Effect of fertilizer, inoculation and sowing time on free amino acids and mineral nitrogen content of field grown mature soybean seeds

The study was conducted on two different sowing dates in response to various level of applied N fertilizer on free amino acids and mineral N content (viz., NO3-N, NH4-N and NO2-N) on mature soybean CV. Williams-82 seeds. Fertilizer treatments were applied to both non-inoculated (non-inoc) and inoculated (inoc) field crop. Results showed that fertilizer treatments in general significantly (P less than 0.05) reduced the free amino acids and NH4- N of both sowing (BS) as well as the NO3-N of early sowing (ES) and NO2-N of late sowing (LS) seeds, but insignificant influence was recorded in NO3-N of LS seeds. While NO2-N showed a significant response in ES seeds. A maximum significant level of free amino acids (0.207-0.223 mg g-1) and NH4-N (0.9520- 1.1448 g kg-1) was noted in T2, while a maximum level of NO3-N (0.0793-0.0867 muM) was noted in T3 of BS field seeds respectively. However, a significant level of NO2 -N was recorded in T1 (3.950 g kg-1) of LS followed by T5 (1.968 g kg-1) of ES seeds. Results further suggested that by comparing the inoc with non-inoc in particular doses of fertilizer, inoculation in general significantly and positively influenced the NO3-N and NO2-N, but decreased the NH4-N of BS field seeds, while the free amino acids were generally increased in LS, but non-significantly respond in ES seeds. A maximum level of free amino acids was recorded in T2 inoc (6.750-3.974 g kg-1), NO3-N in T4 and T3 inoc (0.1057 and 0.1950 muM) and NO2-N in T6 inoc (6.750-3.974 g kg-1), while a maximum level of NH4-N is noted in T2 inoc (0.9013-0.9780 g kg-1) of BS seeds, respectively. Therefore, it can be safely concluded that low level of mineral N content in ES than LS seeds might be due to their rapid incorporation into various nitrogenous organic compounds during the entire course of seed development to maturity. The correlation coefficient (r) studies revealed that free amino acids exhibited significant positive association with NO2-N (0.426), soluble protein (0.824) and oil content (0.618) of LS seeds. While they showed significant positive correlation with NO3- N (0.403), NH4-N (0.454) and soluble sugars (0.601), but negative with grain yield of LS seed.