A comparison of two sampling methods for the estimation of dry matter and mineral content of swede roots

The composition of swede roots is normally estimated from samples of cores, from which the outer tissue is cut off to minimise soil contamination. Cylindrical cores contain a disproportionally large amount of xylem tissue which has a relatively low dry matter (DM), N, Ca, Na and Mg content and a high K content. Segments are the only subsamples of swede roots which have the correct proportions of xylem, phloem and skin. Several hundred samples of cores and segments were analysed to determine whether correction factors could be applied to data obtained from the less laborious method of taking cores. The mean correction factors for the cultivar Doon Major were 1.08 for DM content and 1.11, 1.01, 0.75, 1.30, 1.48 and 1.55 for N, P, K, Ca, Na and Mg, respectively. However, these factors varied, depending on site, season, fertiliser treatment and root size. Therefore, constant correction factors can not be generally applied and cores must be regarded as unsatisfactory for estimating the composition and nutrient uptake of swedes. The errors involved in determining P content from core samples appeared to be relatively insignificant.