17 April 1997

Root nutrient advice queries

NUTRIENT supply from potato and sugar beet residues may need taking into greater account when planning fertiliser strategies, according to ADAS.

Recent experiments have highlighted potential anomalies in current official fertiliser advice, says Wolverhampton-based soil scientist Ross Mitchell.

Findings confirm that on sandy soils sugar beet tends to leave more nitrogen for following cereals than potatoes. But on heavier, medium textured soils the reverse seems to be true.

Crop remains mineralise faster on sands than on heavier land, notes Mr Mitchell. So potato residues, usually incorporated earlier than those of sugar beet, may be broken down soon enough to be leached from sandy soils and lost to the next crop.

But on heavier land crops following immediately tend to get more N from potatoes because beet residues decay too slowly to become available, he explains.

"While these results on heavier soils are consistent with the classification of potatoes as an index 1 crop and sugar beet as index 0, as in current MAFF fertiliser recommendations, they show the opposite on sandy soils. They demonstrate the importance of the interaction between crop residue type and soil texture on the release of N." &#42