R.H. Wanjari

Yield response to applied nutrients and estimates of N-2 fixation in 33-year-old soybean-wheat experiment on a vertisol

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 N 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 N 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 , P (100%) 35, 35 and 26 kg ha and K (100%) 16, 32 and 16 kg ha , 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 N fixed by soybean annually varied from 62.8 to 161.1 kg ha ; 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 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 N fixed was found in the 100% NPK treatment. Balanced use of nutrient is the best option to harness the N fixation potential of soybean.

Characterization of Humic and Fulvic Acid under Long-Term Integrated Nutrient Management of Soybean-Wheat Cropping System in Vertisol

The nature, content, composition and behavior of organic matter in soil are fundamentally important for growth of crops under diverse climatic conditions. Humic substances, present in soil, act as highly reactive natural polymers. The quality of soil organic matter according to functional groups governs the rate of sequestration of organic carbon. In the present investigation, effect of five years application of different integrated nutrient management (INM) interventions was assessed to note the changes in the fulvic acid and humic acid composition using fourier transform infrared (FTIR) technique. Humic acid and fulvic acid from selected treatments viz., control, inorganic NPK fertilizer (25, 30, 20 in soybean and 70, 30, 30 in wheat) and organic manure (8 t FYM ha−1 in soybean and 16 t FYM ha−1 in wheat) were fractionated from soil, separated and prepared for FTIR spectroscopy by following standard procedure. The obtained fractions were analyzed using FTIR spectroscopy. In control plot N-H stretching of amines, amides, aliphatic C-H stretching, C=O stretching of carboxylic acids, amides, ketones salt of carboxylic acid, C2H4-in plane deformation (−CCH), aromatic C-H out of plane bend were found in humic acids, whereas aliphatic C-H stretching asymmetric COO-stretching, C-O stretching of polysaccharides, -C-C-stretching were observed in fulvic acid. Due to long-term humification in treated plots humic acid contained more number of functional groups than fulvic acid. Results indicated that application of 8 t FYM ha−1 in soybean and 16 t FYM ha−1 in wheat in soil helped in the formation of long chain humic acid which can sequester more organic carbon and subsequently improve soil quality and health. Experimental results were discussed with respect to the utility of FTIR spectroscopy in the assessment of organic matter quality in long term fertilizer experiment.