Soil Fertility, Plant Nutrition and Fertilizers MCQs 2026

The principle stating that crop yield is limited by the nutrient in shortest supply is called

1. A Liebig's law of minimum ✓
2. B Blackman's law of limiting factors ✓
3. C Mitscherlich's law of diminishing returns ✓
4. D Shelford's law of tolerance ✓

The three primary macronutrients commonly represented in fertilizer grades are

1. A Calcium, magnesium and sulfur ✓
2. B Nitrogen, phosphorus and potassium ✓
3. C Iron, zinc and boron ✓
4. D Carbon, hydrogen and oxygen ✓

In well aerated agricultural soils, the dominant mineral form of nitrogen absorbed by many crops is

1. A Elemental nitrogen gas ✓
2. B Nitrite ion ✓
3. C Nitrate ion ✓
4. D Organic protein nitrogen ✓

General yellowing that appears first on older leaves of cereals most commonly indicates deficiency of

1. A Iron ✓
2. B Calcium ✓
3. C Boron ✓
4. D Nitrogen ✓

Phosphorus is especially important in plants because it is a major component of

1. A ATP and nucleic acids ✓
2. B Chlorophyll molecule center ✓
3. C Stomatal guard cell waxes ✓
4. D Cellulose microfibril cross-links ✓

The nutrient most directly associated with stomatal regulation and activation of many plant enzymes is

1. A Boron ✓
2. B Potassium ✓
3. C Molybdenum ✓
4. D Chlorine ✓

Sulfur is an essential constituent of the amino acids

1. A Lysine and arginine ✓
2. B Glycine and alanine ✓
3. C Cysteine and methionine ✓
4. D Proline and valine ✓

Interveinal chlorosis on young leaves is a typical field symptom of deficiency of

1. A Nitrogen ✓
2. B Magnesium ✓
3. C Potassium ✓
4. D Iron ✓

Boron is particularly important for flowering crops because it supports

1. A Pollen germination and pollen tube growth ✓
2. B Nitrate reduction in root nodules ✓
3. C Chlorophyll formation in mature leaves ✓
4. D Starch conversion into lignin ✓

Khaira disease of rice is mainly associated with deficiency of

1. A Copper ✓
2. B Zinc ✓
3. C Manganese ✓
4. D Molybdenum ✓

For most field crops in mineral soils, overall nutrient availability is generally best around soil pH

1. A 3.5 to 4.0 ✓
2. B 4.5 to 5.0 ✓
3. C 6.5 to 7.0 ✓
4. D 9.5 to 10.0 ✓

Cation exchange capacity of a soil is a measure of its ability to

1. A Convert nitrate into atmospheric nitrogen ✓
2. B Measure only soluble salts in irrigation water ✓
3. C Fix carbon dioxide during photosynthesis ✓
4. D Hold and exchange positively charged nutrient ions ✓

Humus improves soil fertility mainly by increasing nutrient retention, aggregation and

1. A Water-holding capacity ✓
2. B Soil bulk density only ✓
3. C Salt concentration only ✓
4. D Exchangeable sodium percentage ✓

The bacterium commonly forming nodules on legume roots and fixing atmospheric nitrogen is

1. A Nitrosomonas ✓
2. B Rhizobium ✓
3. C Thiobacillus ✓
4. D Pseudomonas fluorescens ✓

Nitrification in soil is the microbial conversion of ammonium into

1. A Ammonia gas under dry conditions ✓
2. B Organic nitrogen under anaerobic conditions ✓
3. C Nitrate under aerobic conditions ✓
4. D Elemental sulfur under flooded conditions ✓

