Exam practice

Organic fertilizer is made from wastes (dung, leaves, crop remains, kitchen scraps) that would otherwise rot or be burnt, so using it recycles them. It releases nutrients slowly, so little is washed into rivers and wells to pollute them. It adds humus, which keeps the soil soft, alive with earthworms and microbes, and able to hold water, and it doesn’t harm the soil, other living things or people even after many years of use.

DDT doesn’t kill only harmful insects: it also kills useful ones, such as bees and the insects that eat pests. It doesn’t break down for many years, and it is washed into water, where it kills fish and other water animals. It collects in the body fat of animals and builds up at every step of the food chain (biomagnification), so the birds and fish at the top get the largest doses: they grow and breed poorly (birds lay eggs with thin shells that break). With some species dying out and others (the pests, without their enemies) increasing, the balance of the ecosystem is upset.

An NPK fertilizer is a fertilizer that contains all three primary nutrients: nitrogen (N), phosphorus (P) and potassium (K). The three numbers on its bag (such as 20-20-10) give the percentages of N, P₂O₅ and K₂O.
Importance:

1. It supplies all three nutrients plants need most, in one application, giving balanced feeding.
2. Nitrogen makes plants grow fast and leafy, and makes protein and chlorophyll.
3. Phosphorus helps roots grow and seeds and fruits form and ripen.
4. Potassium makes stems strong and helps plants resist disease.
5. Together they increase the harvest.

Nitrogenous: urea (NH₂CONH₂), ammonium sulphate ((NH₄)₂SO₄) (also ammonium nitrate).

Phosphatic: diammonium phosphate (DAP), single superphosphate (also triple superphosphate).

Potassium: potassium chloride (KCl), potassium sulphate (K₂SO₄).

Comparison: plant 1 is short and thin, with few, pale yellowish-green leaves. Plant 2 is tall, with many broad, dark green leaves.

Reason: since the seeds were the same, the difference comes from the soil. The soil of plant 1 lacks nutrients, most likely nitrogen, which plants need for leafy growth and green color (pale yellow leaves and stunted growth are its typical signs). Plant 2’s soil has enough.

Solution: test the soil of plant 1. Add well-rotted compost or manure, and, if the test shows a shortage of nitrogen, a nitrogenous fertilizer such as urea, in the right amount (or an NPK fertilizer if other nutrients are short too).

1. First, test the soil at the nearest soil testing laboratory or agriculture office, to know which nutrients it actually lacks and whether it is acidic.
2. Use plenty of organic fertilizer (compost, farmyard manure, green manure) every season to keep the soil healthy.
3. Add chemical fertilizer only where the test shows a shortage, and only in the recommended amount, at the right time (for example, urea in two or three small doses rather than all at once).
4. Rotate crops, including legumes that add nitrogen.

This way he gets a good harvest now without ruining his soil for later.

Alternatives: organic fertilizers: compost, farmyard manure (cow and buffalo dung), green manure (such as dhaincha, plowed in), oil cake (pina), bone meal and wood ash. Growing legumes in rotation also adds nitrogen.
Advantages:

1. They supply many nutrients, slowly, so the soil stays fertile for long.
2. They add humus, which keeps soil soft and helps it hold water and air.
3. They feed earthworms and useful microbes.
4. They don’t harm the soil or cause pollution, and are cheap, made from wastes on the farm.
5. Crops grown with them carry no chemical residues.

A chemical insecticide is a compound made in factories that is used to kill or control harmful insects that damage crops. Examples: DDT (dichlorodiphenyltrichloroethane) and malathion (also BHC, aldrin, dieldrin).

A bio-insecticide is an insecticide made from natural materials, mostly parts of plants that insects dislike, which repels or kills harmful insects without harming the soil, other living things or people. Examples: jholmol and neem leaves (also ash, asuro and titepati).

Chemical insecticides harm much more than pests, while bio-insecticides do the job without that harm. For example:

1. DDT doesn’t break down; it builds up in food chains and harmed fish and birds so badly that it is now banned. Neem leaves in stored grain keep insects away and break down harmlessly.
2. A farmer spraying malathion without protection can be poisoned, and its residues can remain on vegetables; jholmol, made from local plants and cow urine, protects the crop without poisoning the farmer, the soil or the people who eat the vegetables, and costs almost nothing.

So, wherever bio-insecticides can control the pests, they should be used instead.

Chemical fertilizers:

1. They quickly supply the nutrients that the soil lacks, in concentrated form.
2. They dissolve easily, so plants absorb them fast and grow well.
3. They greatly increase the harvest, which is needed to feed a growing population.
4. They are easy to transport, store and use.

Insecticides:

1. They kill or control the insects that damage crops, in the field and in storage.
2. They protect the harvest, so farmers earn more and more food reaches the market.
3. Some control insects that spread disease, such as mosquitoes.

1. “Feed the soil with compost, not poison: healthy soil, healthy food, healthy people.”
2. “Spray less, test more: a little poison on the field is a lot of poison on the plate.”

(Any short, catchy slogan with the same message gets full marks, for example, in Nepali: “विषादी होइन, जैविक खेती अपनाऔं, स्वस्थ जीवन बचाऔं।”)

1. Harm to human health: residues on vegetables and fruits enter our bodies; people who spray without protection can be poisoned, with harm to the nerves and glands. For example, farmers spraying insecticide on vegetables without a mask can suffer headaches, vomiting and dizziness.
2. Harm to the ecosystem: insecticides kill useful insects such as honey bees, and pollute water, killing fish. For example, DDT built up along food chains and made birds lay thin-shelled eggs that broke, so their numbers fell.

Instead of chemical fertilizers: compost and farmyard manure (gobar mal); green manure such as dhaincha or asuro leaves.

Instead of chemical insecticides: jholmol; neem leaves in stored grain (also ash sprinkled on vegetables).