Fodder Beet - P & K offtake

Background

A three year trial, carried out by Kingshay Farming Trust & Duchy College with support from the PDA, examined the nutrient requirement of different fodder crops, (see PDA leaflet 26). The results indicated a major difference between the removal of potash in fodder beet compared to accepted typical values - Table 1. This is important because nutrient requirements for optimum economic and environmental performance are based on crop removal.

Table 1. Phosphate and potash removed

¹ PDA leaflet 26 Nutrient requirements of fodder crops
² Phosphate and potash removal in crops PDA October 1997

It was subsequently established that the UK typical values for phosphate and potash removal for this crop were largely, if not entirely, based on data for sugar beet. Whilst these two crops are closely related, different varieties are used for the two separate purposes and have distinct characteristics such as root dry matter, sugar % and growth habit. It has been postulated that sugar in the roots of sugar beet replaces potassium as the preferred osmoticum and it is logical to presume that with lower sugar levels this substitution may not be as extensive in fodder varieties. It is also relevant that potassium is regarded as an "impurity" in the sugar extraction process with sugar beet and varietal breeding programmes have included this parameter in varietal selection and development over many years. This has resulted in declining levels of potassium in sugar varieties. A study of sugar beet crops in Germany, indicates a reduction from around 2.7 kg K₂O/t roots to 2.1 kg K₂O/t between 1969 and 1988 - much of this being attributable to breeding.
Data from other Countries where fodder and sugar varieties are separately identified also indicate a distinct difference in potash content between the two crop types.