Cymraeg
Terms

Crop Production
Session 4 - Nutrients for Crop Growth

This resource is suitable to support Level 2 Agriculture courses.

Content

This unit on preparing and cultivating land for planting will contain information on the following:

  • Session 1 - Major and trace elements
  • Session 2 - Maintaining nutrient levels in the soil
  • Session 3 - Liming
    • image of plant in soil with hand about to drop seeds nearby

    Session 1 - Major and Trace Elements

    Plant Nutrients

    When crops are harvested, the nutrients that have been absorbed are removed therefore it is important that the nutrients are replaced and are readily available for the next crop.

  • This can be achieved by the application of chemical (inorganic) fertilisers, organic fertilisers or with organic manures such as FYM and slurry.
    • fertiliser being sprayed

    Groups of Nutrients

    Major Elements:

  • Nitrogen
  • Phosphate
  • Potassium
  • Sulphur
  • Magnesium
  • Calcium
  • Sodium

    • Groups of Nutrients

    Trace Elements

  • Boron
  • Copper
  • Iron
  • Manganese
  • Molybdenum
  • Zinc
  • Cobalt

    • Major elements needed for crop growth

    Nitrogen

    This nutrient is supplied by fertilisers and organic manures.

  • Farmers can use legumes e.g. clovers, peas and beans as a free source of nitrogen because they contain ‘nodule rhizobium bacteria’ that fix nitrogen from the atmosphere to the soil.
    • close up of clovers

    Major elements needed for crop growth

    Nitrogen

    Nitrogen is also produced naturally by a bacterium which decompose organic matter.

  • Nitrogen is lost from the soil through de-nitirification by another type of bacteria.
  • Nitrogen can also be lost by ‘leaching’ where nitrogen is washed away by water.
    • close up of bacteria

    Major elements needed for crop growth

    Phosphate

    This nutrient can be supplied by fertilisers and organic matter from manures or plant debris.

  • Soluble phosphate fertiliser e.g. inorganic fertiliser can be instantly used by the plant but insoluble phosphate fertiliser needs to be broken down by bacteria and weak acid in the soil before it can be used.
    • tractor with fertiliser attachment

    Major elements needed for crop growth

    Potassium

    This nutrient can be supplied by fertilisers, manures and plant debris.

  • In some areas mineralization of the underlying rock releases potassium to the soil.
    • manure on field

    Major elements needed for crop growth

    Sulphur

    This nutrient can be supplied by fertilisers, manures and from rainfall (acid rain).

  • Improved pollution control at coal fired power stations has made rainfall a less reliable source of sulphur and consequently more fertilizer sulphur is now being applied.

    • Nutrient need and the effect on plants and soils

    Plant Nutrient Crops most likely to suffer Conditions where deficiency is likely Deficiency symptoms Effect on growth Effect of excess nutrient
    Nitrogen All crops except legumes All soils except peats, if organic matter is low and after continuous cereals Thin and weak plant, yellow leaves, lack of tillers Speeds up growth, improves quality, encourages clover in grassland Lodging in cereals, delay ripening, susceptible to frost and disease, lowers sugar and starch content
    Phosphorus Root crops and clover Clay soils, high rainfall areas and poor grassland Similar to nitrogen except that leaves are dull with purple or green tints Increases leaf size, rate of growth and yield, makes leaves dark green Causes crop to ripen early therefore reduces yield
    Potassium Root crops and clover Sandy soils, grassland repeatedly cut for silage or zero grazed Stunted growth, tips and edges of leaves die Increases disease and frost resistance, improves quality Delay ripening may cause magnesium deficiency therefore grass staggers in cattle
    Magnesium Cereals, potatoes, sugar beet, peas, beans, kale Light sandy soils Patches appear on leaves Produces chlorophyll and improves potassium use Unlikely to occur
    Sulphur Most crops Sandy soils, if soil is low in organic matter and intensively cropped Similar to nitrogen deficiency Nitrogen made more efficient Unlikely to occur

    Trace Elements

    Trace elements are minerals that are required by crops in small amounts to grow healthily. The trace elements that are most frequently found deficient are:

  • Manganese: Frequently deficient in field crops, associated with high pH levels and high organic matter, both of which lock manganese in the soil.
  • Boron: Deficiency most often seen in root crops and sugar beet.
  • Copper: Deficiency is a problem in peaty, very light sandy soils and inthin, organic chalky soils.

