Productivity and soil fertility status as influenced by integrated use of n-fixing biofertilizers, organic manures and inorganic fertilizers in onion

Abstract

One of the major constraints associated with onion (Allium cepa L.) cultivation is improper nutrient management. This necessitates to ascertain an efficient and economical integrated approach with renewable source such as organic manure and biofertilizers. In this context a field experiment was carried out at Acharya N.G.Ranga Agricultural university, Hyderabad, India to study the productivity and soil fertility status as influenced by integrated nutrient management in onion using cv. N-53. The twelve treatments arranged in randomized complete block design which consisted of two kinds of organic manure i.e. farmyard manure (FYM) and vermicompost (VC) alone and in combination with two kinds of bio fertilizers (Azotobacter chroococum and Azospirillum brasilianse ) and chemical fertilizers which were tested in comparison with recommended dose of fertilizers (RDF) as control. The amount of FYM and vermicompost applied was calculated on the basis of their results of chemical analysis for NPK. Roots were dipped into the slurry of biofertilizer (1 kg in 10 liters) for 20 minutes before planting and thirty days after transplanting the soil between the seedling rows was also treated with biofertilizers at the rate of 2 kg per ha. Productivity indicated by yield and harvest index and soil fertility indicated by available NPK in soil after harvest were significantly increased with the application of biofertilizer in combination with 50% N through organic manure (FYM or VC) and rest of 50% N and 100% PK through chemical fertilizer. Those were significantly superior to the application of 50% recommended N through organic manure with 50% N and 100% PK through chemical fertilizer, application of chemical fertilizer (control) alone and application of organic manure alone, respectively. Judicious application of bio fertilizers, organic manure and chemical fertilizer increased 22% more yield over control (RDF) and economic analysis revealed that highest net return and benefit cost ratio obtained when FYM used as an organic source which replaced the 50% of recommended dose of inorganic nitrogen. Bacterial population of Azotobacter and Azospirillum in soil after harvest was markedly increased with integrated use of bio fertilizer, organic manure and chemical fertilizer system and was reduced with the exclusive application of chemical fertilizers. The results indicated that integrated nutrient management with biofertilizer (Azotobacter and Azospirillum) in combination with 50% inorganic N through organic manure (VC or FYM) and rest of the N and PK through chemical fertilizer is considered most useful for obtaining maximum yield with higher fertility status in soil for onion cultivation.