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Maize and rice are the primary staple cereal food crops in Tanzania, ranking first and
second, respectively. The two crops are also used as cash crops in some parts of the
country. Despite their importance as food and cash crops, their yields per unit area are
generally very low. Recently yield of maize has been noted to be 1.4 t ha-1 while the
potential yield is 5 t ha-1 and rice yield averages between 0.5-2 t ha-1 for upland ecologies
and 4.5-6.0 t ha-1 for irrigated ecologies compared to the potential yield of 5 t ha-1 and 10
11 t ha-1 respectively. There are many factors causing such low yields, but soil nutrient
depletion ranks high. A study was carried out from August 2018 to June 2019 to assess
the response of maize and rice to applied urban green biowaste compost (UGBC). The
study included laboratory soil and biowaste compost analysis, pot experiment and field
trial.
Results for soil analysis indicated that Dakawa soil is sandy clay loam with a near neutral
pH of 7.27, low organic carbon (0.63 %) and very low total N (0.01%). The soil had high
levels of extractable phosphorus and sulphur which were 27.81 and 27.93 mg kg-1,
respectively. The CEC of the soil was very low with a value of 4.2 Cmolc kg-1. The levels
of Fe, Cu and Mn were 62.7, 1.59, and 30.98 mg kg-1, respectively. These values were
above the established critical ranges; this means that the soil had sufficient Fe, Cu and
Mn. The level of Zn was 0.9 mg kg-1. This level of Zn was lower than the critical range
indicating possible Zn deficiency of the soil. On the other hand, results urban green
biowastes compost (UGBC) revealed that UGBC had a high pH of 9.52, very high organic
carbon with 17.37 % value. Total N was 1.0 % which was below the established typical
composition of N in urban compost. The C:N ratio was 17.37 implying that UGBC was
suitable for soil application. The level of P and K in UGBC were 0.43 and 2.15 %,
considered sufficient. The concentrations of micronutrients (Zn, Fe, Mn and Cu) were 139, 4956, 387, 8 mg kg-1, respectively which were all below the established critical
concentrations in urban biowaste compost. The concentrations of heavy metals (Cr, Ni, As
and Pb) in UGBC were 126, 11, 9 and 9 mg kg-1, respectively. These levels of Cr, Ni, As
and Pb were below the maximum acceptable limit of these elements in compost set by
Japan, Australia and United states. This implies that, these materials qualify for soil
application. Based on these findings, the present study concluded that Dakawa soils have
pH which is suitable for maize and rice production. The UGBC materials can be used as
organic fertilizer subject to fortification with N, Zn, Cu, Fe and Mn nutrients.
Results from pot experiment indicated that use of pelletized urban green biowaste
compost (PUGBC) from 0 to 600 mg N kg-1 soil increased plant heights from 59.19 to
82.52 cm for maize and from 80.43 to 84.87 cm for rice. Maize dry matter yield increased
from 3.8 to 8.77 g pot-1 and rice grain weight increased from 14.84 to 26.19 g pot-1. The
increase in all cases was statistically significant (P=0.05). However, the highest maize and
rice plant heights of 92.61cm and 100.43 cm, respectively and maize dry matter yield of
14.46 g pot-1 were recorded in combined fertilization of 300 mg N (PUGBC) kg-1 soil +
300 mg N (UREA) kg-1 soil. Maximum number of effective tillers (9.62), number of
panicles per plant (9.62), panicle length (21.8 cm), panicle weight (2.982 g) and grains
weight per pot (85.17 g) for rice crop were registered in sole application of inorganic
fertilizer (600 mg N (UREA) kg-1 soil). Results of non-pelletized urban green biowaste
compost (NPUGBC) followed the same trend as those of PUGBC for both maize and rice
crops. The overall results indicated that use of combined fertilization of 300 mg N
(PUGBC) kg-1 soil + 300 mg N (UREA) kg-1 soil) or 300 mg N (NPUGBC) kg-1 soil +
300 mg N (UREA) kg-1 soil) improved maize growth and yield parameters. The use of
inorganic fertilizer alone (600 mg N (UREA) kg-1 soil) improved rice growth parameters
and yield. Based on these findings it was recommended that the use of combined
fertilization of 300 mg N (PUGBC) kg-1 soil + 300 mg N (UREA) kg-1 soil) or 300 mg N (NPUGBC) kg-1 soil + 300 mg N (UREA) kg-1 soil) is the best option for better maize
yield and use of inorganic fertilizer alone (600 mg N (UREA) kg-1 soil) is the best option
for rice production. However, these results required verification in the field.
Results from field trial indicated that rice crop had a maximum plant height (99.23 cm),
number of effective tillers per hill (17.07) and chlorophyll content (51.72) were obtained
in a combined fertilization of 75 kg N (UGBC) ha-1 + 75 kg N (UREA) ha-1 treatment. It
was followed by sole application of 150 kg N (UREA) ha-1 with values of 96.57 cm, 16.57
and 49.17 for plant height, effective tillers per hill and chlorophyll content, respectively.
The significant (P=0.05) lowest values for plant height (88.89 cm), effective tillers per hill
(11.67) and chlorophyll content (46.95) were observed in the control (0 kg N ha-1). The
significant highest grain yield of 8127 kg ha-1 equivalent to 8.13 t ha-1 was produced in the
treatment combination (75 kg N (UGBC) ha-1 + 75 kg N (UREA) ha-1). This yield was
approaching the potential yield of rice (10 to 11 t ha-1) under irrigation ecology in
Tanzania. It was followed by 150 kg N (UREA) ha-1 treatment (7751 kg) and the third
treatment was 150 kg N (UGBC) ha-1 (6867 kg). The minimum yield was recorded in the
control treatment (5594 kg). The four treatments exhibited significant difference (P=0.05)
from each other for grain yield. The same trend of results was observed for maize crop
whereby the use of integrated fertilization of 150 kg N (UGBC) ha-1 + 150 kg N (UREA)
ha-1 produced the highest maize grain yield of 8691 kg ha-1 equivalent to 8.69 t ha-1. This
yield was far above the potential yield of maize (5 t ha-1) in Tanzania. The present study
therefore concluded that the integrated use of 75 kg N (UGBC) ha-1 + 75 kg N (UREA)
ha-1 is the best treatment for rice production while the integrated use of 150 kg N (UGBC)
ha-1 + 150 kg N (UREA) ha-1 is the best treatment for maize production. Thus, farmers are
recommended to use 75 kg N (UGBC) ha-1 + 75 kg N (UREA) ha-1 for best growth
performance and high yield of rice and use of 150 kg N (UGBC) ha-1 + 150 kg N (UREA)
ha-1 for best growth performance and high yield of maize. |
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