Andisol soils affected by the eruption of Mount Sinabung have different levels of ash thickness, each thickness has a different microbial activity and nutrient status. The aim of this research was to find non-symbiotic nitrogen-fixing bacteria isolates in several volcanic ash thicknesses. This research was conducted at the Soil Biology Laboratory, Faculty of Agriculture, University of Sumatera Utara. Isolation of non-symbiotic nitrogen-fixing bacteria was carried out using a nitrogen-free growth medium, Jensen medium. The results indicated that 7 bacterial isolates were able to grow on nitrogen-free medium, these isolates had different shapes (B1- B7). In the land which is not covered with ash there are 2 isolates, in the soil covered in thin ash (<2 cm) there are 2 isolates, in the soil covered in medium ash (2-5 cm) there are 2 isolates and in the soil covered in thick ash (> 5 cm) there are 1 bacterial isolate.
Rhizobia fixed nitrogen from the air and supplied legume and effected to soil fertility. The research was conducted in May application of Rhizobia's isolate BGR 3 showed the infektively with root nodule amount criteria (124,00). The isolate Rhizobia's BGR 3 effectively increased N plant level and N absorption (3,80 %; 31,08mg/plant). Application of isolate Rhizobia was not able to increase the level of P plants and P plant uptake. The best interaction was shown (Plant height 85.00 cm, stem diameter 3.93 mm, root nodule 127.50, N level of 3.80%, N absorption 30.16 mg / plant) by treatment of BGR 3 and Lime 1 x Aldd.
Reducing fertilization for increasing production is a tricky thing, but utilization of biochar expected to be a solution. This research aimed to find the best biochar for reducing fertilizer of Nitrogen, Phosphorus, and Potassium in corn growth on Ultisol. This research was conducted using a Non Factorial Randomized Block Design with a level of treatment that ware 100% NPK (2 gram), 75% NPK (1,5 gram) plus corn cobs biochar 100 gram, 75% NPK (1,5 gram) plus corn skin biochar 100 gram, 75% NPK (1,5 gram) plus paddy husk biochar 100 gram, 75% NPK (1,5 gram) plus paddy straw biochar 100 gram, 50% NPK (1 gram) plus corn cob biochar 100 gram, 50% NPK (1 gram) plus corn skin biochar 100%, 50% NPK (1 gram) plus paddy husk biochar 100 gram, 50% NPK (1 gram) plus paddy straw biochar 100 gram, all treatments with 3 replications. The result showed that reducing fertilization NPK down to 50% not significant effect for NPK nutrient uptake on corn and the best biochar for reducing NPK was biochar Husk and straw.
This study aimed to assess the fauna present on plantation land with various treatments of oil palm trunks after being cut.. Treatments of oil palm trunks included (i) palm trunks left in the form of logs; (ii) oil palm trunks were chopped after being cut; and (iii) oil palm trunks were removed from the plantation area. Macrofauna sampling was done by the method of pitfall trap, squared and hand sorting. Mesofauna samples were taken using the Berlesse-Tullgren Funnel method. The results found a variety of macrofauna belonging to 2 phyla, 5 classes, 9 orders, 10 families and 10 species. The value of total macrofauna population density for the treatment palm trunks left in the form of logs was 5115.18 individuals m−2, for chipping treatment was 8010.04 individuals m−2, and a for the treatment palm trunk removed was 2843.47 individuals m−2. Mesofauna obtained in this study belonging to 1 phylum, 5 classes, 1 sub-class, 13 orders and 22 families. The total population density of the mesofauna family for the treatment palm trunks left in the form of logs was 1120 individuals m−2, for chipping treatment was 1200 individuals m−2, for logging treatment was 880 individuals m−2.
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