Edited by RF Brennan, and MDA Bolland

Nitrogen

The nitrogen requirements of non-legume crops are similar for crops grown in the old multiple tillage and no-till cropping systems.  However, much of the nitrogen used by non-legume crops comes from the break down of crop residues and soil organic matter throughout the growing season.  No-till reduces the rate of the organic matter breakdown. 

In the first few years of no-till, the amount of nitrogen released will be reduced so more fertiliser nitrogen needs to be applied.  As organic matter builds up under no-till, the breakdown of organic matter will increase so less fertiliser nitrogen will be required. 

It is advisable to apply some fertiliser nitrogen at seeding as the rate of nitrogen release from organic matter is slower early in the season under no-till.  Avoid too much urea (< 15kg N/ha and nil for canola) or ammonium fertiliser (ammonium sulfate, di-ammonium phosphate [DAP], mono-ammonium phosphate [MAP]) with the seed or under the seed because in warm, moist conditions, especially in alkaline soils, ammonia gas is produced (volatilised) from urea and ammonium fertilisers.  The ammonia is very toxic to germinating seedlings reduces density of emerging plants and grain yields.

Back to top

Phosphorus and micronutrients (copper, zinc, manganese)

All these elements are immobile in soil and remain where applied unless the soil is cultivated.  In the old multiple tillage cropping system the fertilisers were mixed through the top 10cm of soil when the soil was cultivated.  This improved interception of the elements in soil by plant roots of subsequent crops. 

Research showed that the effectiveness of copper fertiliser was improved by using smaller granules and increased cultivation of soil (see Fig. on copper granule size) because smaller particles dispersed more widely through soil were intercepted more frequently by plant roots increasing copper uptake by plants. 

Previous research showed that fertilisers of all the soil immobile elements in the multiple tillage cropping system had a good residual values because the fertiliser residues in soil applied in previous years remained fully effective for many years. 

Paired rows with fertiliser placed in the middle, avoids
fertiliser toxicity.
 

Recent research showed that fertilisers of these elements applied and mixed through soil in the multiple tillage cropping system still remained fully effective for up to 11 years after no-till cropping was used. The experiments were undertaken to assess if for no-till cropping it was better to deep band fertilisers of the soil immobile elements about 8cm below the seed rather than place (drill) the fertiliser with the seed or place it separated from but close to the seed. 

Plant roots cannot take up any nutrient elements from dry soil.  Fertiliser is applied to no-till crops near the sown seed 2-5cm deep.  Soils up to 5cm deep frequently dry out between rains during the growing season.  The theory was that the banded fertiliser would be in moist soil longer and better accessed by plant roots growing deeper into soil from the seed.  However, in the experiments the crops obtained more than enough phosphorus or micronutrients from residues of fertiliser applied in the old multiple tillage cropping system.

The concentration of copper and zinc in young wheat leaves at the boot stage were larger for no-till when fertiliser was banded below the seed than drilled with the seed (see table on copper and zinc concentration). In addition, when soil was cultivated before drilling fertiliser with the seed, the concentration of copper and zinc was also larger than the drilled treatment with no cultivation. 

This was because cultivation mixed copper and zinc drilled with seed in no-till in previous years through the soil increasing interception and uptake of the elements applied in bands in previous years by plant roots of the current crop.

Seed micronutrient fertiliser dressings may increase the number of fertiliser particles in soil but low amounts need to be used as seedling germination may be adversely affected.  In years where the low amounts are used, tissue testing can be used to indicate when foliar application may be needed.

Another possibility is to apply micronutrients as foliar sprays.  The foliar application can be made with liquid fertilisers (eg UAN; Flexi-N), insecticides and herbicides, but compatibility with these products will need to be tested.

Back to top

Potassium

About 75% of the almost 18 million hectares used for agriculture in south-western Australia are sandy soils, and are sandplain soils (uniform deep sandy soils) or sandy duplex soils (sands over loam, clay or lateritic ironstone gravel).  Originally these soils contained adequate amounts of potassium when first cleared for agriculture so fertiliser potassium did not need to be applied to crops and pastures grown on the soils.

Removal of potassium in hay and grain has resulted in most sandy soils becoming deficient in potassium and it has become very profitable to apply fertiliser potassium to crops grown on these soils, including crops sown using no-till.  Colwell soil test potassium values in the top 10cm of soil less than 50mg/kg are highly likely to be potassium deficient for grain production of cereal and canola crops. 

Potassium chloride (muriate of potash, MOP, containing 50% potassium) is the cheapest potassium fertiliser in Western Australia.  MOP is spread over the soil surface (topdressed) for cropping, including no-till.  Never place (drill) MOP with seed of crops because it is often toxic to seedlings, reducing densities of emerging crop plants and decreasing grain yields.  This is particularly so for no-till crops sown using narrow slots so fertiliser drilled with seed is in very close contact with the seed. 

When the soil test indicates likely potassium deficiency, growers need to apply 50 to 75kg of potassium per hectare, present in 100 to 150kg MOP.  In low rainfall (less than 400mm annual average) areas the MOP is topdressed either before seeding, or in front of the seeding tynes while sowing.  In the higher rainfall areas, the MOP is topdressed four weeks after sowing to minimise possible leaching losses of potassium in very sandy soils before the development of sufficient crop roots to take up the potassium.

Back to top