Changes in Soil Properties and Fertility Status Caused by Slash-and-Burn Fires in Nagaland

Abstract

Slash and burn method of land clearing, an integral part of the traditional farming system, is widely
practised by farmers in North Eastern states of India. Thirty sites in fifteen villages of Mokokchung district
of Nagaland were selected for soil sampling to study the impact of first year slash and burn by farmers on
physicochemical properties and macro- and micronutrient status. Pre-burnt sampling was done in January
2018 and soil samples were collected from primary forest fields chosen for slash-and-burn cultivation by
the farmers. Post-burnt sampling was done from the same sites in May 2018, when farmers started sowing.
The results revealed that the pH, electrical conductivity (EC), bulk density (BD), available phosphorus (P),
available potassium (K), exchangeable calcium (Ca) and magnesium (Mg) increased significantly after
biomass burning. In post burnt soils, the pH increased from 4.86 to 5.61, EC 0.15 to 0.18 dS m-1, bulk
density 1.09 to 1.13 Mg m-3, available P 15.1 to 21.0 kg ha-1, available K 144 to 178 kg ha-1, exchangeable
Ca 0.97 to 1.15 cmol(p+)kg-1 and exchangeable Mg 0.35 to 0.45 cmol(p+)kg-1. Porosity, soil organic carbon,
available N, available S, DTPA extractable zinc (Zn), manganese (Mn), iron (Fe) and copper (Cu) decreased
significantly in post burnt soils. Porosity decreased from 53.01 to 50.95%, soil organic carbon 23.56 to
19.01 g kg-1, available N 366 to 311 kg ha-1, available S 26.9 to 21.2 kg ha-1, DTPA extractable Zn, Mn, Fe
and available Cu from 1.00 to 0.78, 29.36 to 25.13, 58.4 to 50.3 and 0.64 to 0.58 mg kg-1, respectively. Soil
texture and particle density did not affect remarkably due to biomass burning. In some cases soil colour
became lighter after biomass burning.