Fertilizers are considered beneficial for plants. We should know about the impact of fertilizer on the environment. This concern refers both to the use of synthetic and organic sources of nutrients, four important issues related to fertilizer have to be highlighted.
Fertilizers are also called as an agrochemical. Agrochemical is a broad term which includes insecticides pesticides and herbicides. A clear distinction must be made between fertilizers, which provide nutrients that are essential for plant growth, and biocides, compounds that kill, which are used for plant protection.
The environmental effects of applying plant nutrients can be positive or negative, and statements on the issue should be objectively balanced. The judicious use of fertilizer doses increases productivity. Excess of fertilizer doses have bad effects on environment and reduces the farmer’s profit. Environmental problems are related to nutrients are depends on nature of nutrients, doses and application methods. Detrimental effects are mostly due to overdoses and unbalanced use at a wrong time and place that can be corrected by best-improved management practices.
The positive effects show when fertilizers increase inherent soil fertility by correcting imbalance of nutrients. Nutrients reduce the problem of erosion on cropped areas because of the protection provided by a dense crop cover. Integrated plant nutrient systems promote the best management of plant nutrients enhances the economic value of the nutrients and limiting nutrients losses to the environment. Low fertility soil produces high yield due to judicious use of fertilizer.
Not all nutrients applied to the soil are taken up by the growing crop and the remainder may become an environmental hazard. Unused nutrients can remain in the soil, be removed in water leaching through the soil or in the runoff, or be lost to the atmosphere by volatilization. The relative importance of these phenomena depends on the physic-chemical and biological reactions in which the nutrients take part.
Nitrogen compounds are fairly rapidly oxidized to nitrate under a favorable temperature and well-drained soil conditions. Nitrate is not highly absorbed by soil particles. Nitrogen is, therefore, the most likely fertilizer element to be leached out into surface water or groundwater or to be lost to the atmosphere by denitrification, partly as nitrogen gas and partly as nitrous oxide, which is a greenhouse gas. Nitrous oxide my escape into the ecosystem and increase nitrogen content. It depleted the ozone layer in the atmosphere. The temperature of the earth increases day by day due to depletion of ozone layer. The run off nitrogen from farms into the rivers increases nitrate levels in water that will be injurious not only for flora and fauna but also specifically to the humans.
Pakistani soil contains very low organic matter. Problems of nitrate leaching in drinking water have been noted where use of organic matter is high, which release nitrogen on decomposition. Researchers are trying to change the nitrate concentration in water by managing nitrogenous fertilizer applications. Animal husbandry is a major cause of nitrogen leaching due to mineralization of nitrogen from urine, manures or slurry. Ammonia volatilizes both from manure heaps and soil after its application. It takes place when urea is applied to high pH soil under dry and warm conditions.
Phosphorus ions are immobilized in the soil. They are adsorbed by the surfaces of iron, aluminum and manganese oxides and hydroxides, and by clay particles. Applied phosphate that is not taken up by the crop remains in the soil unless it is washed off the land by runoff or by soil erosion.
Phosphate can also occur in high concentrations in irrigation water and drainage water from inundated soils. Excess inputs of phosphates to surface waters can lead to eutrophication and algal blooms. Phosphate fertilizers may contain cadmium when sedimentary rock phosphate is used as raw material. Cadmium is also added to the soil by aerial deposition. It causes a lot of problem for animals and humans after entering into the food chain through plants. However, cadmium should be removed when raw materials are processed, wherever possible.
Pakistani soils are calcareous in nature. Phosphorus makes a bond with calcium resulted as a tricalcium phosphate. This makes pool in the soil and will not available to plants. The question is that when these bonded phosphorus will release in future then what will be the condition of the soil? Will the soil be able to produce yield? Will we save productive soil for future generations? Now our efforts in regards to nutrients application require more careful concentration. Today thinking about these questions will save our future.
Potassium ion can be fixed by clay particles. Added potassium that is not taken up by the crop and is not very mobile in clayey soil. In sandy soils, some applied potassium may be leached out. The magnitude of leaching of N is greater than that of K because N leaching occurs in the form of nitrate ion. Nitrate ion is negatively charged and are not adsorbed on negatively charged sites of soil particles. Thus, they exist in soil solution and can leach with speculating water. K cations are adsorbed on negatively charged sites of soil by electrostatic attraction or fixed within clay particles. The very low amount of K exists in soil solution and can leach with water. Major losses of potassium are caused when the element is washed away in liquid manure from farmyards and dairies. Potassium in water has no dangerous effects but may indicate the presence of sewage or animal effluent. Potassium is not a major factor in the eutrophication of surface water.
Good management practices reduce the negative effects of plant nutrients both at low and high rates. The hazards of nutrient depletion are controlled by balanced fertilization. The application of nutrients at right time, right place and in right amount can save farmer’s profit and reduces the losses. Farmers behavior are playing integral role in this regard. We should properly advise the farmers about fertilizer management.
This article is authored by Iqra Ghafoor Department of Agronomy MNS, University of Agriculture Multan.