A CASE-STUDY ON SOIL COMPACTION AND APHANOMYCES ROOT-ROT AS CAUSES OFUNEVEN PEA GROWTH

During a rainy period in 1991, most pea fields in a region in southwes tern Sweden became extremely patchy. Premature yellowing or dying of t he peas developed in a pattern that suggested machinery-induced soil c ompaction to be an important reason. A case study was conducted in suc h a field. When compared with plots with healthy peas, plots with dyin g peas were found to have significantly higher soil penetration resist ance and degree of compactness and significantly lower air-filled poro sity, plant height, number of pods per plant, number of nodules on the roots, and content of macro nutrients in the plants. Increased concen trations of Fe and Mn in the dying plants indicated oxygen deficiency in the soil. In such plots there was also a heavy infestation of Aphan omyces root rot. In plots with severe root rot infestation, but with m ore favourable soil physical conditions the crop was less severely dam aged. The combination of poor soil physical conditions and root rot in festation seemed to have completely inhibited the N-fixation.