Macro-elements

Nitrogen

Nutrient supply and cultivation

Nitrogen is the most important matter of proteins and proteids in living organisms. Nitrogen is the most important yield determining factor.

Nitrogen content of mineral soils varies between 0.02 – 0.4%. Higher plants are autotrophic as for carbon but regarding N this is not so. Atmospheric N provides N-reserves for the life on Earth, which can enter into the

Different Rhizobium species are symbiotic N-fixing bacteria. Rhizobium species live in symbiosis only with definite legume species. Therefore we classify the 16 known nodular root building bacterium strains into 6 groups.

Nitrification

N-compounds to found in the soil, in plant residues and manures are decomposed by mirco-organisms into inorganic formula.

N mobilized by mineralization can reach 1-2 %- of the yearly organic N-content. The rate of N-mobilization is influenced by C/N ratio. N-immobilization occurs at C/N≥ 30 on average.

Denitrification

Denitrification causes N-loss as much as 15-30%. Through nitrite → nitrate → ammonia → molecular N transformation process N fixed symbiotically or by the industry gets back into the atmosphere and can be reused again by plants through the processes described above. Denitrification is the nitrate-N reduction process which results in N (N2) in gas form. The process is done by denitrification bacteria. The process is intensive if there is no air in the soil and the soil is neutral or alkaline and there is a great amount of organic material in the soil.

Then bacteria use up the oxygen of the nitrates to oxidize organic material.

N-deficiency and –surplus in the plants

Symptoms of N-deficiency occur early and are clear. The plants do not reach the normal height, we can observe dwarfism. A typical symptom is the so called rigid halt, which can be observed not only on the stem but on the leaves as well. N-deficiency causes carbohydrate surplus in the plant metabolism, which result in anthocyanin forming. N-deficiency inhibits chloroplast and chlorophyll synthesis, which result in light green and yellowish-green colour and turns into yellowing when N-deficiency increases.

Most important N-fertilizers Ammonium-nitrate – NH4NO3

This is the most commonly spread solid N-fertilizer. It contains 34% of N theoretically. Its advantage is that it contains nitrogen in the form of ammonium and nitrate at a rate of 50-50% respectively. Plants are able to utilize both nutrient ions, therefore no unfavourable companion ions remain in the soil.

Lime and ammonium nitrate – NH4NO3 + CaCO3 or CaMgCO3

It is marketed under the names of „Pétisó” or „Agronit”. Both have ammonium nitrate as agent, which is mixed with lime in Pétisó and with dolomite in Agronit. Pétisó has an agent content of 25, and Agronit 28%.

Ammonium-sulphate – (NH4)2SO4

This is one of the longest known N-fertilizer. Before it could have produced synthetically it had been produced of coal as by products of coke and gas production. It contains 21.1 % N-theoretically. This fertilizer has the highest acidifying effect, because the total N quantity is present in the form of NH4+-ions.

Urea

It is an organic N-compound. This was the first organic, biological origin material that could have been produced in a laboratory (Wöhler 1828). In 1920s industrial production started. This is the most concentrated solid N-fertilizer, its theoretical N-content amounts 46.6%. Its pH-value is physiologically light acidic. Plants utilize its N-content in the form of ammonium as well as nitrate compounds.

Phosphorus

0.75% of the earth crust consists of phosphorous. We can find 0.02-0.1% of it in the soils, which is greatly influenced by the mother rock. Soil phosphorus is in organic and inorganic bonds. Their ratio is about 50-50%.

Original soil inorganic phosphorus content is built up from the bulk crystals of hard soluble hydroxyapatite - Ca5(PO4)3OH - and even harder soluble flourapatite - Ca5(PO4)3F - and only by very slow physical-chemical weathering process.

Water soluble mono-calcium-phosphate – Ca(H2PO4)2 – and citrate-soluble di-calcium-phosphate – CaHPO4 brought to the soils through fertilizers can transform into harder soluble phosphates in the soil relatively quickly.

P-deficiency –surplus in the plants

Similarly to N- P is also an essential building stone of the cells. Phosphate ion is the structural element of materials that regulate life processes and transmit genetic information further on they play an important role in the form of ADP and ATP in the energy household and metabolism of the cells.

P deficiency produces in nearly every plant species the same not very typical symptoms. Plants showing P-deficiency – if the growth-prohibition is not obvious – in most of the cases shows the symptoms of N-surplus, or optimal nutrient supply. “Rigid halt” is typical for P and N-deficiency besides prohibited growth. P-deficiency goes together with anthocyanin-formation, which can result in reddish colorization depending on the basic colour of the foliage. Symptoms occur first on the older leaves.

Phosphorus-surplus– differently form N – occur under open-field conditions very rarely, because phosphate ions are strongly bound in the soil. Large P-doses can endanger Fe- and Zn-supply of plants.

