Responses of wheat and canola to rates of SOP


    Most sandy soils used for cropping in south Western Australia are now deficient in potassium (K) due to the removal of K from soil in hay and grain (Brennan and Bolland, 2007), and profitable grain yield responses to applied K fertiliser especially for MOP (MOP) (KCl) commonly investigated for wheat (Triticum aestivum L.) and canola (Brassica napus L.). However, there are only limited data of SOP comparing the K requirements of these two crop species in the region.

    UWA 1


    This glasshouse experiment aims to determine the optimal rate of potassium as SOP for wheat and canola growth, and plant nutrition.


    • Four rates of SOP (0, 30, 60 and 120 mg K/kg soil; was banded 3 cm under seeds.
    • One soil collected from Bolgart - Basal nutrients have been applied as per Ma et al (2013).
    • Two crops – Wheat (var. Scepter) and canola (var. Hyola 559®TT).
    • Two harvest – Anthesis and maturity.
    • Four replications.
    • Total no of pots (5.4 kg soil each) = 4 x 2 x 2 x 4= 64 pots.
    • Grow for up to maturity.


    Sandy soil was collected from the farmer's paddock at Bolgart


    Wheat (AGT seeds) and canola (Advanta seeds). 


    1. Plant height and tiller number
    2. Shoot DW, root DW, seed yield and yield components
    3. Shoot and root nutrients concentration 


    Brennan RF and Bolland DA (2007) Comparing the potassium requirements of canola and wheat. Crop and Pasture Science 58: 359-366.

    Ma Q., Scanlan C, Bell R, Brennan R. (2013) The dynamics of potassium uptake and use, leaf gas exchange and root growth throughout the phenological development and its effects on seed yield in wheat (Triticum aestivum) on a low-K sandy soil. Plant and Soil 373: 373-384.

    Comparison of locally produced premium SOP and MOP on the yield and quality of cultivated grain and pasture crops

    UWA 2

    The rationale of the project:

    Supplying sufficient food for the rapidly growing population of the world presents one of the greatest challenges facing humanity at present. But it is not only the quantity of food produced that should concern us, but its nutritional quality is also important. Fertilisers offer the best means of increasing yield and of maintaining soil fertility at an adequate level to ensure that good yields and quality. Macronutrients such as nitrogen, phosphorus and potassium are the plant nutrients mostly used. Plants also require large quantities of sulphur, calcium and magnesium and small quantities of some microelements. The intensely weathered nature of Western Australian cropping soils and the long history of potassium depletion by the farming system has resulted in an increased incidence of potassium deficiency in broadacre crops (Brennan and Bell 2013, Damon and Rengel 2007, and Wong et al. 2001). The effect of a single nutrient (like K) in fertiliser may depend upon how it is chemically combined in the fertiliser material, and this affects both yield and crop quality. Because potassium fertilisers are obtained from natural products, they may contain substances other than K, S and Cl, and these substances may affect plant growth. Thus, choosing the right kind of potash fertiliser can be as important as applying the right amount of potash to a crop. This project concerned with this choice and sought to answer the questions: What, for a particular purpose, is a better form of potash? Here we are concerned essentially with the choice between the chloride and the sulphate. How is the value of a potash fertiliser affected by accessory materials, e.g. magnesium, sodium and sulphur contained therein?

    Potassium sulphate and potassium chloride differ in their effects on plants in two ways: the anion accompanying the essential cation (K) has effects on the way in which cations behave and also directly affects plant metabolism, some plants being sensitive to chloride; and the sulphur in potassium sulphate is itself a major plant nutrient, being a constituent of proteins.


    The aims of this experiment are: (i) to compare the effect of SOP and MOP on wheat and canola yield and quality; and (ii) to investigate their role in the improvement of soil health.

    Design of the experiment:

    Year 1: 4 soils (4 sites) x 4 treatments of recommended dose (60 mg K/kg) of potassium (0, KCl, KCl+CaSO4, K2SO4) x 2 crops (wheat and canola) x 2 harvests x 4 replications =256 pots.

    All fertilisers will be banded 3 cm under seeds. Basal nutrients will be applied as per Ma et al (2013).

