Yield benefits from joint application of manure and inorganic fertilizer in a long-term field pea, wheat and potato crop rotation

Joint fertilization with organic and inorganic fertilizers contributes to sustainable crop production. However, quantitatively understanding the joint fertilization efficacy (JFE) with organic and inorganic fertilizers on yield is limited. This study aimed to investigate the quantitative JFE on crop yield. A 15-year field experiment with pea, wheat, and potato rotation was conducted on a constructed terrace in the semiarid area of the Loess Plateau of China. The fertilizer treatments imposed were (i) inorganic N and P fertilizer (NP); (ii) sheep manure (M); (iii) combined manure plus the inorganic N and P fertilizer (MNP); and (iv) unfertilized control (CK). We defined the yield increase of NP, M and MNP relative to CK (ΔYNP, ΔYM and ΔYMNP), and the JFE was calculated as ΔYMNP−(ΔYM+ΔYNP)ΔYM+ΔYNP×100% When the JFE > 10%, it was considered a synergistic effect; when the JFE was between − 10% and 10%, it was a summing effect, and when the JFE