The potential of N-fixing bacteria consortium inoculation and NPK application in increasing soil N-total, plant N uptake and tomato (Lycopersicum esculentum Mill.) yields in Andisol

Nitrogen is an essential nutrient for growing tomato plants (Lycopersicum esculentum Mill.) on Andisol soil order. However, many farmers tend to use an excessive amount of inorganic fertilizers, which can have adverse effects on both the environment and tomato yield. To combat this problem, an alternative solution is to replace the inorganic fertilizer through inoculation of Azotobacter as an N-fixing bacteria. An experiment was conducted to examine the combined effects of the N-fixing consortium with NPK on total soil N, N uptake, Azotobacter spp. population, growth and the tomato plants yield. The experiment was performed on Andisols, located roughly 1250 m above sea level in West Java Province. The experimental design used was a Randomized Block Design, in three replications, consisting of A (Control), B (N-fixing inoculation), C (N-fixing + ¼ NPK), D (N-fixing + ½ NPK), E (N-fixing + ¾ NPK), F (N-fixing + 1 NPK), and G (1 NPK). The experiment revealed that the Lembang Andisol had an acidic pH, moderate available N, and high P retention. Applying Azotobacter sp. and Azotobacter vinelandii (N-fixing consortium) combined with one dose of NPK increased plant height and the total soil N content. N-fixing inoculation combined with 1/4 NPK, ½ NP, and ¾ NPK increased plant N uptake. The inoculation of N-fixing + ¼ NPK increased fruit weight, the number of fruits, and the yield per hectare of tomatoes. Inoculating Azotobacter sp. and Azotobacter vinelandii in mixed culture can reduce NPK usage by 75%, resulting in higher tomato yield.