Agricultural Engineering · Foundations · also Crop Production and Protection Technologies, Horticultural and Field Crops, Agricultural and Fishery Sciences (PRC)
Enough agronomy to design for the crop: sowing geometry for planters, application rates for sprayers, moisture at harvest.
In the exams: Allied agricultural sciences in PRC ABE; core in the ICAR 6th Deans' Committee B.Tech
Crop production for engineers is the agronomy an agricultural engineer needs in order to design for the crop rather than around it. A planter is specified from a target plant population and a row spacing; a fertiliser spreader from a nutrient rate in kilograms per hectare and the grade of the product; a sprayer from a dose of active ingredient and a spray volume; a combine or dryer from the moisture at which the grain is cut and the moisture at which it can be stored. None of these numbers comes from mechanics. They come from the crop, its season, its growth stages and the way it is managed, and an engineer who cannot read them will build machines that work in the test track and fail in the field.
This manual covers the classification of crops and their seasons, crop growth stages and the stages most sensitive to stress, tillage and seedbed preparation, sowing methods with seed rate and plant population calculations, nutrient management and fertiliser arithmetic, crop water requirement and the basics of irrigation scheduling, the principles of weed, pest and disease management with the application-rate calculations a sprayer designer needs, harvest index, crop maturity and harvest moisture, the major cereals, pulses, oilseeds and cash crops with their mechanisation needs, cropping systems and conservation agriculture, and farming-based livelihood systems.
In India the subject is a first-year core course (Crop Production and Protection Technologies) under the ICAR Sixth Deans' Committee B.Tech curriculum, with a companion course on farming-based livelihood systems. In the Philippines it is part of the allied agricultural sciences examined in the Agricultural and Biosystems Engineers Licensure Examination. In Nepal's engineering registration syllabus it appears as crop, soil and watershed management, and in Japan's Professional Engineer agriculture division it sits beside plant protection and agricultural engineering. Everywhere, examiners ask for definitions, for the logic of a practice, and above all for short calculations: seeds per hectare, kilograms of product per hectare, litres per hectare, harvest index and moisture conversions.
Numbers in this manual are standard textbook values or worked illustrations. Seed rates, fertiliser doses, pesticide doses and safe moisture levels vary by country, variety, soil and product label; always take the operational figure from the local recommendation and the product label.
Crops are classified in several ways, and each one answers a different practical question. The agronomic or use classification groups crops by what is harvested: cereals (grasses grown for grain, such as rice, wheat, maize, barley, sorghum and the millets), pulses or grain legumes (chickpea, pigeonpea, lentil, field pea, mung bean, cowpea, common bean; soybean and groundnut are legumes usually grouped with oilseeds because of their use), oilseeds (rapeseed-mustard, sunflower, sesame, safflower, linseed, groundnut, soybean), fibre crops (cotton, jute, kenaf, flax), sugar crops (sugarcane, sugar beet), tuber and root crops (potato, cassava, sweet potato, yams), forage and fodder crops (berseem and other clovers, lucerne or alfalfa, fodder sorghum and maize, grasses), plantation crops (tea, coffee, rubber, oil palm, coconut) and horticultural crops (fruits, vegetables, flowers, spices).
Botanical classification uses families. The two most important families in field cropping are the Poaceae (grasses, which include all cereals and sugarcane) and the Fabaceae (legumes, which fix atmospheric nitrogen through Rhizobium bacteria in root nodules).
Classification by life cycle separates annuals, which complete their life in one season; biennials, which need two seasons and usually a cold period to flower (sugar beet grown for seed, for example); and perennials, which live for several years (sugarcane through ratoons, lucerne, tea). Classification by season is the one that governs a farm's calendar and therefore a machinery fleet's workload.
In South Asia the year is divided into three cropping seasons. Kharif crops are sown with the onset of the south-west monsoon, roughly June–July, and harvested in September–October; rice, maize, sorghum, pearl millet, cotton, soybean, groundnut, pigeonpea and mung bean are typical. Rabi crops are sown after the monsoon in October–November and harvested in March–April; wheat, barley, chickpea, lentil, rapeseed-mustard and potato are typical. Zaid crops are short-duration summer crops grown between rabi and kharif under irrigation, such as watermelon, cucumber and summer mung bean. Exact dates shift by latitude and by the arrival of the monsoon.
In temperate regions the distinction is between winter (autumn-sown) and spring-sown crops. Winter wheat and winter barley are sown in autumn, survive winter as seedlings, and need a period of cold, called vernalisation, before they will flower; spring types are sown in spring and do not need it. In the humid tropics, such as the Philippines and much of South-East Asia, the seasons are wet and dry: rainfed rice dominates the wet season, and the dry season depends on irrigation.
For an engineer, the season decides how many working days a machine has. The window between rice harvest and wheat sowing in north-west India is only a few weeks, which is why residue-handling seeders and fast combines matter there.
Most crops use the C3 pathway, in which the first stable product of carbon fixation is a three-carbon acid; wheat, rice, barley, oats, soybean, potato, cotton and most pulses are C3. C4 crops, among them maize, sorghum, sugarcane and pearl millet, first fix carbon into a four-carbon acid in mesophyll cells and concentrate carbon dioxide around the enzyme Rubisco in bundle sheath cells. This suppresses photorespiration, so C4 crops have higher light-saturated photosynthesis and better water-use efficiency in hot, bright conditions. CAM plants, such as pineapple and agave, open their stomata at night and are adapted to arid conditions.
Photoperiodism is the flowering response to day length. Long-day crops, such as wheat, barley, oats and rapeseed, flower when days lengthen beyond a critical value. Short-day crops, such as many rice varieties, soybean, sorghum and cotton in its wild form, flower when days shorten. Day-neutral crops, which include most modern maize hybrids and many improved rice varieties, flower largely in response to accumulated temperature. Photoperiod sensitivity matters when a variety is moved between latitudes or sown out of season.
