Mixed cropping of oat–hairy vetch improves the forage yield and nutrient use efficiency of oat ( Avena sativa L.) under different fertilizer rates in Ethiopia

The study aimed to investigate the effect of fertilizer rates on quantitative traits and nutrient use efficiency of oat ( Avena sativa ) in oat–hairy vetch ( Vicia villosa ) mixed cropping system in the central highlands of Ethiopia. The oat–hairy vetch mixtures were sown with eight fertilizer rates (0%, 25%, 50%, 75%, 100%, 125%, 150%, and 175%), and sole oat and hairy vetch were also sown with their recommended fertilizer rates using a randomized complete block design with three replications. The results showed that fertilizer and year had significant effects on all measured quantitative traits. Accordingly, all the measured quantitative traits of oat increased with increasing levels of fertilizer up to 150%, and the highest performance of oat was observed in the second year. Thus, the application of 150% fertilizer gave a 107.4% yield advantage over oat sown without fertilizer. The nutrient concentration of oat increased with increasing rates of fertilizer up to 175% (71.8 kg N + 35 kg P ha −1 ) in oat–hairy vetch mixed cropping system. Similarly, the total fodder nutrient uptake of oat increased with increasing levels of fertilizer up to 150%. However, the nutrient use efficiency decreased with increasing levels of fertilizer. The Pearson correlation analysis indicated that the fodder yield of oat associated significantly and positively with all measured quantitative traits, nutrient concentration, and uptake, while it had significant and inverse associations with nutrient use efficiencies. Therefore, application of 150% (61.5 kg N + 30 kg P ha −1 ) fertilizer would increase the fodder yield and economic profitability of oat in oat–hairy vetch mixed cropping system.