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. ALiebig's law of minimum✓
2. BBlackman's law of limiting factors✓
3. CMitscherlich's law of diminishing returns✓
4. DShelford's law of tolerance✓

The three primary macronutrients commonly represented in fertilizer grades are

1. ACalcium, magnesium and sulfur✓
2. BNitrogen, phosphorus and potassium✓
3. CIron, zinc and boron✓
4. DCarbon, hydrogen and oxygen✓

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

1. AElemental nitrogen gas✓
2. BNitrite ion✓
3. CNitrate ion✓
4. DOrganic protein nitrogen✓

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

1. AIron✓
2. BCalcium✓
3. CBoron✓
4. DNitrogen✓

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

1. AATP and nucleic acids✓
2. BChlorophyll molecule center✓
3. CStomatal guard cell waxes✓
4. DCellulose microfibril cross-links✓

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

1. ABoron✓
2. BPotassium✓
3. CMolybdenum✓
4. DChlorine✓

Sulfur is an essential constituent of the amino acids

1. ALysine and arginine✓
2. BGlycine and alanine✓
3. CCysteine and methionine✓
4. DProline and valine✓

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

1. ANitrogen✓
2. BMagnesium✓
3. CPotassium✓
4. DIron✓

Boron is particularly important for flowering crops because it supports

1. APollen germination and pollen tube growth✓
2. BNitrate reduction in root nodules✓
3. CChlorophyll formation in mature leaves✓
4. DStarch conversion into lignin✓

Khaira disease of rice is mainly associated with deficiency of

1. ACopper✓
2. BZinc✓
3. CManganese✓
4. DMolybdenum✓

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

1. A3.5 to 4.0✓
2. B4.5 to 5.0✓
3. C6.5 to 7.0✓
4. D9.5 to 10.0✓

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

1. AConvert nitrate into atmospheric nitrogen✓
2. BMeasure only soluble salts in irrigation water✓
3. CFix carbon dioxide during photosynthesis✓
4. DHold and exchange positively charged nutrient ions✓

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

1. AWater-holding capacity✓
2. BSoil bulk density only✓
3. CSalt concentration only✓
4. DExchangeable sodium percentage✓

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

1. ANitrosomonas✓
2. BRhizobium✓
3. CThiobacillus✓
4. DPseudomonas fluorescens✓

Nitrification in soil is the microbial conversion of ammonium into

1. AAmmonia gas under dry conditions✓
2. BOrganic nitrogen under anaerobic conditions✓
3. CNitrate under aerobic conditions✓
4. DElemental sulfur under flooded conditions✓

Denitrification is favored by waterlogged soils because it converts nitrate into

1. AExchangeable potassium✓
2. BCalcium carbonate✓
3. CAvailable phosphate✓
4. DGaseous forms of nitrogen✓

The nitrogen content of prilled urea fertilizer is approximately

1. A46 percent✓
2. B18 percent✓
3. C26 percent✓
4. D60 percent✓

The fertilizer grade of diammonium phosphate is commonly written as

1. A46-0-0✓
2. B18-46-0✓
3. C0-0-60✓
4. D21-0-0✓

Single superphosphate is valued because it supplies phosphorus along with appreciable

1. APotassium and sodium✓
2. BZinc and molybdenum✓
3. CSulfur and calcium✓
4. DMagnesium and chlorine✓

Muriate of potash is chemically known as

1. APotassium sulfate✓
2. BPotassium nitrate✓
3. CMonopotassium phosphate✓
4. DPotassium chloride✓

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

1. AN, P2O5 and K2O✓
2. BNitrate, phosphate and carbonate✓
3. CCalcium, magnesium and sulfur✓
4. DOrganic carbon, humus and clay✓

Mineralization of organic matter in soil means release of nutrients into

1. AOnly insoluble rock minerals✓
2. BInorganic plant-available forms✓
3. CPermanent unavailable complexes✓
4. DAtmospheric oxygen only✓

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

1. ADeep subsoil gravel✓
2. BExcess exchangeable sodium✓
3. CMicronutrients in standing crops✓
4. DSoil texture class✓

Green manuring improves soil fertility mainly by adding organic matter and

1. ASoluble sodium carbonate✓
2. BExcess chloride salts✓
3. CIndustrial lime dust only✓
4. DBiologically fixed nitrogen when legumes are used✓

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

1. ANutrient availability✓
2. BSoil salinity hazard✓
3. CPesticide persistence✓
4. DSoil crusting by sodium carbonate✓

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

1. AOnly the cheapest fertilizer source✓
2. BProper nutrient proportions✓
3. COne fixed dose for all soils✓
4. DOnly nitrogen at sowing✓

