Table 1 Nutrient agronomic efficiency and profitability calculation formulas
Variable | Abbreviation | Formula | Unit | References |
|---|---|---|---|---|
Yield | Yield | Yield m−2 X 10,000 | kg ha−1 | (Amanullah et al. 2012) |
Increase in yield over control | YieldIOC | Yield ha−1–yield ha−1 in control | kg increase ha−1 | |
Nitrogen-agronomic efficiency | N-AE | YieldIOC ha−1/rate of N applied | kg increase kg−1 N | (Vanlauwe et al. 2011) |
Phosphorus-agronomic efficiency | P-AE | YieldIOC ha−1/rate of P applied | kg increase kg−1 P | (Gitari et al. 2018) |
Potassium-agronomic efficiency | K-AE | YieldIOC ha−1/rate of K applied | kg increase kg−1 K | (Dobermann 2007) |
Yield value | Yieldv | Yield ha−1 X value of produce kg−1 | RWF ha−1 | (Amanullah et al. 2012) |
Cost that vary | Costv | Cost of manure + fertilizer ha−1 | RWF ha−1 | |
Increase in gross returns over control | GRIOC | Yieldv- costv | RWF ha−1 | |
Total cost | Costt | Cost of manure + fertilizer + seed + pesticide + labor (tilling + planting + spraying pesticide + harvesting) | RWF ha−1 | |
Net return | NR | Yieldv- costt | RWF ha−1 | |
Value-cost ratio | VCR | GRIOC/costv | RWF RWF−1 | |
Marginal returns | MR | NR/costv | RWF RWF−1 |