Oats: fertilisers and plant nutrition

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  • Phosphorous (P) is important for oat production. Addition of P fertiliser can increase both hay and grain yield, depending on the soil test P. The optimum P requirement for hay and grain appear to be different. Oat varieties may differ in their P requirements.

Phosphorus is a major nutrient for improved oaten hay and grain production. Phosphorus is a vital component of adenosine triphosphate (ATP), the 'energy unit' of plants. ATP forms during photosynthesis and is used form the beginning of seedling growth through to the formation of grain and maturity. Deficiencies result in slow growth, decreased hay and grain yields, inferior quality and subsequently lost income.

It is suggested that P can be applied at crop establishment since an adequate supply is critical for rapid development. Phosphorus is needed during early growth for plant root development and elongation, so P fertilisers are drilled with the seed during sowing. An economic response is unlikely if the application is delayed for more than 10 days after sowing.

The oat crop response to P will be influenced by the level of Colwell P and the ability of the soil to retain P (phosphorous retention index - PRI). On low P fixing soils (PRI <2 millilitres per gram (mL/g), reactive Fe < 280mg/kg, phosphorous buffering index (PBI) <15), P is held very loosely, making it more available to plant roots and potentially reducing the amount of P required for maximum economic yield. On medium and high P fixing soils (PRI 2-15 and >15mL/g, reactive Fe 280-1000mg/kg and >1000mg/kg, respectively) P is held more tightly with a lesser amount available to plant roots. A better response to applied P is expected where soil Colwell tests are low. Soil testing is, therefore required before deciding what rate of P to apply.

P deficiency symptoms

Phosphorus deficiency results in poor seedling establishment and root development. The deficiency symptoms usually only occur if the deficiency is severe and are more noticeable in young plants as they have a greater relative demand for P than more mature plants. The tips of the old leaves become dark orange-yellow and this colour moves towards the base, usually along the leaf edges. The affected leaves often have green bases, orange-yellow mid-sections and bright red or purple tips and the edges of the leaves are rolled inwards. In severe deficiency, affected areas die and turn red and purple.

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