One Crop Leaves the Soil Richer Than It Found It
Learn to tell kharif crops from rabi ones by their season and water needs, follow the six agricultural practices in order, compare manure with chemical fertiliser, and see why crop rotation keeps soil fertile.
Which crop actually improves the field it grows in?
A pulse crop — gram, moong, peas or any other leguminous plant.
Every other crop takes nutrients out of the soil and leaves it poorer. A pulse crop does that too, but it also carries bacteria in swellings on its roots that take nitrogen from the air and convert it into a form plants can absorb. When the crop is harvested and its roots decay, that nitrogen stays behind.
So planting a pulse is a way of fertilising a field by growing something in it — which is the whole idea behind crop rotation. This page covers the first part of the ICSE Class 8 Biology chapter on food production: crop seasons, the work of a farming year, and how fertility is maintained.
Every other crop takes nutrients out of the soil and leaves it poorer. A pulse crop does that too, but it also carries bacteria in swellings on its roots that take nitrogen from the air and convert it into a form plants can absorb. When the crop is harvested and its roots decay, that nitrogen stays behind.
So planting a pulse is a way of fertilising a field by growing something in it — which is the whole idea behind crop rotation. This page covers the first part of the ICSE Class 8 Biology chapter on food production: crop seasons, the work of a farming year, and how fertility is maintained.
How do kharif crops differ from rabi crops?
By the season they are grown in, and therefore by how much water they need.
Kharif crops are sown at the onset of the monsoon and harvested at the end of the rainy season. They grow through the rains, so they need plenty of water and warm conditions.
Examples: rice (paddy), maize, millets such as jowar and bajra, cotton, groundnut, soybean, and pulses such as moong and urad.
Rabi crops are sown at the beginning of winter and harvested in spring. They grow through the cool dry season, so they need less water — usually supplied by irrigation rather than rain — and a cooler growing period.
Examples: wheat, gram, peas, mustard, barley and linseed.
A third short season, the zaid season, falls between the two in the hot summer, and carries quick crops such as watermelon, muskmelon, cucumber and fodder.
Why rice is a kharif crop and wheat a rabi one. Rice needs its field flooded for much of its growth, which is practical only in the monsoon. Wheat needs a cool growing season and would not set grain in the heat and humidity of the rains. Each crop has been matched to the season that suits it, not the other way round.
Which is why the same field can grow both. A farmer harvests paddy at the end of the rains and sows wheat in the same field a few weeks later, taking two crops from one field in a year. That is only possible because the two crops want opposite conditions.
The word to be careful with. Kharif and rabi describe the season, not the plant. Maize, for instance, is grown in both seasons in different parts of India, so a crop's classification can depend on where it is being grown as well as what it is.
Kharif crops are sown at the onset of the monsoon and harvested at the end of the rainy season. They grow through the rains, so they need plenty of water and warm conditions.
Examples: rice (paddy), maize, millets such as jowar and bajra, cotton, groundnut, soybean, and pulses such as moong and urad.
Rabi crops are sown at the beginning of winter and harvested in spring. They grow through the cool dry season, so they need less water — usually supplied by irrigation rather than rain — and a cooler growing period.
Examples: wheat, gram, peas, mustard, barley and linseed.
A third short season, the zaid season, falls between the two in the hot summer, and carries quick crops such as watermelon, muskmelon, cucumber and fodder.
Why rice is a kharif crop and wheat a rabi one. Rice needs its field flooded for much of its growth, which is practical only in the monsoon. Wheat needs a cool growing season and would not set grain in the heat and humidity of the rains. Each crop has been matched to the season that suits it, not the other way round.
Which is why the same field can grow both. A farmer harvests paddy at the end of the rains and sows wheat in the same field a few weeks later, taking two crops from one field in a year. That is only possible because the two crops want opposite conditions.
The word to be careful with. Kharif and rabi describe the season, not the plant. Maize, for instance, is grown in both seasons in different parts of India, so a crop's classification can depend on where it is being grown as well as what it is.
What are the agricultural practices, in order?
Six main operations, and they follow a fixed sequence from bare field to harvested grain.
1. Ploughing, also called tilling — turning and loosening the soil with a plough or cultivator.
Its purposes: it lets air into the soil for the roots and soil organisms; it brings nutrient-rich soil from below to the surface; it lets roots penetrate deeply; it helps the soil retain moisture; and it uproots weeds. The field is then levelled, so that irrigation water spreads evenly instead of collecting in hollows.