Denitrification is favored by waterlogged soils because it converts nitrate into

1. A Exchangeable potassium ✓
2. B Calcium carbonate ✓
3. C Available phosphate ✓
4. D Gaseous forms of nitrogen ✓

The nitrogen content of prilled urea fertilizer is approximately

1. A 46 percent ✓
2. B 18 percent ✓
3. C 26 percent ✓
4. D 60 percent ✓

The fertilizer grade of diammonium phosphate is commonly written as

1. A 46-0-0 ✓
2. B 18-46-0 ✓
3. C 0-0-60 ✓
4. D 21-0-0 ✓

Single superphosphate is valued because it supplies phosphorus along with appreciable

1. A Potassium and sodium ✓
2. B Zinc and molybdenum ✓
3. C Sulfur and calcium ✓
4. D Magnesium and chlorine ✓

Muriate of potash is chemically known as

1. A Potassium sulfate ✓
2. B Potassium nitrate ✓
3. C Monopotassium phosphate ✓
4. D Potassium chloride ✓

A fertilizer grade written as 17-17-17 shows the percentages of

1. A N, P2O5 and K2O ✓
2. B Nitrate, phosphate and carbonate ✓
3. C Calcium, magnesium and sulfur ✓
4. D Organic carbon, humus and clay ✓

Mineralization of organic matter in soil means release of nutrients into

1. A Only insoluble rock minerals ✓
2. B Inorganic plant-available forms ✓
3. C Permanent unavailable complexes ✓
4. D Atmospheric oxygen only ✓

Foliar application is most useful when the aim is to quickly correct deficiency of

1. A Deep subsoil gravel ✓
2. B Excess exchangeable sodium ✓
3. C Micronutrients in standing crops ✓
4. D Soil texture class ✓

Green manuring improves soil fertility mainly by adding organic matter and

1. A Soluble sodium carbonate ✓
2. B Excess chloride salts ✓
3. C Industrial lime dust only ✓
4. D Biologically fixed nitrogen when legumes are used ✓

Farmyard manure should preferably be well decomposed before field application to reduce weed seeds and improve

1. A Nutrient availability ✓
2. B Soil salinity hazard ✓
3. C Pesticide persistence ✓
4. D Soil crusting by sodium carbonate ✓

Balanced fertilization means applying nutrients according to soil test, crop requirement and

1. A Only the cheapest fertilizer source ✓
2. B Proper nutrient proportions ✓
3. C One fixed dose for all soils ✓
4. D Only nitrogen at sowing ✓

Luxury consumption in plant nutrition most commonly refers to uptake of a nutrient beyond yield need, especially

1. A Oxygen ✓
2. B Carbon dioxide ✓
3. C Potassium ✓
4. D Silicon only ✓

Deficiency symptoms of mobile nutrients usually appear first on

1. A Root hairs only ✓
2. B New buds only ✓
3. C Fruit seeds only ✓
4. D Older leaves ✓

Calcium deficiency most often appears in young growing tissues because calcium is

1. A Relatively immobile in the phloem ✓
2. B A gaseous nutrient in leaves ✓
3. C Stored only in seeds ✓
4. D Converted directly into nitrate ✓

Interveinal chlorosis on older leaves commonly indicates deficiency of

1. A Iron ✓
2. B Magnesium ✓
3. C Boron ✓
4. D Calcium ✓

Molybdenum is required in plants mainly for enzymes involved in

1. A Starch gelatinization in grains ✓
2. B Silica deposition in stems ✓
3. C Nitrate reduction and biological nitrogen fixation ✓
4. D Wax formation on fruit skin only ✓

Copper deficiency in some fruit crops may cause symptoms such as dieback because copper is involved in

1. A Only atmospheric nitrogen absorption ✓
2. B Only potassium chloride formation ✓
3. C Only gypsum dissolution ✓
4. D Oxidation-reduction enzymes and lignification ✓

Integrated nutrient management combines chemical fertilizers with organic manures and

1. A Biofertilizers where suitable ✓
2. B Only saline drainage water ✓
3. C Only insecticides ✓
4. D Only deep ploughing ✓

