Document Type : ORIGINAL RESEARCH ARTICLE

Authors

National Research and Innovation Agency, Cibinong Science Center, Jl. Raya Jakarta-Bogor, Cibinong, Bogor 6991, Indonesia

Abstract

BACKGROUND AND OBJECTIVES: Zinc deficiency is a significant global health concern, affecting around two billion people due to insufficient dietary intake. The extensive utilization of cereal-based meals with inadequate zinc content and limited bioavailability stands as the primary cause for this issue. Children who possess low levels of zinc experience stunted growth and developmental delays. They also have higher rates of morbidity from pneumonia, diarrhoea, and malaria. Inadequate zinc intake has been correlated with a heightened risk of mortality in children due to specific diseases. It is crucial to secure a satisfactory level of zinc in rice grains because of its indispensable function in various biochemical processes that are fundamental for the growth and advancement of plants. A deficiency in zinc can lead to reduced grain yield and nutritional value in rice. Recently, the utilization of registered biofertilizers and microbial technology is widely recognized in contemporary intensive farming practices. Some indigenous zinc-solubilizing bacterial strains discovered can increase rice yield and zinc content in grains. The objective of this study was to impact of a biofertilizer formula consisting of native zinc solubilizer strains on the growth, productivity, and zinc concentration in the grains of three rice varieties, namely Inpari IR Nutrizinc, Inpari 48, and Inpago 13 Fortiz. The study was conducted in a paddy field located in the Inceptisol of Subang Regency, West Java, during the year 2023.
METHODS: The field trial was conducted to study the impact of a biofertilizer comprising a group of non-pathogenic zinc-solubilizing bacteria, including Enterobacter cloacae, Klebsiella pneumoniae, Serratia marcescens, Bacillus thuringiensis, and Enterobacter bugandensis on rice growth, yield, zinc levels, and uptake in grains. The rhizosphere soils were the origin of these bacteria, which were obtained using agar media containing zinc oxide as insoluble zinc compounds. Prior to this, the bacterial strains were evaluated for their capacity to dissolve zinc and generate the plant hormone indole-3-acetic acid. To gauge their zinc-solubilizing prowess, Pikovskaya agar media, supplemented with insoluble zinc oxide and calcium phosphate, respectively, were utilized. The presence of distinct clear areas surrounding the colonies demonstrated the effectiveness of the microbes in converting insoluble zinc and phosphorus into soluble forms. The concentration of the plant hormone indole-3-acetic acid was measured using the Salkowski reagent. The field trial was organized using a split-plot design with three replications. The application of the biofertilizer mixture as a seed treatment was carried out before the transplantation of the rice nursery. The seedlings were prepared individually for each rice variety, with a comparison made between those treated with the biofertilizer and those that were not.
FINDINGS: The study found that the consortium of indigenous non-pathogenic zinc-solubilizing bacteria significantly increased the yield of rice varieties by about 5.6 percent and zinc content in grains by 16.3 percent. However, the application of zinc containing fertilizer treatments did not enhance the rice yield and zinc content in grains in this Inceptisol paddy soil. In terms of zinc content in grains, the rice variety Inpago 13 Fortiz exhibited a notable increase compared to the Inpari IR Nutrizinc variety, with levels of 40.3 milligrams per kilogram as opposed to 34.1 milligrams per kilogram.
CONCLUSION: the utilization of a native combination of carefully chosen zinc-solubilizing bacterial strains could augment the productivity, zinc concentration, and absorption in rice grains of various varieties in a paddy field with Inceptisols soil type, characterized by a moderate to high overall zinc content and limited zinc accessibility. The addition of zinc containing fertilizer treatments did not enhance rice yield compared to the addition of other tratments or control. This is probably because of the medium-high level of the total zinc content of the soil, suggesting that the addition of Biofertizinc will reduce or delete the crop requirement for zinc fertilizer in Inceptisol paddy fields. This implies that the biofertilizer is ecologically sustainable as it eliminates the use of harmful chemicals, reduces the reliance on synthetic fertilizers, and lowers costs.

Graphical Abstract

Application of indigenous zinc-solubilizing bacteria in biofertilizers to enhance zinc nutrition of rice grains in inceptisols paddy fields

Highlights

  • Zn content in rice grains at the application of NPK + Biofertizinc was markedly higher than at the application of NPK and control treatments, suggesting that the Biofertizinc could solubilize unavailable forms of soil Zn to be absorbed by rice roots;
  • This trial revealed that Inpago 13 Fortiz variety exhibited the highest Zn content in grains, followed by the Inpari IR Nutrizinc and the Inpari 48 variety. Interestingly, the Inpago 13 Fortiz (an upland rice cultivar) significantly had a higher Zn content and uptake compared to the Inpari IR Nutrizinc (a low-land cultivar). How this upland rice cultivar (Inpago 13 Fortiz) surpasses the Zn content of the low-land cultivar?
  • This study found that the application of NPK + Biofertizinc + ZnSO4 did not enhance rice yield compared to the addition of NPK fertilizer. This is probably because of the medium-high level of the total Zn content of the soil. Therefore, the addition of Biofertizinc will reduce or delete the crop requirement for ZnSO4 fertilizer in Inceptisols paddy fields.

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