Mycorrhizal dependence of four crops in a P-sorbing soil

The effect of methyl bromide and P fertilization on the growth of four agricultural crops in a P-sorbing soil was studied. Harvestable yields and P tissue content were significantly lower for celery (Apium graveolens L.), onion (Allium cepa L.) and pepper (Capsicum annuum L.) following fumigation. P fertilization up to 330 kg P ha⁻¹ as superphosphate could not reverse this effect. The highest P fertilizer treatment had 25.4 μg g⁻¹ bicarbonate-extractable P and 0.26 μg g⁻¹ water extractable P. This P level produced acceptable commercial yields when vesicular arbuscular mycorrhizae (VAM) were present (non-fumigated) and indicate the importance of the VAM association for these crops. In contrast, melon (Cucumis melo L.) growth was slightly greater following soil fumigation at all P fertilization rates. These findings indicate that crop VAM dependence and efficacy of VAM biotypes must be considered as essential components for P fertilization recommendations on fumigated P-sorbing soils. Formerly Gilat, now University of Kent, Kent, UK