Most important P-fertilizers Raw phosphates

Raw materials of producing phosphor fertilizers (apatites, phosphorites) can be used for P-fertilization alone as well.

Mono superphosphates

Liebig produced it in 1840 through dissolving bone-flour by sulphuric acid. As a result water-soluble Ca-phosphate is produced. Mono-superCa-phosphate are produced by dissolving fine ground raw Ca-phosphates in sulphuric acid of 62-67%, as a result we receive mono-calcium-phosphate and water-free Ca-sulphate – the superphosphate.

Concentrated (enriched, double, triple) superphosphate

If raw phosphate is produced by the mixture of sulphuric-and phosphoric acid the result is an enriched superphosphate. P2O5 content is 18-36% depending on the ratio of the two acids. The production of so called double and triple superphosphate happens through dissolving in pure phosphor-acid. The agent content depends on the P-content of raw phosphates used in the second phase.

Nutrient supply and cultivation

Potassium

Potassium deferring from nitrogen and phosphorus is not a building element of organic materials. The role of K+-ions is important in their effect on swelling plazma-proteids and proteins as well as enzymes i.e. in structure stabilization and activation. K+-ions activate more than 40 enzyme reactions mainly during the formation of protein and carbohydrate compounds of high molecular weight. As an effect of potassium plants can retain more water so they can better survive short term drought.

Potassium deficiency and-surplus in plants

The first visually detectable symptom of K-deficiency is the so called state of “drooping” the cause of which the disturbed turgor-control due to K-deficiency.

Initial K-deficiency occurs in prohibited growth, which later on totally stops, because the plant cannot mobilize the easily moving K from the elder leaves quickly enough to cover the high K-requirements of shoot-meristem and younger leaves totally.

If there is a K-deficiency mobile K+-ions efflux from older leaves therefore the first visual symptoms occur on older leaves.

Most important K-fertilizers

Similarly to phosphorus fertilizers the raw materials of K-fertilizers are minerals, too. An important difference is that their production is simpler and easier after definite mechanical cleaning than that of raw phosphates.

Potash of 40%-

It is produced by mixing finely ground sylvite with potassium-chloride. The K2O-content of the mixture is about 38-42%. Potash of 40% is a fertilizer with favourable effect for plants giving a positive response to Na (e.g. beets).

Potash of 50 or 60%

During production KCl has to be separated from NaCl. The reason is that solubility of the two salts differs with the changing temperatures.

Potassium -sulphate (K2SO4)

It is produced by exchanged decomposition of concentrated KCl and MgSO4 solutions. Its agent content is 48-52%. It is advisable to apply it in chlorine-sensitive crops (potato, tobacco, and grapes).

Calcium

Ca-content of inorganic soil is very high compared to the quantity of other cations that are very important for plant nutrition. Being either as a part of crystal lattice or hard soluble salt, Ca gets free during the weathering processes very slowly and has a role in soil farming processes.

For the soil fertility it is important that sorption complexes be saturated with Ca2+. This state of condition assures long-lasting crumbling structure. Furthermore Ca-ions being fixed to the sorption complexes or being free in the soil assures an easily available Ca-source.

We should distinguish between the tasks of Ca2+ in the soil and in the plants. In this respect Ca2+ as a fertilizer has greater significance. Soil life, crumble stability and soil forming and decomposing processes require to adequate function much larger quantity of Ca that needed by plans to their life cycles. Liming means first of all soil fertilization. If we can maintain the soil‟s Ca-household with liming then we assure enough Ca-nutrition for the plants, too.

Magnesium

Mg behaves in the soil similarly to Ca in many respects. We can find it in several minerals (biotite, serpentine, vermikulite, chlorite and olivine). Further more its carbonates and the dolomite are also very important MG-containing elements of the soils.

In plants Mg as an important component of chlorophyll has an important role in assimilation processes. Besides its structure forming it sis a very important enzyme activator, too therefore Mg-deficiency is accompanied by restricted assimilation as a result of reduced phosphorylation. Good Mg-supply increases the photosynthetic activity. It also has a role in forming of carbohydrates. If there is a deficiency carbohydrate content of plants (e.g. starch content in potatoes).

Sulfur

Similarly to nitrogen sulphur is an essential component of amino-acids, peptides and proteins. There has not been any S-deficiency in our country so far, because, S-requirements are abundantly covered by applied fertilizers and atmospheric deposition. At some parts of the Globe e.g. in USA and Australia S-deficiency had earlier been detected and considerable higher yields were produced as a result of S-fertilization. Through the application of more concentrated P-fertilizers and reducing S-deposition from power plants soils S-reserve would be not enough and plants should be supplied with S adequately.