Crop development is driven mainly by temperature. Growing degree days (GDD), also called thermal time, are calculated each day as the mean of the maximum and minimum temperature minus a base temperature below which development stops, with negative values set to zero. The base temperature is crop-specific: about 10 °C is widely used for maize, and a lower base, often 0 to 5 °C, is used for wheat. Summing GDD from sowing predicts emergence, flowering and maturity better than counting calendar days.
Standard scales let agronomists, engineers and chemical labels refer to the same moment in a crop's life. The Zadoks decimal scale for cereals runs from 00 (dry seed) through 10s (seedling growth), 20s (tillering), 30s (stem elongation), 40s (booting), 50s (ear or panicle emergence), 60s (anthesis or flowering), 70s (milk), 80s (dough) to 90s (ripening). The BBCH scale extends the same decimal logic to almost every crop. Maize uses vegetative stages VE (emergence) and V1, V2 and so on by the number of leaves with visible collars, VT (tasselling), and reproductive stages R1 (silking) to R6 (physiological maturity, marked by the black layer at the kernel base).
A critical stage is one at which stress, especially water stress, causes a disproportionate loss of yield. In general the reproductive phase, flowering and early grain set, is the most sensitive. Textbook examples include crown root initiation and flowering in wheat (crown root initiation is usually cited at about three weeks after sowing in Indian conditions), panicle initiation and flowering in rice, tasselling and silking in maize, flowering and pod formation in pulses, and flowering and pegging in groundnut. Herbicide and pesticide labels are written to growth stages, for example 'apply post-emergence at the two- to four-leaf stage of the weed', so the stage, not the calendar, decides when a sprayer must be in the field.
Tillage is the mechanical manipulation of soil to provide conditions favourable for crop growth. Its purposes are to prepare a seedbed in which seed can be placed at a uniform depth in moist, firm soil with enough fine aggregates around it; to control weeds; to incorporate residues, manures and fertilisers; to break compacted layers; and, in some systems, to shape the surface into ridges, beds or furrows for drainage and irrigation.
Primary tillage is the first, deeper and rougher operation after harvest: mouldboard ploughing, disc ploughing, chisel ploughing or subsoiling. It leaves large clods. Secondary tillage, done with harrows, cultivators, rotavators and planks or rollers, breaks clods, levels the surface and firms the seedbed. Inter-cultivation is tillage within a standing crop, between rows, to control weeds and loosen the surface. A well-prepared seedbed for small seeds such as mustard is fine and firm; large seeds such as maize, groundnut and pulses tolerate a coarser tilth. Puddling, which is tillage of saturated soil for transplanted rice, deliberately destroys soil structure to reduce percolation and to ease transplanting; it leaves a dense layer that later crops such as wheat must cope with.
Tillage systems range from conventional or clean tillage, where most residue is buried, through reduced or minimum tillage, to conservation tillage, which by the widely used USDA definition leaves at least 30 percent of the soil surface covered by residue after planting, and to no-till or zero tillage, where the only disturbance is a narrow slot made by the planter. Strip tillage loosens only the band that will become the crop row. The trend worldwide has been toward less tillage, because each pass costs fuel and time, increases erosion risk and oxidises soil organic matter.
The right moment to till is when the soil is near its lower plastic limit: dry enough to crumble rather than smear, and moist enough not to form hard clods. Tilling wet soil causes compaction and smeared slots; tilling very dry clay makes clods that consume many secondary passes. Repeated passes of heavy machinery at the same depth form a plough pan or hardpan, a compacted layer that restricts roots and drainage; subsoiling or deep chiselling is used to break it, but the benefit lasts only if traffic is controlled afterwards.
Seedbed quality is described by aggregate size distribution, bulk density, surface roughness and residue cover. For good germination the seed needs firm contact with moist soil below and a loose cover above that does not crust. Crust formation after rain on fine, low-organic-matter soils can prevent emergence of small-seeded crops, so press wheels and residue cover are partly crust-control measures.
Broadcasting scatters seed over the surface, by hand or by a spinning-disc spreader, and covers it with a harrow or plank. It is fast and cheap but gives uneven depth and spacing and needs more seed. Line sowing places seed in rows: behind a country plough (sowing in the furrow), with a seed drill that meters seed continuously into each row, or with a precision planter that singulates seeds and places them one at a time at a set spacing. Dibbling places a few seeds in holes made at fixed points, as for cotton or groundnut on small farms. Transplanting raises seedlings in a nursery and moves them to the field; it is standard for rice in much of Asia and for many vegetables, tobacco and some sugarcane systems. Vegetative propagation uses setts (stem pieces) for sugarcane, tubers or tuber pieces for potato, and stem cuttings for cassava and sweet potato.
Sowing depth depends mainly on seed size and soil moisture. Small seeds such as mustard, clover or tobacco are sown shallow, about 1–2 cm; cereals such as wheat at about 3–5 cm; large seeds such as maize, groundnut and soybean at about 4–6 cm, deeper in dry, light soils. A seed placed too deep exhausts its reserves before emergence; a seed placed too shallow dries out.
Precision planting matters most for crops whose yield depends strongly on even spacing, such as maize, cotton, sunflower and sugar beet. Uniformity is measured by the coefficient of variation of spacing, and by the shares of 'misses' (gaps larger than about 1.5 times the target spacing) and 'multiples' (spacings smaller than about half the target), the indices used in ISO 7256 planter testing.
Plant population is the number of plants per unit area, usually per hectare or per square metre. For row crops it follows directly from the geometry: plants per hectare = 10,000 ÷ (row spacing in metres × plant spacing in the row in metres) × plants per hill. Maize at 60 cm × 20 cm with one plant per hill has 10,000 ÷ (0.60 × 0.20) = 83,333 plants per hectare. Transplanted rice at 20 cm × 15 cm has 33.3 hills per square metre, or 333,333 hills per hectare.
