title: Soil carbon dynamics: the effects of nitrogen input, intake demand and off-take by animals.
abstract: Elucidation of the drivers of soil carbon (C) change is required to enable decisions to be made on how to achieve soil C sequestration. Interactions between different components in the ecosystem in combination with feedback mechanisms mean that identifying drivers through conventional experimental approaches or by retro-fitting models to data are unlikely to result in the insights needed for the future. This paper explains soil C dynamics by using a process-based model. Drivers considered in the model include nitrogen (N) fertiliser inputs, intake demand, and off-take of animal products. The effect of the grazing animal in uncoupling the C and N cycles is explained, plus the implications of the farming system ('drystock' versus milk). The model enables depiction of the dynamic equilibrium achieved with time when a proposed change in the drivers is sustained. The results show that soil C loss under lactating cows is a result of N, rather than C, being removed in milk. Counter-intuitively, at the same intake demand, N loss under 'milk' is less than under 'dry-stock', as is C loss in animal respiration. Possibilities for changing the longevity of C in the soil are discussed, and the compromise between food production, N loss and C sequestration is considered.
authors: Institute of Agriculture and Environment, Massey University, PB 11001, Palmerston North, 4021, New Zealand. Electronic address: A.J.Parsons@massey.ac.nz.
authors: A J
authors: AJ
authors: Parsons
authors: J H M
authors: JH
authors: Thornley
authors: P C D
authors: PC
authors: Newton
authors: S
authors: S
authors: Rasmussen
authors: J S
authors: JS
authors: Rowarth
keywords: Dry stock; Environment; Hurley pasture model; Lactating stock; Longevity; Sequestration