Abstract
Oil palm empty fruit bunches (OPEFB) are by-products of the processing of oil palm mills. The addition of nitrogen-fixing microorganisms is carried out to improve nitrogen content in OPEFB compost and it can be used as a growing medium to increase the quality of vegetable crops. The aim of this study is to analyse the potential of empty fruit bunch composts enriched with Azotobacter for improving pak choi (Brassica rapa v. chinensis) growth. The process involved the conversion of OPEFB by fortifying it with Azotobacter into value-added composts. Temperature, pH, conductivity, and nutrient characteristics of composts were analyzed during the composting process. The Completely Randomized Design was conducted to observe the potential of Azotobacter-fortified composts on pak choi growth. The growing media made in seven combinations, namely: F0: 100% soil (control); T1P1: 30% OPEFB composts + 70% soil; T1P2: 50% OPEFB composts + 50% soil; T1P3: 70% OPEFB composts + 30% soil; T2P1: 28% OPEFB composts + 2% Azotobacter sp. + 70% soil; T2P2: 48% OPEFB composts + 2% Azotobacter sp. + 50% soil; T2P3: 68% OPEFB composts + 2% Azotobacter sp. + 30% soil. The research revealed that the highest pH and conductivity values are 8.46 and 1.16 mS.cm-1, which occurred in Azotobacter assisted OPEFB composting. In the application of the compost as the growing media for pak choi, the morphological parameter showed significant effects. The Azotobacer assisted compost promoted significant increase in plant height (23,7 cm), root dry weight (2,84 g), shoot dry weight (2,39 g), root length (28,56 cm), leaf area (73,37 cm2), and number of stomata (36,70 cm-1).
Highlights
Oil palm is considered the largest commodity in Indonesia
Oil palm empty fruit bunches are a lignocellulosic waste, which is the main byproduct of the oil palm mill industries in Indonesia
Data were analyzed using the analysis of variance, and significant treatment means were separated by Tukey - Honestly Significant Different (HSD) at P < 0.05, using STAR 2.0.1 (Statistical Tool for Agricultural Research)
Summary
Oil palm is considered the largest commodity in Indonesia. In 2018, palm oil production reached 3,22 million tonnes. The production of one ton of crude palm oil requires five tonnes of fresh fruit bunches. Empty fruit bunches are a rich source of plant nutrients that can be applied as an organic fertilizer or as compost. Nitrogen and phosphorus are important nutrients for plant growth and vegetative development. Among various growing media inhabitants, Azotobacter is a beneficial bacteria that can be inoculated with organic matter-rich compost to improve soil health (Singh et al, 2019). Azotobacter is a heterotrophic free-living N2-fixing bacterium and produce phytohormone that has the benefit of increasing crop productivity. This bacterium can synthesize indoleacetic acid, gibberelins and B-vitamins which are growth-promoting substances.
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