Assessment of bat guano as source of nutrients for rice production
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Date
2018
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Publisher
Sokoine University of Agriculture
Abstract
Rice production in Tanzania is generally low and continuing to decline partly due to low
soil fertility. Smallholder farmers are continuing cultivating in the same area with little or
without use of fertilizer due to limited access to costly industrial fertilizers. This trend
results into continuous mining of plant nutrients such as phosphorous (P) and other
essential nutrients elements which are needed by rice for growth and development; and
consequently decline in soil fertility and hence rice production. The country has several
bat guano deposits, but none of them are adequately exploited as alternative source of
plant nutrients and soil amendment to improve the soil properties because of lack of
information on their potential suitability. This study, therefore, aimed to evaluate the
agronomic potential of selected bat guano for enhancing soil fertility and improving rice
production. Selected bat guano in Tanzania were studied in a laboratory incubation
experiment for 112 days to assess P release patterns and establish the pick periods of P
mineralization in Department of Soil and Geological Sciences (DSGS) laboratory. Guanos
used in this study were from Kisarawe cave A (BGK-A), Kisarawe cave B (BGK-B) and Sukumawera cave (BGS) with 8.55, 7.03 and 3.45 % total P, respectively. Guano from
each deposit was mixed with soil at varying rates of 0, 10, 20, 40 and 80 mg P 200 g -1 soil.
The incubation experiment was arranged as a 3x5 factorial experiment in randomized
complete design (RCD) with three replications. In addition to incubation experiment pot
experiment was setup to evaluate the response of rice to selected bat guano as a source of
phosphorous. The experiment was carried out in a screen house at Sokoine University of
Agriculture (SUA). The experiment was a 4 × 6 factorial in a Randomized Complete
Block Design (RCBD) replicated three times. The treatments were three bat guano from
Kisarawe cave A (BGK-A), cave B (BGK-B), and Sukumawera (BGS) and Triple Super
Phosphate (TSP) as standard fertilizer all at six application rates (absolute control, 0, 10, 20, 40 and 80 mg P kg -1 soil). Bat guano was supplemented with urea (CO (NH 2 ) 2 ) which
was applied at a rate of 400 mg N kg -1 and zinc sulphate (ZnSO 4 ) was applied at a rate of
2.5 mg Zn kg -1 . Rice SARO variety (TXD 306) was grown as a test crop.
From the incubation experiment, results showed gradual increase of extractable/available
P from 28 days to 84 days followed by a decrease in P release up to 112 days of
incubation. In all days of incubation there was a highly significant interaction effect of P-
sources and application rates (P < 0.05) on P released from guano applied at the rate of 80
mg kg -1 . The soil pH showed a very strong negative correlation with phosphorus released
(r > 0.8) from the first day to 112 th days of incubation.
The pot experiment results indicated that there was a significant (P < 0.05) effect of all three guano and standard P fertilizer (TSP) on dry matter accumulation at maturity in the order TSP > BGK-A > BGS > BGK-B. There was a significantly (P < 0.05) higher effect of P at 80 mg P kg -1 for all P sources on dry matter accumulation at maturity. Interaction effect of P sources and P rates was highly significant (P < 0.05) on dry matter
accumulation at maturity. Plant physiological parameters (number of tillers, plant height, panicle height and number of panicles per plant), as well as rice grain yield were also
significantly higher for plants receiving 80 mg P kg -1 for all P sources. Positive correlation
between grain yield and other yield components was observed indicating better crop
response to P sources and P rates applied. Both incubation and pot experiment results
indicated guano to have similar effect to TSP in releasing P for rice; hence the potential
for application as alterative P source. It was further observed that at application rate of 80
mg P kg -1 of guano, the studied guanos would release adequate phosphorous for plant
growth. Because these results were obtained under controlled environment field trials are
recommended to evaluate the response of rice and other crops to soil applied guano for
meaningful recommendations to farmers.
Description
MSc. Dissertation
Keywords
Rice production, Low soil fertility, Smallholder farmers, Industrial fertilizers costly