Plants utilize nutrition in the form of inorganic minerals for growth and development. Plant nutrients can be divided into two groups and these are macronutrients and micronutrients. Macronutrients are elements required by plants in relatively large quantities and these include Carbon (C), hydrogen (H), oxygen (O), phosphorus (P), potassium(K), nitrogen (N), sulfur (S), magnesium (Mg) and calcium (Ca) (D. R. Decotean, 2005). These elements play different but equally important roles in plant growth and lack of any one of them affects the plant in one way or another.
Deficiency symptoms for any element depend primarily on the function of the element and whether or not the element is readily translocated from old leaves to younger leaves (Purohit, 2003). Carbon, hydrogen and oxygen are the three non-mineral plant macronutrients. These are taken in from the air and water and are essential for respiration and photosynthesis and they also enter into the composition of practically all organic compounds in the plant and account for a major part of the dry weight (Pandey and SInha, 1995). Nitrogen is present in plants in the largest concentration of any of the mineral nutrients.
It is a component of many organic molecules of great importance, including chlorophyll (Decotean, 2005). Nitrogen is a component of amino acids, which are the molecular subunits from which proteins are synthesized. The nucleic acids DNA and RNA also contain nitrogenous bases (adenine, guanine, cytosine and thymine) and these make up the genetic coding sequences (McIntosh, 2010). According to Uchida (2000), nitrogen is also responsible for the improvement of the quality and quantity of dry matter in leafy vegetables and protein in grain crops. Nitrogen deficiency in plants is characterized by chlorosis, which is a yellowing of the leaves.
Nitrogen is a mobile element in plants, and can be moved around as needed. Therefore older leaves tend to be the first plant parts to show signs of nitrogen deficiency as nitrogen is transported to support new growth (Salisbury and Ross, 1999). Chlorosis is often evident when other minerals are deficient as well and depending on the severity of deficiency, the chlorosis could result in the death and/or dropping of the older leaves (Uchida, 2000). Plants grown in poor nitrogen conditions tend to have stunted growth which may be as a result of reduced cell division. They may also have the characteristic of abnormally thin shoots. McIntosh, 2010).
Nitrogen deficiency can also cause early maturity in some crops, which results in a significant reduction in yield and quality (Uchida, 2000). According to Purohit (2003), potassium is best known in the opening of stomata. Potassium serves a critical role in the turgor mediated opening of guard cells stomatal aperture which is determined by guard cell turgor. In photosynthesis, K has the role of maintaining the balance of electrical charges at the site of ATP production (Uchida, 2000). It is also thought to be essential for the conformational stability of the enzyme pyruvate kinase, also known as ATP (Glass, 1989).
It helps to adjust water balance, improves stem rigidity and cold hardiness, enhances flavor and color on fruit and vegetable crops, increases the oil content of fruits and is important for leafy crops (Dorothy Morgan, n. d). Like nitrogen, potassium is highly mobile in plants resulting in deficiency symptoms appearing in the oldest foliage first. The first observable symptom of potassium deficiency is mottled or marginal chlorosis, which then develops into necrosis primarily at the leaf tips, at the margins, and between veins (Taiz and Zeiger, 2002).
Since K+ ions are important in maintaining water balance and turgor, potassium deficient plants are sensitive to water stress and wilt easily. (McIntosh, 2010) Phosphorus is absorbed from the soil as the monovalent phosphate ion H2PO4- or as the divalent ion HPO4- (Purohit, 2003). It is a part of the energy molecules ATP and ADP and is found in the backbone portion of both DNA and RNA. Many organic molecules contain a phosphate group and amino acids incorporated into proteins may be phosphorylated after protein synthesis (Taiz and Zeiger, 2002).
Cell membranes are rich in phosphate groups that are part of the “head” regions of the phospholipid molecules that form the membrane bilayers. Phosphorus also aids in root development, flower initiation, and seed and fruit development (Khalid, 2012). Phosphorus deficiency symptoms can be difficult to identify since they are not very distinct. Phosphorus is important in many metabolic functions as well as in the synthesis of new cell membranes, thus phosphorus deficiency results in slow growth (Berry, 2010).
In a moderate case, the leaves become a darker green than normal with perhaps a blue or purple tint, which can give the illusion of a healthy plant. In addition to darker leaf colour, plants will exhibit stunted growth and thin stems, with longer than normal distance between the branches. In severe cases of phosphorus deficiency chlorosis appears followed by leaf curl and drop (McIntosh, 2010). Lack of phosphorus can cause delayed maturity and poor seed and fruit development (Uchida, 2000). Most of the calcium in plants is found embedded in the cell walls where it is involved in cell elongation and division (Decotean, 2005).
