flower production. Environmentally, excess fertilizers can leach into groundwater or run off into surface waters, causing eutrophication (excessive nutrient enrichment) in aquatic ecosystems, leading to algal blooms and oxygen depletion.

Nitrogen fertilizers can have several environmental impacts if not used properly. These include nitrate leaching into groundwater, which can contaminate drinking water sources; ammonia volatilization, contributing to air pollution; and nitrous oxide emissions, a potent greenhouse gas. Excess nitrogen can also lead to eutrophication in water bodies, causing algal blooms and oxygen depletion.

Advantages of hydroponics include precise control over nutrient delivery, efficient water use, and the ability to grow plants in areas with poor soil. Disadvantages include the high initial setup cost, the need for constant monitoring of nutrient solutions, and the risk of rapid system failure if equipment malfunctions. Hydroponics also requires a good understanding of plant nutrition to maintain optimal nutrient balance.

Plants have evolved various adaptations to thrive in nutrient-poor environments. These include developing more extensive root systems, forming symbiotic relationships with fungi (mycorrhizae) to enhance nutrient uptake, modifying leaf structure to conserve resources, and developing specialized structures like carnivorous traps in extremely nutrient-poor conditions.

The carbon-to-nitrogen (C:N) ratio in organic fertilizers is crucial because it affects how quickly the organic matter decomposes and releases nutrients. Materials with a low C:N ratio (like fresh grass clippings) decompose quickly, releasing nutrients rapidly. Those with a high C:N ratio (like sawdust) decompose slowly and may temporarily tie up soil nitrogen as microbes use it to break down the carbon-rich material.

Temperature and moisture significantly influence fertilizer efficiency. Higher temperatures generally increase the rate of chemical reactions and microbial activity, potentially leading to faster nutrient release but also increased volatilization of some nutrients like nitrogen. Adequate soil moisture is crucial for nutrient dissolution and uptake by plants, while excessive moisture can lead to nutrient leaching or promote conditions for nutrient loss through denitrification.

Plants respond to nutrient deficiencies through various visible symptoms and physiological changes. Common responses include chlorosis (yellowing of leaves), stunted growth, leaf discoloration or deformation, and reduced flowering or fruiting. Plants may also alter their root architecture or exude specific compounds to enhance nutrient uptake from the soil.

Nutrient synergism occurs when the presence of one nutrient enhances the uptake or utilization of another nutrient. For example, nitrogen and sulfur often work synergistically. Nutrient antagonism is when the excess of one nutrient interferes with the uptake or function of another. An example is how high levels of phosphorus can interfere with zinc uptake. Understanding these interactions is crucial for balanced fertilization.

Crop rotation can improve soil fertility by breaking pest and disease cycles, improving soil structure, and balancing nutrient use. Different crops have different nutrient requirements and rooting depths, so rotation can help prevent depletion of specific nutrients. Some rotations, especially those including legumes, can reduce the need for nitrogen fertilizers for subsequent crops.

While not considered an essential nutrient for all plants, silicon can provide significant benefits. It strengthens cell walls, improving plant structure and resistance to pests and diseases. Silicon can also enhance drought tolerance and mitigate the effects of various abiotic stresses. Some crops, like rice, accumulate high levels of silicon and show more pronounced benefits from silicon fertilization.

pH-adjusting fertilizers are designed to alter soil pH while providing nutrients. Acidifying fertilizers, like ammonium sulfate, can lower soil pH, which is useful in alkaline soils. Alkaline fertilizers, such as calcium carbonate, can raise soil pH, beneficial in acidic soils. These fertilizers help create optimal pH conditions for nutrient availability while supplying essential elements.

Luxury consumption refers to the uptake of nutrients by plants in excess of their immediate growth requirements. This often occurs when a particular nutrient is highly available in the soil. While not immediately harmful to the plant, luxury consumption can lead to nutrient imbalances, reduced efficiency of fertilizer use, and potential environmental issues if excess nutrients are lost from the soil.

Nanofertilizers are engineered on a nanoscale (1-100 nm) to enhance nutrient use efficiency. They can provide a more targeted delivery of nutrients, potentially reducing the amount of fertilizer needed. Nanofertilizers may have controlled-release properties, better adherence to plant surfaces, and improved uptake efficiency. However, their long-term effects on soil ecosystems and potential environmental impacts are still being studied.

Beneficial microorganisms play crucial roles in nutrient cycling and availability. They decompose organic matter, releasing nutrients; fix atmospheric nitrogen; solubilize phosphorus and other minerals; produce plant growth-promoting substances; and form symbiotic relationships with plants (e.g., mycorrhizal fungi) that enhance nutrient uptake. Understanding and managing these microorganisms is becoming increasingly important in sustainable agriculture.

Precision agriculture in fertilizer application involves using technology to apply the right amount of fertilizer at the right time and place. This includes using GPS-guided equipment, soil sensors, drone imagery, and data analytics to map field variability and apply fertilizers at variable rates across a field. The goal is to optimize nutrient use efficiency, reduce costs, and minimize environmental impact.

Different forms of nitrogen behave differently in soil. Nitrate (NO3-) is highly mobile and can be easily leached. Ammonium (NH4+) is less mobile, adhering to soil particles, but can be converted to nitrate by soil bacteria. Urea is initially neutral but quickly hydrolyzes to form ammonium, which then follows the ammonium pathway. Understanding these differences is crucial for timing applications and managing nitrogen efficiency.

Biofortification is the process of increasing the nutritional value of crops through breeding or agronomic practices. In relation to fertilizers, agronomic biofortification involves applying