Comparisons Between Different Sources of Phosphate Applied Directly to Soil and via Fertigation

Keywords: Fertigation, Phosphorus, Vegetables, Acid Fertilisers, Slow-release Fertilisers

Fertigation, a system where water and nutrients are supplied to plants simultaneously with irrigation and only in the root region, is probably one of the most efficient currently known methods of irrigation and fertilisation. It permits higher yields, a better use of water and nutrients, lower leaching losses and more controllable application of nutrients during the growing season than other nutrient and water supply methods.

Fertigation systems must use totally water-soluble nutrient sources. In the case of nitrogen and potassium this generally presents no technical problems. However, irrigation water may offer obstacles to the use of phosphoric fertilisers, particularly in alkaline conditions. Calcium phosphates and magnesium phosphates easily precipitate and block the system, making use of the whole system questionable. However, it is known that by lowering the pH of the irrigation water precipitation can be prevented, and lowering the pH of the soil may also be of advantage from the point of view of crop nutrition.

In this series of studies on open field vegetables, it is shown how nutrients supplied by fertigation, particularly phosphorus, act in comparison with nutrients supplied to the soil in the traditional manner. Also investigated are how different phosphoric fertilisers act in fertigation systems, and whether slow-release fertilisers can be used in a fertigation system.

Leena Ristimäki, Kemira Agro OY, Helsinki, Finland

16 pages, 4 tables, 8 figures, 12 refs.