Here is an essay on ‘Fertilisers’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Fertilisers’ especially written for school and college students.
Essay # 1. Fertiliser Application in Relation to Irrigation Timing:
Fertiliser application should be timed to achieve maximum plant uptake, thereby reducing losses of nutrient to the environment. Ideal timing depends on the solubility (mobility) of the nutrient or fertiliser used, crop growth stage and rate of growth (nutrient demand) and the nutrient fixing capability of the soil. Amount of rainfall and/or irrigation experienced or expected also has considerable influence on timing of fertiliser application.
Applying fertiliser long before the plant will take up the nutrient exposes the nutrient to potential loss. This is particularly so with nitrogen fertilisers. Maximum responses and minimal nutrient losses will usually occur if fertiliser is applied when plants are growing rapidly.
It is especially important to apply highly mobile nutrients at times when plants are actively growing to avoid losses to the environment between application and plant uptake and thus to maximise the return on the investment. This is particularly important when highly soluble nutrients are applied in high rainfall or irrigation situations.
Fertiliser often requires water to move it to a site where it can be taken up by plants and, in the case of nitrogen, where it is protected from gaseous losses. Timing of fertiliser application in relation to irrigation or rainfall can be critical to determining the risk of gaseous loss.
Studies on the relation between timing of irrigation and fertiliser application are limited. However, importance of adequate available soil moisture for improving fertiliser use efficiency has been studied elaborately. Scanty information on the relationship between timing of irrigation and fertiliser application is briefly presented.
Pre-sowing irrigation can impact fertiliser management in crop production. Pre-sowing irrigation aids in increased seed emergence, stand establishment and root growth, which can all lead to potentially higher yields. Early increased root growth from adequate soil moisture can be advantageous for soil nutrient acquisition.
This would be beneficial for nutrients that are immobile in the soil, such as P and K. Relationships between soil-water dependent root growth and plant P uptake have been observed in cereal crops, mostly because of the effects of soil moisture on the movement of phosphorus via diffusion and root development.
Researchers have observed that plants take up more native soil P in more moist soil environments and that the uptake of fertiliser P is not as sensitive to changes to soil moisture content. A similar relationship between the plant availability of K and soil water dependent root growth also exists.
Adequate or increased soil moisture content typically leads to increased root growth as well as the diffusive flux of K to the root surface. Providing adequate soil moisture content has also been shown to increase the efficiency of K fertiliser applications.
Interactive effects of irrigation and N, P and K fertilisation have been evaluated with N most commonly being evaluated with P or K or the three together. Response to N fertilisation is typically almost always observed regardless of irrigation or soil moisture content, but response to P and/or K fertilisation along with N fertilisation is dependent on the amount of soil moisture, the timing the moisture is received by the growing crop and the soil type.
Optimum available soil moisture is a must for the solubility and uptake of nutrients by the crop. For irrigated crops, N fertilisers are recommended in split doses to minimise leaching losses as these fertilisers are highly soluble in water. Sparingly soluble P and K fertilisers are, generally, recommended in single application as basal dose since leaching losses are relatively less.
Optimum time of fertiliser application for most crops is when the available soil moisture is around field capacity (25 to 50% DASM). Since N fertilisers are subjected to leaching losses, they should be applied to irrigated crops after 2 to 4 days after irrigation when the soil moisture content is 25 to 50 per cent.
Nitrogen fertilisers should not be applied before starting irrigation to avoid leaching losses. Irrigation water is often subjected to surface runoff with surface irrigation methods. As such, it would be better to apply any fertiliser. (NPK) after irrigation, when the available moisture is adequate for its uptake by the crop.
Importance of adequate available soil moisture for efficient use of fertilisers is evident from the fact that the entire quantity of fertilisers (NPK) is recommended as basal dose at sowing when the crops are sown on stored soil moisture. This is due to the fact that even the highly soluble N fertilisers will not be effective if applied as top dressing when the soil has been dried near to permanent wilting point.