2. Sowing — placing the seeds in the soil.
Good quality seed is selected first, and damaged or hollow seeds are removed by putting them in water, where they float. Sowing is done either by broadcasting — scattering by hand — or with a seed drill pulled behind a tractor, which places seeds at a uniform depth and spacing, wastes less seed, and saves time.
3. Manuring — adding manure or fertiliser to replace the nutrients the previous crop removed. This is the subject of the next section.
4. Irrigation — supplying water at the right times.
Sources: wells and tube wells, canals, rivers, tanks and dams. Methods range from traditional ones — the moat or pulley system, the chain pump, the dhekli and the rahat — to modern ones:
- A sprinkler system, which sprays water over the crop and suits uneven ground and sandy soil
- Drip irrigation, which delivers water drop by drop directly at the roots through narrow pipes
Drip irrigation wastes the least water of any method, because almost nothing is lost to evaporation or run-off. It is the best choice wherever water is scarce.
5. Weeding — removing weeds, the unwanted plants that grow along with the crop.
Weeds matter because they compete with the crop for water, nutrients, light and space, and so reduce the yield. They are removed by uprooting by hand, with a khurpi, with a harrow, or by spraying chemical weedicides.
6. Harvesting — cutting the mature crop, with a sickle by hand or with a harvester.
Two operations follow it: threshing, the separation of grain from the chaff and stalks, done by a thresher; and winnowing, the separation of the lighter chaff by wind. A combine harvester does the cutting and threshing together.
Then storage, which is where a great deal of food is lost if done badly. Grain is dried thoroughly first, since moisture allows fungi and insects to attack it, and then kept in silos or granaries protected from damp, insects and rats. Dried neem leaves are a traditional protection.
Why the order cannot be changed. Each step prepares for the next: ploughing makes sowing possible, sowing makes irrigation worthwhile, and weeding must happen while the crop is still growing. Harvesting before the crop is mature gives poor grain, and harvesting late loses it to the weather.
1. Ploughing, also called tilling — turning and loosening the soil with a plough or cultivator.
Its purposes: it lets air into the soil for the roots and soil organisms; it brings nutrient-rich soil from below to the surface; it lets roots penetrate deeply; it helps the soil retain moisture; and it uproots weeds. The field is then levelled, so that irrigation water spreads evenly instead of collecting in hollows.
2. Sowing — placing the seeds in the soil.
Good quality seed is selected first, and damaged or hollow seeds are removed by putting them in water, where they float. Sowing is done either by broadcasting — scattering by hand — or with a seed drill pulled behind a tractor, which places seeds at a uniform depth and spacing, wastes less seed, and saves time.
3. Manuring — adding manure or fertiliser to replace the nutrients the previous crop removed. This is the subject of the next section.
4. Irrigation — supplying water at the right times.
Sources: wells and tube wells, canals, rivers, tanks and dams. Methods range from traditional ones — the moat or pulley system, the chain pump, the dhekli and the rahat — to modern ones:
- A sprinkler system, which sprays water over the crop and suits uneven ground and sandy soil
- Drip irrigation, which delivers water drop by drop directly at the roots through narrow pipes
Drip irrigation wastes the least water of any method, because almost nothing is lost to evaporation or run-off. It is the best choice wherever water is scarce.
5. Weeding — removing weeds, the unwanted plants that grow along with the crop.
Weeds matter because they compete with the crop for water, nutrients, light and space, and so reduce the yield. They are removed by uprooting by hand, with a khurpi, with a harrow, or by spraying chemical weedicides.
6. Harvesting — cutting the mature crop, with a sickle by hand or with a harvester.
Two operations follow it: threshing, the separation of grain from the chaff and stalks, done by a thresher; and winnowing, the separation of the lighter chaff by wind. A combine harvester does the cutting and threshing together.
Then storage, which is where a great deal of food is lost if done badly. Grain is dried thoroughly first, since moisture allows fungi and insects to attack it, and then kept in silos or granaries protected from damp, insects and rats. Dried neem leaves are a traditional protection.
