Plant Nutrition

New Zealand Journal of Agriculture, Volume 65, Issue 5, 16 November 1942, Page 300

Plant Nutrition

Citrus Notes

Phosphorus Chemical Symbol: P. Occurrence in Nature: Phosphorus never occurs free, as it is readily oxidised, but in combination as phosphates, chiefly calcium phosphate, of which bones are an impure form. Function: Phosphorus is important in respiration and in the formation of proteins. It occurs also in the phosphoproteins of the nucleus and appears necessary for the cell division which is the basis of plant growth. It is concentrated in fruits and seeds and promotes early ripening. Also, it increases root development and helps the plant to resist drought by deepening the root system. Method of Absorption by the Plant: It is absorbed from the soil in the form of phosphate ion. . Recommendations. Phosphorus or phosphates are generally deficient in New Zealand and can be applied in the following fertilisers: Basic slag Ground rock phosphate Seychelles guano . . Blood and bone Fish manure .. Superphosphate Farmyard manures . . Potassium Chemical Symbol: K. Occurrence in Nature: Potassium never occurs free, but its compounds are widely distributed, being present in many silicate rocks. Wood ashes contain 30 per cent, potassium carbo- - nate. It occurs also as kainit and carnallite (compound salts of potassium and magnesium) and as sylvine or potassium chloride. Function: Potassium is connected with the vital activity of protoplasm. It is necessary for protein formation and for the functioning of hydrolysing and condensing enzymes. In its absence cell division is not active. It is replaced by sodium to a limited extent. It increases resistance to disease and improves the quality of fruit. In its absence leaf scorch may appear. Recommendations: Potassium can be applied in the following fertilisers (when available): Sulphate of potash . . Muriate of potash (chloride) ' Potash salts ■9999••• • ♦ • • • . Kainit Farmyard manures ..

Sulphur Chemical Symbol: S. Occurrence in Nature: Sulphur occurs free in volcanic regions and in combination as sulphidesgalena, zinc blende, cinnabar, pyrites, etc.; as , sulphates, e.g., gypsum; and as a gas in combination with hydrogen (sulphuretted hydrogen) and with oxygen (sulphur dioxide). Function: Sulphur is an essential element and often it forms part of the protein molecule. It is absorbed from the soil as sulphate. Recommendations: It is applied as a by-product in many fertilisers as sulphate, e.g., ammonium sulphate, sulphate of potash, and as calcium sulphate (gypsum) in superphosphate, and in the free state in basic slag which contains up to 11 per cent, of sulphur. Sulphur content is very high in the Cruciferae or cabbage family, i.e., radish, mustard, etc. 77 ■ ■ \ •

Magnesium Chemical Symbol: Mg. Occurrence in Nature: Magnesium never occurs free but in the combined form as magnesium carbonate, dolomite (double carbonate of calcium and magnesium) epsom salts (magnesium sulphate), and in carnallite, olivene, and other minerals.

Function: Magnesium is an essential element being a constituent of chlorophyll. It is a major element as far as citrus is concerned.

Recommendations: The symptoms of magnesium deficiency are not apparent with young leaves, but can be observed with mature leaves following the removal of magnesium to satisfy fruit requirements. The leaves gradually turn yellow except for the mid-rib and base of the leaf. These yellow leaves are most noticeable after a heavy crop and are readily shed, especially following dry or cold weather

and injurious sprays. A secondary effect is the death of many twigs due to infection by fungi. Magnesium deficiency is associated with seediness. Citrus trees have a large magnesium requirement and the symptoms appear when magnesium is not applied in the manure programme— on acid soils with pH less than 5 where

magnesium is lost by leaching., Magnesium deficiency is cured by a dressing of dolomite (calcium magnesium carbonate) but ’the effects are not noticeable until the second year. For quicker action add magnesium sulphate (Epsom salts). Magnesium is applied as a by-product in basic slag which contains 2 per cent, to 8 per cent, of magnesium oxide and in potash salts which contain up to 12 per cent, magnesium sulphate.

—A. M. W. GREIG,

Citriculturist,

Auckland.

. . 12-20% P 2 O 5 (insoluble in water) (insoluble in water) . . 26-36% „ „ do. 24% „ „ do. 10% „ „ do. 12% „ „ do. 20% „ ,, (soluble in water) . . 0.3 % „ „ approx.

: 48% KoO k 2 o (soluble in water) (soluble in water) . 50% „ do. - 30% „ do. n do. . 20% „ do. 99 do. . 14% „ do. 5 , do. . 0.5% „ 99 approx. approx.