Sole and Combined Application of Biodigestate, N, P, and K Fertilizers: Impacts on Soil Chemical Properties and Maize Performance.

The fertilizing effects of biodigestate produced from biogas plants on crop and soil productivity are very scarce. Hence, a field study was conducted in 2022 at the Teaching and Research Farm of Bowen University, Iwo, Osun State, Nigeria. The study evaluated the effects of biodigestate fertilizer, applied alone or in combination with urea, single superphosphate, or muriate of potash fertilizers at low (N 1 , K 1 , and P 1 ) and high (N 2 , P 2 , and K 2 ) rates on soil chemical properties, growth, and yield of maize ( Zea mays (L.)). The treatments were biodigestate alone (D), D + N fertilizer (urea) at 60 kg·ha -1 (DN 1 ), D + N at 120 kg·ha -1 (DN 2 ), D + P fertilizer (single superphosphate) at 30 kg·ha -1 (DP 1 ), D + P at 60 kg·ha -1 (DP 2 ), D + K fertilizer (muriate of potash) at 30 kg·ha -1 (DK 1 ), D + K 60 kg·ha -1 (DK 2 ), D + N 1  + P 1  + K 1 (DN 1 P 1 K 1 ), D + N 2  + P 2  + K 2 (DN 2 P 2 K 2 ) (10), and control. The 10 treatments were arranged in a randomized complete block design and replicated three times. Results showed that both low and high rates of fertilizer application improved soil chemical properties, growth parameters, and yield of maize compared with the control. High fertilizer rates (N 2 , P 2 , and K 2 ) significantly enhanced soil chemical properties and growth parameters, but lower rates (N 1 , P 1 , and K 1 ) resulted in higher maize yield. DN 1 fertilizer significantly increased maize yield compared with DN 2 , DP 1 , DP 2 , DK 1 , and DK 2 . Overall, the treatment of DN 1 P 1 K 1 demonstrated the highest grain yield, likely due to optimal nutrient supply from N, P, and K fertilizers, along with an improved soil environment facilitated by the biodigestate. The study recommends a balanced and sustainable fertilizer application strategy of 60 kg·N·ha -1 , 30 kg·P 2 O 5 ·ha -1 , and 30 kg·K·ha -1 with 2500 L·ha -1 of biodigestate to enhance maize production while minimizing cost and environmental impact. However, for those aiming for maize fodder production, a higher fertilizer rate of 120 kg·N·ha -1 , 60 kg·P 2 O 5 ·ha -1 , and 60 kg·K·ha -1 with 2500 L·ha -1 of biodigestate is advised.