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Reducing uncertainty – are high-resolution CO2 flux measurements after fertilizer application necessary for reliable estimates of net ecosystem exchange?

Nicole Jurisch1, Ulrike Hagemann1, Natalia Pehle1, Jürgen Augustin1
1 Institute for Landscape Biogeochemistry, Leibniz Centre for Agricultural Landscape Research (ZALF)

P 3.6 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

In order to quantify the net ecosystem exchange (NEE) of field crops accurately, CO2 exchange measurements on arable sites must account for typical management events such as soil cultivation (tillage), harvest, and fertilization. In particular, especially organic fertilization is known for temporarily intensified ecosystem respiration (Reco) fluxes. While long-term development of CO2 exchange is captured by regular monthly measurements, short-term flux changes are often disregarded. This potentially leads to considerable uncertainties in the modeled ecosystem CO2 exchange. Therefore, we analyze the impact of high resolution Reco flux measurements immediately following mineral and organic fertilization to the annual CO2 balances of different crops like winter triticale, winter wheat, corn, and sorghum.

In case of winter cereals organic fertilizer was directly applied on the soil surface, whereas for corn and sorghum organic fertilizer was immediately incorporated into the soil prior to sowing. To gain Reco, CO2 flux measurements were conducted for 3-4 days following fertilization with a frequency of 3-4 times per day, using an opaque flow-through non-steady-state closed chamber system.  For the remainder of the year, regular measurements of Reco and NEE (transparent chambers) were performed monthly. Periods between measurements were filled by using the temperature-dependent Lloyd-Taylor model in case of Reco, and the PAR-dependent Michaelis-Menten kinetic for gross primary production (GPP), calculated as NEE–Reco. To determine the short-term effect of fertilization on annual balances, NEE-models were calculated by in- and excluding the high-resolution post-fertilization measurements, respectively.

The impact of the high-resolution measurements on the overall NEE balance differs according to temperature, composition and amount of fertilizer, as well as the cultivated crop. However, the results indicate a higher CO2 loss by surface application of organic fertilizer partially exceeding 10% of the annual NEE. In contrast, incorporation of organic fertilizer results in a much lower impact on the annual NEE (<5%). High-resolution Reco measurements following application of mineral fertilizer (always on the soil surface) had no effect on annual balances of Reco and NEE.

Letzte Änderung 19.06.2014