Why the order cannot be changed. Each step prepares for the next: ploughing makes sowing possible, sowing makes irrigation worthwhile, and weeding must happen while the crop is still growing. Harvesting before the crop is mature gives poor grain, and harvesting late loses it to the weather.
Is manure better than chemical fertiliser, and what is crop rotation?
Each is better at a different thing, which is why good farming uses both.
Manure is a natural substance formed by the decomposition of plant and animal waste — cow dung, crop residues, kitchen waste — by the action of bacteria and fungi. It is prepared by composting, or by vermicomposting, which uses earthworms.
- It adds a large quantity of organic matter (humus), which improves the soil's texture, its water-holding capacity and its aeration
- Its nutrient content is low, so a large quantity is needed
- It acts slowly
- It is cheap, can be made on the farm, and causes no pollution
Chemical fertiliser is a manufactured inorganic substance rich in one or more specific nutrients — urea and ammonium sulphate for nitrogen, superphosphate for phosphorus, potash for potassium, and mixed NPK fertilisers.
- Its nutrient content is high and specific, so a small quantity suffices
- It acts quickly and raises the yield markedly
- It adds no humus, so the soil's texture deteriorates with continued use
- Excess use makes soil less fertile, harms soil organisms including earthworms, and runs off into water, causing water pollution
- It is costly
So the honest comparison is this. Fertiliser feeds the crop; manure feeds the soil. A field given only fertiliser produces well for some seasons and then degrades, because nothing has maintained its structure. A field given only manure keeps good soil but may not yield enough to be worth farming.
Crop rotation is the practice of growing different crops in a planned sequence in the same field in successive seasons, instead of the same crop every time.
The standard pattern alternates a cereal — which takes a great deal of nitrogen out of the soil — with a leguminous crop such as gram, moong or peas.
Why the legume matters. Leguminous plants carry root nodules containing Rhizobium bacteria, which take nitrogen from the air and convert it into compounds the plant can use. When the crop is harvested, the nodules and roots decay and that nitrogen stays in the soil.
What crop rotation achieves:
- Maintains soil fertility naturally, and reduces the need for fertiliser
- Breaks the life cycle of pests and diseases, which build up when one crop is grown repeatedly
- Uses different soil depths, since different crops root to different levels
- Reduces the risk of total loss, since not everything depends on one crop
Which is the point of the whole section. A farmer can buy nitrogen in a bag, or can grow a crop that puts it there for free and gives a harvest of pulses as well. That is why crop rotation appears in a chapter about soil fertility rather than one about planning.
Manure is a natural substance formed by the decomposition of plant and animal waste — cow dung, crop residues, kitchen waste — by the action of bacteria and fungi. It is prepared by composting, or by vermicomposting, which uses earthworms.
- It adds a large quantity of organic matter (humus), which improves the soil's texture, its water-holding capacity and its aeration
- Its nutrient content is low, so a large quantity is needed
- It acts slowly
- It is cheap, can be made on the farm, and causes no pollution
Chemical fertiliser is a manufactured inorganic substance rich in one or more specific nutrients — urea and ammonium sulphate for nitrogen, superphosphate for phosphorus, potash for potassium, and mixed NPK fertilisers.
- Its nutrient content is high and specific, so a small quantity suffices
- It acts quickly and raises the yield markedly
- It adds no humus, so the soil's texture deteriorates with continued use
- Excess use makes soil less fertile, harms soil organisms including earthworms, and runs off into water, causing water pollution
- It is costly
So the honest comparison is this. Fertiliser feeds the crop; manure feeds the soil. A field given only fertiliser produces well for some seasons and then degrades, because nothing has maintained its structure. A field given only manure keeps good soil but may not yield enough to be worth farming.
Crop rotation is the practice of growing different crops in a planned sequence in the same field in successive seasons, instead of the same crop every time.
The standard pattern alternates a cereal — which takes a great deal of nitrogen out of the soil — with a leguminous crop such as gram, moong or peas.
Why the legume matters. Leguminous plants carry root nodules containing Rhizobium bacteria, which take nitrogen from the air and convert it into compounds the plant can use. When the crop is harvested, the nodules and roots decay and that nitrogen stays in the soil.
