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The development of plant nutrition systems that enhance soil productivity through the use of mineral fertilizers combined with organic fertilizers has recently gained increased attention. Two field experiments were conducted in 2018 (from February to June) and 2018/19 (from December 2018 to April 2019) to assess the effects of complementary application of inorganic nitrogen (N) and phosphorus (P) fertilizers (INPF) and winery solid waste (WSW) composts on maize yield and soil health indicators. The INPF and optimum rates of microbially inoculated and uninoculated WSW compost types were combined at different ratios (0:0, 75:25, 50:50, 25:75 and 0:100 w/w) to supply proportionate N and P amount. The recommended INPF rates for maize (200 kg N ha-1 and 90 kg P ha-1) were mixed and included as a standard control. The interaction of compost type and application rate had no significant effects on total biomass yield (TBY), grain yield (GY) and harvest index (HI). The compost type had significant effects on GY and HI in 2018/19. The TBYs obtained from the 50:50, 75:25 and 100:0 compost-INPF combinations were significantly higher than that recorded from untreated control across the compost types in 2018. The 25:75 and 50:50 compost-INPF combinations gave GYs which were significantly higher than that obtained from the untreated control in 2018/19. In many instances, soil pH and the contents of organic C, NO3, P, K, Na and Zn recorded from treatments with the different mix ratios of compost and INPF were higher than that recorded from the untreated control. Grain yield correlated significantly and positively with the contents of soil NH4 (r = 0.59) and P (r = 0.53) indicating that these nutrients contributed to the final GY. In conclusion, the joint application of compost and INPF at 25:75 and 50:50 ratios appears promising for improving GY. Increase in soil K content suggested the need for a controlled application of WSW compost followed by frequent soil testing exercise to monitor and avoid unnecessary K build-up that may induce the deficiencies of other plant nutrients.

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