Potash for Potatoes

Introduction

Potash is a very important input for potatoes affecting yield, quality and profitability. This leaflet reviews earlier and new information available on this topic. It provides guidance on best practice for potash use where crops are being produced for different markets, for different anticipated yields and where the crop is grown on different soil types.

Importance of potash for potatoes

Potash (potassium, K) is an essential nutrient for all plants and has a major effect upon yield and quality of potatoes as well as the general health and vigour of the crop. It is involved in regulating the amount of water in the plant; in the absence of sufficient potassium crops do not use water efficiently. Also adequate K levels in the plant help it to withstand water stress during periods of drought. Potassium plays a vital role in maintaining the turgidity (rigidity) of plant cells. Because of its importance in turgor maintenance, potassium is essential to obtain maximum leaf extension and stem elongation. This helps to achieve rapid ground cover so maximising interception of sunlight and
thus the rate of growth in the critical early periods of the growing season which is of particular importance for spring sown crops such as potatoes. Another need to ensure an adequate supply of K is because it plays a vital role in the movement of sugars, produced in the leaf by photosynthesis, to the tubers where the sugars are converted to starch. Potassium also contributes to various aspects of tuber quality that may be vital for a marketable sample. The balance between nitrogen (N) and K supply is of particular importance for this crop.

There is little doubt that crops deficient in potash are less able to handle stress caused by drought, waterlogging, frost, heat, wind, etc. However, it appears that there is no advantage to gained from applying larger amounts of K than those justified for yield or replacement requirements. Whilst yield variation will occur according to the growing conditions in different years, smaller yields in "poor" years can be minimised by ensuring an adequate potash supply.

Potash shortage leads to:

• Low yield
• Poorer marketable quality
• Thinner cell walls and less lignification
• Weaker stems
• Reduced resistance to disease
• Lower starch content of the tubers
• Increased susceptibility to bruising and mechanical damage
• Greater susceptibility to the adverse effects of drought
• Lack of response to nitrogen