Groundnut

Nutrient Management

• Groundnut is energy-rich crop but it is grown under energy-starved conditions.
• An average crop of groundnut removes about 112 kg N, 27 kg P₂O₅ and 34 kg K₂O from 1 ha of land.
• The nutritional needs of groundnut must be satisfied to attain maximum yields.
• Groundnut being a leguminous crop, it is capable of fixing atmospheric nitrogen by the root nodule bacteria.
• Application of nitrogenous fertilizer is not required but that lower doses of nitrogen would be sufficient to raise a good crop.
• Also application of phosphorus and potassium become more essential and these need to be supplied in adequate quantities for obtaining higher yields.

• Being a leguminous plant, groundnut may not respond to large application of nitrogen.
• It is, however, a major limiting factor in the proper growth of groundnut plant.
• In early stages of plant growth, nitrogen is very much in demand.
• Nitrogen is recommended in two equal split doses, i.e. half of the nitrogen at the time of sowing and the remaining half after 35-40 days of sowing preferably after weeding.
• For obtaining higher fertilizer efficiency, it should be top-dressed at proper moisture level in soil followed by harrowing.
• Nitrogen may be supplied preferably in the form of ammonium sulphate because it also contains sulphur, a nutrient also required by groundnut for synthesis of oil besides nitrogen.
• The following nitrogenous fertilizers are commonly used in groundnut crop.

• It is oldest N-synthetic fertilizer.
• It contains about 20% N in ammonium form and is a white crystalline salt.
• It is readily soluble in water but only slightly hygroscopic.
• It has a strong acidifying action on the soil.
• Among the available nitrogenous fertilizers, ammonium sulphate is preferred for groundnut crop because of its sulphur content (24%).
• It can be used in both rainfed and irrigated conditions.
• In top-dressing also, it can be used before irrigation or after irrigation at the time of proper soil condition.
• The ammonium ion (NH₄+) is absorbed by negatively charged colloids in the soil and its mobility through leaching is hence reduced.
• It can be absorbed directly by plant roots.

• It is a white granulated organic compound and contains 46% N
• Urea is easily soluble in water (1.0 kg/litre at 20^oC) having low specific weight (bulk density, 0.7 kg/litre).
• Urea is very popular and commonly used in groundnut.
• It can be used as basal-dressing in rainfed as well as irrigated conditions, for while top-dressing in rainfed, as well as irrigated conditions, but while top-dressing it should be applied at optimum soil moisture followed by harrowing.
• Decomposition of urea in the soil is effected by microbial enzymes (urease) and is temperature dependent.
• It is converted to ammonium carbonate and then to ammonium which usually immediately further gets converted to nitrate.
• Loss of gaseous ammonia may occur under certain conditions (high soil reaction and temperature) after applying the fertilizer on the soil surface.
• It can also be used as foliar nutrient but proper care should be taken about its concentration since higher concentration may burn the foliage of groundnut.

• It is granulated white (sometimes green or brown) water-soluble inorganic compound and contains 26% N.
• Due to Ca content it is an important fertilizer for groundnut crop.
• As it contains both the forms of annomical and nitrate nitrogen, it is easily available to the plant root.
• It can be used in basal application as well as in top-dressing.
• Top-dressing should be done after irrigation at proper soil moisture and should be followed by harrowing.

• Phosphorus is an important nutrient for groundnut crop.
• It stimulates the setting of pods, decreases the number of unfilled pods (pops) and hastens the maturity of the crop.
• About 25-50 kg P₂O₅/ha has been recommended for different groundnut-growing regions in the country.
• It has been found that single superphosphate is the best source of phosphorus as it contains calcium (19.5%), sulphur (12.5%) and phosphorus (16%).
• It also contains zinc and magnesium in traces. Entire P₂O₅ should be applied at the time of sowing as a basal-dressing.
• Furrow placement is the best method of phosphorus application in the soil as it minimizes the fixation of P₂O₅ with soil colloids.
• Description of some sources of phosphatic fertilizers commonly used in groundnut is given below:

