Soil Aggregate Carbon and Diversity of Mycorrhiza as Affected by Tillage Practices in a Rice-Wheat Cropping System in Northern India

Abstract

This study analyses the effect of tillage practices on organic carbon storage in soil aggregates and the diversity of arbuscular mycorrhizal (AM) fungi in a rice-wheat cropping system (located at Uchana, 29 51' N and 76 57' E) in northern India. The rice crop was grown under conventional tillage (CT) and the wheat crop under conventional tillage (CT), zero-tillage (ZT) and furrow irrigated raised bed (FIRB) tillage systems. After seven years, soil organic carbon was: zero-tillage, 0.61%; conventional tillage, 0.44% and FIRB 0.35%. In the zero-tillage (ZT) and furrow irrigated raised bed (FIRB) tillage systems, microaggregates (<250 µm to 53 µm) formed 48.47 to 61.64% of total soil aggregates fractions and protected most of organic carbon and nitrogen in the soil. The clay and silt fractions of the soil (<53 µm) varied from 39.58 to 49.26% in different tillage systems.

The total number of arbuscular mycorrhizal (AM) fungal spores in the soil under wheat crop at different depths was: 1.3-7.5 g ¹ soil CT, 1.4-9.1 g ¹ soil ZT and 1.2-9.3 g ¹ soil FIRB. The species richness of AM fungal spores was greater during the wheat growing season than during the rice crop. The AM fungal root colonization was: 13.22 to 68.16% in rice crop and 17.60 to 87.78% in wheat crop. The AM fungal root colonization in both wheat and rice was greater at 0-15 cm soil depth. The relative density of the AM fungal spores under different tillage practices in wheat crop was: 7.58-18.31% Acaulospora sp., 5.04-11.38% Gigaspora sp., 67.00-83.3% Glomus sp. and 3.86-5.75% other species.