Water is an essential element for the life of all living organisms on our planet. Its quality and quantity is fundamental for survival of flora and fauna. In rose plants it represents the 75-85% of its fresh weight. That means that for every kilogram of plant, about 750-850 grams are made up of water! It is therefore vitally important to pay the right attention to the principal characteristics of irrigation water as well as the nutrient requirements of the plant (as it is the carrier of the various nutrient inside the plant). Before using the water, every grower should check the following parameters:

• Temperature.
• Presence of possible chemical pollution and pathogen or micro-organisms.
• Quantity of the common chemical elements naturally found in irrigation waters.
• pH and salinity.
• Oxygenation (oxygen quantity in the water).
• Required quantity for the plants needs.

Ideally, water should have an average temperature of between 15-16°C and 22-23°C for rose cultivation on substrates (soil-less cultivation). Below 15 to 16°C, metabolism gradually slows down, and so does the uptake by the roots as well as the photosynthesis of the plant. Water temperatures over 23°C result in a gradual oxygen impoverishment of the water which compromises the breathing of the roots. Obviously, temperatures over 30-35°C are highly undesirable.

The effect of the water temperature relates to the greenhouse environment. The greater the difference between the environmental temperature and the root temperature, greater will be the stress effect on the plant.

To verify if the water is polluted, it is necessary to collect samples and have them analysed by specialized laboratories for spores of common root diseases (e.g. Pythium, Fusarium) or the levels of toxic chemical elements. The latter is essential especially if the cultivation area is near an industrial area. Fig. 2 shows the maximum values of elements toxic to roses. Some variation to the values can be allowed in the case of soil cultivation but they are critical in the case of soil-less cultivation such as an inert growing medium (rockwool or perlite).

Another important parameter for the quality of the irrigation water is the content of naturally beneficial elements, i.e. nutrients (fig. 1).
Irrigation water is divided in the following three classes:

• 1st Class: the water has characteristics suitable for Roses on any growing medium.
• 2nd Class: the water can cause some problems for the cultivation in limited rooting environments (soil-less cultivation), due to presence of certain elements (saline) that are difficult to remove. Their values are tolerated in soil cultivation.
• 3rd Class: the water is unsuitable for soil-less cultivation. It can be used in some types of soil, e.g. sandy soil.

The three principal elements on which the plants mostly feed are: Carbon (C), Oxygen (O2) and Hydrogen (H2). They are fundamental for the synthesis of the organic substances (sugars, lipids, proteins etc.) that develop through biochemistry inside the plant. Oxygen and Carbon combined (CO2) are absorbed through the stomata. Oxygen and Hydrogen combined (H2O) are absorbed by the roots.

The other nutrients are categorised as macro-elements (absorbed in large quantities), trace- and micro-elements (absorbed in average and small quantities in the ratio 1:1,000 up to 1:10,000). They have the same fundamental importance on the physiology of the plant, because each of them have specific and important functions for the vegetative metabolism.

Some of the nutrients in the vegetative tissues are mobile ions that easily move from the old leaves to the young, others are slightly mobile or immobile. This means that if there is nutrient deficiency in the old leaves, it would be a mobile element moved by the plant, whilst if this occurs in the young leaves, it is due to slightly mobile and immobile elements. For example, if the root uptake of a mobile element (for example K) slows down or stops, it is moved, transferred by the plant, from the older leaves to the younger ones through the phloem (conductor vessels). The lack of it is therefore evident in the older leaves. The opposite occurs with elements that have been immobilized or fixed by the plant in the old leaves. In this case the deficiency symptoms are evident on the young leaves and shoots. The immobile or fixed elements only move through to the xylem flow (conductor vessels). The xylem flow carries the nutritive elements and water from the roots to all the other vegetative parts of the plant. The phloem flow (conductor vessels), on the other hand, transfers the photosynthesis products (sugars) and the nutrients stored in the leaves from the top to the roots and from the top shoots to young shoots and leaflets.

