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In the relatively dry winter season 2, the ratio TFLN: TPPN associated with diseased grapevines was increased by composted cow manure and rice hulls, but these favourable effects had disappeared by the following season.
The organic amendments increased the non-plant-parasitic nematode and decreased the parasitic nematode populations, as seen by the increased TFLN : TPPN ratios compared with the controls, particularly in the final spring samples after a period of relatively high rainfall.
Reasons for increased TFLN: TPPN ratios with organic amendments
This enhanced soil biological activity may have been a major cause of the increased TFLN: TPPN ratio.
However, in the present investigation, the ratio of non-plant-parasitic to plant-parasitic nematodes (TFLN: TPPN) was still significantly elevated by PL biochar compared with the control treatment; therefore, the overall change was still favourable to the plant.
and TPPN populations in the relatively dry winter season 2, although the TFLN : TPPN ratio remained unchanged.
For asymptomatic grapevines, composted cow manure and composted green waste increased the ratio TFLN : TPPN by 11.6- and 7.8-fold, respectively.
We show that application of the organic amendments caused decreased plant-parasitic and increased free-living (non-plant-parasitic) nematode populations, as illustrated by increased TFLN; TPPN ratios at the final sampling date by of 5.8-15.9-fold.
Nevertheless, direct effects of pH on the soil biology may have occurred, as measurements for all locations (n = 108) showed that pH(Ca[Cl.sub.2]) was weakly correlated with microbial activity, TFLN and microbial biomass C (r=-0.58, -0.18 and -0.34, respectively).
There was also some evidence of this in the summer rainfall zone, with a weak correlation between exchangeable K and both TFLN and microbial activity (r = 0.36 and 0.34, respectively).
Cu concentrations at most of our surveyed sites were above this value, and yet there was a weak correlation between Cu levels and both TFLN and microbial activity (r = 0.46 and 0.40, respectively).
Matrix of correlation coefficients (r-values) for selected soil biological and biochemical properties for all locations (n = 108) surveyed in winter and summer rainfall zones in spring 2003 Labile C (mg/g), microbial biomass C (mg/g), total organic C (mg/g), total N (mg/g), microbial activity ([micro]g FDA/g.min) and total free-living nematodes (TFLN, number/200 mL soil).
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