Potassium for winter resilience
In anticipation of spring growth, growers will apply a general fertiliser, with the emphasis on nitrogen, to stimulate new growth with warming temperatures. But sometimes the crop or turf doesn’t survive the winter in the first place.
Anecdotal evidence suggests that potassium (K), and maybe sulphur (S) and silicon (Si), applied in autumn can improve the plants’ winter-hardiness. When we get calls in spring from councils because their ovals have died yet nearby ovals remain healthy, nutrition is a likely factor (because weather isn’t). Soil testing then often reveals low K and S.
The important point to recognise is that when playing fields deteriorate over winter, the cause is hard playing on a surface that cannot grow and repair itself during winter (most turf species grown in most of NSW are warm-season species). And frosts don’t help either. Nevertheless, appropriate fertilising in autumn could prevent this.
Potassium
Exactly how K might protect plants over winter is not clear. K is crucial for plant nutrition, growth, enzyme function and internal water pressure of cells, among other processes (Schachtman & Schroeder 1994). K regulates the opening and closing of the stomata, reducing water loss from the leaves and thus increasing drought tolerance (Wikipedia). These dual roles of maintaining internal water pressure and controlling water loss are probably relevant.
In addition, K promotes thickening of cells walls by promoting the production of cellulose (Handreck & Black 2002). This can protect turf against the wear and tear typical of playing fields. K also protects against disease, perhaps through both improved physical strength and supporting enzymes involved in fighting off disease (Marschner 1995). In the case of legumes such as lucerne, K increases winter hardiness, possibly by promoting the storage of carbohydrates as food reserves (Russell 1973).
Sulphur and silicon
S may also have a role in improving winter hardiness. S is an essential component of some amino acids and thus of all proteins. It is also essential in the manufacture of chloroplasts, which capture light. In proteins, chemical bonds between some neighbouring S atoms (called disulphide bonds) greatly strengthen the protein structure. An animal (and fungal) protein called keratin, which forms hair and nails, is particularly high in these S–S bonds, explaining their strength. So perhaps insufficient S in plants before winter leaves plants weaker than they could be.
In addition, Si improves plant strength through its incorporation in cell walls, increasing root mass, volume and surface area for nutrient and water uptake (Barker & Pilbeam 2007).
Fertilise in autumn
Whatever the explanation, it appears that applying K and possibly S and Si fertiliser in autumn can help strengthen your crop or turf during winter, allowing it to survive the winter.
If you have noticed your turf or crop failing to survive winter, the first thing to do is get a soil and plant test in autumn (that’s now!). If low K (or S or Si) is evident, then apply an appropriate fertiliser in autumn while the weather is still warm enough for the plants to take it up. Let us know how it goes.
Further reading
Barker AV, Pilbeam DJ. 2007. Handbook of Plant Nutrition. Taylor and Francis, Boca Raton, FL, USA.
Handreck K, Black N. 2002. Growing Media for Ornamental Plants and Turf, 3rd ed. UNSW Press, Sydney.
Marschner H. 1995. Mineral Nutrition of Higher Plants, 2nd ed. Academic Press, London.
Russell EW. 1973. Soil Conditions and Plant Growth, 10th ed. Longman, London.
Schachtman DP, Schroeder JI. 1994. Structure and transport mechanism of a high-affinity potassium uptake transporter from higher plants. Nature 370: 655–658.
Wikipedia: Plant nutrition.