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Nitrogen is the most abundant nutrient required for plant growth. It forms 16% of all plant proteins, and is a vital component in chloroplasts - the factories that synthesize energy from sunlight. N management is one of the most important issues in our quest to build both profitability and sustainability. Excess N burns out organic carbon and contributes to the “Greenhouse Effect”. Nitrogen toxicity is a significant cause of loss in production when nitrogen is overused or misused. Potassium and calcium will inevitably be deficient when plant nitrgen levels are excessive. Nitrogen and potassium imbalances in plants is also a major disease "calling card".

Currently nitrogen losses account for up to 50% of applied nitrogen. Nitrates contaminate waterways, groundwater and drinking water; remove oxygen from the blood and are proven carcinogens. Excess nitrates in plants encourages pest and diseases to flourish. Brix levels in plants cannot be raised with excess nitrates. Excessive N causes the top to outgrow the weakened roots i.e. “nutrient dilution” which seriously reduces yield and quality.

Good nitrogen management increases quality - the key to increased profitability. We need to concentrate on capturing free nitrogen from the atmosphere; each hectare has the equivalent of over 74,000 tonnes of nitrogen above it in the atmosphere.

Deficiency symptoms include yellowing of older foliage (being mobile in the plant it transfers from older to younger leaves); reduced plant-leaf size and "ground" cover. This all amounts to fewer solar panels -> less photosynthesis -> less sugar -> lower yield and quality. Fewer stems; dwarfed plants; thin and upright habit; stems and petioles rigid; reduced tillering in cereals. 150 - 200 million tonnes of N are utilised in agricultural each year. The vast majority of nitrogen comes from the atmosphere via nitrogen fixation by soil microbes into plant available ammonium and nitrate, as well as lightning and rain which oxidises nitrite to nitrate.

nitrogen nutrient image

Atmospheric nitrogen is the cheapest form of Nnitrogen you can get.

Modern misuse of nitrogen

Most nitrogen is applied in large amounts early in the season results in large amounts of nitrate at the crucial, fruit-filling phase of crops. The pH of plant and soil go out of balance therefore the crop is subjected to nutrient deprivation, pest and disease attack plus misuse of all important photosynthates needed for maximum yield.

Nitrogen management - keeping excesses to a minimum.

1) CEC of your soil. Lighter soils require spoon feeding. When ammonium can’t store on clay or humus colloid, nitrate conversion is guaranteed.

2) Soil balance improves nitrogen efficiency; calcium is “the trucker” and is essential for uptake, while sulphur is necessary for conversion of nitrates into essential amino acids. High or low magnesium soils require at least 50% more nitrogen to achieve the same yields as soils with correct magnesium.

3) Crop rotation, pasture composition; legumes can leave considerable quantities of nitrogen in the soil for use by other crops.

4) Levels of humus and organic matter. Undigested OM present during a crop cycle can consume considerable amounts of nitrogen during decay causing nitrogen drawdown. Begin stubble digestion with shallow incorporation immediately after harvest.

Radioactive tagging methods have shown that every 1 kg of nitrogen supplied over and above plant requirements will burn out 100 kg organic carbon. Microbes devour nitrogen and carbon in set proportions.

Adding compost protects valuable soil organic carbon. Always add carbon to nitrogen.

nitrogen nutrient image
nitrogen nutrient image

5) Cover crops protect the environment from free-roaming nitrates. Winter cover crops help reduce nitrogen leaching. Barley, oats and triticale are planted between vine rows of vineyards and similar to help capture nitrogen and recycle it following incorporation. By the time the primary crop is harvested, the remaining nitrogen is in the nitrate form via nitrification. Cover crops take up nitrates for early vegetative growth and convert them into proteins, thereby stabilising the nitrogen. Decomposing protein then releases ammonium to be taken up by plants or converted back to nitrate where it is still in a plant available form.

6) Manure and compost application: the nitrogen content should always be factored into the equation.

Nitrogen forms the basis of amino acids and proteins, the building blocks of life; an essential constituent of nucleic acids, DNA, RNA, and enzymes, which are all made up of proteins. It is a necessary component of vitamins biotin, thiamine, niacin and riboflavin.

Nitrate is paramount to the formation of chlorophyll which is the green pigment within chloroplasts where photosynthesis takes place. The central part of the chlorophyll molecule consists of a magnesium atom surrounded by four nitrogen atoms plus carbon, hydrogen and oxygen.

Protein is decomposed by aerobic soil organisms and the nitrogen is released from these organisms as ammonia gas which is quickly converted to plant available ammonium in ideal situations.

Forms of nitrogen in fertilisers and their impact on soil and plants.

Ammonium – ammonium sulphate, mono-ammonium phosphate, di-ammonium phosphate

Nitrate – potassium nitrate calcium nitrate magnesium nitrate

Urea (NH2-CO-NH2) is in the amine form. The most commonly used nitrogen source in agriculture. The cheapset product, but notoriously unstable, and with negative down-stream consequences.

Zeolite: capable of holding onto nitrogen (especially ammonium) and is a permanent addition to the soil and increases its water and nutrient holding capacity.

Humates: as liquid or granules which dissolve at the same rate as urea; can extend the life of nitrogen in urea by 60 days. Humic acid should be used at a rate 5%-10%. Humic acid also provides a source of food for microbes.

Ammonium can attach to negative soil particles or form compounds with nitrates, sulphates or phosphates, and will be plant available and secure from leaching.

However, in warm, moist conditions, microbes quickly convert ammonium to nitrate which can then be leached away. Stabilising with humic acid and zeolite will help slow down nitrification.

The conversion of ammonium to amines to amino acids occurs in the roots. The energy used causes plants to send more sugar to the roots. The plant is then stimulated to produce more chlorophyll.

The increase in photosynthesis is the reason why ammonia turns leaves dark green and actually results in net gain of energy to the plant.

Nitrate is the end product of nitrification. Most fertiliser applications force plants to take in nitrogen in this form during the production phase of the crop. This goes against nature’s intentions. That is, nitrate should go in during the vegetative stage of the crop and ammonium during the reproductive stage of the crop. Nitrate conversion to amine (NH2) is an energy expensive process which relies on sunlight and Molybdenum to enable the nitrate reductase enzyme to be activated. Ammonium from decay is released near live plant roots and taken up before nitrification takes place.

The pH surrounding the rhizosphere is low to stimulate soil microbes and promote the uptake of nutrients to stimulate further production of chlorophyll. Nitrates are needed for cellular pH maintenance, obtained through decomposing organic matter on the soil surface which goes through nitrification. Also nitrogen is made available from atmospheric oxidation of nitrgoen, nitrate and rain carrying nitrate to roots.

The nitrogen cycle

nitrogen nutrient image

   OM %

Boron

Sulphur

Nitrate

2.85

0.67

3

3.2

3.29

1.33

3

3.2

3.67

0.92

4

6.8

4.06

0.91

5

4.5

5.37

1.67

11

17.5

8.83

2.59

15

34.9

Organic matter is important to be able to build anion levels in the soil. (Figures in ppm.) The higher the OM, the higher the anions.

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