With fertigation, when the dissolved urea is injected during the entire irrigation time, soil nitrogen concentrations for each soil depth in the furrow (top, middle and bottom third) will be similar along the entire length of the field. Nevertheless, if the dissolved urea is injected during the first half of the irrigation, nitrogen concentrations in the soil will be higher at the lower end of the field than at the upper end because of the longer infiltration opportunity time of nitrogen-amended water at the lower end.
Soil nitrogen concentrations along the furrows where nitrogen injection was made during the last half of the irrigation will be higher at the head end of the field, with almost no nitrogen at the lower end of the field. This is due to the early rapid infiltration of un-amended water in the furrows at the upper end of the field. Injection during the last half of the irrigation resulted in little total nitrogen at the tail end of the field and the largest accumulation of total nitrogen at the head end of the field.
Continuous injection of dissolved urea during the entire irrigation time appears to be the best distribution uniformity of added nitrogen for higher yield in many crops, whereas injection of the dissolved urea during the first half of the irrigation time appears to be the next.
Essay # 2. Depth of Irrigation in Relation to Fertiliser Application:
At each irrigation, the depth of irrigation water application should be equal to that required to bring the soil to field capacity. Depth of application should be equal to the predetermined depletion level of available soil moisture (25, 50, 75 DASM) for scheduling irrigation.
Deep placement of fertilisers is recommended for all crops as it ensures adequate available soil moisture for fertiliser dissolution and its uptake by the crop. Deep placement is, especially, important for those fertilisers supplying P and K as these are relatively immobile nutrients in the soil.
Land submergence (5 cm) is recommended for lowland rice as it leads to efficient use of soil and fertiliser supplied nutrients. Land submergence also increases the availability of other nutrients, especially P, K, Fe, Zn etc.
For lowland rice, ammonia or ammonia forming N fertilisers should be applied in the root zone (rhizosphere placement) to minimise N losses due to nitrification. When urea fertiliser is applied to the soil, it combines with water (hydrolysis) to form ammonium carbonate [(NH4)2CO3] through the catalytic action of urease.
NH2 – CO – NH2 → (NH4)2 CO3
Ammonium carbonate is unstable. It decomposes into gaseous ammonia (NH3), carbon dioxide and water. When incorporated to the soil, NH3 is converted to ammonium (NH4+) with hydrogen ion (H+) coming from soil solution or from soil particles. The positively charged ammonium ions are then fixed into the negatively charged soil particles where they remain until absorbed by plant through the roots or used by bacteria as source of energy and converted to nitrate (NO3–) in the process of nitrification.
A summary reaction for the hydrolysis of urea [CO (NH2)2] leading to the formation of ammonium ion (NH4+) is given below:
CO (NH2)2 + H+ + 2H2O + urease → 2NH4+ + HCO3–
As a general rule, urea should not be applied on the soil surface without immediate incorporation. When applied on the soil surface, NH3, a product of urea hydrolysis, will escape into the air being a gas. This is called ammonia volatilisation.
A substantial loss of nitrogen from urea and ammonium sulphate can be reduced or eliminated by deep placement. This can be done by tillage, such as plowing under or by disking or by irrigation. Being highly soluble in water, the urea fertiliser will be carried into the soil and there behaves just like other nitrogen fertilisers.
Essay # 3. Fertilisers in Relation to Water Quality:
Fertilisers cause problems with water quality when they runoff into rivers or percolate into groundwater. In fact, agriculture is the largest source of non-point water pollution.
There are basically two types of water pollution, in terms of their sources:
1. Point source pollution, which, as the name implies, is pollution that comes from a discrete source, such as where a pipe carrying factory wastes dumps into a river
2. Non-point source pollution, again as the name implies, is pollution that comes from more diffuse sources, such as runoff from roads or from agricultural fields.
Nitrates (NO3–) are highly water soluble and move readily with surface runoff into rivers or with water percolating through the soil profile into the groundwater below. Much of the concern about fertilisers and water quality relates to nitrates, which can cause health problems in humans.
