Judul: Soil Testing to Establish Phosphorus Critical Level for Potato (Solanum Tuberosum L.) in Andisol of Lembang
Abstrak: Evaluation of fertility status of the soil based on its capacity to supply nutrients can help to improve productivity and increase fertilizer efficiency. Soil testing is a method of evaluation of soil fertility status in order to know the level of nutrient availability for a certain crop in a given soil type. Soil test phosphorus (STP) is a measure of plant available phosphorus (P) in a soil extracted by various extractant later the STP calibrated with crop response in order to determine P fertilizer requirement. The basic aim of soil testing is to assess nutrient status, thereby identifying current and potential need for fertilization. In Lembang district, Indonesia Andisol covers appreciable area, and defined taxonomically its andic properties and contains high allophanic materials. However, in volcanic ash soil P is strongly sorbed by non-crystalline aluminum and iron materials, it lowers P availability for plant uptake. Hence, inadequate P concentration in soil can restrain plant growth in the district and low P fertilizer efficiency reduces farm profitability. This study, soil testing to establish P critical level for potato (Solanum Tuberosum L.) in Andisol was conducted in Lembang district, west Java, Indonesia in greenhouse from February – June 2018 at Indonesian Agricultural Technologies Research Center (BPTP) in Lembang. In the study area farmers grow intensively agricultural crops including potato. However, the farmers apply blanket method of P fertilizer to grow potato is commonly practiced. The blanket method of fertilizer application does not consider the spatial and temporal soil fertility variations and farmers apply the same P fertilizer rate to their fields regardless of fertility difference. As a result profitability of potato production can be restrained by low P fertilizer efficiency. Therefore, the objective of this study was soil testing to establish P critical level for potato in Andisol of Lembang by graphical approach in order to increase P fertilizer use efficiency. Hence, soil P tests are useful to identify soils deficient in P and provide a guide to determine P requirement as to the magnitude of the crop's response to applied P. In turn, it allows for the growers more efficient utilization of P fertilizer. For the selection of representative soil across the area 30 soil samples (0- 15cm depth) were collected before the onset of the trial. Selected soil physical and chemical properties such as soil texture, organic carbon, Cation Exchange Capacity, exchangeable basic cations, total nitrogen, and available P were analyzed by respective methods. Soil test P was extracted by Olsen extraction method and the soil categorized in to low P (soils with P concentration <25 mg kg-1) and high P (Soils with P concentration >46 mg kg-1) using standard rating of Olsen extraction method. The number of treatments were 7 rates of phosphorus fertilizer (0, 25, 50, 75, 100, 125, and 150 kg P ha-1), replicated thrice for both low P and high P soil. Total number of pots were 42 (21 pots for low P soil and 21 pots for high P soil). After three weeks of planting soil samples taken from each pots (5cm depth) in order to analyze
Keyword: Andisol, Critical level, Fertilizer, Phosphorus, Potato, Soil test