Soil Science and Fertilizers

Fertilizer burn can occur when too much fertilizer is applied resulting in drying out of the leaves, damage or even death of the plant.

Nitrogenous fertilizers leach away from the soil easily due to their high solubility in water and pollute the water bodies. Nitrogen leaching is a naturally occurring process, it occurs when nitrogen leaves the soil in drainage water. Nitrate is soluble and mobile. It is no problem when it is within the root-zone, but once it gets into the groundwater and other freshwater bodies it is an environmental pollutant.

Nitrogen has to be converted to nitrate, in order to be used by plants. Hence, using nitrate fertilizers directly would be the quickest way to provide nitrogen to the plants. Ammonium nitrate is an important fertilizer with the NPK-rating 34-0-0 (34% nitrogen). It is less concentrated than urea (46-0-0), giving ammonium nitrate a slight transportation disadvantage. Ammonium nitrate's advantage over urea is that it is more stable and does not rapidly lose nitrogen to the atmosphere. During warm weather it is best to apply urea soon before rain is expected or to cover it with soil to minimize nitrogen loss. 

All plants require sufficient supplies of macronutrients for healthy growth, and nitrogen (N) is a nutrient that is commonly in limited supply. Nitrogen deficiency in plants can occur when organic matter with high carbon content, such as sawdust, is added to soil. Soil organisms use any nitrogen to break down carbon sources, making N unavailable to plants. This is known as "robbing" the soil of nitrogen. All vegetables apart from nitrogen fixing legumes are prone to this disorder.

Some symptoms of nitrogen deficiency (in absence or low supply) are given below:

1. The chlorophyll content of the plant leaves is reduced which results in pale yellow colour. Older leaves turn completely yellow.
2. Flowering, fruitings, protein and starch contents are reduced. Reduction in protein results in stunted growth and dormant lateral buds

Biomagnification stands for Biological Magnification, which means the increase of contaminated substances or toxic chemicals that take place in the food chains. These substances often arise from intoxicated or contaminated environments. The contaminants include heavy metals namely mercury, arsenic, fertilizers&pesticides such as DDT, and polychlorinated biphenyls (PCBs) compounds which are then taken up by organisms because of the food they consume or the intoxication of their environment.

The uses of fertilizer are :

1. They boost crop yields.
2. Increases the protein content of the plants.
3. Imparts dark green colour to the leaves.
4. Improves overall quality of the plants.
5. Help in blooming and seed formation.
6. Increases vigour, resistance to frost and insects, pests and diseases.
7. Helps in the development of healthy root system.
8. Makes the stalks stronger.
9. Helps in ripening of cereals and fruits.
10. Increases vigour and diseases resistance in the plants.
11. Enhances the synthesis of carbohydrates.

Soil pH is considered a master variable in soils as it affects many chemical processes. It specifically affects plant nutrient availability by controlling the chemical forms of the different nutrients and influencing the chemical reactions they undergo. 

Growers apply ammonium sulfate primarily where they need supplemental N and S to meet the nutritional requirement of growing plants. Since, ammonium sulfate contains only 21 percent N, other fertilizer sources are more concentrated and economical to transport, often making them a better choice for N-deficient fields. However, ammonium sulfate provides an excellent source of S, which supports or drives numerous essential plant functions, including protein synthesis.

Disadvantages of fertilizers are:

1. Constant application is needed.
2. Cause soil pollution, water pollution.
3. Cause plant toxicity.
4. Lead to biomagnifications.

To produce fertilizer in the most usable form, each of the different compounds, ammonium nitrate, potassium chloride, ammonium phosphate, and triple superphosphate are granulated and blended together. So, commercial fertilisers are available mostly in the form of granules.

The characteristic of good fertilizer are:

1. It should be soluble in water so that it can penetrate the soil and thus it may be easily assimilated by the plants.
2. It must have essential elements in the form of a compound, which can be easily assimilated by plants.
3. It should not alter the acidity or alkalinity of soil.
4. It should not be fairly stable i.e it not decompose rapidly in soil and lose its essential element.
5. It storage properties must be good with little or no tendency to setting or deliquescence.

Foliar fertilizers are applied directly to leaves. The method is almost invariably used to apply water-soluble straight nitrogen fertilizers and used especially for high value crops such as fruits.

The addition of fertilizer to irrigation water is called "fertigation".

There are actually only two classes of fertilisers: liquid and solid, but the majority of fertilisers used in agriculture are in solid state.

Liquid fertilizer is inorganic substance produced industrially and introduced into the soil in a liquid state. Liquid fertilizers include nitrogenous fertilizers,, anhydrous liquid ammonia, aqueous ammonia, ammoniates, concentrated solutions of ammonium nitrate and urea, and complex fertilizers containing two or three basic plant food elements(nitrogen, phosphorous, and potassium) in various proportions.