Azotobacter is used as a biofertilizer because it can

1. A Produce potash from feldspar instantly ✓
2. B Fix atmospheric nitrogen non-symbiotically ✓
3. C Remove all soil salts permanently ✓
4. D Convert clay into sand ✓

Phosphate-solubilizing bacteria help crops mainly by

1. A Increasing soil sodium adsorption ratio ✓
2. B Stopping transpiration in leaves ✓
3. C Converting insoluble phosphorus into more available forms ✓
4. D Replacing all nitrogen fertilizers ✓

The main purpose of soil testing before fertilizer recommendation is to assess

1. A Only crop market price ✓
2. B Only seed germination percentage ✓
3. C Only rainfall forecast ✓
4. D Available nutrient status and soil constraints ✓

Band placement of phosphatic fertilizer near the seed row often improves efficiency by reducing

1. A Phosphorus fixation by soil minerals ✓
2. B Nitrogen fixation by legumes ✓
3. C Root interception by young seedlings ✓
4. D Water infiltration in sandy soils ✓

Split application of nitrogen fertilizer is recommended mainly to reduce losses and match

1. A Seed dormancy after harvest ✓
2. B Crop demand during growth stages ✓
3. C Soil texture classification ✓
4. D Harvest index only ✓

Liming an acid soil generally increases soil pH and supplies

1. A Sodium carbonate only ✓
2. B Chloride salts only ✓
3. C Calcium, and sometimes magnesium ✓
4. D Nitrate gas only ✓

Gypsum is different from lime because gypsum supplies calcium and sulfur but has little direct effect on

1. A Replacing exchangeable sodium ✓
2. B Providing sulfate sulfur ✓
3. C Improving sodic soil structure ✓
4. D Raising soil pH ✓

Among mineral nutrients, the macronutrient usually required by crops in the largest amount is

1. A Nitrogen ✓
2. B Boron ✓
3. C Zinc ✓
4. D Molybdenum ✓

Micronutrients are called micronutrients because they are

1. A Needed only by microbes and not plants ✓
2. B Essential but required in very small amounts ✓
3. C Always toxic at any concentration ✓
4. D Absent from fertile soils ✓

Fertigation is the practice of applying fertilizers through

1. A Dry seed storage rooms ✓
2. B Harvest threshers ✓
3. C Irrigation water ✓
4. D Grain polishing machines ✓

Controlled-release fertilizers are designed to supply nutrients

1. A Only before seed germination in one hour ✓
2. B Only as insoluble rock particles ✓
3. C Only after crop harvest ✓
4. D Gradually over an extended period ✓

Neem-coated urea improves nitrogen management mainly by slowing

1. A Nitrification and nitrogen loss processes ✓
2. B Photosynthesis in crop leaves ✓
3. C Phosphorus fixation by iron oxides ✓
4. D Potassium release from mica only ✓

Crop residues with a very high carbon-to-nitrogen ratio initially tend to cause

1. A Instant nitrate leaching only ✓
2. B Nitrogen immobilization by soil microbes ✓
3. C Complete potassium removal from clay ✓
4. D Immediate soil sterilization ✓

Blossom-end rot of tomato is most closely linked with deficiency or poor transport of

1. A Molybdenum ✓
2. B Chlorine ✓
3. C Calcium ✓
4. D Nickel ✓

The critical nutrient concentration is the plant tissue level that separates deficiency from

1. A Permanent wilting point ✓
2. B Soil texture class ✓
3. C Seed dormancy stage ✓
4. D Adequate or sufficient nutrition ✓

Fertilizer use efficiency generally expresses crop response or nutrient uptake per unit of

1. A Nutrient applied ✓
2. B Rainfall evaporated ✓
3. C Soil clay dispersed ✓
4. D Seed moisture removed ✓

Soil fertility is best defined as the soil's capacity to supply plants with

1. A Only mechanical support for roots ✓
2. B Essential nutrients in available forms and proper balance ✓
3. C Only irrigation water at field capacity ✓
4. D Only pesticide residues after spraying ✓