    • The Need for Trace Elements

    The need for trace elements is likely to be greatest:

  • On infertile soils.
  • Where soil conditions high or low pH, and very high soil organic matter make them unavailable.
  • On intensively farmed land where large amounts of trace elements are extracted by crops.
  • Where manures such as FYM and slurry are not used to recycle trace elements.
    • image of wheat

    Soil Chemical Analysis

    Soil chemical analysis is important before applying trace elements.

  • This identifies which trace elements are deficient and ultimately saves on cost.
  • Poor crop growth may be due to other factors such as poor drainage, drought, frost, mechanical damage, viral or fungal disease.
    • image of leafy crops in field

    Trace Element Application

    Too high an application rate of trace elements can damage or even kill the crop. Trace elements can be applied to the land as:

  • Chelates, which are water-soluble complexes of the trace element.
  • Foliar sprays, sometimes as a supplement with compound fertiliser.
  • ‘Frits’, which is glass containing the element, broken into small particles to be distributed to the soil.

    • Trace Element Application Methods

    Foliar sprays

    image of tractor spraying in field

    Fritted Fertilizers

    F∙T∙E", produced by fritting six elements (manganese, boron, iron, zinc, copper, and molybdenum).

  • F∙T∙E is an environmentally friendly composite vitreous micronutrient made to slowly dissolve for absorption during the crop growing season.

    • Session 2 - Maintaining Nutrient Levels in the Soil

    Maintaining Nutrient Levels in the Soil


    Manures

    Manure is applied on agricultural land as a means of disposing of animal waste accumulated during housing, it has the added benefit of introducing organic matter to the land and being a cheap source of nutrients such as Nitrogen (N), Phosphate (P), Potassium (K) and Sulphur (S).

    manure in field

    Farm Yard Manure (FYM)

    Usually contains bedding material such as straw thereby giving it a high Dry Matter (DM) and organic dry matter content (ODM), It is a by-product of housing dairy cattle, beef cattle, sheep, pig and poultry.

    manure in field

    Slurry

    A mixture of urine and manure of a low DM giving it a liquid texture. It is a by-product of pig and cattle housing in cubicles or on slats where bedding is not mixed with manure. It is the product of feeding dairy cattle on low DM silage.

    tractor spreading slurry

    Dirty Water

    Water used to wash areas where animals have deposited waste.

  • This is predominantly a by-product of dairy cattle e.g. parlour washings, and is usually stored and applied to the land mixed with slurry.
    • image of cows in parlour washing

    Nutrient Content

    The nutrient content of different types of manures varies according to animal type, diet and storage method e.g. dairy cattle fed on high protein diet produce manure with a higher N content than beef cattle manure.

  • Poultry produce manure with a very high N content.

    • Quantities of nutrients produced by livestock during housing (Ioan Rhys Williams)

    Livestock Body weight (kg) Housing period (days per year) Undiluted excreta (m3 or tonnes) Nitrogen (kg) Phosphate (kg) Potash (kg)
    Dairy cattle 550 183 9.6 48 19 48
    Beef cattle 400 240 6.2 31 12 31
    Pig 200 365 4 20 20 16
    Poultry (1000 hens) 2200 365 41 660 545 360
    Sheep 65 30 0.1 0.8 0.2 0.4

    Environmental Hazards

    There are two environmental hazards associated with the use of manures.

    1. Water Pollution

  • This is a result of poor storage or field spreading procedures.
  • Manures have a high biochemical oxygen demand that depletes water of oxygen, if they find their way into rivers and water courses they will starve aquatic life such as plants and fish of oxygen.
    • water storage

    Environmental Hazards

    There are two environmental hazards associated with the use of manures.

