Nitrogen is probably the nutrient that most often limits plant growth. The bulk of soil N is found within 2 feet of the surface. Soil N is present in three major forms.

Elemental N, found in a gaseous form in the soil atmosphere, is of direct significance to plants only as it may be involved in bacterial fixation. (e.g., symbiotic N fixation associated with a legume plant or small amounts of N fixation by free-living bacteria).

Organic N makes up about 5 percent of the soil organic matter (humus) by weight and about 98 percent of the total soil N. Although organic N is not available to plants, soil organisms convert a portion of it each year to inorganic forms (ammonium and nitrate) that are readily used by plants. Organic N fertilizers (e.g., manures and biosolids) are popular for lawns and gardens because of their "slow release" and long-lasting properties. The relatively low concentration of N in organic materials means several tons per acre are required to supply sufficient N for commercial field crop production. The economics of transporting these bulky materials are a major factor when considering their use as an N source.

Nitrogen in fertilizers for agricultural crops is largely inorganic N consisting of three types: ammonium (NH 4 + ), nitrate (NO 3 - ), and urea (CO(NH 2 ) 2 ). Although urea is an organic N fertilizer, it is rapidly converted to the ammonium form within a short time after exposure to moist, aerated soil. Therefore, under most conditions urea acts more like inorganic ammonium fertilizers than like natural organic fertilizers.

In warm, moist soils with a pH above 5.0, the majority of ammonium N is converted to nitrate N by soil organisms rather quickly (within days). Therefore, most N taken up by plants is in the NO 3 - form, although NH 4 + is taken up when present in the soil solution. Thenitrate ion (NO 3 - ) carries a negative charge which prevents its retention by the negatively- charged soil colloids. Since it is soluble and mobile, the nitrate ion is readily and easily available to plants.

Nitrate moves in the soil solution and can be leached below the plant root zone when soil moisture is excessive. The loss of nitrate by leaching is a common problem on coarse-textured, sandy soils. Leaching losses of fertilizer N are minimal when rates of application conform to recommendations consistent with the yield potential for the crop and soil in question. Nitrate N is also subject to denitrification, a process in which the nitrate ion (NO 3 - ) is reduced through several intermediate steps to a gaseous N oxide or to elemental N.

Potassium (K)

Potassium is one of the sixteen nutrient elements which is needed by plants for healthy growth. It is second only to nitrogen in the quantities required by plants.

Potassium is very mobile within plants, and performs a wide range of vital roles in plant systems, including photosynthesis, enzyme activation, stomatal control and transporting plant sugars.

Although potassium occurs naturally as up to 3.5% of the earth's crust, only a small proportion of it is available to plants.

After many years of agricultural production, and removal of potassium in produce harvested from the field, even soils which were naturally well supplied will become depleted.

If soil potassium supplies are insufficient to meet plant requirements, supplementation by potash fertilisers - fertilisers containing potassium - is necessary to maintain healthy plant growth and a sustainable agricultural environment.

Potassium (K) is absorbed by plants in larger amounts than any other mineral element except N and, in some cases, Ca. Potassium is supplied to plants by soil minerals, organic materials, and inorganic fertilizer. Due to the highly weathered status of soils, their K supplying power is quite low in most cases. Potassium occurs in the soil solution as a monovalent cation (K + ). The cation exchange capacity (CEC) of the soil controls the retention of K + and in very sandy soils (low cation exchange capacity) under high rainfall, K is subject to leaching losses.

Potassium, unlike N and P, is not found in organic combination with plant tissues. Potassium plays an essential role in the metabolic processes of plants and is required in adequate amounts in several enzymatic reactions, particularly those involving the adenosine phosphates (ATP and ADP), which are the energy carriers in the metabolic processes of both plants and animals. Potassium also is essential in carbohydrate metabolism, a process by which energy is obtained from sugar. There is evidence that K also plays a role in photosynthesis and protein synthesis.

Potassium Nitrate

Potassium nitrate, sometimes also known as saltpetre, is often used in foliar sprays or fertigation because it is highly and quickly water soluble. Its nutrient composition is approximately:

Duet has the following composition

Potassium: 37%
Nitrogen: 12%

Potassium nitrate has application as a potassium source for crops which are highly sensitive to chloride, such as tobacco. Potassium nitrate is an oxidising agent and should be handled and stored with care.

Dosage and method of application