• It is most commonly used phosphatic fertilizer in groundnut.
• It contains16% P₂O₅ besides Ca (19.5%) and sulphur (12.5%)
• The P content of this fertilizer is in the form of 90% water soluble and thus acts immediately.
• Water-soluble phosphate is converted in the soil into typical soil phosphate.
• Conversion is primarily to apatites (Ca phosphates), in neutral soil and to iron and aluminium phosphate in acid soil.
• The duration of this conversion which implies reduced mobility, depends not only on the inherent causative factors but also on the contact with fine soil particles.
• Contact with the soils should be minimum if the water-soluble form is to be maintained to a large degree.
• This requires placement of the fertilizer.
• Single superphosphate should be used as a basal-dressing only by placement method.
• It is not suitable for foliar spray as it contains some amount of gypsum and diphosphate which are not easily soluble in water.

• It is very popular granular fertilizer having both nitrogen (18%) and phosphorus (46% P₂O₅).
• Nitrogen content of this fertilizer is in ammoniacal form, and is thus immediately available to the plant root.
• Similarly all P content is water soluble and becomes available immediately.
• Application of di-ammonium phosphate (DAP) to the soil should be done before sowing as a basal-dressing.
• To minimize the fixation of P, it should be applied in furrows through placement.
• However, due to its high solubility in water, it may be used as foliar spray also.

• It is a concentrated form of superphosphate containing 46-50% P₂O₅.
• It is granulated, grey in colour and easily soluble in water.
• Triple superphosphate should be applied before sowing by placement method.
• However, it can be used for foliar spraying as the phosphorus content is high.
• While applying to the soil it should be placed closer to the root zone so that it becomes readily available to the root.

• Normally, about 50 kg K₂O/ha will be adequate for the soil deficient in potassium.
• Potassium may be supplied regularly in the form of potassium sulphate.
• All K₂O should be applied at the time of sowing as a basal-dressing by adopting furrow placement method.

• It is a white or slightly coloured, granulated, water-soluble fertilizer having 60% K₂O.
• When applied to the soil it is readily available to the plant root. Entire quantity of fertilizer may be applied to the soil prior to or at planting time.
• However, recent studies have indicated that application in two splits is superior than single application, depending upon the texture of the soil.

• It is a common fertilizer for groundnut which contains sulphur besides 50% K₂O.
• Due to its sulphur content, potassium sulphate is a better fertilizer for groundnut than potassium chloride.
• The K component is water soluble and, therefore is readily available to the plant roots.
• It can be used either as basal-dressing or top-dressing.
• The sulphate ions are retained by the soil more strongly than chloride ions but less strongly than phosphate ions.
• The sulphate ions are retained more in the soil with high content of calcium than in soils with low calcium content.
• Thus application of potassium sulphate, generally, will be more appropriate in soils which are calcarious in nature and alkaline in reaction.
• Under wet conditions, it is preferable to apply potassium sulphate than potassium chloride as leaching of potassium sulphate will be less.
• Similarly potassium sulphate will be more effective on light and medium soils than on heavy soils.

• Boron (B) deficiency has been reported from many groundnut growing areas in India.
• It occurs on deep, highly weathered soils. Boron deficiency in Tamil Nadu has been established.
• In Uttar Pradesh 19% of the soil samples tested were found deficient in boron.
• Some parts of Gujarat and Maharashtra also show its deficiency.

• The inner faces of the boron deficient groundnut cotyledons are depressed and discoloured.
• This is classified as a form of internal damage and has been termed hollow heart.
• Necrotic areas are localized near the leaf margin.
• Soils with hot water extractable boron below 0.2 ppm are considered deficient.

