Individual study: Effects of burning and grazing on soil nutrients and soil microorganisms in dry tropical savanna at Telburva and Ranitali, Uttar Pradesh, India
Singh R.S., Srivastava S.C., Raghubanshi A.S., Singh J.S. & Singh S.P. (1991) Microbial C, N and P in dry tropical savanna: effects of burning and grazing. Journal of Applied Ecology, 28, 869-878
Fire and grazing are both important factors in controlling savanna plant species composition and structure, and are widely accepted as valuable tools for the management of this open habitat. In this study of dry tropical savanna in northern India, the effects of burning and grazing on soil nutrients and soil microorganisms were assessed.
Study sites: Two savanna sites (Telburva and Ranitali) lying 18 km apart were selected. The sites are located on the Vindhyan plateau in the Sonbhadra district of Uttar Pradesh, northern India (24º 19'-24º 26' N, 83º 3'-83 º3' 5” E) at 299-323 m.a.s.l.
The tree species in the savanna are Lagerstroemia parviflora, Hardwickia binata, Acacia catechu and Diospyros melanoxylon with average total
density of 180 stems/ha. Each site had a paired grazed and ungrazed area. The ungrazed area at Telburva had been fenced by the State Forest Department since 1979 and at Ranitali since 1984.
Experimental design: At Telburva, six plots in the fenced area and three in the grazed area, each 20 x 10 m, were delineated. Three plots in the fenced area were burned in both January and November 1988. Thus, there were three treatments: protection from grazing, protection from grazing plus burning, and grazing.
At Ranitali, three similar-sized plots in the fenceded area and three in the grazed area were established. There were two treatments, ungrazed and grazed. The treatments were set up in a randomized block design.
The effects of burning and grazing on the level of available nutrient pools and microbial C (carbon), N (nitrogen) and P (potassium) were assessed.
Soil sampling and analysis: Five soil samples from the upper 10 cm layer were collected at random from each plot in each of the three seasons for two annual cycles (1987 and 1988 in Ranitali, and 1988 and 1989 in Telburva).
Part in field-moist condition was used for determining inorganic nitrogen, sodium bicarbonate-extractable inorganic phosphorus and microbial C, N and P. The other part was air-dried for all other analyses.
The following were determined: soil pH; water holding capacity; gravimetric soil water; soil particles sizes; organic C; total N; total P; organic P; and inorganic N (NH+4+ NO3-). Microbial nutrients were analysed.
The maximum amounts of available nutrients and microbial biomass were similar for all the treatments at both sites. N and P values were highest in the dry season (summer) and lowest in the rainy season.
Burning and grazing increased inorganic N by 54% and 15-49%, respectively and also increased bicarbonatc-extractable inorganic P by 35% and 27-32%, respectively.
Mean annual microbial C varied from 361 to 466 µg/g, microbial N from 35 to 4l µg/g and microbial P from 16 to 23 µg/g dry soil. The mean annual microbial C, N and P were positively related to each other.
Burning increased microbial C by 18%, microbial N by 26% and microbial P by 35%. Grazing increased microbial C by 15-18%, microbial N by 14-23% and microbial P by 19-29%.
Conclusions: The increases in available nutrients and microbial biomass found in this study after burning and grazing, suggest that prescribed winter burning or moderate grazing could be important management tools for savanna in this region of India.
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