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

1. AOxygen✓
2. BCarbon dioxide✓
3. CPotassium✓
4. DSilicon only✓

Deficiency symptoms of mobile nutrients usually appear first on

1. ARoot hairs only✓
2. BNew buds only✓
3. CFruit seeds only✓
4. DOlder leaves✓

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

1. ARelatively immobile in the phloem✓
2. BA gaseous nutrient in leaves✓
3. CStored only in seeds✓
4. DConverted directly into nitrate✓

Interveinal chlorosis on older leaves commonly indicates deficiency of

1. AIron✓
2. BMagnesium✓
3. CBoron✓
4. DCalcium✓

Molybdenum is required in plants mainly for enzymes involved in

1. AStarch gelatinization in grains✓
2. BSilica deposition in stems✓
3. CNitrate reduction and biological nitrogen fixation✓
4. DWax formation on fruit skin only✓

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

1. AOnly atmospheric nitrogen absorption✓
2. BOnly potassium chloride formation✓
3. COnly gypsum dissolution✓
4. DOxidation-reduction enzymes and lignification✓

Integrated nutrient management combines chemical fertilizers with organic manures and

1. ABiofertilizers where suitable✓
2. BOnly saline drainage water✓
3. COnly insecticides✓
4. DOnly deep ploughing✓

Azotobacter is used as a biofertilizer because it can

1. AProduce potash from feldspar instantly✓
2. BFix atmospheric nitrogen non-symbiotically✓
3. CRemove all soil salts permanently✓
4. DConvert clay into sand✓

Phosphate-solubilizing bacteria help crops mainly by

1. AIncreasing soil sodium adsorption ratio✓
2. BStopping transpiration in leaves✓
3. CConverting insoluble phosphorus into more available forms✓
4. DReplacing all nitrogen fertilizers✓

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

1. AOnly crop market price✓
2. BOnly seed germination percentage✓
3. COnly rainfall forecast✓
4. DAvailable nutrient status and soil constraints✓

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

1. APhosphorus fixation by soil minerals✓
2. BNitrogen fixation by legumes✓
3. CRoot interception by young seedlings✓
4. DWater infiltration in sandy soils✓

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

1. ASeed dormancy after harvest✓
2. BCrop demand during growth stages✓
3. CSoil texture classification✓
4. DHarvest index only✓

Liming an acid soil generally increases soil pH and supplies

1. ASodium carbonate only✓
2. BChloride salts only✓
3. CCalcium, and sometimes magnesium✓
4. DNitrate gas only✓

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

1. AReplacing exchangeable sodium✓
2. BProviding sulfate sulfur✓
3. CImproving sodic soil structure✓
4. DRaising soil pH✓

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

1. ANitrogen✓
2. BBoron✓
3. CZinc✓
4. DMolybdenum✓

Micronutrients are called micronutrients because they are

1. ANeeded only by microbes and not plants✓
2. BEssential but required in very small amounts✓
3. CAlways toxic at any concentration✓
4. DAbsent from fertile soils✓

Fertigation is the practice of applying fertilizers through

1. ADry seed storage rooms✓
2. BHarvest threshers✓
3. CIrrigation water✓
4. DGrain polishing machines✓

Controlled-release fertilizers are designed to supply nutrients

1. AOnly before seed germination in one hour✓
2. BOnly as insoluble rock particles✓
3. COnly after crop harvest✓
4. DGradually over an extended period✓

Neem-coated urea improves nitrogen management mainly by slowing

1. ANitrification and nitrogen loss processes✓
2. BPhotosynthesis in crop leaves✓
3. CPhosphorus fixation by iron oxides✓
4. DPotassium release from mica only✓

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

1. AInstant nitrate leaching only✓
2. BNitrogen immobilization by soil microbes✓
3. CComplete potassium removal from clay✓
4. DImmediate soil sterilization✓

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

1. AMolybdenum✓
2. BChlorine✓
3. CCalcium✓
4. DNickel✓

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

1. APermanent wilting point✓
2. BSoil texture class✓
3. CSeed dormancy stage✓
4. DAdequate or sufficient nutrition✓

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

1. ANutrient applied✓
2. BRainfall evaporated✓
3. CSoil clay dispersed✓
4. DSeed moisture removed✓

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

1. AOnly mechanical support for roots✓
2. BEssential nutrients in available forms and proper balance✓
3. COnly irrigation water at field capacity✓
4. DOnly pesticide residues after spraying✓