Biology || Class VIII || Crop Production & Management [ Part 2]

追加: 2026-05-20

[00:00:06]Hello students.

[00:00:08]Today we are going to learn about the second part of the chapter crop production and management. We have learned the first chapter earlier. You have the first video on that where you have learned about the different ways by which the crop bed or the field is prepared before the seeds are sown.

[00:00:27]Today what we are going to learn is from thereafter. How the seeds are sown, what happens after the seeds are sown, what are the different ways by which the fertility of the soil is improved. So all this will be covered in today's video. So let us move on to the first slide.

[00:00:45]We will start with sowing seeds. How are the seeds sown? You can see the seeds sown in a field in a particular manner.

[00:00:54]That means there must be some thought process going on behind the planting of seeds. We will see this one by one.

[00:01:07]So what is this that is being shown over here? It says the precautions to be taken.

[00:01:14]What are the precautions that has to be taken before the seeds are sown? So the first precaution before the seeds are to be sown is that you have to take healthy seeds for sowing.

[00:01:28]Healthy seeds are to be taken and the sick seeds or the unhealthy seeds, the infected seeds are to be discarded.

[00:01:38]But how are you going to distinguish between what is a good seed and what is not a good seed? So the best thing to do is before presume I'm a farmer. So before I start sowing seeds, what I'll do is I'll take the seeds and put them in a bowl of water.

[00:01:54]Right? Those seeds which are healthy, they are intact, so they will sink down.

[00:02:00]The unhealthy ones, the infected ones, the ones that have holes inside them, they will gradually float on the top.

[00:02:08]So, I will clearly be able to distinguish which are the ones which are floating on the top. That means the unhealthy ones. So, what will I do? I will discard these seeds and then take the healthy seeds which are at the bottom of the container and then start by sowing the seeds.

[00:02:26]Okay? Now, let us see what are the different ways by which the seeds are sown. But again, before that, couple of more two more precautions.

[00:02:35]So, healthy seeds are to be taken. Then, seeds have to be sown at the right depth.

[00:02:49]So, say, if I take some seeds and simply scatter them on the top of the field, what will happen? Birds may come and eat them. Rats may eat them. Then, uh you know, if there's a strong wind or if there's a rain, then these seeds may be carried away to a different place. Not only that, they may be dried up by the heat of the sun. So, keeping them on the on the um field is not a very good option, not a very intelligent option. So, I have to sow them little deep into the soil. But how deep?

[00:03:21]So, on the top or right under the top is ruled away. Because because then the seeds become susceptible to drying up by the sun or they may be eaten up by the insects or the birds. So, I'm going to sow them at a certain distance under the soil. So, suppose if this is the soil, the surface of the soil, if I sow them here or very close to a soil surface, you know, it is a wrong practice. So, these two are ruled out.

[00:03:54]Fine? Now, if I sow them very deep under the soil, you know, this area deep inside the soil, here there is no oxygen. So, the small baby plant inside the seed will not be able to breathe and will hence die. Not only that, you know, these small roots, even if they come out, even if the small shoot comes out, they will find it very difficult, the shoot, because it's a small young shoot, it's very soft and very delicate, it will find it very difficult to make its way up and come to the top. Likewise, the root also being very soft and delicate will find it very difficult to make its way through into the hard rocks that are there deep inside. That means, when you sow a seed very deep into the soil, this is also not a good option.

[00:04:48]So, what is another thing to do? Sow it at a proper depth.

[00:04:53]Little under the soil, so that it is neither, you know, picked up by the rats or the birds, it is protected from the heat of the sun, it is protected from strong wind or a rainfall, and at the same time, it is placed in such a depth where the roots or the small baby plant coming out will get enough oxygen and the shoot and the root will be able to easily grow on the top and towards the bottom, respectively. That means, I have to sow the seed at this this distance, and this is the right depth under the soil where the seeds have to be sown. Sown. Next is, the seeds should be sown sown at the right interval.

[00:05:45]That means, the gap between the seeds should be should be taken care of. How? Suppose for example, this is the surface of the soil.

[00:05:59]I place two seeds very close to each other.

[00:06:04]Right?

[00:06:07]Then I place two seeds somewhat distance from each other.

[00:06:13]And then I place two seeds very far away from each other.

[00:06:18]See, so this is one set. This is another set. This is the third set. In the first set, what happens? In the first set, where the seeds are very close to each other, the root, when they come out, they will start they will start competing with each other for nutrients, water, space. So with the shoots, they will start fighting, they will start competing with each other. So hence, none of these small plants will be able to grow properly, and hence this is a bad option.