    Bottom sealed pot will be selected with a capacity of 5.4kg and filled with sieved soils after air-drying at ambient temperature. Plants will be watered at about 70% of field capacity by weighing.

    Harvesting and measurements:

    • Crops will be harvested at anthesis and maturity.
    • Shoot and dry root matter, yield and yield components will be recorded at each harvest.
    • N, P, K and S content in soil (before and after the experiment) and in-plant samples (shoot, roots and grains);
    • Protein content in grains and oil content in canola seeds.
    • Calculation of K and S budgets.
    • Soil DNA sequencing.


    Brennan, R. F. and M. J. Bell (2013) Soil potassium-crop response calibration relationships and criteria for field crops grown in Australia. Crop & Pasture Science 64: 514-522.

    Damon, P. M. and Z. Rengel (2007) Wheat genotypes differ in potassium efficiency under glasshouse and field conditions. Crop and Pasture Science 58: 816-825.

    Ma Q., Scanlan C, Bell R, Brennan R. (2013) The dynamics of potassium uptake and use, leaf gas exchnage and root growth throughout the phenological development and its effects on seed yield in wheat (Triticum aestivum) on a low-K sandy soil. Plant and Soil 373: 373-384.

    Wong, M. T. F., et al. (2001) A decision support system for mapping the site-specific potassium requirement of wheat in the field. Australian Journal of Experimental Agriculture 41: 655-661.

    Comparisons of potassium leaching of SOP and MOP


    Sandy soils are generally poor in K-bearing minerals and hence in non-exchangeable K; they release only small amounts of K by weathering and have low adsorption capacities (Mengel & Kirkby, 1987). The cycling and availability of K in these soils are therefore quite dynamic and easily affected by management practices. On sandy soils with little clay content and low cation exchange capacity, K can, on the one hand, become a limiting factor and, on the other, be lost by leaching if applied in large amounts.

    Potassium leaching is generally dependent on the amount of exchangeable K in the soil, which largely reflects the level of K input and resulting K surpluses (Askegaard et al., 2003; Kayser, 2003; Alfaro et al., 2004a). This is influenced by clay content and varies with soil type, amount and time of fertiliser application (Whitehead, 2000).


    Information on K leaching from soil of croplands in WA is scarce. To fill this gap, we will investigate K leaching either from potassium sulphate or from MOP using a mini-lysimeter system under glasshouse conditions.

    Design of the experiment:

    One soil (Bolgart) x 4 treatments of the recommended dose (60 mg K/kg soil banded 3 cm under seeds) of potassium (0, KCl, KCl+CaSO4, and K2SO4) x 1 crop (wheat) x 3 replications =12 Lysimeters.


    Lysimeter size will be selected 10.5 cm diameter and 30 cm long PVC pipe filled with 3.5 L sieved soils after air-drying at ambient temperature (Madiba et al. 2016). Water holding capacity will be measured and plants will be watered at about 70% of field capacity by weighing. Leaching event will be carried out by adding 500 ml water per lysimeter and collect leachate for analysis of K and other properties.


    Wheat (var. Scepter)

    Data collection:

    • Leachate collection and K measurement.
    • Plants will be harvested at anthesis.
    • Shoot and root dry matter will be recorded at each harvest.
    • K and S content in soil (before and after the experiment) and in-plant samples (shoot and roots).


    Madiba OF, Solaiman ZM, Carson JK and Murphy DV (2016) Biochar increases availability and uptake of phosphorus to wheat under leaching conditions. Biology and Fertility of Soils 52: 439-446.

    Establishment of crops – SoP effect on seed germination and seedlings growth


    Agricultural researchers still have difficulty in deciding appropriate fertilisers and application rates to use with seed to minimise the risk of germination damage. The type and rate of fertilisers may have detrimental effects on seed germination and growth of seedlings.


    To determine the effect of SOP on seed germination and seedlings growth

    Design of the experiment:

    • Two application methods of SOP (mixed with soil or banded 3 cm under seeds) x 2 crops (wheat and canola) x 1 dose (60 mg K/kg) x 3 replications = 12 germination/seedlings trays (100 seeds per tray).
    • Three trays for each crop will be included without SOP application as a control.


    Bolgart soil 

    Data collections:

    Germination counting, seedlings shoot and root growths (at 4-5 weeks).