Optimum populations differ widely by crop, variety, water supply and country. Irrigated maize hybrids in the United States are commonly grown at roughly 75,000–90,000 plants per hectare, while rainfed maize in semi-arid Africa may be grown at 30,000–45,000. Wheat is sown at a target of a few hundred plants per square metre, commonly in the 150–400 range depending on region and sowing date. Higher populations compensate for late sowing and poor tillering; lower populations suit dry conditions.
Square planting gives each plant an equal area; rectangular planting with wide rows and close in-row spacing is used because it allows tractor wheels and inter-row cultivators to pass. When a planter is designed, row spacing is set by the toolbar and the tractor track width, and in-row spacing by the metering mechanism and its drive ratio.
Seed rate is the mass of seed sown per hectare to achieve the target population. The basic relation is: seed rate (kg/ha) = target plants per hectare × thousand-seed weight (g) ÷ 1,000,000 ÷ (germination fraction × purity fraction × field-emergence or survival fraction). Thousand-seed weight, also called test weight or thousand-grain weight, varies by variety and seed lot; typical ranges are about 35–50 g for wheat, 20–30 g for rice and 200–400 g for maize, much more for groundnut and less than 5 g for mustard.
Example. Maize at 60 × 20 cm, one seed per hill, thousand-seed weight 250 g, germination 90 percent, purity 98 percent. Plants per hectare = 83,333. Pure germinating seed needed = 83,333 × 250 ÷ 1,000,000 = 20.83 kg. Dividing by 0.90 × 0.98 = 0.882 gives 23.6 kg/ha. The usual student error is to multiply by germination instead of dividing, which gives about 18.4 kg/ha and an under-populated field.
Example. Wheat with a target of 300 established plants per square metre, thousand-grain weight 40 g, germination 85 percent and field emergence 90 percent. 300 plants/m² = 3,000,000 plants/ha. Mass = 3,000,000 × 40 ÷ 1,000,000 = 120 kg; divided by 0.85 × 0.90 gives about 157 kg/ha.
Pure live seed (PLS), used in many countries for grasses and forages, is purity × germination; seed rate on a bulk basis = PLS seed rate ÷ PLS fraction.
A seed drill is calibrated by turning the ground wheel the number of times that corresponds to a known area and weighing the seed delivered. The area covered per wheel revolution is π × wheel diameter × effective working width, where working width = number of rows × row spacing. The number of revolutions for a calibration area A is A ÷ (π D W). In the field the wheel slips or skids, so the effective distance per revolution is reduced by a slip factor, and calibration is repeated until delivered seed matches the target.
For a precision planter with a cell plate or vacuum disc, in-row spacing = distance travelled by the drive wheel per revolution of the plate ÷ number of cells. If the plate is driven from a ground wheel of diameter D through a ratio in which the plate turns n times per wheel revolution, spacing = π D (1 − slip) ÷ (n × cells). Thus the agronomist's in-row spacing becomes the engineer's choice of plate and sprocket. Seed size grading matters: plates are matched to seed size classes, and ungraded seed gives misses and multiples.
Seventeen elements are generally accepted as essential for higher plants. Carbon, hydrogen and oxygen come from air and water. The primary macronutrients are nitrogen (N), phosphorus (P) and potassium (K); the secondary macronutrients are calcium (Ca), magnesium (Mg) and sulphur (S); the micronutrients are iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl) and nickel (Ni). An element is essential if the plant cannot complete its life cycle without it, it cannot be replaced by another, and it is directly involved in metabolism.
Deficiency symptoms follow mobility within the plant. Mobile nutrients, N, P, K and Mg, are moved from old leaves to new growth when supply is short, so their deficiency shows first on older, lower leaves: general yellowing for N, purpling for P in many crops, marginal scorching for K, interveinal chlorosis for Mg. Immobile nutrients, Ca, B and, largely, Fe and S, show first on young leaves and growing points: interveinal chlorosis of young leaves for Fe, die-back of tips for Ca and B. Zinc deficiency in rice ('khaira' in South Asia) and in maize (white bud) is common on alkaline and calcareous soils.
Liebig's law of the minimum states that yield is limited by the nutrient in shortest supply relative to need, so adding a non-limiting nutrient gives no response. Soil testing and plant analysis identify which nutrient is limiting; recommendations are then made as kilograms of nutrient per hectare.
Fertilisers are labelled by grade, the percentage by mass of N, P₂O₅ and K₂O, in that order. Phosphorus and potassium are expressed as oxides by long convention, not because they exist as oxides in the bag. To convert: P = P₂O₅ × 0.436 (P₂O₅ = P × 2.29), and K = K₂O × 0.830 (K₂O = K × 1.205).
Common straight fertilisers: urea, 46 percent N, the most concentrated solid nitrogen fertiliser; ammonium sulphate, about 21 percent N and 24 percent S; calcium ammonium nitrate, about 25–27 percent N depending on the country's grade; anhydrous ammonia, 82 percent N, applied by injection as a pressurised liquid. For phosphorus: single superphosphate (SSP), about 16 percent P₂O₅ plus about 11–12 percent S and calcium; triple superphosphate (TSP), about 46 percent P₂O₅; rock phosphate, slowly available and suited to acid soils. For potassium: muriate of potash (potassium chloride, MOP), 60 percent K₂O; sulphate of potash, about 50 percent K₂O. Complex fertilisers include diammonium phosphate (DAP), 18-46-0, and monoammonium phosphate (MAP), commonly 11-52-0. Exact grades vary slightly by manufacturer and national standard; always read the bag.
Physical form matters to the engineer. Prilled urea and granular products differ in size, density and strength, and so spread to different widths from the same spinning-disc spreader; manufacturers' spread tables are made for specific products. Urea and nitrate products are hygroscopic and cake when damp. Liquid fertilisers are applied through nozzles or injected through irrigation systems, which is called fertigation.