It is also found in membranes where it influences the flexibility of membranes. Calcium is necessary for fat metabolism, formation of membrane, nitrate assimilation and also binding of nucleic acids with proteins and counteraction of metal toxicity (Pandey and Sinha, 1995). Newly emergent leaves are usually the first parts of a plant to show symptoms of calcium deficiency. Calcium is not mobile and is not easily translocated in the plant, so symptoms first appear on the younger leaves and leaf tips (Uchida, 2000). The young leaves will be malformed, with ragged margins, and eventually turn brown.
Roots also are affected and will turn brown, and develop a swollen bulbous appearance accompanied by stunted growth. In fruit bearing plants, a lack of calcium interferes with normal cell division and elongation, causing blossom end rot on developing fruit (McIntosh, 2010). A magnesium ion (Mg2+) is the core component of every chlorophyll molecule, making it an important part of photosynthesis (Muhammad, 2012). Magnesium ions also serve as enzyme cofactors, notably in ATP metabolism. Some magnesium is also present in cell walls.
Magnesium is of high importance in photosynthesis, thus a lack has a huge negative effect which is difficult to recover from. Chlorosis between the veins of older leaves, because Mg is highly mobile, is another deficiency symptom, with perhaps the addition of a red or orange tint (Muhammad, 2012). Growth is strongly inhibited. Magnesium has a complex relationship with Ca2+, K+ and NH4+ ions, and an imbalance among them can lead to magnesium deficiency (McIntosh, 2010). Sulphur is found in plants as a component of sulphur-containing amino acids like methionine and sulfhydryl group of certain enzymes (Decotean, 2005).
Although only two amino acids contain sulphur (S), few proteins would function normally without them. Sulphur is also found in plant hormones, and in molecules involved in chemical defence, odour and taste (McIntosh, 2010). Many organic molecules, intermediate compounds and proteins, contain or are modified with sulphate side-groups Sulphur deficiency is difficult to distinguish from nitrogen deficiency. One difference between the two is that a lack of sulphur tends to cause more of an overall yellowing of a plant, rather than a yellowing of the older leaves first (Pandey and Sinha, 1995).
With advanced sulphur deficiency brown lesions and/or necrotic spots often develop along the petiole, and the leaves tend to become more erect and often twisted and brittle (Berry, 2010). Complete absence of any of the essential elements will stop growth of the plant completely though under normal conditions, the elements are not completely absent. Because of this, when the elements present are in quantities lower than the optimum, certain abnormalities develop (Pandey and Sinha, 1995).
Decotean, D.R. (2005) Principles of Plant Science USA: Pearson Prentice Hall. Glass, A.D.M (1989) Plant Nutrition: An Introduction to Current Concepts USA: Jones and Bartlet Pubolishers. Pandey, S.N. and Sinha, B.K. (1995) Plant Physiology 3rd Revised Edition New Dehli: Vikas Publishing House. Purohit, S.S (2003) Plant Physiology India: Student Edition Salisbury, F.B. and Ross, C.W (1999) Plant Physiology India: CBS Publishers and Distributors. Taiz, L. and Zeiger, E. (2002) Plant Physiology, Third Edition Sunderland: Sinauer Associates. Berry, W. (2010) Topic 5: Symptoms of deficiency in essential minerals, Plant Physiolgy 5th Edition Online, www.5e.plantphys.net/article.php?ch=t&id=289 (Accessed 5 March 2012).
Khalid, A.K. (2012) “Effect of NP and foliar spray on growth and chemical compositions of some medicinal Apiaceae plants grow in arid regions in Egypt” Journal of Soil Science and Plant Nutrition, 2012, 12 (3), pp618 (online) http://www.scielo.cl/scielo.php?pid=S0718-95162012000300018&script=sci_arttext (Accessed 6 March 2013). McIntosh, P. (2010) “Plant nutrient elements Part 1: Macronutrients”, www.hydrogrowersusa.com/en/plant-nutrient-elements-part-1-macronutriens.php (Accessed 5 March 2013). Morgan, D. (n.d) “What is plant nutrition”, www.retirees.uwaterloo.ca/~jerry/orchids/nutri.html (Accessed 5 March 2013). Muhammad, F.A. (2012) “Plant Nutrition: Lecture 6” www.slideshare.net/fahadansari131/plantnutrition-by-muhammad-fahadansari12ieem14-12905621 (Accessed 3 March 2013).
Uchida, R. (2000) “Chapter 3: Essential nutrients for plant growth: Nutrient functions and deficiency symptoms”, www.ctahr.hawaii.edu/oc/freeputs/pdf/pnm3.pdf (Accessed 4 March 2013).