Comparing the Net Ecosystem Exchange of Two Cropping Systems for Dairy Feed Production

Abstract:

A three-year study was conducted from 2012 to 2014 to determine the net CO₂ fluxes from corn and hay, the two main feed crops used in dairy production. The aim of this study is to better understand the net ecosystem exchange (NEE) in annual and perennial cropping systems used in dairy production to benefit greenhouse gas emission model developments and the life cycle analysis of dairy production. The study was conducted on two 4-ha plots where one plot was a 5-year old hayfield and the other plot was planted in a continuous cycle corn. All plots were continuously monitored using the flux-gradient method deployed with a tunable diode laser trace gas analyzer and sonic anemometers. All plots received dairy manure as fertilizer applied according to common practice. The cumulative NEE for the three years of the study was -873.15 g C m^-2 for corn and -409.36 g C m^-2 for hay. Differences in respiration between the two cropping systems was found to be the larger factor compared to differences in gross ecosystem production (GEP) that resulted in the contrasting cumulative NEE where cumulative respiration for the three years for hay was 3094.23 g C m^-2 as opposed to 2078.11 g C m^-2 for corn. Cumulative GEP for the three years was 3503.60 and 2951.31 g C m^-2 for hay and corn respectively. Inter-annual and inter-crop variability of the NEE, GEP and respiration will be discussed in relation to biomass production, climatic conditions and crop physiological characteristics.