The basic relation is: product (kg/ha) = nutrient required (kg/ha) × 100 ÷ percentage of that nutrient in the product. To supply 120 kg N/ha from urea needs 120 × 100 ÷ 46 = 260.9 kg urea per hectare.
When a complex fertiliser supplies two nutrients, satisfy the nutrient that only it supplies first, credit the other nutrient, and make up the balance with a straight fertiliser. Suppose a recommendation is 120 kg N, 60 kg P₂O₅ and 40 kg K₂O per hectare, using DAP, urea and MOP. DAP for 60 kg P₂O₅ = 60 × 100 ÷ 46 = 130.4 kg, which also supplies 130.4 × 0.18 = 23.5 kg N. Remaining N = 120 − 23.5 = 96.5 kg, so urea = 96.5 × 100 ÷ 46 = 209.8 kg. MOP = 40 × 100 ÷ 60 = 66.7 kg. Forgetting the N in DAP over-applies about 51 kg of urea per hectare.
For a plot, convert hectares to square metres (1 ha = 10,000 m²). A rate of 260.9 kg/ha on a 20 m² plot is 260.9 × 20 ÷ 10,000 = 0.522 kg, or 522 g. For split application, divide the nitrogen among stages: a common pattern for irrigated cereals is part at sowing and the rest as one or two top-dressings at active tillering and before panicle or ear initiation, but the split differs by crop, soil and country.
Nutrient use efficiency is measured in several ways. Agronomic efficiency = (yield with fertiliser − yield without) ÷ nutrient applied, in kilograms of grain per kilogram of nutrient. Apparent recovery efficiency = (nutrient uptake with fertiliser − uptake without) ÷ nutrient applied, as a fraction. Recovery of applied nitrogen by cereals in a season is commonly well under half in farm conditions, which is why placement and timing matter.
Organic manures add nutrients and organic matter that improves structure and water holding. Bulky organic manures include farmyard manure (FYM), compost, vermicompost and green manures; concentrated organic manures include oilcakes, bone meal and poultry manure. Their nutrient content varies widely with the source animal, bedding, storage and losses; well-rotted FYM is often quoted at roughly 0.5 percent N, 0.2 percent P₂O₅ and 0.5 percent K₂O, but analysis of the actual material is the only safe basis. Only a fraction of the nitrogen in manure is available in the first season. Green manuring grows a legume, such as sunn hemp or Sesbania, and incorporates it before flowering; Sesbania rostrata also forms stem nodules.
Biofertilisers are living microbial inoculants: Rhizobium for legumes (specific to the host group), Azotobacter and Azospirillum as free-living or associative nitrogen fixers for cereals, phosphate-solubilising bacteria and fungi, mycorrhizae, blue-green algae (cyanobacteria) and the Azolla–Anabaena symbiosis in flooded rice.
Integrated nutrient management combines organic, inorganic and biological sources to sustain yield and soil fertility. The 4R nutrient stewardship framework asks for the right source, at the right rate, at the right time, in the right place. Placement options are broadcasting, band placement beside and below the seed, deep placement of urea briquettes in flooded rice, foliar sprays for micronutrients, and fertigation. Each has a machine: a broadcaster, a fertiliser-cum-seed drill, an applicator for briquettes, a sprayer and an injection pump.
Crop water requirement is the depth of water needed to meet the evapotranspiration of a disease-free crop growing in large fields under non-limiting soil water and fertility. The FAO-56 method computes it in two steps. Reference evapotranspiration (ET₀) is the evapotranspiration of a hypothetical well-watered grass surface, calculated from weather data with the FAO Penman-Monteith equation, or estimated from pan evaporation multiplied by a pan coefficient. Crop evapotranspiration is then ETc = Kc × ET₀, where Kc is the crop coefficient.
Kc follows the crop's development: it is low in the initial stage when the ground is mostly bare, rises through crop development, peaks in the mid-season stage when the canopy is full (for many field crops Kc mid is about 1.0–1.2), and falls in the late season as leaves senesce. The FAO tables give Kc and stage lengths by crop and climate; local values should be used where available. Example: ET₀ of 5 mm/day and a mid-season Kc of 1.15 give ETc = 5.75 mm/day.
Field capacity is the water content after free drainage has largely stopped, commonly associated with a matric potential of about −33 kPa (−10 kPa for sands). The permanent wilting point is the water content at which plants wilt and do not recover overnight, conventionally −1500 kPa. The difference, multiplied by root depth, is the total available water. Only part of it can be used before yield suffers; the allowable or management depletion, often 30–60 percent depending on crop and evaporative demand, defines readily available water.
Irrigation is scheduled by deciding when and how much. When: at a fixed depletion of available water, at a soil-water tension measured by a tensiometer or sensor, at a ratio of irrigation water to cumulative pan evaporation (the IW/CPE approach widely used in India), at critical growth stages, or at fixed intervals. How much: net depth = (field capacity − current water content) × root depth, with volumetric water contents; gross depth = net depth ÷ application efficiency.
Example. A soil with field capacity 0.30 and current water content 0.21 (volumetric) and a root zone of 0.6 m needs a net depth of 0.09 × 600 = 54 mm. At 60 percent application efficiency the gross depth is 90 mm. With mass-based water contents, multiply by bulk density ÷ water density first.
The irrigation interval is readily available water ÷ ETc. With 54 mm of readily available water and ETc of 6 mm/day, the interval is 9 days. Detailed design of surface, sprinkler and drip systems is covered in the irrigation subjects.