• Application of 10 kg / ha borax to soil increased the yield.
• In black calcareous soil the soil application of 5.8 kg / ha boric acid increased the yield.
• Foliar application of 0.5 kg / ha boron to groundnut having a leaf boron content at pre-bloom stage of 6 - 18 ppm increased the pod yield.
• Only small quantities of boron are needed for optimum production.
• On sandy soils 0.5 - 1 kg / ha boron is sufficient.
• Foliar application of boron as low as 0.1 ppm also increased the yield.

• In some soils of Uttar Pradesh copper (Cu) deficiency has been reported.
• Low available Cu content was found in alkaline soils in Rajasthan.
• Enough reports are not available to know the locations and extent of loss due to Cu deficiency.

• The copper (Cu) deficient plants are stunted and rosette.
• The stunted plants are green and wilted in early growth stage.
• The entire leaflet becomes cupped, and the leaflet margins turn upward.
• Some bronzing and necrosis of outer edge of the leaflet may occur.

• Small amount of soil applied CuSO₄ is able to correct the copper (Cu) deficiency on calcareous soils.
• Apply 2 - 6 kg Cu / ha as copper sulphate once in 3 - 4 years.
• Application should be discontinued with Cu build up in the soil and those with 0.2 ppm Cu or more should not be fertilized with Cu.

• These two nutrients are considered together as both are taken up from the pod zone by the pegs and developing pods.
• Calcium requirements of the groundnut plant is quite heavy.
• Therefore, availability of this nutrient in the soil in adequate quantities is very essential for meeting the nutritional requirements of the crop, specially in the case of acidic soil.
• Even in neutral and alkaline soils of sandy texture, calcium deficiency may become serious.
• Besides its requirement for good growth, major function of calcium in groundnut nutrition is the improvement in the quality of the nuts as evidenced by thin strong shell besides well - filled pods.
• Sulphur is directly involved in the biosynthesis of oil and is usually deficient in the groundnut soils.
• About 10ppm of heat - soluble sulphur is the critical limit of available sulphur for groundnut.

• Gypsum is the cheapest source of calcium and sulphur.
• It is relatively soluble source of Ca and S therefore, readily available to the developing pods.
• But it will be lose - completely to almost complete loss from the soil by the time groundnut crop is harvested.
• Higher quantities of gypsum than necessary are, therefore, applied at early flowering stage to ensure adequate calcium supply in the pod zone.
• Since there is little residual effect of gypsum it is necessary to repeat application every season.
• Groundnut has the unique characteristic of uptake of Ca and S by the developing pegs and pods.
• As Ca is relatively immobile in plant tissues and is not translocated in sufficient quantities from the roots to developing pods, Ca and S have to be made available in adequate quantities in pod zone.
• A well - powdered gypsum should be applied on soil surface when the crop is in peak flowering stage.
• Application should be as close to the base of the plant as possible because Ca present in the pod zone of 5cm depth of soil is taken up by the pegs and developing pods.

• Iron deficiency is characterized initially by inter - veinal chlorosis on the younger leaves.
• Under severe deficiency the veins also become chlorotic and leaves become white.
• Iron - deficient plant has limited root system which may cause other nutrient deficiencies.
• The plant analysis for Fe content would be misleading, as the chlorotic leaves have higher iron content.
• Ferrous iron test appears to be very suitable for diagnostic purposes.

• Spraying of 0.5 - 1.0% FeSO₄ + 0.1% citric acid has been found to correct the deficiency.
• Chelated Fe sources such as Fe - EDDHA are effective for soil application, but are expensive.
• Spray of ferrous ammonium sulphate corrects the Fe deficiency for a few weeks.
• Addition of 0.2% urea in the spray solution seems to aid Fe absorption.
• Spray with ferrous sulphate before irrigation improves the yield.
• But needs repeated sprays as the deficiency symptoms re-appear in new growths due to highly immobile nature of Fe in plant.

• Most of the Indian soils are deficient in magnesium.
• Deficiency has been reported in the acid soils, as well as in the soils having pH more than 9.