[00:06:53]Okay? Coming to the second case, in the second case, there is enough space for the root to grow down, for the branches to come out, for the shoot to go up, and for the leaves to come out and make food for the plant by performing photosynthesis in a proper manner.

[00:07:15]In the In the last case, in the third case, there is no problem as such, but the only drawback is this. Here, if you keep the seeds so far away from each other, then there is an unnecessary wastage of space. Hence, this is also ruled out.

[00:07:31]So this is the right gapping, and this is the right depth under which the seeds have to be sown. So these precautions have to be taken in mind by the farmer when he is sowing seeds. Now, let us come to the actual ways of sowing seeds.

[00:07:47]Let us see these.

[00:07:49]So, you see these are the different methods by which the seeds are sown. Let me name them one by one.

[00:07:56]In this case, the farmer has taken the seeds and he's simply scattering them on the field. This is manual scattering on the field. So, this method is called broadcasting.

[00:08:11]It's called broadcasting.

[00:08:14]Here, the farmer is simply planting the seed on the soil and hence this process is called manual planting.

[00:08:30]In the third case, you find it is a machine which is sowing the seed. So, this machine is called a seed drill.

[00:08:40]It is used to make holes and put seeds into the soil. And this last process, it is very interesting. This is known as transplantation.

[00:08:55]It's called transplantation.

[00:08:58]So, these are the different ways by which commonly seeds are sown. So, let us come to this uh topic so come to these types one by one.

[00:09:08]The first one is broadcasting where I told you the farmer takes the seeds and simply scatters them on the field.

[00:09:14]Problem with this is that the seeds lie on the top. So, if you go back to the precautions that we have learned about, by the method of broadcasting, the second point, that means seeds should be sown at the right depth, this cannot be maintained. And the last point, seeds should be sown at the right interval, that also cannot be maintained. So, So means in this case, in case of broadcasting, the seeds are susceptible to being damaged by birds, rats, wind, rainfall, all this.

[00:09:46]Okay? Coming to manual planting, manual planting, the farmer need not put them on the top. He can make little bit small holes and plant them inside the soil. But again, in this case, it's a tiresome process. It's a time-consuming process. And since it is done by hand, exactly the gap between the seeds or the right depth under the seed is very difficult to ensure.

[00:10:12]Let us go to the third one. What is the third technique? Here, you find that these compartments which you see over here, these blocks, these blocks are actually shaped like a funnel.

[00:10:25]Right? And through these funnels, you add seeds on the top of the funnel. And through the funnel, seeds come out one at a time. That means, each of these, they have got funnels.

[00:10:38]They have got these cone-shaped structures through which seeds come out.

[00:10:42]But the seeds come out one at a time.

[00:10:46]Many seeds don't come out at the same time. So what but and you see this is connected to a tractor. So as the tractor moves, the seeds are dropped ensuring that the gap between the seeds is correct. Also, they are falling under the right depth. So this is a very, very sophisticated manner of sowing seeds, that is by using a machine called a seed drill.

[00:11:10]Now, the last one, transplantation, it is very common in our uh state which is West Bengal, especially in paddy cultivation. What happens here is that these small paddy plants, that means the rice plants, when they are small, they are first the seeds are sown in small in small fields which are called seed beds or nurseries.

[00:11:35]These are called seed beds or nurseries.

[00:11:41]Right? Now, when the seeds have developed into small seedlings, when the small baby plant has come out of them, then what does the farmer do? The farmer takes these seedlings from the seed bed or the nursery and takes them to the main field where the small plants are planted once again. So, that is called transplantation where the seeds are carried from here and then planted onto the main field.

[00:12:12]Why is this done? This is because if you see in the picture, this field has a lot of water in it. Paddy requires a lot of water throughout its entire course of germination and then its subsequent growth also into a into a mature plant.

[00:12:28]So, a lot of water In fact, the field has to be flooded with water.

[00:12:32]So, in such a waterlogged soil, if you sow seeds, you know that seeds will not be able to grow because there will be hardly any air in the soil. Hence, what is done is the seeds are first made to grow into small seedlings in a proper field in a small field which is called a seed bed or a nursery. Then, when they have become small plants, then those small plants or the seedlings are taken out and they are replanted on the main field which is flooded with water.

[00:13:05]The advantage of this is that here, when the farmer is picking up the seedlings from the seed bed or the nursery, he knows which are the ones which are going to grow into healthy plants. So, the ones that are not going to grow into healthy plants, the ones that look weak, somehow infected, so those plants can immediately be discarded. So, the farmer can ensure that almost all his plants which he has transplanted into the main field will grow into a good crop. Okay?

[00:13:38]So, these are the different ways by which seeds are sown in the main field.

[00:13:44]See, this is a seed drill. This is how a seed drill looks like. And this seed drill, each of these they have a funnel.