    2. Ammonia and Odour Pollution

  • Farm buildings and spreading procedures are sources of ammonia and odour pollution.
  • Manures release ammonia to the atmosphere that can cause acidification and nitrogen enrichment leading to a decline in species diversity.
  • Odour pollution represents a nuisance factor to the public.
    • farm building

    Inorganic Fertilisers

    These are chemical fertilisers that are purchased and applied to the land to increase available nutrients.

  • They can be purchased as ‘straights’ or ‘compounds’.
    • bags of Nitram

    Straights

    These have a single main chemical ingredient, therefore when applied to the land they will only supply that particular nutrient.

    Compounds

    Many crops need more than one of the three main nutrients (N, P and K), therefore it’s convenient to apply all the nutrients at the same time, for this purpose, manufacturers have produced a range of compound fertilisers which is many nutrients in one fertiliser.

    Compounds

    Compound fertilisers are more expensive than straights but the extra cost can be justified if more than one nutrient is needed since there would be an extra cost of spreading or mixing and difficulty in getting an effective spread.

    compound fertiliser on back of tractor

    Composition of a Compound Fertilizer

    The composition of a compound fertiliser is stated in terms of a ratio N:P:K.

  • The table shows examples of three compound fertilisers.
    • Compound Content Use
    20:10:10 Mostly N and an equal amount of P and K A general purpose fertiliser
    25:0:15 Mostly N, no P and some K Used on grass aftermath
    0:15:15 No N but an equal amount of P and K Used in a cereal seedbed

    Fertilizer Types

    Fertilisers in the U.K are available in either solid or liquid form:

    Solids

    The advantages of solid fertilisers are:

  • High concentration of nutrient in the material, reducing transport and storage costs.
  • Easy to handle eg tonne bags handled with tractor mounted forks.
  • Easy to store, allows farmer to buy in bulk.
    • solid blue fertiliser pellets

    Solid Fertilizer

    Solid fertilisers can come in different forms:

    1. Powders

  • Some fertilisers need to be in this form to ensure the activity of the material in the soil.
  • They can be difficult to spread evenly on the land.
    • powder solid fertiliser being layed

    Types of Solid Fertilizers

    2. Granules

  • They break down quickly to release the nutrients.
  • Their size and texture will have an effect on the sowing rate and width.

    • 3. Prills

  • Similar to granules but have a smooth surface and flow more freely.

    • 4. Fragments

  • Made by coarse grinding of solid material, they behave in a similar way to granules.

    • Liquid Fertilizer

    Some fertilisers need to be in liquid form because they do not exist as solids, e.g. urea. Liquid fertilisers hold a fairly small share of the fertiliser market, these are some of their main features:

  • Easy to handle because they can be pumped in and out of stores and spread with sprayers but storage tanks are needed which can be expensive.
  • Relatively low concentration of nutrients.
  • Possible to mix with herbicide to reduce spreading costs.
  • Specialist equipment is required.

    • Organic Fertilizer

    Organic fertilisers are derived from either plant or animal material.

    Advantages of Organic Fertilizers

    They are not immediately soluble to water therefore are not as susceptible to leaching as inorganic fertilisers.

    They have to break down to become soluble therefore are a slow-release source of plant nutrient.

    Unlike inorganic fertilisers, they can be applied at heavy rates without risk of injury to roots or germinating leaves.

    They can stimulate microbial activity.

    tramlines in wheat field

    Sources of Organic Nutrients

    Nutrient Source
    Nitrogen (N) Blood
    Hoof and horn
    Composted manures
    Plant waste materials
    Shoddy (wool waste)
    Phosphate (P) Meat and bone
    Rock phosphate
    Basic slag
    Potassium Rock potash
    Adularian shale
    Sylvinite
    Wood ash
    Calcium (Ca) and Magnesium (Mg) Epsom salts
    Calcareous magnesium rock
    Ground chalk and limestone
    Calcified seaweed
    Sulphur (S) Flowers of sulphur
    Potassium sulphate
    Trace elements Liquid and dried seaweed

    Fertiliser Handling and Storage

    Inorganic fertilisers can be purchaser as solids in bags of various weights eg 600kg.