A weed is a plant growing where it is not wanted. Weeds compete with the crop for light, water and nutrients, host pests and diseases, contaminate harvested produce and interfere with machines; tall or viny weeds such as morning glory and some grasses wrap on combine reels and augers and raise grain moisture and foreign matter at harvest. Weeds are grouped by life cycle (annual, biennial, perennial), by morphology (grasses, sedges and broadleaf weeds, the last also called dicots) and by association with crops. Perennial weeds that spread by rhizomes, tubers or stolons, such as purple nutsedge (Cyperus rotundus), Bermuda grass (Cynodon dactylon) and Johnson grass (Sorghum halepense), are the hardest to control because tillage cuts and spreads their underground organs.
The critical period of crop–weed competition is the span of crop growth during which weeds must be kept out to avoid unacceptable yield loss. Before it, weeds can be tolerated; after it, newly emerging weeds do little harm. For many annual field crops it falls in roughly the first one-third to one-half of crop duration, but it must be determined for each crop and region. This period decides when inter-row cultivators and post-emergence sprayers are needed.
Two indices are used in experiments. Weed control efficiency = (weed dry matter in the unweeded control − weed dry matter in the treatment) ÷ weed dry matter in the control × 100. Weed index = (yield of the weed-free plot − yield of the treatment) ÷ yield of the weed-free plot × 100; it is the yield loss caused by the weeds left in that treatment.
Preventive methods stop weeds arriving: clean certified seed, clean machinery moving between fields, screened irrigation water, and well-rotted manure in which weed seeds have been killed by heat. Cultural methods help the crop win: competitive varieties, optimum population and narrow rows, correct sowing time, stale seedbeds (irrigate, let weeds emerge, kill them, then sow), crop rotation, cover crops, mulches and flooding in rice. Mechanical methods include hand weeding, hoeing, inter-row cultivators, rotary weeders for line-transplanted rice, and mowing. Biological control uses insects or pathogens against specific weeds.
Chemical control uses herbicides. They are classified by selectivity (selective, which kill weeds but not a specific crop; non-selective, which kill all green vegetation), by time of application (pre-plant incorporated; pre-emergence, applied after sowing but before crop or weeds emerge; post-emergence, applied to growing weeds), by movement (contact, which kills only the tissue it touches; systemic, which is translocated through the plant) and by mode of action. Examples of mode of action groups: glyphosate inhibits the enzyme EPSP synthase and is non-selective and systemic; 2,4-D and MCPA are synthetic auxins selective against broadleaf weeds in cereals; atrazine inhibits photosystem II and is used pre-emergence in maize and sorghum; pendimethalin, a dinitroaniline, inhibits root and shoot growth of germinating seedlings and is used pre-emergence; ACCase inhibitors such as clodinafop control grasses in broadleaf crops and wheat. Registration differs by country, and several herbicides are banned in some countries and permitted in others.
Herbicide resistance develops when the same mode of action is used repeatedly. A well-known case is little seed canary grass (Phalaris minor) in the rice–wheat system of north-west India, which became resistant to isoproturon in the 1990s. Rotating and mixing modes of action, combining chemical with cultural and mechanical control, and preventing seed set are the basis of integrated weed management.
In crop protection, pests include insects, mites, nematodes, rodents, birds and, in the broad sense, weeds and pathogens. Plant diseases are caused by fungi, bacteria, viruses, phytoplasmas and nematodes; the disease triangle states that disease needs a susceptible host, a virulent pathogen and a favourable environment at the same time. Well-known field-crop examples include rice blast (a fungus), bacterial leaf blight of rice, wheat rusts (stem, leaf and stripe rust, fungi), late blight of potato (an oomycete, Phytophthora infestans), and many virus diseases spread by insect vectors such as whiteflies and aphids.
Integrated pest management (IPM) combines methods to keep pests below the level that causes economic loss, with least hazard to people and the environment. The economic injury level (EIL) is the pest density at which the cost of control equals the value of the damage it prevents. The economic threshold level (ETL), also called the action threshold, is the density at which control should start so that the population does not reach the EIL; it is set below the EIL. Thresholds are crop-, pest- and price-specific.
IPM tools are cultural (resistant varieties, sowing date, rotation, field sanitation, trap crops), mechanical and physical (light traps, pheromone traps for monitoring and mass trapping, sticky traps, exclusion nets), biological (parasitoids such as Trichogramma wasps released against moth eggs, predators, entomopathogens such as Bacillus thuringiensis and nuclear polyhedrosis viruses, the fungus Trichoderma against soil-borne pathogens), host-plant resistance, and chemical pesticides used only when monitoring shows they are needed.
Pesticides are classified by target (insecticides, fungicides, herbicides, nematicides, rodenticides, acaricides), by mode of entry (contact, stomach, systemic, fumigant) and by chemical group. A product contains an active ingredient (a.i.) and inert ingredients that make up the formulation. Common formulations are emulsifiable concentrates (EC), soluble liquids (SL), suspension concentrates (SC), wettable powders (WP), water-dispersible granules (WG), granules (G) for soil application and dusts (D). The percentage or concentration on the label, such as 50 WP or 500 g/L SC, is the a.i. content.
Acute toxicity is expressed as LD₅₀, the dose in milligrams per kilogram of body weight that kills half of a test population; the lower the LD₅₀, the more toxic the product. The World Health Organization classifies technical products as class Ia (extremely hazardous), Ib (highly hazardous), II (moderately hazardous), III (slightly hazardous) and U (unlikely to present acute hazard). Many countries also use coloured label bands. The pre-harvest interval is the minimum time between the last application and harvest, and the maximum residue limit is the legal limit of residue in food; both are set by national regulators and Codex Alimentarius and must be taken from the label.
Spray application is described by two separate quantities: dose, the mass of active ingredient per hectare, and volume, the litres of spray liquid per hectare that carries it. Matthews' widely used classification for field crops is high volume above 600 L/ha, medium volume 200–600 L/ha, low volume 50–200 L/ha, very low volume 5–50 L/ha and ultra-low volume below 5 L/ha. Lower volumes need finer droplets for coverage, which increases drift risk.
