Low pH and aluminum tolerance of Bradyrhizobium strains isolated from acid soils in Indonesia

Sixty-seven strains of Bradyrhizobium isolated from soybean plants growing on acid soils in West Java and Sumatra, Indonesia, were examined for the effect of the pH and aluminum concentration on their growth in nutrient media, compared with 61 strains of Bradyrhizobium from soils in Japan. The results in this study indicated that the indigenous population of Bradyrhizobium in the soils of Indonesia showed a large difference in acid- and Al-tolerance from that of Japan. Eighty-five and 48% of the isolates from Japanese soils and Indonesian soils, respectively, were unable to grow in YEM broth at pH below 4.5. The acid-tolerance was correlated with AI-tolerance of the isolates on YEM agar plates at pH 4.4. Seventy-five percent of the isolates that grew in YEM broth at pH 4.5 were also resistant to 400 µM Al on the YEM plates. Acetylene reduction assay of the root nodules revealed that 3 of the acid- and Al-tolerant isolates from Indonesian soils showed a significantly high nitrogen fixation activity.     

Influence of water depth and soil amelioration on greenhouse gas emissions from peat soil columns

Recently, large areas of tropical peatland have been converted into agricultural fields. To be used for agricultural activities, peat soils need to be drained, limed and fertilized due to excess water, low nutrient content and high acidity. Water depth and amelioration have significant effects on greenhouse gas (GHG) production. Twenty-seven soil samples were collected from Jabiren, Central Kalimantan, Indonesia, in 2014 to examine the effect of water depth and amelioration on GHG emissions. Soil columns were formed in the peatland using polyvinyl chloride (PVC) pipe with a diameter of 21 cm and a length of 100 cm. The PVC pipe was inserted vertically into the soil to a depth of 100 cm and carefully pulled up with the soil inside after sealing the bottom. The treatments consisting of three static water depths (15, 35 and 55 cm from the soil surface) and three ameliorants (without ameliorant/control, biochar+compost and steel slag+compost) were arranged using a randomized block design with two factors and three replications. Fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from the soil columns were measured weekly. There was a linear relationship between water depth and CO₂ emissions. No significant difference was observed in the CH₄ emissions in response to water depth and amelioration. The ameliorations influenced the CO₂ and N₂O emissions from the peat soil. The application of biochar+compost enhanced the CO₂ and N₂O emissions but reduced the CH₄ emission. Moreover, the application of steel slag+compost increased the emissions of all three gases. The highest CO₂ and N₂O emissions occurred in response to the biochar+compost treatment followed by the steel slag-compost treatment and without ameliorant. Soil pH, redox potential (Eh) and temperature influenced the CO₂, CH₄ and N₂O fluxes. Experiments for monitoring water depth and amelioration should be developed using peat soil as well as peat soil–crop systems.