Fertiliser (N) input
Throughout the analyses and examples, we see fertiliser N input as a lead ‘driving’ variable. It features therefore as the x-axis in the illustrations of how the system responds to all other inputs and management variables.
It may seem a break from convention, that a section on ‘fertiliser N input’ deflects a reader elsewhere, but the implications of fertiliser N input, are so profound, it is important to see the effects of N inputs in the context of how these drive, and interact with all other variables.
N input and system C and N balances
For each, we depict the effects of fertiliser (or other) N inputs on the rate of ‘production’ (we use units of kg protein-N for consistency across eg milk and meat); on C sequestration; on the total release of nitrogen to the environment; and on methane emissions. We also show the effects on ’emissions intensities’ (N releases per unit products; and methane emissions per unit product), and on ‘Nitrogen Use Efficiency’ (N in products per unit N inputs).
A breakdown of the effects of management variables on the whole C and N cycles (and a breakdown of the multiple release routes involved), are shown, both as the eventual sustainable steady states, but also during transitions between management combinations, under the headings above.