Effects of Mineral and Organic Fertilization on Forage Maize Yield, Soil Carbon Balance, and NPK Budgets, Under Rainfed Conditions in the Azores Islands (Portugal)

Green organic fertilizers can be a valuable option to reduce the use of chemical fertilizers, improve the physical and chemical properties of soil, and promote circular agriculture. The effects of two fertilization schemes, (i) a combination of mineral fertilizers with dairy farm slurry (TA) and (ii) an organic substrate (SO) from green waste (TB), on soil fertility and forage maize (Zea mays L.) yield were studied in an on-farm trial in the Azores Island of S. Miguel (Portugal). For this purpose, soil chemical parameters were evaluated on three sampling dates, forage maize yield and yield components were compared, and the balances of soil carbon (SC), nitrogen (N), phosphorus (P), and potassium (K) were evaluated. The results showed that the maize yield obtained in TB was significantly higher than in TA. The differences in precipitation that occurred over the two years influenced the yield in both treatments. The SC, available P, and pH were significantly higher in TB at every sampling date, mainly in the subsurface layer, and overall enrichment in nitrogen was observed. Despite the need to extend this evaluation over a longer period, the results indicate that the application of SO could be an alternative to conventional mineral fertilization in forage maize in the Azores and in similar cropping systems in regions of temperate insular nature.