Abstract
Predicting and accounting for the nitrogen (N) supplied by organic amendments can reduce the application of mineral N fertilizer without yield penalty as well as decreasing N2O emissions. Automated chambers were employed over 12 months to measure N2O emissions together with soil mineral N and crop yields from optimized organic and conventional N management in an intensive, irrigated vegetable rotation in subtropical Australia. Five different fertilizer strategies were investigated. The conventional urea application rate (CONV) was compared to raw (Ma) and composted (Co) chicken manure at a conventional (Ma + CONV, Co + CONV) and reduced urea rate (Ma + Rd, Co + Rd). The reduced rates represented an 18–20 % less urea being applied and were calculated by accounting for the potential N mineralized from organic amendments. Three consecutive crops (green beans, broccoli, and lettuce) plus a cover crop (sorghum) showed no significant differences in yield and biomass production between treatments receiving either organic or mineral fertilizer. Overall, fertilizer-induced emissions were low and were unaffected by compost addition. Raw organic amendments increased N2O emissions with the first crop in the rotation contributing the highest emissions, 38–57 % of the annual cumulative N2O. The incorporation of post-harvest crop residues was a substantial trigger for N2O emissions, while the application of N fertilizer and heavy rainfall events had only marginal effects. Highest cumulative N2O emissions of 1748 g N2O-N ha−1 yr−1 were measured in the Ma + Rd treatment, with the compost treatments reducing N2O emissions by up to 45 % with emissions similar to the zero N application (0N). This study demonstrated that the strategic application of composted organic amendments integrated with reducing N fertilizer rates by up to 20 % can be an effective pathway to reduce greenhouse gas (GHG) emissions without compromising crop growth and yield.
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