Awareness of seed burn

• Awareness
• Row spacing and seed burn
• Fertiliser and external environmental factors
• Application equipment and soil factors
• Crop species

Awareness

The amount of starter fertiliser that can be placed with the seed at sowing is influenced by a number of factors. These include physical and chemical product characteristic, soil texture, soil moisture, application method and the amount of water that is in, or placed with, the product.

 

Row spacing and seed burn

Increasing the row spacing and/or changing to a disc or narrow point can have a major impact on the maximum acceptable fertiliser rate.

The effect of seed-placed fertiliser on the success of crop establishment depends on a complex interaction of factors that are classified broadly into five categories – fertiliser characteristics, external environment, application equipment, soils and crop species.

top

Fertiliser and external environmental factors

The osmotic effect of a fertiliser on seed during germination is primarily related to the chemistry of the fertiliser and the solution concentration (salt index). The osmotic effects on germination are most commonly shown as delayed or staggered emergence, rather that complete failure of the crop.

The salt index of high analysis ammonium-based fertilisers, like DAP, means there is a higher potential for seed damage when using high rates with the seed of sensitive species, than when using single superphosphate to apply the same rate of phosphorus.

‘Ammonia (NH3) potential’ is the term to describe the potential for fertiliser containing ammonium (NH4+) to cause metabolic damage during germination, root or shoot growth. Fertilisers such as urea, DAP, MAP and Gran-Am® that produce a high NH4+ concentration and have high solution pH and high solubility, pose the greatest risk to a germinating seed. Similarly, liquid products such as EASY NP®, EASY NP+Zn™, EASY N and EASY ATS® pose similar risks.

The rate of soil drying can be as important as the initial soil moisture during the germination and establishment phase. If soil moisture levels fall post sowing, the potential for reduced emergence may be increased.

top

Application equipment and soil factors

Fertiliser concentrations in the seed zone are greatly influenced by the amount of soil disturbance, air velocity, ground speed, seedling depth, stubble cover, soil texture and moisture content during the seeding operation and its interaction with the concentration of fertiliser delivered to each seed row.

Seed bed utilisation (SBU%) is a term that describes the volume of soil through which fertiliser is mixed.

SBU% = width of seed row
row spacingx 100

Generally, the higher the SBU% in single-shoot seeding systems, the higher rate of fertiliser that can be applied with the seed.

The texture of the soil influences water retention and the ability of the soil to adsorb ammonia ions. Soils with a high proportion of clay are better able to retain water and adsorb ammonia ions released from nitrogen fertiliser compared with coarse textured soils. There is a greater risk of seedling damage at a given fertiliser application on sandy soils than heavier clay soils.

top

Crop species

In winter crop species, the potential damage relative to SBU% is canola > wheat > barley > oats, with canola being the most sensitive to fertiliser damage.

Table 1 and 2 show the approximate safe rates (kg/ha) of nitrogen as urea with wheat and canola if the seedbed has good to excellent soil moisture.

 

Table 1: Safe fertiliser rates when sowing wheat

25 mm seed spread eg discs, knife point				50 mm seed spread
Row spacing (cm)				Row spacing (cm)
Soil texture	15 cm	22.5 cm	30 cm	15 cm	22.5 cm	30 cm
	SBU%			SBU%
	17%	11%	8%	33%	22%	17%
Light (sandy loam)	20 kg N/ha	15 kg N/ha	10 kg N/ha	30 kg N/ha	25 kg N/ha	20 kg N/ha
Medium-heavy (loam to clay)	30 kg N/ha	25 kg N/ha	20 kg N/ha	40 kg N/ha	35 kg N/ha	30 kg N/ha

 

Source: Adapted from ‘Fertiliser Management in Direct Seeding System’, Better Crops, Vol 81 (1997, No 2)

 

Table 2: Safe fertiliser rates when sowing canola

25 mm seed spread eg discs, knife point				50 mm seed spread
Row spacing (cm)				Row spacing (cm)
Soil texture	15 cm	22.5 cm	30 cm	15 cm	22.5 cm	30 cm
	SBU%			SBU%
	17%	11%	8%	33%	22%	17%
Light (sandy loam)	10 kg N/ha	5 kg N/ha	0 kg N/ha	20 kg N/ha	15 kg N/ha	10 kg N/ha
Medium-heavy (loam to clay)	15 kg N/ha	10 kg N/ha	5 kg N/ha	30 kg N/ha	20 kg N/ha	15 kg N/ha

 

Source: Adapted from ‘Fertiliser Management in Direct Seeding System’, Better Crops, Vol 81 (1997, No 2)

 

For further information, contact your local EASY N Distributor or freecall 1800 009 832.

www.incitecpivot.com.au

This is a guide only, which we hope you find helpful as a general tool. While Incitec Pivot Fertilisers has taken all reasonable care in the preparation of this guide, it should not be relied on as a substitute for tailored professional advice and Incitec Pivot Fertilisers accepts no liability in connection with this guide. Talk to your local Incitec Pivot Fertilisers Distributor Agronomist about soil testing and arranging a specific fertiliser recommendation that best suits your needs.

®EASY Liquids, Gran-Am, EASY N, EASY U Sol, EASY PK, EASY Cal, EASY ATS and EASY KS are registered trademarks of Incitec Pivot Limited. ® Coppersol, Zincsol, Mangasol and Topfoliar are registered trademarks of Top Australia Limited.

Incitec Pivot Fertilisers is a business of Incitec Pivot Limited, ABN 42 004 080 264.

top