Agriculture Reference
In-Depth Information
economic returns depending on the input and output prices [32,33]. Low
response in the 2009 WS can be explained by the negative effects of a
typhoon and the early harvest. The low response in the 2008/09 DS could
be due to the combination of a very fertile soil (high grain yield in the 0%
RR treatment) and a limited yield potential in that season (low maximum
yields in the 100% RR treatment).
The tested biofertilizers did increase grain yield signifi cantly, and
especially the BN biofertilizer did so consistently. Even in seasons in
which no signifi cant effect could be detected due to the yield variability
between plots, the grain yield with biofertilizer was usually better than
without. The seasonal yield increase across fertilizer treatments was be-
tween 5% and 18% for the BN biofertilizer (up to 24% for individual
treatments; Table 5), which is within the 5-30% range reported for
Azo-
spirillum inoculums
and non-rice crops by [4,11]. Similarly, the here-ob-
served yield increase for the
Trichoderma
-based BS (3-13%) was close
to the 15-20% rice yield increase described by [22]. The trend of yield
increases between the different inorganic fertilizer treatments was not
so clear across seasons but yield increases were often lower at higher
inorganic fertilizer rates (Figure 1), which was also reported by [24].
Absolute grain yield increases due to biofertilizer were usually below
0.5 t·ha
−1
(Table 1, Figure 1), corresponding to an estimated additional
N uptake of less than 7.5 kg N ha
−1
(based on 0.5% N in straw, 1.0% N
in grain, and harvest index 0.5). Both values are far below grain yield
increases and additional N uptake reported by [6] and [8], but similar to
the rice grain yield increases reported by [24].
The calculated AEN values (Table 6) suggested higher N use effi ciency
for treatments with biofertilizer use. Increased nutrient uptake and fertil-
izer use effi ciency were also reported for
Trichoderma
spp. [16,17,34] and
for
Azospirillum
spp. [11]. But, the results could be explained in several
ways. One possibility is that the biofertilizer stimulated root growth and
thereby increased the uptake of indigenous N from the soil (the higher
AEN would then be only an artifact of the calculation method). Second,
the increased root growth could reduce N fertilizer losses, and the third
option could be biological N fi xation (which could explain the superior
performance of the BN biofertilizer, supposedly containing organisms ca-
pable of biological N fi xation). But, our experiment cannot answer the
