The effects of biochar, compost and their mixture and nitrogen fertilizer on yield and nitrogen use efficiency of barley grown on a Nitisol in the highlands of Ethiopia

The effects of organic amendments and nitrogen (N) fertilizer on yield and N use efficiency of barley were investigated on a Nitisol of the central Ethiopian highlands in 2014. The treatments were factorial combinations of no organic amendment, biochar (B), compost (Com), Com + B and co-composted biochar (COMBI) as main plots and five N fertilizer levels as sub-plots, with three replicates. Application of organic amendment and N fertilizer significantly improved yield, with grain yield increases of 60% from Com + B + 69 kg N ha⁻¹ at Holetta and 54% from Com + 92 kg N ha⁻¹ at Robgebeya, compared to the yield from the maximum N rate. The highest total N uptake was obtained from Com + B + 92 kg N ha⁻¹ at Holetta (138 kg ha⁻¹) and Com + 92 kg N ha⁻¹ at Robgebeya (101 kg ha⁻¹). The agronomic efficiency (yield increase per unit of N applied, AE), apparent recovery efficiency (increase in N uptake per unit of N applied, ARE) and physiological efficiency (yield increase per unit of N uptake, PE) responded significantly to organic amendments and N fertilizer. Mean AE and ARE were highest at B + 23 kg N ha⁻¹ at Holetta and at B + 23 and B + 46 kg N ha⁻¹ at Robgebeya. The PE ranged from 19 to 33 kg grain kg⁻¹ N uptake at Holetta and 29–48 kg grain kg⁻¹ N uptake at Robgebeya. The effects of organic amendments and N fertilizer on AE, ARE and PE were greater at Robgebeya than at Holetta. The enhancement of N use efficiency through application of organic amendments emphasizes the importance of balanced crop nutrition, ensuring that barley crops are adequately supplied with N and other nutrients. Overall, the integration of both organic and inorganic amendments may optimize N uptake efficiency and reduce the amount of N fertilizer required for the sustainable barley production in the long-term