TABLE CONTENTS

Nematode Communities and Phosphorus Availability in an Andosol under
Compost Application and Winter Cover Cropping
Takeda, M. (1), T. Nakamoto (1), K. Miyazawa (2), T. Murayama (2) & H. Okada (3)
(1) Graduate School of Agricultural and Life Sciences, the University of Tokyo, Japan, 113-8657;
(2) National Agricultural Research Center for Tohoku Region, Japan, 960-2156; (3) National Institute for Agro-
Environmental Sciences, Japan, 305-8604
Soil nematodes participate in the decomposition of organic amendments and mediate
microbial P turnover. Nematode community analysis was conducted to develop an
understanding of how P becomes available to crops under the application of organic
amendments. Two types of amendments were investigated: composted cattle manure (0, 61,
and 183 kg P ha -1 ) and cover crop residues (no crop, rapeseed, and cereal rye). Cover crops
were grown over winter and incorporated into the soil two weeks before compost application.
In the 3 x 3 factorial experiment, soybean was planted as a test crop in 2006 and 2007 on a P-
deficient Andosol in Fukushima, Japan. Compost application increased free-living nematodes
in the soil. Although the bacterial-feeder Rhabditidae was dominant in the nematode
community of the compost, compost application stimulated fungal-feeding nematodes to a
greater degree than bacterial-feeding nematodes in the soil. The increase of free-living
nematodes was less pronounced in the cover-crop treatments compared to the compost
treatments; only bacterial-feeding nematodes consistently increased after the rye treatment.
Bray-2 soil P (i.e., readily soluble and desorbable P) increased only in the compost treatment.
Soil phosphatase activity and microbial P, both representing the potential of P mineralization,
were enhanced in the treatments of compost and rye. Rapeseed had minor effects on the soil
P parameters. Soybean P uptake at flowering was improved under the application of compost
and/or rye residue. The different changes in the community composition of soil nematodes
and the P parameters suggest that the use of a rye cover crop improved P availability to
soybean differently than compost application. The density of Pratylenchidae, the prevailing
plant-feeder in the soil investigated, declined in the soils applied with compost and/or rye
residue while increasing in the rapeseed-applied soil. This may also have affected soybean P
uptake.
Onion Stunting in the Murray Mallee, South-Eastern Australia
Walker, G.E.
SARDI Plant Research Centre, GPO BOX 397 Adelaide, South Australia 5001
Stunted patches, with reduced emergence and yields, are increasingly reported in onions
grown in sandy Murray Mallee soils, under a two-cropping system that uses a herbicidekilled,
cereal ‘nurse’ crop.
Surveys showed Lesion Nematodes (Pratylenchus spp.) were commonly present in both soil
and onion roots, but populations did not tend to be higher in affected patches. Rarely, Stubbyroot
Nematode (Paratrichodorus sp.) was shown to be the likely cause of stunting. Other
pathogens, including Rhizoctonia solani, Fusarium spp. and Pythium spp., are likely to be
involved.
Greenhouse experiments, using naturally-infested, field soils ± fertilizers to investigate
factors influencing onion disease severity, demonstrated:
5 th International Congress of Nematology, 2008 288