P & the four R's
Phosphorous (P), a crucial nutrient for plant growth and establishment, plays a vital role in energy transfer, photosynthesis, and nutrient movement within plants. The old ‘rule of thumb’ approach is to apply soluble P fertilisers based on type, quantity, and application rates. However, now best practice is following the 4R’s: right place, right time, right rate, right form.
By following the 4R’s, farmers can optimise their fertiliser use while managing direct P losses. When managed very poorly, direct losses can be up to 85 percent of P fertiliser applied. Under best practice, P losses generally contribute to less than 10 percent.
Right place
Generally, P losses can be small on soils that are well structured, well-drained, have good ground cover and/or slope is less than 15 degrees. Conversely, saturated, heavily textured, compacted, with low ground cover soil a slope greater than 15 degrees faces a higher risk of P loss. The Code of Practice for Fertiliser Nutrient Management identifies risks such as erodible slopes, areas where nutrients applied could end up in drains or streams, and soils with low Anion Storage Capacity (ASC).
Right time
As the saying goes, ‘timing is everything.’ That is especially true for P fertiliser. The timing of application is essential to ensuring its effectiveness and minimising environmental impacts. Apply fertiliser when the probability of surface runoff or leaching is lowest. This means avoiding the heavy rainfall months or within two weeks of significant irrigation, and taking into consideration hydrophobic (water repellent) soil conditions.
Right rate
Monitoring the soil’s Olsen P levels with regular soil testing assists in determining maintenance levels of phosphate required for economic optimum. Another test is the ASC test. Previously termed phosphate retention, ASC relates to the phosphorus immobilisation property of the soil. Soils with a low ASC (less than 15 percent) are at greater risk than soils with a higher ASC. It is recommended that any capital P fertiliser dressings should be split on low ASC soil types. Include an ASC test to establish the value for each soil type. One test is enough, as it is an inherent property of the soil and does not change. There are numerous forms of P fertilisers with different characteristics appropriate for different solutions. Solubility, salt index, nutrient concentrations, nutrient combination, availability, and cost are all considerations in selecting the right option for your situation.
Right form
By selecting Fertmark registered products, you are assured the label matches what is in the bag.
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