Babanpreet Kour, Prasanta Kumar Prusty, Sagar S.P., Yashbir Singh Shivay and Balasubramanian Ramakrishnan
Abstract
Biological nitrogen fixation is a significant source of fixed nitrogen in paddy soils and is influenced by the chemical N fertilizer application. The objective of this study was to quantify the abundance of nifH gene copies in different paddy soils and to characterize the impact of N fertilizers in the rhizosphere of rice as influenced by conventional flooding (CF) or direct seeded rice (DSR) during vegetative and flowering stages of plant growth. A microcosmic experiment was conducted with the amendment of three N concentrations (0, 10, and 100 mM) in six distinct paddy soils. Further, a field experiment was carried out by employing CF and DSR methods of rice cultivation with T1-RDF and T2-50% N as urea and KNO3 at 75:25 with full PK. The nifH abundance ranged from 2.20Ã105 to 1.01Ã107 g-1 soil and diverged significantly among distinct soil types. Soils treated with 10 mM of N had 16 to 58% higher nifH abundance, while the addition of N at 100 mM reduced nifH gene copies by 4 to 8%. Similarly, the application of 50% N relative to the recommended fertilizer N dose, led to the enrichment of nifH in rice rhizosphere under both CF (9- 25%) and DSR (11-29%) methods. Unlike the DSR (3.56 to 8.85Ã106 g-1 soil), conventionally flooded fields (6.14Ã106 to 1.01Ã107 g-1 soil) had higher nifH abundance in the rice rhizosphere. Furthermore, nifH abundance peaked during the flowering stage of plant growth and was 0.38 to 1.2 folds higher than at the vegetative stage. This study signifies that overuse of N fertilizers may restrict biological N fixation, while adequate N supply can enhance the abundance of nifH gene copies. Conventional flooding method of rice cultivation induced nifH abundance in the rice rhizosphere, which peaked during the flowering stage.