• Older leaves become chlorotic, beginning at margins and spreading towards midribs, followed by orange colouration of margins under acute deficiency conditions.
• Young leaves are also affected.
• The concentration of Mg below 0.3% shows deficiency symptoms. Mg deficiency is conducive to tikka attack.

• Spray of foliage with 1% MgSO₄ solution to correct the deficiency.

• Low availability of manganese (Mn) is usually associated with alkaline soils and excess of Mn with acid soils.
• In India since groundnut is mostly grown in the soils having pH more than 7.5 there is high incidence of Mn deficiency.
• Soils of Uttar Pradesh and Karnataka are low in exchangeable Mn.

• The typical Mn deficiency is interveinal chlorosis, but there may also be a distinguishing characteristic of brown spots on the leaf margin.

• Foliar application of different forms of manganese proved superior to soil application.
• MnSO₄ was found to be better for foliar application @ 0.12 kg Mn/ha.
• Leaf Mn was usually 50-100 ppm and Mn deficiency may be expected when it is less than 20 ppm.

• The deficiency of molybdenum (Mo) is confined largely to acid soils.
• Mo availability increase with the increase in pH.
• In Uttar Pradesh 24% soils are deficient in Mo.
• Its deficiency is quite likely in high pH soils also.

• The role of Mo in enzyme system of symbiotic nitrogen fixation suggests that the Mo-deficient groundnut would in fact become deficient in nitrogen.
• The deficiency symptoms are paling, wilting, marginal rolling and scorching of leaves.

• Application of 1 kg/ha ammonium molybdate to a crop receiving NPK increased the yield by 45% in an irrigated trial.
• While the response of NPK was only 20%.
• Soil application of 0.56-1.72 kg/ha ammonium molybdate and foliar spray of 100-200 ppm ammonium molybdate before flowering increased the yield.
• Mo is a toxic element and critical limits for its sufficiency and deficiency are very much narrow.

• Zinc (Zn) deficiency is likely to occur (i) when soils are alkaline or low in organic matter, (ii) under high levels of soil P, and (iii) when the soils are cool and wet during the vegetative phase.
• Zn deficiency is widespread all over the country Marked effect of Zn deficiency is due to the influence of Zn on the auxin level.
• Zn increases the chlorophyll content in the leaves and pod production.
• Nodule number and weight also increases.
• The crop yield is reduced by about half when the Zn level in the soil is lower than 1.2 ppm.

• In Zn deficient leaves wider chlorotic strips are found, which may run the entire length of the leaflets.
• The bands will usually be on the leaf portion nearest to the petiole.
• Zn deficiency symptoms may occur concurrently with Fe deficiency symptoms and the two can easily be confused.
• The entire leaflet will become chlorotic if the deficiency is severe and prolonged.

• Application of 15 kg Zn / ha to the soil or 10 kg Zn / ha to the foliage as zinc sulphate increases the yield.
• In Andhra Pradesh 50 kg ZnSO₄ / ha substantially increased the yield.
• Residual effect of Zn to the groundnut taken after wheat also proved highly beneficial.
• Foliar application of Zn suppresses sclerotinia blight during fruit development.

• The uptake of sulphur from the soil is generally in the form of sulphate.
• The availability of Suphur to plants depends on the ability of the soil to supply sufficient soluble sulphate.
• Wide occurrence of Sulphur deficiency in the country's soils has been reported.
• Soils with less than 10 ppm available sulphur are deficient for groundnut.

• The leaves turn pale. young as well as middle leaves show chlorosis.
• under severe conditions the leaves become papery .
• The deficiency symptoms of iron and sulfur appear together in groundnut.