When ingested, nitrates are converted into nitrite in the intestine, which then combines with hemoglobin to form methemoglobin. Methemoglobin has a reduced oxygen-carrying capacity and is particularly problematic in children, who are most readily affected by this nitrite poisoning or blue baby syndrome. Elevated levels of nitrate are common in groundwater in agricultural areas. Levels of nitrate in water that are not harmful to humans may be harmful to some species of amphibians.
Phosphates are also applied abundantly in fertiliser and contaminate water. Unlike nitrate, however, phosphate is not water soluble, so moves only with soil movement, as it adheres to soil particles. When it erodes on soils from agricultural fields, it is essentially non-recoverable, washing into sediments in oceans.
Eutrophication:
Eutrophication is the enrichment of surface waters with plant nutrients. Runoff of nitrate and phosphate into lakes and streams fertilises them and causes accelerated eutrophication (eu = true or well; trophy = food) or enrichment of the waters.
Eutrophication is a natural process that typically occurs as lakes age. However, human caused, accelerated eutrophication (called “cultural eutrophication”) occurs more rapidly and causes problems in the affected water bodies, as described below. It is estimated that 50-70 per cent of all nutrients reaching surface water (principally N and P) originate on agricultural land as fertilisers or animal waste.
Eutrophication problem:
Rich nutrient input stimulates growth of algae which change the lake or stream as their populations increase. This is particularly the case when they undergo population explosions, referred to as “blooms.” Basically, the fertilisers make the lake more productive, as they stimulate algal primary productivity.
However, from a multiple use perspective, such stimulation has undesirable consequences:
1. Penetration of light into the water is diminished. This occurs because the algae forms mats as a result of being produced faster than they are consumed. Diminished light penetration decreases the productivity of plants living in the deeper waters (and hence their production of oxygen)
2. Water becomes depleted in oxygen. When the abundant algae die and decompose, much oxygen is consumed by those decomposers. Oxygen in the water is also lowered by lack of primary production in darkened deeper waters.
3. Lowered oxygen results in the death of fish that need high levels of dissolved oxygen (“DO”), such as trout, salmon and other desirable sport fish. The community composition of the water body changes, with fish that can tolerate low DO, such as carp predominating. As you can imagine, changes in fish communities have ramifications for the rest of the aquatic ecosystem as well, acting at least in part through changes in food webs.
4. Further, some of the algal species that “bloom” produce toxins that render the water unpalatable
5. Infilling and clogging of irrigation canals with aquatic weeds (water hyacinth is a problem of introduction, not necessarily of eutrophication)
6. Loss of recreational use of water due to slime, weed infestation and noxious odour from decaying algae
7. Impediments to navigation due to dense weed growth
8. Economic loss due to change in fish species, fish kills etc.
Essentially, the entire aquatic ecosystem changes with eutrophication. Pollutants can also seep down and affect the groundwater deposits.
Role of Fertilisers in Eutrophication:
Water quality impacts of fertilisers leads to the following problems:
1. Fertilisation of surface waters (eutrophication) results in, for example, explosive growth of algae which causes disruptive changes to the biological equilibrium, including fish kills. This is true both for inland waters (ditches, river, lakes) and coastal waters.
2. Groundwater is being polluted mainly by nitrates. In all countries, groundwater is polluted to an extent that it is no longer fit to be used as drinking water according to present standards.
The following are the major categories of impacts caused by manures and fertiliser use in agriculture:
1. Fertilisation of surface waters, both as a result of direct discharges of manure and as a consequence of nitrate, phosphate and potassium being leached from the soil
2. Contamination of the groundwater as a result of leaching, especially by nitrate. Phosphates are less readily leached out, but in areas where the soil is saturated with phosphate this substance is found in the groundwater more and more often
3. Surface waters and the groundwater are being contaminated by heavy metals. High concentrations of these substances pose a threat to the health of man and animals. To a certain extent these heavy metals accumulate in the soil, from which they are taken up by crops. For example, pig manure contains significant quantities of copper
4. Acidification as a result of ammonia emission (volatilisation) from livestock accommodation, manure storage facilities and manure being spread on the land. Ammonia constitutes a major contribution to the acidification of the environment, especially in areas with considerable intensive livestock farming.