Is Long-term Cassava-based Agriculture Sustainable? (Case Study of Potassium Content in the Soil)

Farmer's interest in planting cassava is relatively high because cassava is one of tolerant commodities toward drought, and low soil fertility. With minimum input, cassava still grow and produce. However, cassava absorb greater nutrients, especially potassium (K), leading to the depletion of essential nutrient availability. This research was carried out in Pati, Central Java, aimed to determine K nutrients status in the soil at the various durations of cassava land use. The research consisted of two factors, i.e 1) duration under cassava (five years, 10 yr, and 15 yr), and 2) slope (8 to 15% and 15 to 40%), each repeated four times. Soil and plant samples were taken at each location to determine K nutrients in the soil and plant (at harvest). Exchangeable K varies from low to moderate content, i.e. 0.44 to 0.50 cmol/kg (slope 1) and 0.22 cmol/kg (slope 2). Cassava land use showed an imbalance between input (fertilizer) and output (crop harvest) with negative results in the range of 114.59 to 524.78 kg K/ha. Exchangeable K content in the soils decreased with increasing K imbalance, meaning the longer period under cassava could lead to impoverishment of nutrients. Nutrient input should be increased to reduce the nutrient imbalance on the cassava farming system.