Finally, considering that at times growers have the tendency to use excessive amounts of fertilizers, some leaf discolorations due to nutritional deficiencies, can be caused by: antagonisms among elements; unfavourable pH level; temperatures lower or higher than the optimum. Other factors that limit the availability of nutrients could be strong transpiration for a longer period of time (a week). It results in the shoots receiving insufficient nutrients, hence high humidity, in combination with lower light levels, may lead to nutrient deficiencies. Calcium deficiency for example is a well-known problem of high humidity conditions.

Similar symptoms of nutrient deficiency are also observed when:
• plants are attacked by nematodes
• during the initial states of rotting which damages the root and the collar of the plant
• root asphyxia
• inadequate root airing
• high levels of salinity (E.C.).

Nitrogen: A notably important mobile element used by the plant as a component of proteins. It is primarily absorbed by the roots as the ions NO3- and NH4+. In the plant all nitrates are first converted into ammonium form, in order to build the amino-acids. Nitrogen, as all elements, is carried by the xylem vessels to the leaves, and is converted there through a metabolic process, into organic compounds (amino-acids). Subsequently it is distributed to the other plant parts via phloem vessels (to the root too).

Nitrogen is particularly important during the spring-summer period. However, when highly concentrated, the ammonium form, NH4+, suppress the absorption of other cations, such as Ca++ and Mg++. It is also toxic to the plant at high concentrations. A greater absorption has been noticed during the maturing of the floral bud.
Deficiencies: sometimes they occur when the soil, of a sandy or loose nature, has a low cationic exchange capacity (C.E.C.) and is subject to continuous heavy irrigations (leaching). The deficiency symptoms are an increased yellowing of the foliage that slowly and gradually covers the whole plant, passing from the oldest to the youngest leaves.

At the start the colour turns from yellow-green to yellow. In addition, the older leaves tend to drop. Shorter internodes, reduced stem diameter and lighter colouring are also observed. These are consequences of the reduction of the protein synthesis.

The deficiency of Nitrogen involves a rapid translocation from the oldest leaves to the youngest, therefore the latter rarely show symptoms of deficiency (yellowing).
Excesses: Excess Nitrogen promotes the vegetative growth and causes the abundant production of weak vegetative tissue, which are tender and more susceptible to parasitic attacks. It can indirectly cause a deficiency of Potassium, especially when lots of ammonium fertilisers are used (NH4NO3). Added to a rise in soil salinity it increases the coriaceous, dark green leaves.

Potassium: The element that is absorbed by the plant most, possesses a good mobility through the phloem and easily moves from the oldest tissue to the youngest. Although not present in organic substance, it influences the protein synthesis, the circulation of the sugars, and it is responsible for the cells turgidity. Furthermore, because of its strong mobility it has a fundamental role in water up-take. The requirement for the plant increases with lower temperatures and with fewer light hours (winter). It is absorbed by the plant as the ion K+.

Deficiencies: The deficiency of Potassium starts with a necrosis at the borders of the oldest leaves. The most central part of the leaf usually remains green, although necrotic spots might occur. Shorter stems, bud necrosis and small discoloured flowers are ulterior consequences.

The deficiencies of the element are more frequent in clay soils with a high C.E.C. Also, excesses of Ca++, NH4+ and in particular Mg++ can promote the deficiency of K+.

Excesses: Excess Potassium is caused by a deficiency of Mg++, Ca++ and NH4+ due to the opposing action of K+ to these elements and at high salinity. Leaf necrosis on the borders and wiling of the tender shoots occurs.

Calcium: It is the principal constituent of the cell wall. It possesses good mobility only in the xylem flow (immobile element). A sub-alkaline or alkaline soil reaction does not usually need intervention with the supply of Calcium, therefore a deficiency in the plant is usually due to its poor mobility in the plant, rather than due to low levels in the soil. It plays an important role in the absorption of nitrogen at the points of vegetative growth (apex meristem) and is an element of mechanical resistance (the plants are more resistant). Once accumulated in the more adult tissues, it no longer moves to the young ones. It is absorbed as ion Ca++.

