Microorganisms, Elaeis guineensis, biofertilizers, economic efficiency, root

147  dynamics

Oil palm (Elaeis guineensis Jaq) is one of the most productive oilseeds in the world. In

118  Brazil, the main commercial plantations of this crop are concentrated mainly in the state

119  of Pará. Achieving the standard requires a long nursery period, high consumption of

120  chemical fertilizers and high operating costs. Due to this problem, plant growth promoting

121  rhizobacteria (PGPR) are free-living microorganisms that inhabit the soil, colonize host

122  plant roots and exert favorable effects on plant growth through various direct and indirect

123  mechanisms. The objective of this study was to evaluate the growth promotion, hormonal

124  levels, nutritional contents and to analyze the economic efficiency and dynamic of thin

125  roots in oil palm seedlings in response to rhizobacteria inoculation. The first experiment

126  was conducted in a completely randomized design under nursery conditions, with three

127  treatments and 10 replications. Treatments: T1: no inoculation + 50% fertilization (C-);

128  T2: with inoculation + 50% of fertilization (UFRAB01) and T3: without inoculation +

129  100% of fertilization (C +). Inoculated plants increased hormone levels by 66% indol-3-

130  acetic acid (IAA), 44% abscisic acid (ABA), as well as increased macro and micronutrient

131  content per plant. There was a 24% reduction in 1-aminocyclopropane carboxylic acid

132  (ACC) levels. Inoculation promoted plant growth by increasing by 110% shoot dry matter

133  (MSPA), 123% root dry matter (MSR), 39% plant height (AP) and 19% stem diameter

134  (DC), all in relation to the control plant. Economic efficiency analysis showed that

135  microbial technology reduces nursery time and reduces the cost of seedling production.

136  The use of inoculation reduced by 11% the value of oil palm seedling. The second essay

137  aimed to analyze the dynamics of thin roots in inoculated seedlings. The design was in

138  randomized blocks (DBC), using five treatments with 6 replications. The treatments were:

139  T1: (C-) without inoculation + 50% of fertilization; T2: plants inoculated with R-146 +

140  50%; T3: plants inoculated with R-46 + 50% fertilization; T4: plants inoculated with R-

141  92 + 50%; T5: (C +) without inoculation + 100% fertilization. Inoculation positively

142  influenced the very thin root length (Ф ≤ 0.5 mm), increasing 60% in R-146 and 59% R-

143  46 when compared to the control. Given this, microbial technology is presented as an

144  alternative method increasing yields of agricultural production and optimizing chemical

145  fertilizer use converging to a more sustainable agriculture.