[00:13:52]And when the seed drill is drilled on the field, as the seed drill moves, what will happen? The seeds are dropped at regular intervals from each other and also at the right depth under the soil.

[00:14:06]This is a picture of transplantation.

[00:14:08]It's a clearer view where a seedling is See, the seedling is picked up from a nursery bed and it is replanted onto the main field. This shows the process of transplantation.

[00:14:21]Okay? So, this basically was how the seeds are sown. First thing is the farmer has to be careful about the seeds that he's selecting. Then, the depth under the soil where the seeds are sown and the gaping between the seeds when the seeds are sown. And then, there are these processes by which the farmer There are so many ways by which the seeds can be sown and the farmer can ensure a good growth.

[00:14:49]Now, this is about sowing seeds. What is the next step? The next step is adding manure or fertilizers to the field. Why?

[00:14:58]Why is this important? Manure and fertilizers are food for the soil and this food is going to be taken up by the plant for its growth. Okay?

[00:15:10]Manure provides organic materials to the soil. Fertilizers provide inorganic materials to the soil. Both organic as well as inorganic materials are required by the plant. And so, these can go into the plant and then that will help the plant grow healthy and produce a good a good produce, okay? So, we'll see about this manure.

[00:15:39]What is a manure? It is an organic material. That means something which has come from a living source. Maybe a plant source, maybe an animal source. And these have been piled up together and very fertile material is made which is called manure.

[00:15:57]It is an organic fertilizer.

[00:16:00]Fertilizer means which improves the fertility of the soil and is organic in nature, nothing chemical about it.

[00:16:06]Coming from or obtained from a living source and it is made from biodegradable domestic waste.

[00:16:14]Biodegradable domestic waste. Either domestic waste or agricultural waste.

[00:16:18]Whatever say vegetable peels, fruit peels, leftover food, egg shells, any biodegradable material. Say for example, the dead animals in a field or the crop residues. Once the crop has been cut, once the grains have been taken, then the remaining plant is a crop residue.

[00:16:37]So, all these can be used to make a manure. And this manure is full of organic substances which boosts the growth of plant. So, what are the types of manure? We have compost, vermicompost, and green manure. Let us see what these are one by one.

[00:17:02]See, this is a farmyard manure. I hope you know, this is nothing but cow dung and this works as an excellent manure for the field. It is full of organic substances which adds a lot of humus to the soil. Hence, it is very important for the growth of plants.

[00:17:21]What else?

[00:17:22]See, this person is preparing a compost.

[00:17:26]How is the compost being made? You can see all these vegetables, the peels of the vegetables, tea leaves, all these biodegradable waste that come out either from the house of the farmer or from his agricultural field. All these biodegradable waste, he can simply put them into a pit, cover the top, and let it rot.

[00:17:48]There are some very good bacteria and fungi, small microorganisms present over here, which will gradually break down these substances and convert all of this into a loose soil-like material. That is nothing but that's a compost or a manure, which can improve the fertility of the soil. So, this is about composting.

[00:18:13]This is a slightly different way of making a compost where you're using these creatures. What are these creatures? These creatures are nothing but earthworms.

[00:18:27]Or these are also called red worms commonly.

[00:18:32]Right? Earthworms or red worms, the same thing. You can use the same material as you use for composting. Only thing is you have to add the earthworms over here. Then what happens? The job of the earthworm is the earthworms can hasten the process of composting. It makes the process of composting faster. That is the reason why we add earthworms to the pit where the compost is made. Okay?

[00:18:58]Now, what is this? It's a green manure. See the word the name clearly says it is a green manure. Green means we are using all plants.

[00:19:15]We are not using their breakdown products. We are not making them rot.

[00:19:19]Right? They are normal plants, but they are grown for the purpose of producing manure to the plants.

[00:19:27]Now, how is this possible? See, all these plants that you see over here, Crotalaria juncea, Sesbania rostrata, cowpea, cluster bean, Sesbania aculeata, all these plants, they are you know, they have roots, and inside those roots, there are some very good bacteria present. Let's come to the green manure crops. Mark what it says. It says green manure.

[00:19:55]Right? It is not a manure. It is not something which looks brown like this farmyard manure, nor does it look like this, nor does it look like this, which is a vermicompost or a compost. Here, we are seeing proper plants. Plants which are used as manure. Yes, indeed. Here, these plants, Crotalaria, Sesbania, cowpea, cluster bean, Sesbania aculeata, all these are plants which are used as manure.

[00:20:27]How is that possible? Let us see. Now, these plants that you see, they, if you see their roots, suppose for example, this is the root of the plants.

[00:20:41]These are the branches. If you see the roots very carefully, you will find such swellings on them.