Deficiency: The root pressure must be sufficiently high during non-transpiration periods (night) to supply sufficient calcium to young non-transpiring parts. Deficiency in the leaves develops when transpiration is extremely low, for example with high air humidity. It also develops in places with a low xylem supply, such as young shoots. The young leaves become yellow, the older ones show a grey-green colour. The leaf margins bend due to these symptoms since there is a reduced functioning of cell and membranes causing the tissue to collapse and die. In severe cases the death of the meristem apexes happens. The best solution is to prevent the damage by applying base fertilization before planting.
Excesses: This causes the appearance of chlorosis due to the fixation, or insolubility, of Iron and other microelements (Boron).

Sulphur: It is made up of some amino-acids and of numerous enzymes, and so is of some importance for the growth of the plant. It is absorbed as the ion sulphate (SO4--). It is not very mobile and it's deficiency is rather rare.
Deficiencies: Sulphur deficiency shows itself mainly in the young leaves because it is an almost immobile element. This means, as already mentioned that the sulphur is not transferred from the old leaves to the young ones when the element is deficient in the soil. The symptoms show themselves with a dark red coloration along the main and secondary veins of the upper-side of the young leaves.

Excesses: An excess of this element is very rare, but when it occurs, the pH of the plant sap tends to drop to dangerous levels (element has an acid chemical reaction).

Iron: It possesses a very low mobility therefore Fe deficiency always occurs in the youngest leaves. It plays a very important role in the synthesis of chlorophyll and in the photosynthesis process. It activates numerous biochemical reactions and is absorbed as the ion Fe++ or Fe+++. In sub-alkaline and alkaline soils it can become unavailable due to it's insolubility with Carbonates and Phosphates (in these cases, it is necessary to raise the normally recommended dosage).

Deficiencies: The rose leaves are sensitive to fluctuations of Iron, showing itselEnviromental Parametersf as interveinal chlorosis (yellowing) on the youngest leaves. In serious cases, initially there is a leaf de-coloration to creamy yellow, and the leaves become smaller. Thereafter the necrosis of the leaf apexes and interveinal zones occurs. In an advanced stage of deficiency the leaf veins become yellow as well. It is advisable to add the element during the base fertilization, before planting.

Excesses: It can cause deficiency of Manganese.

Zinc: It is important for the synthesis of chlorophyll, for respiration and for growth, because of the indole-acetic acid involved in the synthesis (a vegetative growth hormone). It is responsible for cell elongation of stems and petioles. It is not mobile and therefore it's deficiency is visible especially on the young leaves. It is absorbed as the ion Zn++.

Deficiencies: The plant shows slow growth, short internodes, deviant colour, bushy appearance and deviant leaf shape. To overcome this, Zinc sulphate is added to the soil when it has the correct pH, or through leaf fertilization if the pH is not optimal.

Excesses: It produces a general weakening of the plant with a light yellowing among the veins of the younger leaves similar to that caused by a deficiency of Iron or Magnesium. In extraordinary cases it can cause plant intoxication. Sometimes even condensation from the zinc-coated structures of the greenhouse can poison the plant.

Molybdenum: This is involved in the synthesis of chlorophyll, and in the numerous enzymes including those involved in the metabolism of the nitrogenous compost (conversion of NO3 into NH4 in the plant). It is absorbed as the ion MoO4-- and it possesses good mobility.

Deficiencies: They are prevalent especially in soils of semi-acid and acid pH. Deficiency is manifested in chlorosis of the old leaves between the veins.
Excesses: It is necessary to be extremely careful when a Molybdenum based correction is carried out as slightly excessive dosages can be toxic for the plants.

(Colombia) Nearly all the bigger companies get their irrigation water from streams near the greenhouses.

(Kenya) Stocked water basic coming from Naivasha Lake.

(Ecuador) Stockage water basin (Cotopaxi area)

Average concentration of nutrient elements in the plant, expressed in Mole/g and % (Epstein).

(Kenya) Fertigator system with small laboratory for the EC and PH control.

In Holland liquid fertilizers are used for the plants.

Calcium deficiency in full-grown five-leaflet leaves in various stages. Symptoms of a Calcium-Boron imbalance appear first in the active growing points (shoots).

Iron deficiency in advanced stage.

Zinc toxicity in a young on water culture. The first shoot managed to develop well.

Zinc defidiency in a mature in a shoot (left), compared to a healthy.