06 November, 2018
Cotton requires a good supply of both macro and micro nutrients to produce high yields. Most soils require the application of nitrogen, phosphorus and potassium, and some growers will need to apply zinc and other micronutrients.
In developing a fertiliser program, it is best practice to:
• Determine on how much is required and left in the soil, using pre season soil testing.
• Calculate expected crop nutrient requirements, taking into consideration expected yield , cropping history, and your cropping system.
• Develop a crop fertiliser application plan that ensures expected crop demands are met.
• Monitor crops through the season to determine whether the crop is sufficient in nutrient levels.
A fertiliser plan outlines how, when and in what form the fertiliser inputs are required by cotton crops. There are different forms of fertiliser that can be used, such as manures and composts, granular fertilisers, anhydrous ammonia (NH3), liquid or foliar fertilisers.
Composts and manures need to be spread and incorporated in advance of planting. NH3 cannot be applied too close to planting as seedling damage may occur from ammonia burn. When applying all the nutritional requirements up front, reduced efficiencies and losses from the system should be considered. Split applications can improve efficiencies and although application rates can be adjusted to meet crop demands, the timing becomes critical as irrigation and rain can impact the ability to apply fertilisers, increasing the risk of crops being stressed.
Fertiliser rates will depend on the type being used and when it will be applied. If all will be applied up front, adjustments must be made to consider losses. If a starter fertiliser is being used at planting with later in-crop application, the rate must be adjusted. The rate is determined by soil analysis in the winter prior to planting the crop.
Most fertilisers are applied to the soil. Nitrogen contained in fertilisers can be lost into the atmosphere through ammonia volatilisation and should be applied below the soil surface. Other fertilisers can be broadcast and then incorporated later to maximise contact between the roots and fertiliser. Applying fertilisers too close to the plant line may cause seedling damage effect.
Fertiliser plans must have the capacity to be modified through the season if conditions change or if leaf petiole analyses identify a problem, and indicate a change to the nutritional requirement of the crop and fertiliser program.
By Chris Barry, Extension & Development Agronomist – Queensland.
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