The Role of Azotobacter-like and Azospirillum-like to Reduce the Rate of Inorganic Nitrogen Fertilizer on Lowland Rice

Abstract

Increasing rice productivity must be achieved continously to meet government and national target production. One of efforts to increase rice productivity is by N fertilization. Nitrogen availability in the soil is one of limiting factors to support rice growing and productivity. Nitrogen-fixing bacteria have ability to utilize atmosphere nitrogen become available in the soil. The use of nitrogen-fixing bacteria could be potential to reduce application of nitrogen fertilizer. The aims of the research were (1) to evaluate the ability of some nitrogen-fixing bacteria isolated from lowland rice and bio-fertilizers to fix atmosphere nitrogen, (2) to determine the effect of nitrogen-fixing bacteria in reducing inorganic N fertilizer on lowland rice. The research consisted of two experiments. The first experiment was a laboratory experiment, to isolate and select isolates that having a high capability to fix nitrogen. The research was conducted in September 2011-March 2012, at the Soil Biotechnology Laboratory, Department of Soil Science and Land Resources, IPB. Source of isolates were commercial bio-fertilizers (three types of liquid and one type of solid), and soil from lowland rice field at Sawah Baru Experimental Station. Medium used for growing of microbia i.e. nitrogen free mannitol (NFM), nitrogen free bromthymol blue (NFB), and nutrient agar (NA). Based on the results, two isolates have been selected (one Azotobacter-like bacteria and one Azospirillum-like bacteria, i.e At523 and Ap533, both have the highest solubility of ammonium, not antagonistic, and the ability to grow faster) and used for field experiment. The second experiment was a field experiment, to test the effect of nitrogen-fixing bacteria on lowland rice. The research was conducted in April-August 2012 at the plastic house of Babakan Sawah Baru Experimental Station, IPB. The experiment was arranged in randomized block design (RBD) with two factors, namely nitrogen fertilizer and type of bacteria. The rates of N fertilizer (urea) factor, i.e. 0, 50, 75 and 100 kg N ha-1. The types of bacteria factor, i.e. without bacteria, Azotobacter-like, Azospirillum-like, and consortium. Data were analyzed using analysis of variance and followed by Duncan's Multiple Range Test (DMRT) with standard error 5%. The results of the laboratorium experiment showed that all isolates of bacteria performed no significant differences on N fixing capability. Field research showed that consortium of Azotobacter-like and Azospirillum-like applied with 75% of inorganic N fertilizer from recommended dosage the highest agronomic effectiveness (117.01%) and yield increase up to 8.59%. According to this result, application of consortium bacteria could reduce 25% recommended dosage of N inorganic fertilizer.