Agriculture Reference
In-Depth Information
survival of most vegetables was similarly unaffected by compost rates, with
the exception of carrot (P
¼
0
:
048, R
2
¼
0
:
78) and onion (P
¼
0
:
060, R
2
¼
0.74). The average time of germination increased with increasing compost
rates for tomato (P
¼
0
:
031, R
2
¼
0
:
83), carrot (P
¼
0
:
013, R
2
¼
0
:
86), lettuce
(P
¼
0
:
012, R
2
¼
0
:
91) and okra (P
¼
0
:
001, R
2
¼
0
:
98). For these vegetables,
the average time for germination was 1-2 days longer at high compost rates
(
>
50 per cent) than low rates (
<
6.25 per cent). Differences in shoot weight
were not apparent after 21 days except for okra, which had the greatest
shoot biomass at 6.25 per cent compost.
With the exception of carrot and onion plants, seed germination and
seedling growth of most vegetables were unaffected by the phytotoxic
compounds in the compost. Compost applications to carrot and onion
nursery beds should be limited to low amounts or entirely avoided. The delay
in germination of some plants is most likely due to low levels of salinity in
the compost, which interfered with the imbibition phase of the seeds.
Nematode suppression experiment
Root galls were observed for the majority of plants inoculated with root knot
nematodes. Tomato and lettuce plants without compost and those infected
with nematodes were either dead or highly infected at the time of harvest.
Root galling in tomato (P
¼
0
:
001, R
2
¼
0
:
70) and lettuce plants (P
¼
0
:
002,
R
2
¼
0
:
97) decreased with increasing compost rates. A significant reduction
in root galling from the 0 per cent compost treatment was observed in
tomato plants at 6.25 per cent compost and in lettuce plants at 50 per cent
compost. Phytotoxic effects of compost significantly reduced plant weight
when compost rates exceeded 50 per cent in tomato and 25 per cent in
lettuce. The optimum compost rate for greatest yield was between 6.5 per
cent and 12 per cent for tomatoes and 12 per cent for lettuce. This research
supports other findings which have shown that composted biowaste reduces
the incidence of many diseases in a wide range of vegetables (Tuitert et al,
1998; Blok et al, 2002).
Field fertilizer experiments
Three farmers volunteered a limited number of lettuce beds to be used in the
experiment. The resulting experimental design had each farmer managing a
single replicate of each treatment on their lettuce beds. This design
introduced the farmers as a new factor along with fertilizer type and
application rate. To discount the effects of the farmers, we attempted to
control the management of the lettuce beds. The date of planting and
harvesting, quantities and method of fertilizing, watering and hand-weeding
were the same for all of them. Nonetheless, differences between them were
confirmed through statistical analysis (P
¼
0
:
01) and these were caused by
differences in management history, location of lettuce beds and pest incidence
among the three farmers' plots. Contrast analysis showed that poultry
manure treatments had greater yield (P
¼
0
:
004) than compost treatments.
The compost and poultry manure treatments with the same application rates
