Hans Olav Eggestad

Seniorforsker

(+47) 924 49 405
hans.olav.eggestad@nibio.no

Sted
Ås - Bygg O43

Besøksadresse
Oluf Thesens vei 43, 1433 Ås (Varelevering: Elizabeth Stephansens vei 23)

Sammendrag

Program for jord- og vannovervåking i landbruket (JOVA) ledes av NIBIO divisjon for miljø og naturressurser og gjennomføres i samarbeid med Divisjon for bioteknologi og plantehelse, flere av forskningsstasjonene i NIBIO og andre institusjoner. JOVA overvåker jordbruksdominerte nedbørfelt over hele landet, og feltene representerer ulike driftsformer og ulike jordbunns-, hydrologiske og klimatiske forhold. JOVA rapporterer årlig om jordbruksdrift, avrenning og tap av partikler, næringsstoffer. Tap av partikler og næringsstoffer rapporteres for agrohydrologisk år, 1. mai – 1. mai. Tap av plantevernmidler overvåkes i for fem av feltene og rapporteres for kalenderår.

Sammendrag

Livestock husbandry has raised enormous environmental concerns around the world, including water quality issues. Yet there is a need to document long-term water quality trends in livestock-intensive regions and reveal the drivers for the trends based on detailed catchment monitoring. Here, we assessed the concentration and load trends of dissolved reactive phosphorus (DRP) in streamwater of a livestock-intensive catchment in southwestern Norway, based on continuous flow measurements and flow-proportional composite water sampling. Precipitation and catchment-level soil P balance were monitored to examine the drivers. At the field level, moreover, the relationship between soil P balance and soil test P (measured using the ammonium lactate extraction method, P-AL) was assessed. Results showed that on average of 20 years 95 % of the P was applied to the catchment during March–August, when 40 % of annual precipitation and 25 % of annual discharge occurred. The low runoff helped reduce P loss following P applications. However, flow-weighted annual mean DRP concentration significantly increased with increasingly cumulative soil P surplus (R2 = 0.55, p = 0.0002). With a mean annual P surplus of 8.8 kg ha−1, the annual mean DRP concentration (range: 49–140 μg L−1; mean: 80 μg L−1) and annual DRP load (range: 0.35–1.46 kg ha−1; mean: 0.65 kg ha−1) significantly increased over the 20-year monitoring period (p = 0.001 and 0.0003, respectively). At the field level, P-AL concentrations were positively correlated with soil P balances (R2 = 0.48, p < 0.0001), confirming the long-term impact of P balances on the risks of P loss. The study highlights the predominant role of long-term P balances in affecting DRP loss in livestock-intensive regions through the effect on soil test P.