Soil Testing to Establish Phosphorus Critical Level for Potato (Solanum Tuberosum L.) in Andisol of Lembang

Abstract

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 Olsen extractable P. Potato tuber yield was harvested after three months of planting. The analysis of variance of the experiment result indicated that there were significant (P < 0.05) responses of tuber yield to P fertilizer rates. Similarly, extractable P concentration extracted after three weeks of planting by using Olsen extraction method were also significantly differed (P < 0.05) among P fertilizer rates. The correlation between relative tuber yield response and soil P measured with Olsen method was indicated that the critical level of extractable P concentration for potato using data of soil test P and corresponding relative tuber yield for all treatments, tested by Olsen extraction methods 68.8 mg kg-1 and 191 mg kg-1for low P and high P soils respectively determined by Cate-Nelson graphical method. Result showed that the increase in soil P response to P fertilizer application was linear up to 75 kg P ha-1 on low P soil and the increase in soil P response to P fertilizer application was linear up to 50 kg P ha-1 on high P soil, but the increase in yield was not significantly different beyond 75 and 50 kg P ha-1rate for low and high P soils respectively. The highest tuber yield (17125 kg ha-1) was recorded from 50 kg P ha-1 with mean relative yield response of about 100% on high P soil and (16921 kg ha-1) with mean relative yield response about 100% on low P soil. According to the results it can be concluded that potato tuber yield responded to P fertilizer rate significantly different as compared with yield obtained without P fertilizer on Andisol of the study area. The results of this experiment clearly revealed the importance of soil test based P fertilizer application for improving yield of potato and P fertilizer efficiency on Andisol of Lembang district, Indonesia. In turn, farmer’s economic return can be increased. Extractable P concentration extracted after three weeks of planting by using Olsen extraction method was also significantly differed among P fertilizer rates. Using the Cate and Nelson graphical method the critical level of soil extractable P concentration for potato production was on low P soil 68.8 mg kg-1 and on high P soil 191 mg kg-1 by Olsen extraction method. At soil test P values less these critical values of extractable P, P fertilizer should be applied to increase potato tuber yield.