Lecture
Chemicalization of agriculture is the introduction of chemical industry products into agricultural production in order to increase its efficiency. Such chemical industry products include: mineral fertilizers, pesticides, chemical ameliorants, artificial substrates and polymer films in protected-ground technologies, feed additives and veterinary preparations in livestock farming, and preservatives for food safekeeping.
Mineral fertilizers and chemical ameliorants are used to increase soil fertility and improve the quality of agricultural produce.
Mineral fertilizers are chemical compounds containing the chemical elements needed for plant nutrition. As you already know from the material of § 40, plants most often lack such biologically important elements as nitrogen, potassium, and phosphorus, which is made up for with simple or compound nitrogen, potassium, and phosphorus fertilizers. In addition, plants have a high need for calcium, magnesium, sulfur, and iron. Like nitrogen, potassium, and phosphorus, these are classified as macronutrients.
Plants need much smaller amounts of elements such as Fe, Mn, Zn, Cu, Co, Na, Mo, B, and I. Na, Si, Se, Cl, Ni, and others are also required in lesser amounts. These are called micronutrients. They strengthen plant immunity, prevent the onset of disease, and speed up a number of biochemical reactions.
To improve the acid-base properties of soils, they undergo chemical amelioration — the addition of substances that regulate pH. This is necessary because the vast majority of agricultural crops can develop and bear fruit well only in soils with a neutral or near-neutral environment. When grown on acidic soils, plants take up nitrogen, phosphorus, potassium, and other elements less efficiently, root system development and metabolism in the roots are hindered, and the activity of beneficial microorganisms is suppressed.
To eliminate excess soil acidity, ameliorants are applied. Soil acidity can be lowered, that is, its pH raised, by adding calcium hydroxide, known as slaked lime, or fluff lime, dolomite CaMg(CO3)2, cement dust, ground chalk or limestone (CaCO₃), or wood ash (CaCO3, CaSiO3, K3PO4, Na3PO4).
For example, insoluble calcium carbonate, under the influence of СО2 present in the soil, gradually converts into soluble Са(НСО3)2:
СаСО3 + СО2 + Н2О = Са(НСО3)2.
The resulting bicarbonate ions neutralize the acidic environment:
+ H+ 
H2O + CO2.
The combined effects of diseases, pests, and weeds lead to crop losses. Plant disease agents include fungi, nematodes (worms), bacteria, and viruses.
Pesticides are a large group of chemical substances used to protect plants. Modern pesticides are complex organic substances. They have toxic properties toward bacteria, fungi, harmful insects, some types of weeds, and warm-blooded animals. Pesticides also include substances that cause changes in cultivated plants desirable to humans: growth regulators and defoliants.
Growth regulators are used to suppress the growth of plants and insects that are undesirable in agriculture.
Defoliants cause premature aging and shedding of leaves ("artificial leaf fall"), which makes harvesting easier.
Fungicides are chemical substances for combating fungal plant diseases. As you already know, crystalline hydrates of copper(II) and iron(II) sulfates are used to treat plants and wood to protect against fungal diseases.
It must be remembered that many chemical crop protection agents are toxic substances, or agrochemical poisons. To one degree or another, they can cause harm to the environment and human health. Therefore, they must be used with great care: they can enter the human and farm-animal body with water and food. However, they cannot be given up entirely, since their use makes it possible to supply the constantly growing population of our planet with food and other products. For human safety and the protection of natural resources, monitoring must be established for the content and accumulation of chemical crop protection agents in the environment and in food products.
Insecticides are chemical preparations intended for destroying harmful insects and protecting plants, humans, and animals from them.
Pheromones are pesticides that are practically harmless to humans. These are volatile substances released by animals, insects, and sometimes plants, which provide communication between individuals of the same species. They modify the behavior, physiological, or emotional state of other individuals of the same species. Unlike insecticides, they have no toxic effect on animals or the environment. Pheromones that attract insects make it possible to destroy significant numbers of pests. Scientists have learned to synthesize many insect pheromones artificially.
Cleanliness is the key to health for both humans and domestic animals. That is why chemists have developed chemical agents for disinfecting the premises where animals are kept, feeders, drinkers and other animal care equipment, dairy equipment, vehicles for transporting animals, and so on.
