Wetland development nutrient accumulation and runoff in New Zealand dairy pastures with very high annual rainfall
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Date
2012-06-17
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Aarhus University
Abstract
Agricultural activity in regions with high annual rainfall raises particular
challenges for managing nutrient runoff. Here we report on a four-year
study of patterns of nutrient accumulation and loss in dairy pastures from a
catchment of the West Coast of the South Island of New Zealand, receiving
up to 3500 mm annual rainfall. Due to poor drainage in the gley soils, farming
practice involves contouring the pasture in broad corrugations, termed
‘humps and hollows’, to improve drainage; grazing is restricted to the
humps, whilst wetland vegetation (predominantly a marsh of Juncus and
Carex species) naturally colonizes the wetter drainage hollows. We aimed to
quantify nutrient accumulation and runoff at this site, paying particular attention
to the function of the wetland hollows in nutrient cycling. Subsurface
flow was found to be negligible in the poorly draining soil, with water loss
and nutrient yields restricted to surface flows. No fertiliser was applied the
first year at one site. Specific nitrogen and phosphorus yields ranged from
11-56 kg N ha-1 yr-1 and 2.0-13.4 kg P ha-1 yr-1. The highest P yield (mostly in
particulate form) was recorded even when no P fertiliser was applied. Wetland
vegetation and soils showed prolonged accumulation of both N and P
throughout their development, but failed to intercept peak events that occurred
when cattle were allowed to graze the pastures following heavy rainfall
events. Potential soil denitrification, measured from denitrification enzyme
activity experiments, was very low, with median values < 50 ng N g-1
h-1 throughout the study, predominantly due to low nitrate concentrations.
We conclude that (i) significant nutrient discharge is a feature of this system;
(ii) the natural wetland formation in drainage hollows is an important nutrient
sink that mitigates discharge; and (iii) much of the remaining discharge
could be ameliorated by improved farming practices. © University, DCE – Danish Centre for Environment and Energy
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Keywords
Wetlands, Nutrients, Fertilizers, Agriculture, Ecosystems, New Zealand, Rain, Runoff, Dairy industry, Drainage, Plants, Phosphorus compounds
Citation
Chagué-Goff, C, Sorrell, B., Duncan, M., & Cotton, S. (2012). Wetland development nutrient accumulation and runoff in New Zealand dairy pastures with very high annual rainfall. Paper presented at 7th SWS 2012 European Chapter Meeting, "Wetland restoration - challenges and opportunities", 17-21 June 2012, Aarhus, Denmark.