a1 Indian Institute of Soil Science, Nabibagh, Berasia Road, Bhopal 462038, Madhya Pradesh, India
a2 Jawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur 462004, Madhya Pradesh, India
a3 Senior Principal Scientist, Environment and Resource Sciences and Adjunct Professor, Agriculture and Food Sciences, University of Queensland, Australia
a4 Project Coordinator, AICRP LTFE, Indian Institute of Soil Science, Nabibagh, Berasia Road, Bhopal 462038, Madhya Pradesh, India
Soybean–wheat systems are the major grain production systems on vertisols in Madhya Pradesh, India. A study on yield response to nutrients (N, P, K, S and Zn) and estimation of N2 fixation by soybean under different nutrient combinations was studied in a 33-year-old, long-term experiment on soybean–wheat–maize system. For estimation of N2 fixation, annual input–output N balance technique was used. The experiment was initiated in June 1972, comprising eight treatments, viz. control (no fertiliser and no manure), 100% N, 100% NP, 100% NPK, 150% NPK, 100% NPK + 15 t farmyard manure (FYM), 100% NPK + Zn and 100% NPK – S with four replications arranged in a randomised block design. The amount of N applied (100%) to each crop of soybean, wheat and maize was 20, 120 and 80 kg ha−1, P (100%) 35, 35 and 26 kg ha−1 and K (100%) 16, 32 and 16 kg ha−1, respectively. FYM was applied one week before the onset of monsoons. Both soybean and wheat yields responded to applied N and P during all these years. The yield response to K was observed after 10 years. The estimated amount of N2 fixed by soybean annually varied from 62.8 to 161.1 kg ha−1; however, the net gain of N in soil after offsetting the N derived by soybean from soil varied from 24.2 to 66.5 kg ha−1 annually. Maximum N gain was recorded on application of P. There was a linear relationship between the amount of harvestable biomass N and residual biomass N, whereas quantity of N added to soil has a curvilinear relationship with the harvestable biomass N. The highest percentage of N derived from the atmosphere (% Ndfa) was recorded in the control treatment, but the highest amount of N2 fixed was found in the 100% NPK treatment. Balanced use of nutrient is the best option to harness the N2 fixation potential of soybean.
(Accepted April 06 2011)
(Online publication April 02 2012)