Effect of Organic Matter on Soil Chemistry of Composted Mounds under Sweet Potato Production in the Highlands of Papua New Guinea

Abstract

The reduced fallow period and continuous cultivation of sweet potato on the same land have resulted in the depletion of soil nutrients and poor yields in Papua New Guinea (PNG) highlands, necessitating improved soil fertility management practices. In this study, we conducted a field experiment to understand the roles of organic matter in composted mounds used for sweet potato production in the highlands of PNG, utilizing cogon grass material (high carbon) and fern leaves (high nitrogen). The first treatment was set without amendment and planted as control. The second and third treatments were solely amended, respectively, and the fourth was amended with a combination of the two. All treatments were replicated five times, set up in a randomized complete block design, planted with the same number of vines, and allowed to grow in the field for twelve months. During production, soil and tuber samples were taken after six and twelve months, processed, and subjected to instrumental analysis. The average data from four replicates of each treatment were pooled, averages calculated, and statistically analysed. The results showed that composted mounds improve soil parameters and increase the concentration of nutrients in both the soil and tubers. In almost all cases, nutrient availability in the soil and tissue was dependent on the type of organic matter and the time of production. Nutrient availability was high in the six months and then decreased thereafter, implications for human and livestock consumption of sweet potato, as well as sustainable soil health.