Carbon exchange of a maize (Zea mays L.) crop: Influence of phenology

A study was carried out to quantify the carbon budget of a maize (Zea mays L.) crop followed by a rye cover crop in the Netherlands, and to determine the importance of the phenological phases and the fallow phase when modelling the carbon budget. Measurements were made of carbon fluxes, soil respiration, biomass and Plant Area Index (PAI). On the basis of PAI the annual cycle was subdivided into 5 phases: juvenile-vegetative, adult-vegetative, reproductive, senescence and fallow. To model the annual carbon budget, it should be sufficient to assess the light response in the juvenile-vegetative phase, the growing season and the fallow phase, combined with the length of these phases and the PAI development. We conclude that emphasis should be put on determining off-season fluxes while the growing season can be estimated from radiation only. During the cultivation period (from sowing to harvest) 5.97 tC ha−1 was sequestered by the maize crop. The amount of carbon exported from the field was 7.5 tC ha−1, and the estimated amount of carbon imported by organic fertilizer was 0.51 tC ha−1, resulting in a carbon loss of 1.02 tC ha−1 from the soil. The fallow phase, with a rye cover crop at the field, decreased the amount of carbon fixed in the cultivation period by 2.65 tC ha−1 (44% reduction). To enable determination of the carbon sequestration or emission of croplands, farmers should be required to analyze, apart from the nitrogen content, also the carbon content of organic fertilizers.