What crop rotation achieves:
- Maintains soil fertility naturally, and reduces the need for fertiliser
- Breaks the life cycle of pests and diseases, which build up when one crop is grown repeatedly
- Uses different soil depths, since different crops root to different levels
- Reduces the risk of total loss, since not everything depends on one crop
Which is the point of the whole section. A farmer can buy nitrogen in a bag, or can grow a crop that puts it there for free and gives a harvest of pulses as well. That is why crop rotation appears in a chapter about soil fertility rather than one about planning.
What was the Green Revolution, and what is organic farming?
The Green Revolution was a programme that greatly increased India's production of food grains, particularly wheat and rice, by combining several changes at once:
- High-yielding varieties (HYV) of seed, bred to give far more grain per plant
- Assured irrigation, through canals and tube wells, so the crop no longer depended on the rains
- Chemical fertilisers, to supply the heavy nutrient demand of the new varieties
- Pesticides, to protect a dense uniform crop
- Mechanisation — tractors, threshers and harvesters
Its great achievement was to make India self-sufficient in food grains, ending dependence on imports to feed the population.
Why all five changes were needed together. A high-yielding variety produces more grain only if it is given more water and more nutrients. Given the old amounts it performs no better than the old seed. This is why the programme could not be adopted piecemeal, and why it succeeded first in the well-irrigated regions and much less in the dry ones.
Its drawbacks, which became clear later:
- Heavy chemical use damaged soil structure and polluted water
- Groundwater levels fell where tube wells were used intensively
- Loss of crop diversity, as many traditional local varieties were abandoned for a few high-yielding ones
- Pesticide residues in food, and pests becoming resistant
- The benefits were unevenly distributed between regions and between large and small farmers
Organic farming is farming without synthetic fertilisers, pesticides or growth regulators, relying instead on:
- Manure, compost and vermicompost
- Biofertilisers — cultures of nitrogen-fixing bacteria and blue-green algae
- Crop rotation and mixed cropping
- Biological pest control — using neem preparations, and encouraging natural predators such as ladybird beetles that eat crop pests
Its advantages: healthier soil with a better structure, no chemical residue in the food, no water pollution, lower and mostly on-farm input costs, and a system that can continue indefinitely — which is what sustainable means.
Its difficulties: the yield is often lower, especially in the first few years while the soil recovers; it needs more labour and knowledge; and produce needs certification to be sold at a premium.
The comparison worth making. The Green Revolution solved the problem of not enough food, and did so decisively. Organic farming addresses the problem the Green Revolution created — soil and water damage over the long term. They are answers to different questions, and which matters more depends on whether a country is short of food or short of good soil.
- High-yielding varieties (HYV) of seed, bred to give far more grain per plant
- Assured irrigation, through canals and tube wells, so the crop no longer depended on the rains
- Chemical fertilisers, to supply the heavy nutrient demand of the new varieties
- Pesticides, to protect a dense uniform crop
- Mechanisation — tractors, threshers and harvesters
Its great achievement was to make India self-sufficient in food grains, ending dependence on imports to feed the population.
Why all five changes were needed together. A high-yielding variety produces more grain only if it is given more water and more nutrients. Given the old amounts it performs no better than the old seed. This is why the programme could not be adopted piecemeal, and why it succeeded first in the well-irrigated regions and much less in the dry ones.
Its drawbacks, which became clear later:
- Heavy chemical use damaged soil structure and polluted water
- Groundwater levels fell where tube wells were used intensively
- Loss of crop diversity, as many traditional local varieties were abandoned for a few high-yielding ones
- Pesticide residues in food, and pests becoming resistant
- The benefits were unevenly distributed between regions and between large and small farmers
Organic farming is farming without synthetic fertilisers, pesticides or growth regulators, relying instead on:
- Manure, compost and vermicompost
- Biofertilisers — cultures of nitrogen-fixing bacteria and blue-green algae
- Crop rotation and mixed cropping
- Biological pest control — using neem preparations, and encouraging natural predators such as ladybird beetles that eat crop pests
Its advantages: healthier soil with a better structure, no chemical residue in the food, no water pollution, lower and mostly on-farm input costs, and a system that can continue indefinitely — which is what sustainable means.
Its difficulties: the yield is often lower, especially in the first few years while the soil recovers; it needs more labour and knowledge; and produce needs certification to be sold at a premium.
The comparison worth making. The Green Revolution solved the problem of not enough food, and did so decisively. Organic farming addresses the problem the Green Revolution created — soil and water damage over the long term. They are answers to different questions, and which matters more depends on whether a country is short of food or short of good soil.
