Maximising nitrogen availability to crops

Nitrogen is vital to crop growth but it is mostly present in soil in an organic form that plants cannot take up. When it exists in an inorganic form, it can be lost from the soil to the atmosphere or leached below the root zone.

Key Points

• ––Organic nitrogen must be solubilised or converted into an inorganic form to be available to plants. 
• ––Plant-available N forms include nitrate, ammonium and some soluble organic compounds, all of which can be lost from the soil if they are not taken up by plants. ––
• Peak nitrogen demand of crops can be four to five times the rate of nitrogen mineralisation. ––
• Increases in soil organic matter ensures there is a larger pool of nitrogen to mineralise. 
• ––A ‘bulge’ of mineral nitrogen can be held at 80 centimetres down the soil profile. –– 
• In 10 years’ time, paddocks under continuous cropping will require 40 per cent more nitrogen fertiliser.

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Region South, North

• 2.37 mbPlant-Available Nitrogen Fact Sheet (August 2013)Maximising nitrogen availability to crops: Nitrogen is vital to crop growth but it is mostly present in soil in an organic form that plants cannot take up. When it exists in an inorganic form, it can be lost from the soil to the atmosphere or leached below the root zone.