  • The big bags have a top-lift hook facility to allow easy loading into spreaders but they are difficult to stack.
  • Fertiliser can also be purchased in fluid form.
  • it is vitally important that all fertilisers are handled and stored correctly for environmental and health and safety reasons as well as to minimise waste.

    • Solid Fertilizers

    Permanent Stores

  • Locate away from heat sources to minimise fire risk.
  • Avoid prolonged outdoor storage but where unavoidable, ensure it is protected from rain and sunlight with wrapping and sheeting.
  • Keep storage areas clean and rodent free.
  • Sweep up spillages and dispose in slurry pit or spread thinly on growing crops.
  • Do not use sawdust as an absorbent.
    • fertilisers being storaged

    Session 3 - Liming

    Liming

    The pH scale is used to measure the acidity or alkalinity of soil. pH 7 is neutral, a pH value less than 7 is acidic and pH values higher than 7 are alkaline.

  • Optimum bacterial and crop growth occurs at a pH of 6.3 - 6.8.
    • grass

    Leaching

    Significant leaching in high rainfall areas creates an acidic (sour) soil where crops will not grow satisfactory.

  • Calcareous soils are naturally alkaline and peaty soils naturally acidic.
    • rain landing on ground

    pH of Cultivated Ground

    Most cultivated soils have a pH level of between 4.5 and 8. Maintaining the optimum pH 6.5 will optimise the availability of soil nutrients.

  • Where there is a tendency for soils to become acid then lime that contains calcium carbonate is applied to neutralise the acidity.
    • tractor churning soil

    How is Lime Removed from the Soil?

    Lime is removed by the soil by:

  • Drainage – Removed in the water that leaves.
  • Fertilisers and manures – Sulphate and ammonia counteract the effect of calcium carbonate.
  • Crops e.g. 7kg of calcium carbonate is lost with every tonne of straw.
  • Stock e.g. a 500kg bullock removes 16kg of calcium carbonate in his bones, 18kg of calcium carbonate leaves the farm with every 5000 litres of milk.
    • wheat field

    Indicators of Low Lime Status in the Soil

  • Crops failing in patches, especially acid sensitive ones such as barley and sugar beet.
  • On grassland, the emergence of poor types of grasses such as bents and a mat of undecayed vegetation.
  • On arable land, weeds such as ‘sheep’s sorrel’ and ‘spurrey’ are common.
  • A soil analysis showing a pH ﹤ 6.5
    • wheat in field

    The Main Benefits of Liming

  • It improves the availability of other plant nutrients (over liming can make some nutrients unavailable).
  • It neutralizes the acidity.
  • It supplies calcium for plant nutrition.
  • It improves soil structure.
    • wheat

    Optimum pH for Different Crops

    The optimum or correct pH level depends on the soil type and the crop that is to be grown, grassland has a lower requirement than arable crops.

    tractor with fertiliser

    Table Shows the Minimum Soil pH Level Suitable for Different Crops:

    Crop Minimum soil pH level
    Barley, sugar beet, beans, peas and lucerne 6.5
    Maize, oilseed rape, oats, wheat, cabbage and carrots 6.0
    Potatoes and rye 5.5
    Ryegrass and fescues 5.0

    Lime Requirements

    The amount of lime needed to apply to the land to convert the pH to its optimum level is dependent on:

  • Optimum pH of the crop to be grown.
  • Soil texture.
  • Organic matter content.
  • Current pH level.
    • crops in field

    Table shows the tonnes per hectare of lime required for soils of different types and cropping with a certain pH level

    Soil pH Sands and loamy sands Sandy loams and silt loams Clay loams and clay Organic soils Peaty soils
    Arable Grass Arable Grass Arable Grass Arable Grass Arable Grass
    6.2 3 0 4 0 4 0 0 0 0 0
    6.0 4 0 5 0 6 0 4 0 0 0
    5.5 7 3 8 4 10 4 9 3 8 0
    5.0 10 5 12 6 14 17 14 7 16 16

    https://ahdb.org.uk/knowledge-library/liming-for-a-grassland-reseed

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