Evaluating resource use efficiency and stock balances of nitrogen and phosphorus fertilizers inputs: The effect of soil supply capacity in Tigray (Ethiopia)

In sub-Saharan Africa crop productivity is generally low, which affects food security and livelihoods. The application of mineral fertilizers in many cases is seen as a straightforward way to improve crop productivity. In Tigray, Northern Ethiopia, agricultural extension bureaus recommend the application of considerable amounts of fertilizers. Farmers, however, hesitate to adopt these recommendations and perceive that the use of fertilizers leads to “addiction”. Different indicators are available to evaluate effectiveness of fertilizer application. We considered six different indicators: Agronomic Use Efficiency (AUE), Value-Cost-Ratio (VCR), Recovery Efficiency (RE), Capture Efficiency (CE), Soil Supply Capacity (SSC) and (partial) Nutrient Balances (NB). On-farm experiments were conducted for four years at 16 different locations. Crops involved were wheat, teff and hanfets. Experimental
outcomes were evaluated using laboratory data on nitrogen, phosphorus and potassium (NPK) content of both soil and crops. Significant differences between the crops were found for CE, RE, NB and VCR. Wheat overall was found most extractive. Correlation between SSC and N-total and between RE and N-uptake was significant for all crops. For both nitrogen and phosphorus, NB correlated significantly with SSC for wheat and teff. Interaction between SSC, RE and NB demonstrated a significant trend for wheat: soils with higher SSC had lower NB and higher RE than soils with lower SSC. We concluded that achieving efficient use of mineral fertilizer goes at the cost of nutrient stock sustainability. The use of Integrated Soil Fertility Management-strategies is recommended to address these complex feedback and interaction mechanisms and to arrive at a sound balance between efficiency and sustainability of fertilizer use.