Exam tip
Exam tip: give the purpose of each practice, not just the name
Every agricultural practice is marked on its purpose. Ploughing loosens the soil so air enters, roots penetrate and nutrient-rich soil is brought up earns the mark; ploughing means digging the field does not.
Name kharif and rabi crops correctly, with at least two examples each — rice, maize, cotton, groundnut for kharif; wheat, gram, peas, mustard for rabi. Give the season and the water need.
For manure versus fertiliser, answer in pairs across the four points — nutrient content, quantity needed, effect on soil texture, and cost or pollution. The key line is that fertiliser feeds the crop while manure feeds the soil.
For crop rotation, name the leguminous crop and Rhizobium bacteria in the root nodules, and say they fix atmospheric nitrogen. Without those words the answer is incomplete.
Say drip irrigation wastes the least water and explain why — delivered at the roots, so little is lost to evaporation.
Distinguish threshing (separating grain from chaff) from winnowing (separating chaff by wind). These are two separate one-mark answers.
For the Green Revolution, name high-yielding varieties, irrigation, fertilisers, pesticides and mechanisation together, and give its achievement — self-sufficiency in food grains — as well as its drawbacks.
And for organic farming, give the substitutes it uses, not merely what it avoids.
Name kharif and rabi crops correctly, with at least two examples each — rice, maize, cotton, groundnut for kharif; wheat, gram, peas, mustard for rabi. Give the season and the water need.
For manure versus fertiliser, answer in pairs across the four points — nutrient content, quantity needed, effect on soil texture, and cost or pollution. The key line is that fertiliser feeds the crop while manure feeds the soil.
For crop rotation, name the leguminous crop and Rhizobium bacteria in the root nodules, and say they fix atmospheric nitrogen. Without those words the answer is incomplete.
Say drip irrigation wastes the least water and explain why — delivered at the roots, so little is lost to evaporation.
Distinguish threshing (separating grain from chaff) from winnowing (separating chaff by wind). These are two separate one-mark answers.
For the Green Revolution, name high-yielding varieties, irrigation, fertilisers, pesticides and mechanisation together, and give its achievement — self-sufficiency in food grains — as well as its drawbacks.
And for organic farming, give the substitutes it uses, not merely what it avoids.
Did you know
Why do pulses grow well in poor soil?
Nitrogen is the nutrient crops run short of first, and the air around us is nearly four-fifths nitrogen. Yet no ordinary plant can use a molecule of it, because the two nitrogen atoms are bound together too tightly for a plant to separate.
Leguminous plants get round this by subcontracting. Their roots grow small swellings — nodules — and inside those nodules live Rhizobium bacteria, which can break nitrogen molecules apart. The bacteria convert the nitrogen into compounds the plant absorbs, and the plant supplies them with food and shelter in return. Neither partner could do it alone.
So a gram or moong plant carries its own nitrogen supply and does not need the soil to provide it — which is exactly why pulses grow on land too poor for wheat.
And the arrangement outlasts the crop. When the plant is harvested, the nodules decay in the soil and release their nitrogen for whatever is planted next. A field that has grown pulses is measurably richer than one that has not, which is a return no bag of fertiliser gives for free.
Leguminous plants get round this by subcontracting. Their roots grow small swellings — nodules — and inside those nodules live Rhizobium bacteria, which can break nitrogen molecules apart. The bacteria convert the nitrogen into compounds the plant absorbs, and the plant supplies them with food and shelter in return. Neither partner could do it alone.
So a gram or moong plant carries its own nitrogen supply and does not need the soil to provide it — which is exactly why pulses grow on land too poor for wheat.
And the arrangement outlasts the crop. When the plant is harvested, the nodules decay in the soil and release their nitrogen for whatever is planted next. A field that has grown pulses is measurably richer than one that has not, which is a return no bag of fertiliser gives for free.
Key takeaways
Crops, farming practices and soil fertility: quick revision
- Kharif crops are sown at the onset of the monsoon and harvested at the end of the rains, needing plenty of water — rice, maize, jowar, bajra, cotton, groundnut, soybean, moong.
- Rabi crops are sown at the start of winter and harvested in spring, needing less water and usually irrigation — wheat, gram, peas, mustard, barley, linseed. A short zaid season carries melons and cucumber.
