The study aimed at elucidating the utilization of coal fly ash and oil palm empty fruit bunch compost to improve the soil phosphorus uptake and yield of maize grown on Ultisol. The investigation was carried out in a greenhouse. The treatments tested were a combination of four coal fly ash doses (0, 20, 40, and 80 t ha-1) and three doses of oil palm empty fruit bunch compost (0, 10, and 20 t ha-1). At 2, 4, 6 and 8 weeks after planting, plant height, leaf number and stem diameter were observed. At the time of harvest (10 weeks after planting), fresh and dry weights of cobs, roots, stem, leaves, and seeds, as well as P uptake on the plant tissues, were observed. The results showed that the application of coal fly ash and oil palm empty fruit bunch compost significantly increased the P uptake, growth and yield of maize. The combination of 80 t coal fly ash ha-1 with 20 t oil palm empty fruit bunch compost ha-1 resulted in the highest P uptake, growth and yield of maize. Compared to the control treatment, the increase in P uptake by maize, the fresh cob weight, the dry cob weight, the biomass dry weight, and the dry seed weight were 303.23%, 285.39%, 364.91%, 329.59% and 1,591.70%, respectively.

Currently, land use is considered intensive for various purposes that affect the soil as the main series of land and the environment. The other side of the soil in Kalimantan is naturally formed from material that is poor in nutrients so it is not fertile and acidic. This study attempted to evaluate the status of soil damage to the carrying capacity for biomass production in Tanjung Selor District. The overlay analysis of land slope, rainfall, soil type and land cover in the form of a map produces indicative areas of low, medium and high damage. High damage indicative areas were selected for verification, observation and soil sampling to obtain soil damage parameter data, carried out in March 2020. Analysis of the relative frequency score of the damaged parameters aims to determine the status of carrying capacity and soil damage. The results of the study based on 10 soil damage parameters obtained a score of 6 with the status of lightly damaged soil damage, the main factor being soil acidity (R.I-a) with a high carrying capacity of 1,684 ha. The acidity factor with a pH of <4.5 (very acidic) has the most effect, 80% is damaged, but is relatively easy to repair. Efforts to improve cultivated plants are stressed by soil acidity by using soil amendments to raise the pH above the minimum range that is more suitable to increase biomass production and carrying capacity, namely agricultural lime and compost followed by N, P and K fertilization as needed.

Evaluation of the level of land suitability for rice crops is used in planning agricultural land use so that inhibiting factors and solutions can be found in processing land to be planted. This study aims to evaluate the suitability of land for rice crop plants by implementing a geographic information system that facilitates and accelerates the data processing process so that research output can be used for consideration in land use in Tanjung Selor Subdistrict of Bulungan District. The variable used in this study was temperature, water availability (rainfall), oxygen availability (soil drainage conditions), root media (soil texture), erosion hazard (slope), flood hazard (inundation), and land use. Rainfall data are obtained from the analysis of climate factor data from 2011 to 2020, soil texture data is obtained from field observations and soil maps, slope data were obtained from the Digital Elevation Model in 2014, and land use data is obtained from land-use map interpretation in 2019. Of the seven parameters, four parameters are obtained from the map, namely rainfall map, soil map, slope map, and land use map. Soil sampling and observations in the field in 2021 are carried out to obtain data on temperature, flood hazards, and soil drainage conditions. Based on the results of the analysis of land suitability of rice in Tanjung Selor Subdistrict, 13,65% is suitable marginal, and 86,35% is not suitable for planting rice. Tanjung Selor Subdistrict is dominated by areas that cannot be planted on and can be planted, but the results are less than optimal.