[00:20:49]Swellings.

[00:20:51]Just like a mosquito bite.

[00:20:54]You'll find such swellings on them. Now, what are these swellings called? These swellings are called the root nodules.

[00:21:04]These are called the root nodules. And in each of these nodules, you find millions of nitrogen-fixing bacteria.

[00:21:18]Millions of nitrogen-fixing bacteria in each of these nodules.

[00:21:27]Now, what do these bacteria do? Why are they called nitrogen-fixing? They are called nitrogen-fixing because these bacteria they can convert atmospheric nitrogen.

[00:21:39]You know, we have a lot of nitrogen in the atmosphere. So, they can convert atmospheric nitrogen into nitrates.

[00:21:51]All right? So, the root nodules over here, they have got millions of what bacteria? They have millions of nitrogen-fixing bacteria. And what do these nitrogen-fixing bacteria do? They take atmospheric nitrogen and convert them into nitrates. Okay? Now, when these plants are ready when they when these plants have matured, then they are harvested, they are cut, and then what happens is they are mixed along with the soil when the field is being plowed for the next season's cultivation. So, remember the first video? When you're plowing the field before sowing the seeds, during that time, these plants are cut into pieces and they are added to the soil.

[00:22:35]They are It's called mulching. They are mulched into the soil with the help of a plow, and that supplies a ready-made source of nitrates to the soil.

[00:22:46]Right? And these nitrates can now be used by the plants which are going to sow the seeds of subsequently, and these plants can take up these nitrates, and the nitrates will help in the good growth of the plants. That is why these plants are called green manure.

[00:23:04]Okay? Now, let us see this.

[00:23:10]This is nothing organic. It's all chemical. It's inorganic. And these are made in the factories by human beings.

[00:23:19]There's nothing natural about them. Only thing is these are rich source of substances or elements like potassium, phosphorus, and nitrogen.

[00:23:34]So, these inorganic chemicals are also very essential for the growth of plants.

[00:23:40]They not only need organic material.

[00:23:42]Organic material comes from manure or vermicompost or the green manure. That is for the organic part. What about the inorganic necessity of the plant? The inorganic necessity is filled by these uh chemicals which are called fertilizers. Fertilizers provide nitrogen, phosphorus, and potassium to the soil. Again, which is very important for plant growth.

[00:24:10]So, you've learned that manure is something which is organic, which comes from a organic source. That means which comes either from a plant or an animal.

[00:24:20]And a fertilizer is something which is made in the factories. Now, let us see the differences. A fertilizer is an inorganic salt. Whereas here, it's a natural substance obtained from the decomposition.

[00:24:35]Decomposition means by the breakdown of cattle dung, human wastes, plant residues. So, this is an organic product, whereas here, this is a inorganic product. Next, a fertilizer is prepared in the factories, whereas manure is prepared in the fields. Next, a fertilizer does not provide humus. I told you a fertilizer is not a source of organic material. It is meant to provide only inorganic chemicals, hence it does not provide any organic material. In other words, it does not provide any humus to the soil. Whereas manure, they provide a lot of humus to the soil.

[00:25:15]Okay? And see on the other side, fertilizers may not be providing humus, but what do they provide? They provide important nutrients. They provide important chemicals like nitrogen, phosphorus, and potassium. Whereas manures, they do not have so much of these chemicals. Manures, the job of manure is not to provide these chemicals, but to provide organic substance to the soil, which will not only help in the plant to grow, but will also improve the structure of the soil.

[00:25:47]Okay? So, another very important fertilizer. Now, this is a biofertilizer.

[00:26:01]Something living about this fertilizer.

[00:26:04]What is living? See, these are all bacteria.

[00:26:08]These are all bacteria or blue-green algae.

[00:26:12]As Azotobacter, Azospirillum, Rhizobium, all these are bacteria. And this is blue-green algae. So, what do they do?

[00:26:20]These are biofertilizers.

[00:26:22]That means these are bacterial preparations which can be bought by the farmers from these agricultural shops that they have in their villages. And this can be directly applied to the soil. These will immediately provide a source of nitrates to the soil. All these, they can fix up atmospheric nitrogen. They can fix up in the soil. They can fix up atmospheric nitrogen. They can take atmospheric nitrogen, convert them into nitrates, and thus provide a readymade source of nitrates to in the soil for the plants.

[00:26:57]So, with that we come to the end of the class today. I hope you have enjoyed the different ways by which the seeds are sown and the different ways by which the fertility of a soil can be improved. We will see more on this. We will come to the next part of the chapter. We will learn about irrigation and we will be learning about certain other agricultural practices like weeding, harvesting, storage, all that in the next video. Thank you. Have a nice day.