The effect of traditional slash-and-burn agriculture on soil organic matter, nutrient content, and microbiota in tropical ecosystems of Papua New Guinea

Slash-and-burn agriculture followed by tillage and western style agriculture often lead to loss of soil organic matter and soil degradation. Traditional slash-and-burn agriculture affects large areas of land across the tropical zone. However, there are few detailed studies about this practice. To evaluate the effect of traditional slash-and-burn agriculture on soil properties (total C, N, P, and C fractions of soil and available P, Ca, Mg, K, NO3, pH, and microbial community biomass and composition), we studied a chronosequence represented by active gardens, abandoned gardens (5-10 years old), secondary forest in abandoned garden sites (20-40 years old), and primary forest with no evidence of cultivation for at least 60 years. No significant differences between individual succession stages were found in total C, N, and P and in C fractions, pH, conductivity, and microbial biomass. In addition, stocks of C, N, and P in the soil did not differ between succession stages. By contrast, the concentration of available P, Ca, Mg, K, and NO3 was highest in active gardens. Litter was absent in active gardens, and the highest amount of litter on the soil surface was found in primary forest. Our results show that traditional slash-and-burn agriculture had a strong effect on nutrient availability but no effect on the total CNP stocks and soil C fractions.