Better than expected summer rain across key winter crop growing areas has set up a favourable window for 2024 winter crop planting. But, with the latest Bureau of Meteorology three-month outlook pointing to a drier autumn, there’s a risk crop establishment could be compromised if traditional seed placed fertiliser strategies are followed.
Incitec Pivot Fertilisers (IPF) technical agronomist Clint Sheather explains while the last thing growers want to do when applying fertiliser at planting is delay or reduce plant emergence, there is potential for seed damage when fertiliser is placed with the seed.
“Damage to seeds can be caused when ammonia is released from fertiliser granules placed with the seed at planting. There is also the potential osmotic effect where the fertiliser competes with the seed for soil moisture,” Mr Sheather says.
“Crops vary in their tolerance to fertilisers, with oats, barley and wheat more tolerant than lupins and chickpeas. Canola is highly susceptible to fertiliser toxicity.
“While placing fertiliser with the seed is an efficient and convenient way to apply the nutrient early in the season, the potential for seed damage is always present and it is worth considering whether alternative application strategies can improve establishment and maintain yields.”
In 2021 and 2022, IPF trials at Young and Cowra in Central West NSW looked at different placement options for phosphorous (P) in canola, demonstrating how a split P application can help maintain yield and increase flexibility for growers.
Multiple rates of P were applied (0, 5, 10, 20, 30 and 40 P/ha) as MAP and SuPerfect using four different placement methods, including a control with no fertiliser; seed placed; surface broadcast prior to seeding; and a split application including broadcast pre-planting and seed placement.
MAP was used as the P source with all seed placed fertiliser applications.
“Seeding conditions were ideal, and there was little difference in plant establishment between the treatments, highlighting the importance of adequate soil moisture when seed placing fertilisers,” Mr Sheather said.
Where soil Colwell P levels are above optimum, starter P rates as low as 5kgP/ha could be placed with the seed at planting to ensure root growth and early season vigour. When using a rate of P less than crop removal rates, soil testing is important to ensure soil P levels do not drop below established optimums.
“Seed placed P proved to be an efficient application method maintaining yield. Split applications improved yield and provided more flexibility, and broadcasting P improved yield compared to the control.”
Routine soil testing is also key to determining fertiliser strategies and mitigating establishment risks. Existing nutrient levels will inform whether a split Starter P strategy could provide the best return on investment.
“Starter P supplies small rates of P at 5kg P/ha to ensure root growth and early season vigour, with additional reserves supplied from the soil,” Mr Sheather says.
“Where capital applications are required, a split application strategy could minimise toxicity risk by combining seed placed starter P to maintain yields with a pre-plant broadcast to make up the balance of required inputs.”
Fertiliser type and seeding equipment are other key considerations for growers planning to place fertiliser with the seed.
“MAP is a more suitable choice for susceptible crops like canola. DAP has a higher osmotic potential than MAP, and higher potential to cause ammonia toxicity,” he said.
“Seeding equipment can also have a bearing on establishment, and the safest application equipment allows the fertiliser and seed to be applied in separate bands.
“Placement below and to the side of the plant line with a minimum of 50mm of separation is the most effective method of avoiding seed or root contact.”
Any change in application equipment should be considered for its potential to increase or decrease seed safety, even changes to row spacing.
“There is more than one grower out there who has learnt the hard way that increasing the row spacing and keeping fertiliser rates the same can result in reduced plant population,” Mr Sheather says.
“The safest way to manage fertiliser application with the seed is to calculate the Seed Bed Utilisation percentage (SBU percentage).
“SBU percentage factors in the width of the seed row and row spacing, and is a risk analysis tool used to determine the potential for emergence damage.”
Safe rates tables are the best way to determine safe application rates based on fertiliser type, crop type, soil moisture and soil type.
They can be viewed at https://www.nutrientadvantage.com.au/~/media/Files/IPF/Documents/Agritopics/SBU.pdf.