Boom sprayer output follows from nozzle flow, forward speed and nozzle spacing: application rate (L/ha) = 600 × nozzle flow (L/min) ÷ (forward speed (km/h) × nozzle spacing (m)). The constant 600 comes from 10,000 m²/ha × 60 min/h ÷ 1,000 m/km. With 0.8 L/min per nozzle, 0.5 m spacing and 6 km/h, the rate is 600 × 0.8 ÷ (6 × 0.5) = 160 L/ha. Doubling speed halves the volume applied unless the flow is raised; because nozzle flow varies with the square root of pressure, doubling flow needs four times the pressure, which also shrinks droplets, so speed is usually controlled rather than compensated by pressure alone.
Product needed (per hectare) = dose of a.i. (kg/ha) ÷ fraction of a.i. in the product. A dose of 1.0 kg a.i./ha from a 50 percent WP needs 2.0 kg of product per hectare. A dose of 0.75 kg a.i./ha from a liquid containing 500 g a.i. per litre needs 1.5 L/ha. If the sprayer applies 300 L/ha and the tank holds 400 L, one tank covers 400 ÷ 300 = 1.33 ha and needs 1.5 × 1.33 = 2.0 L of product. Spray concentration can also be expressed as a percentage: for a 0.1 percent a.i. spray made from a 25 percent EC, the product is 0.1 ÷ 25 of the spray volume, so 1,000 L of spray needs 4 L of product.
Physiological maturity is the stage at which the seed or grain reaches maximum dry matter; after this no more yield is added, and the crop only dries. In maize it is marked by the black layer at the kernel base, where it attaches to the cob, at a grain moisture typically around 30–35 percent wet basis. In wheat and other small grains it corresponds to loss of green colour from the glumes and peduncle, with grain moisture still well above safe storage levels. Harvest maturity is later: the moisture at which the crop can be harvested with acceptable losses and handled by the machine.
Harvesting too early means wet grain, extra drying cost and possibly immature, shrivelled kernels; too late means shattering, lodging, bird and pest damage, fissured rice kernels and weather losses. For rice, harvesting at about 20–25 percent moisture is commonly recommended to limit shattering and fissuring, followed by prompt drying. Wheat is often combined at below about 20 percent and stored at 12–13 percent. Maize may be harvested as shelled grain from about 25 percent downward and dried, or left to dry in the field where weather allows. Pulses and oilseeds such as mustard, sesame and soybean shatter readily when over-dry, so harvest is timed to pod colour and moisture, sometimes with desiccation.
Safe storage moisture depends on crop, temperature and storage period. Cereals are commonly stored at about 12–14 percent wet basis; oilseeds, which have less water-holding starch, need lower values. Local standards should be used.
Biological yield is the total above-ground dry matter (roots are usually excluded because they are hard to recover). Economic yield is the harvested product, such as grain, tuber, lint or seed cotton. Harvest index (HI) = economic yield ÷ biological yield, usually as a fraction or percentage.
Example. Wheat yields 4.5 t/ha of grain and 6.0 t/ha of straw. Biological yield = 10.5 t/ha and HI = 4.5 ÷ 10.5 = 0.429, or 42.9 percent. A common mistake is to divide grain by straw (0.75), which is the grain-to-straw ratio, not the harvest index.
Harvest index explains much of the yield gain of the Green Revolution: semi-dwarf wheat and rice varieties partition more of their biomass to grain, with harvest indices commonly around 0.45–0.50 against about 0.3 or less for older tall varieties. For the engineer, harvest index and grain-to-straw ratio decide the material-other-than-grain load on a combine's threshing and cleaning system, the amount of straw that a residue-management system or a baler must handle, and the biomass available for bioenergy.
Moisture content on a wet basis (Mwb) is water mass ÷ total mass; on a dry basis (Mdb) it is water mass ÷ dry-matter mass. Agronomists and grain traders use wet basis; drying theory uses dry basis. The conversions are Mdb = Mwb ÷ (1 − Mwb) and Mwb = Mdb ÷ (1 + Mdb). Grain at 20 percent wet basis is 25 percent dry basis.
When grain is dried, the dry matter is unchanged. Final mass = initial mass × (1 − initial Mwb) ÷ (1 − final Mwb). Drying 1,000 kg of maize from 22 percent to 14 percent wet basis gives 1,000 × 0.78 ÷ 0.86 = 907.0 kg; the water removed is 93.0 kg. The tempting wrong answer subtracts percentage points (8 percent of 1,000 = 80 kg), which ignores that the percentage refers to a shrinking total.
Yield trials report grain yield at a standard moisture so that plots harvested on different days can be compared; the standard differs by crop and country (for example, 14 percent for rice and wheat in many reports and 15.5 percent for maize in the United States). The same dry-matter relation is used: adjusted yield = harvested mass × (1 − harvest moisture) ÷ (1 − standard moisture).
Rice (Oryza sativa) is grown under flooded transplanted, flooded direct-seeded, rainfed lowland, upland and deepwater systems. Transplanting by machine needs seedlings raised as mats on trays or polythene beds of uniform density, about two to three weeks old, so the nursery is part of the machine system. Puddled transplanted rice uses large volumes of water for land preparation; direct-seeded rice with a drill saves labour and water but needs effective weed control. Combines for rice need tracks or high-flotation tyres on soft paddy soil, and rice straw, with its high silica content, is hard to chop and is often burned, a major source of air pollution in north-west India.
Wheat (Triticum aestivum for bread wheat, Triticum durum for pasta) is the most widely grown cereal by area. It is sown with seed drills at row spacings of about 15–25 cm, and in rice–wheat systems increasingly with zero-till drills that can cut or move loose rice straw. Combine harvesting is universal in large-scale wheat.
