Symptoms of Nutrient Disorders
Symptoms of nutrient disorders in greenhouse crops do not differ in principle from those in field crops. Most of the characteristics of nutrient disorders found with field crops also occur in greenhouse crops. So there is no reason for an extended description of these symptoms. However, the specific climatic conditions in greenhouses sometimes induce symptoms accompanied by specific characteristics. Therefore, a short description will be given of the most characteristic symptoms of the nutrient disorders with possible relation to greenhouse conditions. The symptoms differ for crops, growing conditions and growth stage and often cannot unambiguously be described. Sometimes a diagnosis requires comparison of different descriptions and pictures of several crops to make good supposition and even then a tissue test can be necessary to confirm the diagnosis. Especially the diagnosis for the innumerable exotic flower crops grown in greenhouses offers problems in the recognition of nutrient disorders and requires often research to discover the real cause of the problem and the conditions under which they appear.
For the following description of symptoms authors brought in their experiences while reference is made to the presentation of De Kreij (1993). Furthermore, the books of Roorda Van Eysinga and Smilde (1980, 1981) and Winsor and Adams (1987) contain many pictures of nutritional disorders of greenhouse crops. Symptoms of many crops are described also by Chapman (1966).
K - In advance the deficiency appears with coarse chlorotic spots on young leaves. With serious deficiency yellow colouring on the edges of older leaves appear, which later on become necrotic. The symptoms can occur over the full length of the plant.
Ca - In leaves Ca deficiency will appear in the young leaves or tops of the plant. Coarse yellow spots appear on the edges of the young leaves and the growing point can die. The deficiency in leaves mostly is connected with humid growing conditions and a high growth rate. Ca deficiency in fruits sometimes becomes in advance visible by glassy spots, later on changing into the well known necrotic or soft spots on the blossom end of the fruits. It is strongly related to the transport of this element in the plant and a low humidity in the greenhouse aggravates the disorder in the fruit. Ca deficiency is a phenomenon frequently occurring in greenhouse cultivation with a great diversity of symptoms and will extensively discussed in Chapter 9.
High Ca concentrations in fruits promote the appearance of gold specks and green spots on fruits, which appear mostly in the upper part of the fruit. Pictures of different Ca disorders of vegetable fruit crops are presented in chapter 9 and by Savvas et al. (2008).
Mg - Deficiency is characterized by course yellowing in the older leaves. The leaves are cracking and thick.
N - The deficiency of N is characterized by growth reduction, often thin tops and a pale colour of the leaves, with heavy deficiency older leaves prematurely fall from plant.
P - Deficiency is shown by a strong growth reduction. The colour of the leaves is dark green with sometimes a reddish glow. This glow also can appear on the stems. Older leaves will prematurely fall from the plant.
Toxic symptoms occur in specific crops and cultivars with an insufficient control on the P uptake. Leaves and especially cotyledons can show discoloured spots and even chlorosis.
S - S deficiency looks often like N deficiency, showing a pale colour of the leaves over the whole plant.
Fe - Many greenhouse crops can suffer from Fe deficiency. The most characteristic symptom is chlorosis in the tops of the plant. In serious deficiencies the symptoms survive in older leaves too. However, in advance the problem occurs in the top and is grown out with the age of the leaves.
Fe toxicity can occur in crops, but has not been found often in greenhouse crops. The "bronzing" going together with the toxicity occur mainly in water logged soils.
Mn - The symptoms of Mn deficiency occur just like those of Fe deficiency in the tops of plants, where also chlorosis occurs. Therefore, it is often difficult to distinguish the symptoms of Mn deficiency from those of Fe. Utmost, both deficiencies are strongly aggravated by comparable conditions, being a high pH in the root environment. With rose leaf drop occur (Voogt and Sonneveld, 2009).
Mn toxicity is also well known in greenhouse culture. It frequently occurs in soils after steam sterilisation, which will be discussed in Chapter 10. The symptoms will be found mainly in the old leaves merely by necrosis on the tops of long narrow leaves or on the edges of different shaped leaves. In some crops necrosis alongside the veins and yellowing of the small veins is visible. In rose dropping of older leaves occur, while purple spots on the stems are shown (Sonneveld and Koningen, 1973).
Zn - Zn deficiency is characterized by misshapen form of the plant, small leaves and shortening of the internodes, mostly described as "little leave" and "rosetting", respectively. The symptoms often go together with chlorosis.
Zinc toxicity in greenhouse cultivation is well know and often occurred in combination with galvanized greenhouse constructions; dripping of condensation water and the use of rain water for irrigation caught in galvanised gutters. Nowadays, the constructions often are made of aluminium and the symptoms disappeared. Zn toxicity is characterized by necrosis alongside the veins, in advance it often induces Fe or Mn chlorosis.
B - Deficiency of B causes misshapen growing points and fruits. The symptoms in fruits are quite specific, fruits sometimes burst, dry out and seeds become visible. The tissues become cracking, tops will die off and leaves are misshapen when developed. Brown blockings are sometimes visible in the veins of leaves.
The typical symptoms of B toxicity are the appearance of chlorosis and necrosis on the edges or tips of mature leaves.
Cu - Cu deficiency is well known from the use of high moor peat as a substrate. The complex formation in this growing medium between the soluble organic matter and the Cu ion requires high Cu applications to ensure a sufficient uptake of this element in peat substrates. The symptoms of deficiency are characterized by a pale colour of the whole plant, misshapen fruits, an insufficient flower formation and when developed misshapen flowers in ornamental crops. With serious deficiencies old leaves die off.
Cu toxicity can induce Fe deficiency and thus chlorosis occurs in young leaves. Cu is accumulated in the roots and so with tissue analysis due to determine Cu toxicity, often the roots should be analysed for a sound conclusion.
Mo - Mo deficiency merely develops in young plants and the symptoms are often very characteristic. The so called whiptail formations in young leaves are well known by cauliflower. In other crops it induces wilting in older leaves of young plants or chlorosis in mature leaves. Mo deficiency especially occurs at low pH values in the root environment.
Mo toxicity so far is not known in mature greenhouse crops. It is peculiar that in fodder crops high Mo concentrations are rather dangerous for animals than toxic to crops (Marschner, 1997).
For some major elements no toxicity symptoms are mentioned, like for K, Mg, N and S. Generally, in such cases, no specific symptoms are known at high applications of these elements. However, sometimes too high concentrations of these elements induce deficiency of other elements. This is caused by ionic competition, like can happen with high applications of K, Ca or Mg. Best known are those for high additions of K, which aggravate the occurrence of Ca or Mg deficiency. Furthermore, high applications of all macro elements induce a low osmotic potential (high EC) in the root environment and symptoms of high salinity can occur. These symptoms are less specific, but are generally characterized by discolouring and necrosis in oldest leaves (Sonneveld, 1978).
Post a comment