Such agents include: bleaching powder — a mixture of Са(СlO)2, СаСl2, Са(ОН)2; sodium hypochlorite (NaClO); slaked lime (Са(ОН)2); soda ash (Na2CО3); caustic soda (NaOH); formalin (СН2О); baking soda (NaHCО3); potassium permanganate (KMnO4); phenol (С6H5OH).
High-quality feed, balanced in all nutrients, is necessary for obtaining high productivity indicators in farm animals. To produce such feed, a large number of diverse components must be used. It is especially difficult to balance finished feed in terms of vitamin, mineral, and essential amino acid content. Balancing feed with premixes is the optimal solution.
Premixes are vitamin-mineral additives for compound feed that contain all the vitamins, micro- and macronutrients an animal's body needs. In addition to biologically active substances, premixes include a filler — bran, crushed grain or its processing products, oilcake, feed yeast, and the like. The qualitative and quantitative composition of feed additives is adjusted depending on the species of animal, its breed, age, and the local raw material used as filler.
Chemicalization of agriculture is the introduction of chemical industry products into agricultural production in order to increase its efficiency.
Mineral fertilizers, feed additives, pesticides (insecticides, pheromones, fungicides, herbicides, etc.), and disinfectant preparations are widely used in agriculture.
1. Give three examples of chemical substances used in the care of animals and plants in your family.
2. Explain the need for, and name, methods for combating increased soil acidity. Propose a method for determining soil acidity.
3. Explain what the disinfecting action of bleaching powder, potassium permanganate, and sodium hydroxide is based on.
4. Every year, more than 3 million tons of phosphorus are carried away from fields worldwide together with the harvest. Calculate how many tons of phosphorus-containing ore must be processed to make up for the phosphorus losses. Take the phosphorus content of the ore, expressed as Р2О5, to be 41%. Disregard losses during ore processing.
5. For disinfecting farm premises, the preparation "Formalin," a 40% solution of methanal, can be used. Calculate the volume of "Formalin" needed to disinfect the floor and walls of a pig house measuring 12 × 76 × 6 m3, given a consumption rate of 0.5 dm3 of a 6% solution per 1 m2 for disinfection. The density of the 40% methanal solution is 1.111 g/cm3; that of the 6% solution is 1.017 g/cm3.
6. Bordeaux mixture (a mixture of copper sulfate and freshly slaked lime in a mass ratio of 1 : 0.75) is used to effectively combat apple scab. Its application rate, calculated on copper sulfate, is 20 kg/ha of apple orchard. Calculate the mass of components needed to prepare Bordeaux mixture for treating 2 ha of apple orchard. Can Bordeaux mixture be prepared in tanks:
7. It is generally accepted that the content of the nutrient element in nitrogen fertilizers is calculated in terms of elemental nitrogen, in phosphorus fertilizers in terms of Р2О5, and in potassium fertilizers in terms of K2O. Estimate, as a percentage, the content of nutrient elements in the pure:
8. In what mass ratio should the nitrogen fertilizers (NH4NO3, (NH2)2CO, KNO3) be used so that their nitrogen content is the same?
9. An effective way to increase the yield of various crops is to use compound fertilizers containing two or three nutrient elements. Calculate the mass ratio in which ammonium nitrate (NH4NO3), double superphosphate (Ca(H2PO4)2 · H2O), and potassium chloride (KCl) must be mixed so that the mass ratio of nutrient elements in the resulting fertilizer is: m(N) : m(P2O5) : m(K2O) = 1 : 2 : 2. In what mass ratio should ammophos (NH4H2PO4), carbamide ((NH2)2CO), and potassium chloride KCl be mixed so that the ratio of nutrient elements remains the same?
10. Boron, molybdenum, and manganese are micronutrients required for plant nutrition. Their content (by mass) in industrially produced superphosphate (Ca(H2PO4)2 · H2O) is: 0.2% B, 0.13% Mo, 1.5% Mn. Calculate the masses of H3BO3, (NH4)2MoO4, and MnSO4 · 5H2O that must be added to 500 kg of superphosphate to obtain the stated micronutrient content in it.
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