2.7 Nutrient roles in crop production

Details of those nutrients commonly required in fertilisers in SA. 

NITROGEN (N) 

• Necessary for quantity and quality of growth. 

• Directly responsible for plant protein content. 

• Found in plant protein and chlorophyll. 

• Major part of the plants genetic material DNA. 

• Required in large quantities when plants are growing rapidly. 

Deficiency symptoms 

• Nitrogen is quite mobile in the growing plant, so deficiencies are first seen in older leaves. 

• Plants show a general yellowing, or pale green, are stunted and mature early. 

• Low protein levels in the plant or grain are a good indicator of low soil nitrogen levels. 

PHOSPHORUS (P)

• Essential for plant growth. Promotes rapid growth, leaf size, tillering and hastens maturity stimulating flower, seed and fruit production. Rapid root and seedling development and improves cold tolerance Important for nodule development in legumes

Deficiency symptoms 

• Stunted plants with poor root growth and low vigour. 

• Leaves may be distorted with older leaves being affected before younger ones. 

• Often difficult to detect in a field crop as the whole paddock is generally affected. 

• Poor tillering in cereals and delayed maturity in all crops.

SULPHUR (S)

• Essential for the formation of plant proteins, amino acids some vitamins and enzymes. 

• Sulphur also influences chlorophyll production. 

• Canola has a high demand for sulphur during the vegetative growth stage. 

• Essential for nitrogen fixation in legumes. 

• It gives the characteristic odour to garlic, mustard and onions. 

Deficiency symptoms 

• Visible but are easily confused with other nutrient problems.

• In sulphur deficient cereals the youngest leaf is palest while the nitrogen the oldest leaf is palest. 

• More noticeable where nitrogen supply is good. 

• Canola crops are often deficient during the 4 to 8 leaf stages, recovering as the weather warms up and soil mineralisation increases. 

ZINC (Zn)

• Involved in the production of plant growth substances, enzymes systems and metabolic reactions. 

• Essential for production of chlorophyll and carbohydrates (structure and energy source) Influences resistance to root disease.

Deficiency symptoms 

• Difficult to diagnose in pasture and grain legumes. 

• Shortening of the internode and leaves may fail to expand properly. 

• In cereals usually seen in the seedling stage. 

• Longitudinal pale green stripes on one or both sides of mid-vein in young leaves. 

• Symptoms appear to be worse in cold wet seasons with low light intensity. 

MANGANESE (Mn)

• Necessary in plants enzyme systems, for chlorophyll production. Promotes germination and accelerates plant maturity. Associate with disease resistance eg. take-all in wheat. Helps increase phosphorus and calcium availability. 

Deficiency symptoms 

• Weak, floppy pale green/yellow leaves. 

• Can appear water stressed. 

• Closer inspection will reveal slight inter-veinal chlorosis; distinct yellowing between green veins. 

• Rather immobile in the plant so younger leaves affected first. 

• In oats deficiency is seen as grey/brown necrotic lesions with and orange margin. 

COPPER (Cu)

• Necessary for chlorophyll formation. 

• Promotes strong cell walls and consequently resistance to fungal attack. 

• Influences pollen viability - seed set. 

• Affect plant respiration, plant pores and consequently water use efficiency.

Deficiency symptoms 

• Plant symptoms rarely seen in field. 

• In cereals shrunken heads with gaps due to poor seed set. 

• This is caused by sterile pollen and delayed maturity. 

• In pasture legumes the leaves are pale and erect often remaining cupped. 

• In livestock deficiency symptoms include: steely wool in sheep, say-back in lambs and rough, pale coats and ill-thrift in young cattle.

2.7 Nutrient roles in crop production

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