In deep soil, for the first 18 months (16 June 2009-13 July 2010) the application of organic amendments did not consistently increase or decrease the TPPN compared with the control treatments, except for a
On the final measurement date, during the wetter spring season 3, every organic amendment associated with asymptomatic vines except rice hulls decreased deep soil TPPN: PL biochar by 12.9-fold, composted cow manure by 9.5-fold and composted green waste by 4.5-fold (Table 7).
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.
The reduction in TPPN with PL biochar applied at a rate of 6.9tha 1 is in agreement with the results of Zhang et al.
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.
At the final sampling, composted green waste increased the TPPN associated with diseased grapevines but also increased the non-plant-parasitic nematode levels, with no deleterious effects on plant health.