Maize (Zea mays) is grown for grain, silage and green cobs. It is planted in rows 60–75 cm apart with precision planters, harvested by combines fitted with corn headers that snap ears and leave stalks, or by forage harvesters for silage.
Pulses, or grain legumes, include chickpea, pigeonpea, lentil, field pea, faba bean, mung bean, urd bean (black gram), cowpea and common beans. They fix nitrogen and break cereal pest and disease cycles, but their yields are lower and less stable than cereals'. For machines, pulses are difficult: many varieties are short with pods close to the ground, they lodge, pods shatter when dry, and indeterminate types such as pigeonpea and mung bean mature unevenly. Engineers respond with low-cutting flexible headers, pickup reels, adjusted concave clearance and lower cylinder speed to avoid splitting seed, and with breeding for taller, erect, machine-harvestable varieties, which has been an explicit goal for chickpea in India and Australia. Seed coats of pulses are easily cracked, which reduces germination; seed for sowing is therefore threshed gently at moderate moisture.
Major oilseeds include soybean, rapeseed-mustard (including canola), groundnut (peanut), sunflower, sesame, safflower, linseed and, as a tree crop, oil palm. Soybean is harvested by combines with flexible cutter bars because the lowest pods are close to the ground. Rapeseed and mustard shatter readily; they may be swathed (cut and left in windrows to dry) or desiccated before combining. Groundnut is a geocarpic crop, meaning its pods develop underground from pegs; it is harvested by diggers or digger-shakers that lift and invert plants for field drying before threshing, and pod losses in hard soil are a major design issue. Sunflower heads are harvested with special header attachments. Small-seeded oilseeds such as sesame demand precise seed metering at low rates, often achieved by mixing seed with an inert carrier such as sand or by using fine-cell plates. Oilseeds are harvested and stored at lower moisture than cereals because of their high oil content.
Sugarcane is propagated from setts, stem pieces usually with two or three buds, at a seed requirement of several tonnes of cane per hectare. It is planted in furrows or trenches, usually at row spacings of about 75–150 cm depending on the system, with wider rows where mechanical harvesting is planned. It is a long-duration crop, often 10–18 months for plant cane, followed by one or more ratoon crops from the stubble. Mechanised systems use sett-cutter planters and chopper harvesters that cut cane into billets; billets deteriorate quickly and must reach the mill within hours. Sugar recovery, the percentage of sugar obtained from cane, depends on cane quality, maturity and the delay between cutting and crushing.
Cotton is grown for lint and seed. Machine picking requires defoliation and uniform boll opening; spindle pickers remove seed cotton from open bolls, while strippers remove whole bolls and need more cleaning at the gin. Hand picking remains common in South Asia and Africa. Potato is planted with automatic or semi-automatic planters on ridges and harvested by diggers or harvesters that separate tubers from soil and haulm; bruising during lifting is the main quality issue.
A cropping pattern is the yearly sequence and spatial arrangement of crops and fallow on a given area. A cropping system is the cropping pattern together with its interaction with farm resources, technology and environment. Monocropping grows the same crop year after year on the same land. Multiple cropping grows two or more crops on the same land in a year and takes two forms. Sequential cropping grows crops one after another in the same year: double cropping (rice–wheat, maize–wheat, soybean–wheat) or triple cropping. Intercropping grows two or more crops at the same time on the same field: mixed intercropping without row arrangement; row intercropping in distinct rows, such as sorghum with pigeonpea or maize with soybean; strip intercropping in strips wide enough for separate machinery but narrow enough for the crops to interact; and relay intercropping, in which a second crop is sown into the standing first crop before its harvest, such as lentil or lathyrus relayed into rice in eastern India. Ratoon cropping harvests a second crop from the stubble regrowth, common in sugarcane and possible in rice and sorghum. Crop rotation is the planned succession of different crops on the same land over years, such as the maize–soybean rotation of the US Corn Belt or the cereal–legume–oilseed rotations of temperate Europe and Australia.
Cropping intensity = gross cropped area ÷ net sown area × 100. A farm with 150 ha net sown area, of which 120 ha carries a second crop and 30 ha a third crop, has a gross cropped area of 300 ha and a cropping intensity of 200 percent.
The land equivalent ratio (LER) compares intercropping with sole cropping. LER = (yield of crop A in intercrop ÷ yield of crop A as sole crop) + (yield of crop B in intercrop ÷ yield of crop B as sole crop). It is the relative land area that sole crops would need to produce the intercrop's yields. An LER above 1 means the intercrop uses land more efficiently. Example: maize yields 5.0 t/ha sole and 4.0 t/ha intercropped; soybean yields 2.0 t/ha sole and 0.9 t/ha intercropped. LER = 4.0 ÷ 5.0 + 0.9 ÷ 2.0 = 0.80 + 0.45 = 1.25, so 1.25 ha of sole crops would be needed to match one hectare of intercrop.
Intercropping advantages arise from complementary use of resources (deep and shallow roots, tall and short canopies, different peak demand times), nitrogen transfer from legumes, reduced pest spread and lower risk of total failure. The disadvantage for mechanisation is that two crops in one field have different sowing depths, harvest dates and machine settings. Strip intercropping, with strips matched to the width of the planter and combine header, is the usual engineering compromise.
FAO defines conservation agriculture (CA) by three linked principles: continuous minimum mechanical soil disturbance, which means no-till or direct seeding; permanent organic soil cover by crop residues or cover crops; and diversification of plant species through rotations, sequences and associations. All three are needed; no-till without residue cover or rotation often gives disappointing results.
Benefits documented in many regions include reduced erosion, higher infiltration and soil water storage, gradual increases in surface soil organic matter and biological activity, lower fuel and labour costs, and timelier sowing. Constraints include weed control that relies more on herbicides in the early years, residue-borne pests and diseases, slower soil warming in cool climates, nitrogen immobilisation under surface residues and, above all, the need for suitable machinery. CA is widely practised in the Americas and Australia and is spreading in South Asia and Africa.
