Deep banding immobile fertiliser nutrients in clay soils to support rain-fed cropping.

Key points

• Removal of phosphorus (P) and potassium (K) from subsoils without replacement is increasingly limiting the ability of crops to use stored soil water
• Apart from starter fertiliser applications, enriching topsoil is generally ineffective as these layers are often dry for extended periods. Neither P nor K will leach into deeper soil layers in clay soils
• Aggressive tillage can re-distribute surface P and K into deeper profile layers, but this leaves the surface without stubble cover and can also lead to rapid P sorption and reduced plant P availability
• Deep fertiliser bands are effective, as they limit soil-fertiliser interactions and place P and K in soil layers that are wetter for longer. Placement of K with/near P bands can enhance crop K uptake
• Uptake of P and K from deep bands is limited by the volume of fertilised soil, drying of the soil around the band and the frequency with which bands are re-wet
• Residual benefits from deep P and K banding are substantial, although longevity does vary between nutrients. Crop K uptake >> P uptake, and rates of removal in grain differ between nutrients and species
• Choice of fertiliser form, blending of products, application rate, band spacing and application frequency will all affect deep banding responses

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