- Rice needs a flooded field; wheat needs a cool season — which is why one field can give two crops a year.
- Six practices — ploughing (loosens soil, lets air in, brings up nutrients, allows root growth), then levelling; sowing by broadcasting or a seed drill (uniform depth and spacing); manuring; irrigation; weeding; harvesting.
- Damaged seeds are removed because they float in water.
- Irrigation sources: wells, tube wells, canals, rivers, tanks, dams. Drip irrigation wastes the least water, delivering it at the roots.
- Weeds compete for water, nutrients, light and space, and reduce yield; removed by hand, khurpi, harrow or weedicides.
- After harvesting come threshing (grain from chaff) and winnowing (chaff separated by wind); a combine does both. Grain is dried before storage in silos or granaries.
- Manure — natural, from decomposed waste by composting or vermicomposting; adds humus, improving texture, water-holding and aeration; low nutrient content, large quantity, slow, cheap, no pollution.
- Chemical fertiliser — manufactured, high and specific nutrient content (urea, superphosphate, potash, NPK); small quantity, fast, raises yield; adds no humus, degrades soil, pollutes water, costly.
- Fertiliser feeds the crop; manure feeds the soil.
- Crop rotation grows different crops in sequence, alternating a cereal with a legume whose root nodules hold Rhizobium bacteria that fix atmospheric nitrogen. It maintains fertility, cuts fertiliser use, breaks pest cycles and uses different soil depths.
- The Green Revolution combined high-yielding varieties, irrigation, fertilisers, pesticides and mechanisation, making India self-sufficient in food grains. Its drawbacks: soil and water damage, falling groundwater, loss of crop diversity, pesticide residues, and uneven benefits.
- Organic farming replaces chemicals with manure, compost, vermicompost, biofertilisers, crop rotation and biological pest control (neem, ladybird beetles). It gives healthier soil and residue-free food, but often a lower yield and more labour.
Try listing the six practices with a purpose for each, then writing the manure-versus-fertiliser comparison in pairs — those two answers cover most of what this chapter asks.
- Rabi crops are sown at the start of winter and harvested in spring, needing less water and usually irrigation — wheat, gram, peas, mustard, barley, linseed. A short zaid season carries melons and cucumber.
- Rice needs a flooded field; wheat needs a cool season — which is why one field can give two crops a year.
- Six practices — ploughing (loosens soil, lets air in, brings up nutrients, allows root growth), then levelling; sowing by broadcasting or a seed drill (uniform depth and spacing); manuring; irrigation; weeding; harvesting.
- Damaged seeds are removed because they float in water.
- Irrigation sources: wells, tube wells, canals, rivers, tanks, dams. Drip irrigation wastes the least water, delivering it at the roots.
- Weeds compete for water, nutrients, light and space, and reduce yield; removed by hand, khurpi, harrow or weedicides.
- After harvesting come threshing (grain from chaff) and winnowing (chaff separated by wind); a combine does both. Grain is dried before storage in silos or granaries.
- Manure — natural, from decomposed waste by composting or vermicomposting; adds humus, improving texture, water-holding and aeration; low nutrient content, large quantity, slow, cheap, no pollution.
- Chemical fertiliser — manufactured, high and specific nutrient content (urea, superphosphate, potash, NPK); small quantity, fast, raises yield; adds no humus, degrades soil, pollutes water, costly.
- Fertiliser feeds the crop; manure feeds the soil.
- Crop rotation grows different crops in sequence, alternating a cereal with a legume whose root nodules hold Rhizobium bacteria that fix atmospheric nitrogen. It maintains fertility, cuts fertiliser use, breaks pest cycles and uses different soil depths.
- The Green Revolution combined high-yielding varieties, irrigation, fertilisers, pesticides and mechanisation, making India self-sufficient in food grains. Its drawbacks: soil and water damage, falling groundwater, loss of crop diversity, pesticide residues, and uneven benefits.
- Organic farming replaces chemicals with manure, compost, vermicompost, biofertilisers, crop rotation and biological pest control (neem, ladybird beetles). It gives healthier soil and residue-free food, but often a lower yield and more labour.
Try listing the six practices with a purpose for each, then writing the manure-versus-fertiliser comparison in pairs — those two answers cover most of what this chapter asks.