Synnøve Rivedal
Stasjonsleder
(+47) 975 85 474
synnove.rivedal@nibio.no
Sted
Fureneset
Besøksadresse
Furenesvegen 210, 6967 Hellevik i Fjaler
Sammendrag
The decline of soil organic carbon (SOC) content is a major concern in agricultural soils, and reduction of tillage frequency is proposed as a measure to counteract this tendency. Here, we assessed the effect of tillage and renewal frequency on grassland SOC content based on a long–term experiment at Fureneset, Western Norway. The objective was to compare permanent and unrenewed grassland treatments with treatments ploughed and renewed 6 to 15 times from 1974 to 2016. Mean SOC content of the permanent grassland was 64 ± 9 g kg−1 (one standard deviation) at 0 to 40 cm depth and soil contained 210 Mg C ha−1, compared to 60 ± 6 g kg−1 and 190 Mg C ha−1 for grassland renewed with ploughing. Higher SOC contents were associated with reduced forage dry matter yields (DMY) of the permanent grassland, but not in frequently renewed grasslands. High SOC contents correlate with high porosity and water content, as soil properties approach those of organic soils. This may cause a wetter soil and reduced plant growth and increase soil compaction. In areas with generally high SOC contents in agricultural soils, increased carbon content due to no tillage may thus make the soils more agronomically challenging to manage
Forfattere
Sissel Hansen Synnøve Rivedal Samson Øpstad Johannes Deelstra Trond Børresen Torfinn Torp Peter DörschSammendrag
To study the effect of drainage intensity on GHG emissions and N drainage losses in cool-humid Norway, we established drainage systems with 6 and 12 m drain spacing in a previously undrained sandy loam (Mollic gleysol) collecting data in the years 2014–2016. After sowing a mixed grass ley, subsurface drainage was larger (1271 versus 699 mm) and mean ground water table (GWT) lower (102 versus 79 cm) with 6 than with 12 m drain spacing. Water filled pore space (WFPS) remained high throughout most of the year (> 80 %). It was highest in 12 m drain spacing, but shortly after fertilizations no differences between the two drainage systems were found. N2O emissions after fertilization were larger in the 12 m system than in the 6 m system. Cumulative N2O emissions in the 6 and 12 m system were 4.0 versus 2.5 kg N ha−2 yr−1. N leaching for the entire observation period (29 months) was larger in the 6 m (42 kg ha−1) than the 12 m (19 kg ha−1) system. Grass yields, plant N-recovery and fertilizer N use efficiency was larger with 6 than 12 m. The mean N2O emission factor was significantly higher with 6 than with 12 m drain spacing (1.4 versus 0.8 % N2O-N of N applied). The 6 m system acted as a net sink for CH4, whereas the 12 m system was a net CH4 source and had a higher climate forcing than the 12 m system (1390 versus 1110 g CO2 eq. m−2 yr−1), but scaled for grass dry matter yield the climate forcing was similar. We conclude that larger N2O emissions with 6 m drain spacing were likely due to a combination of less complete denitrification and a naturally higher SOM content at this site, releasing extra mineral N. Our study can therefore not confirm that increased drainage intensity intrinsically reduces N2O emissions from crop production in cool-humid climates.
Sammendrag
Beitebruk er viktig for ressursutnyttelse, selvforsyning, dyrevelferd og kulturlandskap, og det er et politisk mål å øke beiting. Klimaeffektene av beiting har imidlertid vært lite vektlagt. Rapporten sammenstiller kunnskap om hvordan beitedyr påvirker klima gjennom både klimagassutslipp og endringer i vegetasjon og areal. Effektene varierer betydelig mellom arealtyper, beitetrykk, dyreslag og lokale forhold, noe som gjør det vanskelig å trekke generelle konklusjoner. I klimagassregnskapet er beiting særlig relevant for arealbruksendringer, som avskoging til beite og utslipp fra tidligere drenert myr. Effekter på enterisk metan og utslipp fra husdyrgjødsel er relativt små, selv om enkelte norske studier antyder noe lavere metanutslipp ved godt beite på fulldyrka jord. Biogeofysiske effekter som albedo er lite kartlagt, men kan ha nedkjølende effekt i noen områder. Rapporten peker på to hovedutfordringer: behov for sterkere insentiver til å bruke eksisterende innmarksbeiter fremfor nyrydding, og potensial for mer beiting av melkekyr på fulldyrka jord. Det trengs mer forskning for å bedre beregne effekter av beiting i klimagassregnskapet, særlig knyttet til enterisk metan, jordkarbon og beitetrykk i utmark.