The engineering heart of CA is the no-till seeder. It must cut or move residue (with coulters, row cleaners or straw-chopping rotors), open a narrow slot at a controlled depth in untilled soil, place seed and fertiliser separately, and close the slot with press wheels, all without blocking. Residue must also be spread evenly by the combine's straw chopper and spreader, because a windrow of straw behind the combine will block any seeder that follows. Controlled traffic farming, in which all machines use the same permanent wheel tracks, complements CA by confining compaction to a small fraction of the field.
A farming system is the whole farm as a unit: the household and its goals, the land, crops, livestock, trees, fish, labour, capital, machines and off-farm work, and the flows between them. In most of the world, and especially among the hundreds of millions of smallholders in Asia and Africa, the farm is a livelihood system rather than a crop factory: it must feed the family, provide cash through the year, carry risk, and use family labour that has few other outlets.
An integrated farming system (IFS) combines two or more enterprises so that the outputs of one become inputs of another. Common combinations include crop–dairy, in which crop residues feed cattle and dung returns as manure or biogas slurry; rice–fish or rice–duck culture, in which fish or ducks feed on weeds and insects in the paddy and add manure; crop–poultry–fish, in which poultry litter fertilises the fish pond and pond silt is returned to fields; agroforestry and silvopasture; and kitchen gardens. Integration recycles nutrients, spreads income across the year, reduces risk from a single crop failure and raises employment, but it demands more management skill and labour.
The ICAR Sixth Deans' Committee placed farming-based livelihood systems in the agricultural engineering degree because many of the engineer's clients are smallholders whose decisions are made at the farm-system level. Technologies that suit them include small-scale and two-wheel-tractor-based machinery; custom hiring centres that rent machines to farmers who cannot buy them, a model promoted in India and in parts of Africa and South-East Asia; small biogas plants that convert dung to cooking fuel and slurry manure; solar pumps, dryers and cold rooms that cut post-harvest losses; and small processing units, such as mini rice mills, oil expellers and dal mills, that keep value addition on the farm or in the village.
Several indicators judge a farming system. System productivity is often expressed as the total output converted to equivalent yield of a base crop. Profitability is measured by net returns and the benefit–cost ratio. Employment generation is counted in person-days per year. Resource use efficiency covers water, energy and nutrients, and sustainability considers soil health and risk. An engineer evaluating a machine or a structure for a smallholder must ask the same questions: whether it raises returns for the household after its cost, whether the household can operate and maintain it, whether it displaces paid labour in a way the community will accept, and whether it fits the cash flow of the season.
Learn the handful of formulas that the exams test every year and practise them until they are automatic: plants per hectare from spacing; seed rate from thousand-seed weight, germination and purity; product per hectare from nutrient and grade, including the DAP-urea sequence; sprayer litres per hectare from nozzle flow, speed and spacing; product per tank; harvest index; and moisture conversions between wet and dry basis. Then learn the vocabulary that lets you talk with agronomists: kharif and rabi, Zadoks stages, critical periods, pre- and post-emergence, ETL and EIL, LER and cropping intensity. In the field course, calibrate a seed drill and a knapsack sprayer yourself, weigh seed and grain, and measure moisture with an oven, because these are the numbers your machines will later be judged on.
A five-year engineer in a machinery firm, a testing station or an extension agency turns agronomic recommendations into machine settings. Typical tasks: setting a planter plate and sprocket to give the population an agronomist asked for and checking misses and multiples in the field; calibrating fertiliser drills and spinning-disc spreaders for the products actually sold locally; selecting nozzles, pressure and speed so that a sprayer delivers the label dose in the right spray volume with acceptable drift; advising when to start combining given grain moisture and the dryer's capacity; and planning how many machines a custom hiring centre needs to cover the sowing window of a village. The practical judgement is knowing which agronomic number is firm (the label dose) and which is a range that can be traded against machine capacity (sowing date, harvest moisture).
With twenty-five years of experience, an engineer shapes systems rather than settings. Decisions include whether a region's rice–wheat system can move to direct-seeded rice and zero-till wheat and what fleet of seeders, combines with straw spreaders and herbicide applicators that requires; how a sugar mill should balance harvesting capacity, billet delay and cane quality; whether a state's subsidy for machinery should favour individual ownership or service providers; and how to design a mechanisation package for pulses that farmers will adopt. Such engineers sit on standards committees for planters and sprayers, review testing protocols, and work with breeders on machine-harvestable varieties. They must speak agronomy fluently, because the strongest objections to a machine usually come from its effect on the crop.
A researcher with twenty-five years of experience works where crop science and engineering meet: modelling the interaction of seed placement, soil physical condition and emergence; designing variable-rate seeding and nitrogen application from yield maps and canopy sensors; quantifying spray drift and deposition for regulatory risk assessment; measuring the long-term effect of conservation agriculture and controlled traffic on soil carbon, structure and yield stability; and analysing farming systems to see where mechanisation raises household income and where it only displaces labour. The research questions require field experiments designed with agronomists and statisticians, crop simulation models used critically, and honest reporting of where results do not transfer between climates and soils.
This manual gives the agronomy an engineer needs, not a full agronomy course. It does not give crop-by-crop fertiliser recommendations, pesticide doses, herbicide choices or seed rates for any country, because these depend on variety, soil test, product registration and label and change often; values quoted are illustrations or broad textbook ranges. It does not cover horticultural crop production, protected cultivation, plant breeding, soil classification or detailed entomology and plant pathology. Crop water requirement and scheduling are only introduced; system design is in the irrigation subjects. Machine design for tillage, sowing, spraying and harvesting is in the farm machinery subjects. Farming-systems economics is outlined, not developed. Statistics on areas, yields and losses are deliberately omitted because they vary by year and source.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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