(Institute of food science and Nutrition, UOS)
Natural fertilizers are the valuable gift of Almighty. These are derived from animal or plant source with zero or least side effects. It is a best way to reduce the use of pesticides and ultimately their harmful effect on human life. Natural fertilizers like egg shells can be use more easily in home gardening rather than in fields. Memon et al. (2016) reported that Pakistan has been producing 10,000 million eggs per annum. An average Pakistani consumes about 65-70 eggs per year so why not utilize these eggs waste as a beneficial product rather than throwing them away in trash.
Egg which is considered the most nutritious diet can also be used as a fertilizer in whole form. But it can spread rotten odor if you don’t dig the soil deep down and bury them. It is difficult to decompose in soil which makes it less effective. Also it is not economical to use whole egg as fertilizer. It attracts rodents which dig the soil and destroy the roots of plants so ultimately makes the condition worst. Not only eggs but egg shells also have their nutritional benefit that’s the reason we can use egg shells as natural fertilizer. Study shows that Powder of eggshells increases the size of red clover plant of 10mm than usual (planting Science.org, 2011). As chicken eggs are common in Pakistan so we are mainly concern here with chicken egg shells. Egg shell comprises 10.2% of egg along with shell membrane. Chicken egg shells made up of approximately 96% calcium carbonate. Calcium carbonate has porous structure which makes shells semi permeable for air and moisture and let life breath inside the egg shells. Egg shells also protective by a coating called bloom (cuticle). It plays an important role as a barrier and prevents the penetration of microbes and dust inside the shell. Egg shell also contains sulphur, potassium, sodium, magnesium and calcium. Residues of protein adhere with egg shells act as nitrogen source.
Uses of Eggshells in Agriculture
1: Eggshells act as pest repellent especially for pests belong to the phylum mollusca such as slugs and snails. Sharp pieces of shells cause abrasion to the fragile feet of snails thus act as a pest deterrent.
2: Egg shells as a whole can also use as seed germination pot. Fill the egg cups with moist soil and seeds and let them grow enough that they are able to transplant in your desired place i.e. garden or yard.
3: Eggs shells are also going to be use as bird feed. Shells powder is mixed with bird food to regulate their digestive system.
4: Being a source of calcium it increases the calcium level of soil. Calcium in turn enhances the uptake of minerals and nutrients by roots and also decreases the level of soil acidity.
Preparation of egg shells as a fertilizer:
1: Wash the shells with water to remove egg white portion and dried them. Shells can be dried by dryer or simply spreading them under sun light.
2: Ground the egg shells in to fine ground powder.
3: store the powder in closed jar.
Mitchell (2005) performed a test to find out the effect of shells on pH of soil. He found that coarse pieces of shells do not help to decrease pH neither act as lime source. So to make it effective we need to ground it in to fine particles. He also observed that egg shells bring change in the pH of soil having pH near 4.8 (acidic) But it does not bring any change in soil having pH near 6.8 as it stop decomposing at this point. It happens because calcium carbonate is insoluble in water and alkaline medium. It is just soluble in acidic medium; even it shows less solubility in less acidic medium that’s the reason egg shells work best as a fertilizer for acidic soil.
Oliveira, D. A., Benelli, P., & Amante, E. R. (2013). A literature review on adding value to solid residues: egg shells. Journal of cleaner production, 46, 42-47.