• S-deficient plants have low chlorophyll content.
• soil application of 250kg /Ha gypsum is able to improve the deficiency and increase the pod yield.
• Gypsum should be used when P is not deficient and superphosphate when P is also deficient.
• The reports available indicate that S increases the protein and oil content in groundnut.
• Nutrients take part in the various metabolic processes of the plant.
• The deficiency of the nutrients in the plant will bring about derangement in the metabolism, which in turn manifests in the development of visible deficiency symptoms such as yellowing of the leaves, interveinal chlorosis, purpling of the leaves and stems, stunted plant growth and other abnormalities.
• These deficiency symptoms are characteristic of a given element.
• In the case of deficiency of more than one element, or severity of deficiency, the identification of the symptoms for a given nutrient would be difficult and requires experience.

• Calcium (Ca) requirement of groundnut plant is quite high and it is more during the pod-filling stage.
• Acid soils are deficient in calcium.
• Serious Calcium deficiency may occur in neutral and alkaline soils of sandy texture.

• Calcium is needed for good plant growth and pod yield.
• If Calcium is deficient in the fruiting zone, aborted and shrivelled pods (pops) are obtained.
• The kernels have dark plumule.
• The germination and seedling survival is poor.
• Distinguishing foliar deficiency symptoms of calcium in groundnut are not known.
• Symptoms like pitted areas on lower surface of older leaves are found.
• Later on large necrotic spots are found on both the surfaces, which give leaves a bronze colour.
• Youngest foliage appears distorted.

• To get good yields, the availability of Calcium in the fruiting zone must exceed a defined critical level during the time of pod development.
• The requirements of calcium for groundnut are 1 meq/100 g soil in the root zone and 3 meq/100 g soil in the pod zone.
• Depending on soil test, 250-500 kg/ha gypsum may be applied in the fruiting zone at 0-5 cm depth.

• To obtain maximum pod yield, adequate supply of every essential nutrient as per plant requirement at different growth stages has to be ensured.
• Soil is the main source of nutrients to the plant.
• But the nutrients are rarely available in adequate quantities in the soil to fulfil the nutritional needs of the groundnut crop, especially when the high - yielding varieties are grown.
• The nutrients in the soil may be present in insufficient quantities or in complex form which hinder their availability to the plant.
• Nutrient deficiency is therefore mainly due to soil conditions.
• Most suitable soils for groundnut cultivation are red sandy soils, sandy loam, alluvial, coastal alluvial, mixed red, black and medium black soils.
• The availability of the nutrients depends on factors such as pH of the soil, moisture content, cropping pattern, rate of release of micronutrients from the soil mineral, and the presence of other ions in the soil.
• Extreme pH ranges (alkaline soil pH > 8 and acid soil pH< 6) are not well suited to groundnut.
• It is well known that soils pH influences the availability of the nutrients.
• In the acidic and alkaline soil pHs the availability of most of the nutrients is reduced.

• The soil pH of 6-7.5. seems to be ideal for the availability of nutrients. Alkaline and acid soils are more prone to nutrient deficiency in the plant.
• The presence of other ions in excess also influences the availability of nutrients to the plant, e.g on calcareous soils iron deficiency is due not to a lack of iron but to its being immobilized or inactivated by carbonates or bicarbonates.
• In coastal soils affected by salinity, the uptake of nutrients may be reduced. These soils may be deficient in zinc also.

• There is immence scope to increase the groundnut yield through correction of micronutrient deficiency.
• Another strategy that needs attention is to genetically manipulate the efficient plants for the deficient soils.
• Marked variation in the ability of groundnut varieties to cope with nutrient-deficiency situations, at least in some cases of nutrients, raises the hope of evolving nutritionally efficient varieties.
• Groundnut yield per unit area in our country is quite low.
• There is a wide gap between the national average yield (870 kg / ha) and the potential achievable yield (5,000 kg / ha).
• Besides paucity of irrigation water and poor disease and pest management, inadequate supply of essential nutrients could be one of the reasons for such a wide gap.
• More than 40% of the world's cultivated soil is deficient in nutrients, and the condition in India is still worse.