MACRO NUTRIENTS Introduction Plant nutrients occur in the soil in form of soluble substances. These substances are taken in by the plants in different quantities depending on their roles in the plant tissues. Essential Elements These are nutrients needed by plants for various uses. They are divided into two broad categories namely: \tMacronutrients \tMicronutrients. Macro-nutrients - These are also referred to as major nutrients. - They are required by the plant in large quantities. They include; \tcarbon, \thydrogen, \toxygen, \tnitrogen, \tphophorus, \tpotassium, \tsulphur, \tcalcium \t - Nitrogen, phosphorus and potassium are referred to as fertilizer elements, - Calcium, magnesium and sulphur, are referred to as liming elements. ROLE OF MACRO NUTRIENTS IN PLANTS Nitrogen (N03, NH4) Sources \tArtificial fertilizers \tOrganic matter \tAtmospheric fixation by lightning \tNitrogen fixing bacteria. Role of Nitrogen in Plants \tVegetative growth \tChlorophyll formation \tBuildup of protoplasm. \tImproves leaf quality in leafy crops such as tea and cabbages Deficiency Symptoms \tYellowing of the leaves/chlorosis. \tStunted growth. \tPremature ripening. \tPremature shedding of the leaves. \tLight seeds. Effect of Excess Nitrogen \tScorching of the leaves. \tDelayed maturity. Loss of Nitrogen from the Soil: \tSoil erosion. \t \t \tCrop removal. \tUsed by microorganisms. Phosphorus (H, P04, HPO"4 P105) Sources: \tOrganic manures \tCommercial fertilizers \tPhosphate rocks Role of Phosphorus \tEncourages fast growth of the roots. \tImproves the quality of the plant. \tHastens maturity of the crops. \tInfluences cell division. \tStimulates nodule formation in legumes. Deficiency symptoms \tGrowth of the plant is slow. \tMaturity is delayed. \tLeaves become grey, purple in colour. \tYield of grains, fruits and seed is lowered. Loss of Phosphorus from the Soil \tSoil erosion. \tLeaching \tCrop removal \tFixation by iron and aluminum oxide. Potassium (K‘, K20) Sources \tCrop residue and organic manures. \tCommercial fertilizers \tPotassium bearing minerals e.g. feldspar and mica. Role of Potassium in Plants \tIncreases plant vigour and disease resistance. \tIncreases the size of grains and seeds. \tReduces the ill-effects due to excess nitrogen. \tPrevents too rapid maturation due to phosphorus. Deficiency Symptoms \tPlants have short joints and poor growth. \tPlants lodge before maturing. \tLeaves develop a burnt appearance on the margin. \tLeaves at the lower end of the plant become mottled, spotted or streaked. \tIn maize, grains and grasses firing starts at the tip of the leaf and proceeds from the edge usually leaving the midrib green. Loss of Potassium from the Soil \tCrop removal. \t \tSoil erosion. \tFixation in the soil. Calcium (Ca2+) Source: \tCrop residues and organic manures. \tCommercial fertilizers. \tWeathering of soil minerals. \tAgricultural limes for example dolomite, limestone. Role of Calcium in Plants \tImproves the vigour and stiffness of straw. \tNeutralizes the poisonous secretions of the plants. \tHelps in grain and seed formation. \tImproves the soil structure. \tPromotes bacterial activity in the soil. \tCorrects the soil acidity. Deficiency symptoms \tYoung leaves remain closed. \tThere are light green bands along the margins of the leaves. \tLeaves in the terminal bud become hooked in appearance there is a die-back at the tip and along the margins. Loss of Calcium \tCrop removal \tLeaching \tSoil erosion Magnesium (Mg2+) Sources: \tCrop residues and organic manures \tCommercial fertilizers \tWeathering of soil minerals. \tAgricultural limes. Role of Magnesium in Plants \tForms part of chlorophyll. \tPromotes the growth of the soil bacteria and enhances the nitrogen fixing power of the legumes. \tActivates the production and transport of carbohydrates and proteins in the growing plant. Deficiency symptoms \tLoss in green colour which starts from the bottom leaves and gradually moves upwards. \tThe veins remain green. \tLeaves curve upwards along the margins. \tStalks become weak and the plant develops long branched roots. \tThe leaves become streaked. Sulphur (S04 2', SO,) Sources: \tCommercial fertilizers. \tSoil mineral containing sulphides \tAtmospheric sulphur from industries. \tRain water Role of Sulphur in Plants \tFormation and activation of coenzyme-A. \tSulphur is a constituent of amino acids. \tInfluence plant physiological processes. Deficiency Symptoms \tSmall plants/stunted growth. \tPoor nodulation in legumes. \tLight green to yellowish leaves/chlorosis. \tDelayed maturity.