Agriculture Reference
In-Depth Information
Table 2.4 Yield of lettuce following application of the compost and
poultry manure
Crop
1
Treatment
Rate
Time of
application
Mean of
all crops
(kgm
2
)
1st
(kgm
2
)
2nd
(kgm
2
)
3rd
(kgm
2
)
0 kgm
2
Control
n.a.
0.9 b
1.0 b
0.8 cd
0.9 d
1 kgm
2
Compost
Every crop
1.4 ab
1.2 ab
1.3 bcd
1.3 cd
2 kgm
2
Compost
Every crop
1.2 ab
0.9 b
1.4 abcd
1.2 d
4 kgm
2
Compost
Every crop
2.4 a
1.7 ab
1.6 abc
1.9 abc
1 kgm
2
Poultry manure
Every crop
2.0 ab
1.7 ab
2.2 a
2.0 ab
2 kgm
2
Poultry manure
Every crop
1.8 ab
1.3 ab
1.8 ab
1.6 abc
4 kgm
2
Poultry manure
Every crop
2.4 a
2.3 a
2.0 ab
2.2 a
2.5 kgm
2
Compost
First crop
1.4 ab
1.0 b
0.7 d
1.1 d
5 kgm
2
Compost
First crop
1.7 ab
1.2 ab
0.7 d
1.2 d
10 kgm
2
Compost
First crop
2.2 ab
1.6 ab
0.7 d
1.5 bcd
1
Values in each column for each crop and the mean of crops followed by similar letters are not
significantly different than Tukey's HSD test (P < 0:05). Letters indicate treatment groupings
that are statistically different from one another. Grouping rank decreases with alphabetical
order (e.g. group 'a' is greater than group 'b').
were paired on the same bed to allow for direct visual comparisons.
Although the only significant differences between paired treatments were at
the lowest application rate (1 kgm
2
) in the third crop (Table 2.4), all
farmers agreed that lettuce plants were larger and greener in poultry manure
treatments compared with compost treatments. Furthermore, the farmers'
perceptions agreed with the statistical analysis, which showed that 4 kgm
2
compost had greater lettuce yield (P
<
0
:
05) compared with the control but
only in the first crop. Marketable yields of 1.5 kgm
2
were obtained from all
poultry manure treatments and from the highest compost application
(4 kgm
2
) (Table 2.4). Lettuce yields increased linearly with increasing
compost application in the first crop and marketable yields (about 1.5 kgm
2
)
were achieved for the 50 and 100 kgNm
2
treatments. In the second crop,
marketable
lettuce yields were attained only with addition of
the
100 kgNm
2
treatment.
Lettuce yields in treatments that only had a compost application on the
first crop were not different from the control in each crop nor for the mean
of all crops. Yields obtained from the control treatment remained the same
for the crops in the three cropping seasons. Since no soil nutrients were
added, it would have been expected that the continued extraction of nutrients
in harvested lettuce would deplete the nutrients in the control plot to a level
where no crop would have grown. This is because nitrogen mineralized from
the organic matter in the sandy soil was unlikely to provide su
cient
nutrients to explain these yields. However, irrigation water used in this study
