Nitrogen Fertilizer and Microbial Inoculations Determined the Nutrient Uptake and Productivity of Soybean

Abstract Soybean is an important commodity in Indonesia. This study aimed to identify the application of microbe inoculations with dosage of N in form of urea toward the growth, N uptake and yield in soybean. This research was conducted on October 2017 to January 2018 in Panunggalan village, Pulokulon, Grobogan, Central Java. It used the Randomized Complete Block Design 2 factors: urea dosages (0; 50; 100 kg ha−1) and microbe inoculations (no inoculation; Rhizobium (R); Rhizobium + Trichoderma (R+T); Trichoderma(T)). The result showed that combination of urea dosage and microbe inoculations significantly influenced plant height and number of trifoliate leaves. Urea dosages and microbe inoculations or combination of both factors did not imply nodulation process. Higher N dosage and microbe inoculations increased N uptake of biomass on vegetative period but had no effect on flowering and pod filling periods. The combination of 100 kgHa-1 urea with microbes or without microbes produced the highest productivity. However, treatment without urea and no inoculation also achieved the highest production. This suggested that there was a native population of Rhizobium bacteria strains that effectively supplied N for plants. Besides, application of urea of 100 kg ha-1 or 46 N kg ha-1 was too small to interfere fixation nitrogen by local Rhizobium population. Therefore, N application in form of anorganic fertilizer or microbe for symbiotic N-fixation was not recommended for existing agro climatic conditions of area with soybean history. Thus, it could simultaneously save the cost of agricultural production.