Complementary effect of zoo compost with mineral nitrogen fertilisation increases wheat yield and nutrition in a low-nutrient soil

Excess nitrogen (N) fertiliser use in agriculture is associated with water pollution and greenhouse gas emissions. While practices and programs to reduce N fertiliser application continue to be developed, inefficient fertiliser use persists. Practices that reduce mineral N fertiliser application are needed in a sustainable agricultural ecosystem to control leaching and gaseous losses for environmental management. This study evaluated whether fully or partially replacing mineral N fertiliser with zoo compost (Perth Zoo) could be a good mitigation strategy to reduce mineral N fertiliser application without affecting wheat yield and nutrition. To achieve this, a glasshouse experiment was conducted to assess the complementary effect of zoo compost and mineral N fertiliser on wheat yield and nutrition in a sandy soil of southwestern Australia. Additionally, a chlorophyll meter was used to determine whether there was a correlation between chlorophyll content and soil mineral N content, grain N uptake, and grain protein content at the tillering (42 d after sowing (DAS)) and heading (63 DAS) growth stages. The standard practice for N application for this soil type in this area, 100 kg ha⁻¹, was used with a soil bulk density of 1.3 g cm⁻³ to calculate the amount of mineral N (urea, 46% N) and Perth Zoo compost (ZC) (0.69% N) for each treatment. Treatments comprised a control (no nutrients added, T1), mineral N only (100 kg N ha⁻¹, T2), ZC only (100 kg N ha⁻¹, T7), and combinations of mineral N and ZC at different rates (mineral N at 100 kg N ha⁻¹ + ZC at 25 kg N ha⁻¹ (T3), mineral N at 75 kg N ha⁻¹ + ZC at 25 kg N ha⁻¹ (T4), mineral N at 75 kg N ha⁻¹ + ZC at 50 kg N ha⁻¹ (T5), and mineral N at 50 kg N ha⁻¹ + ZC at 50 kg N ha⁻¹ (T6)). The T6 treatment significantly increased grain yield (by 26%) relative to the T2 treatment. However, the T7 treatment did not affect grain yield when compared to the T2 treatment. All treatments with mineral N and ZC in combination significantly improved the 1 000-grain weight compared to the T2 treatment. Chlorophyll content was better correlated with soil mineral N content (r = 0.61), grain N uptake (r = 0.62), and grain protein content (r = 0.80) at heading (63 DAS) than at tillering (42 DAS). While ZC alone could not serve as an alternative to mineral N fertiliser, its complementary use could reduce the mineral N fertiliser requirement by up to 50% for wheat without compromising grain yield, which needs to be verified in the field. Chlorophyll content could be used to predict soil mineral N at the heading stage, and further studies are warranted to verify its accuracy in the field. Overall, the application of ZC as part of integrated nutrient management improved crop yield with reduced N fertiliser application.