Abstract

Nutrient  stock:balance  (NSB)  ratio  is  a  valuable  tool  for  assessing  the  sustainability  of agricultural land. The experiment design was split plot in randomised complete block design (RCBD) done in triplicate. The NSB ratio was monitored by the effect of applied fertilizer (N and K) and soybean nitrogen contribution in cassava/soybean intercrop system. With respect to nitrogen nutrition, sole soybean produced the highest NSB ratio (14.58) and highest nutrient balance of +1597.52 Kg ha^-1 followed by intercrop with NSB ratio of 11.00 and nutrient balance of 3461.86 Kg ha^-1. Lowest NSB ratio (1.99) was obtained at sole cassava having a negative nutrient balance (-11.33 Kg ha^-1). Within the fertilizer rates, N0K50 gave the highest NSB ratio hence sole soybean at N0K50  fertilizer rate will be the most sustainable (15 years), followed by intercrop at N0K50 fertilizer rate (11 years.) while sole cassava cropping system at all fertilizer rates will be the least sustainable (1 or 2 years). Nutrient stock:balance (NSB) ratio for potassium was also highest in sole soybean (12.02), followed by intercrop (8.74). Lowest NSB ratio was obtained at sole cassava (0.86). Within the fertilizer rates, N0K50  gave the  highest  NSB ratio, hence sole soybean at N0K50  fertilizer rate will be the most sustainable (12 years), followed  by intercrop at N0K50 fertilizer rate (10 years.) while sole cassava cropping system at N0K0 and N45K0 fertilizer rates will be the least sustainable (1 year).

Key words: Intercrop, nutrient balance, nutrient stock, sustainability.