The effect of four different pasture species compositions on nitrate leaching losses under high N loading

Malcolm, Brendon & C. Cameron, K & J. Di, H & Edwards, G.R. & Moir, Jim. - Article in Soil Use and Management

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

This research article looks at the effect of four different pasture species compositions on nitrate leaching losses under high N loading. Nitrate is highly mobile in most soils and is prone to leaching when there is drainage, particularly during cool periods when pasture growth and N uptake are minimal, evapotranspiration rates are low and drainage is high.

What is the problem?

Nitrate (NO 3 ) leaching can cause elevated concentrations of NO 3 -N in water, which can have adverse impacts on water quality and human health.

This study aimed to quantify the effect of pasture species compositions on NO 3 -N leaching losses from soil under animal urine patch areas and to examine the effect of root architecture and seasonal plant activity on NO 3 leaching losses.

What did the research involve?

This research was conducted on the Lincoln University Research Dairy Farm (LURDF), 15 km south-west of Christchurch, New Zealand (43°38′S, 172°28′E; 17 m asl).

Lysimeters. Large undisturbed soil monolith lysimeters (50 cm diameter 9 70 cm depth) were collected from a pasture site at LURDF, Canterbury.

Field plots. Large field plots (2.1 9 6 m) were established in conjunction with the lysimeters on bare lightly cultivated Templeton fine sandy loam soil at LURDF for the purposes of destructive soil sampling to determine root architecture of the pasture species used in the lysimeter experiment.

The lysimeter experiment was arranged in a completely randomized design with four replicates of four pasture species treatments (16 lysimeters).

Lysimeters. Drainage water from the lysimeters was collected when the volume of drainage was ca. 2 L or once per week. Total drainage volume was measured, and leachate samples were analyzed for NO 3 -N concentration by flow injection analysis (FIA) (Tecator Inc., Sweden).

Field plots. In the spring of 2010 and 2011 (September/ October), a 1.8-tonne excavator was used to expose the soil profile for each field subplot down to a depth of ca. 1 m.

The variability in total NO 3 -N leached, total and winter pasture DM yield, average daily N uptake, average root length density and total root surface area was analyzed statistically by analysis of variance (ANOVA) using GenStat (14th Edition, Lawes Agricultural Trust) to test for treatment effects.

What were the key findings?

Average daily air temperatures were similar to long-term district normal temperatures with marginally warmer temperatures recorded in December and January of 2010 and May and June of 2011 (data not given).

In the 2010/2011 season, peak NO 3 -N concentrations were recorded at 370–430 mm of drainage water (early-mid August 2010) and returned to near background levels at ca. 430–500 mm of drainage, except T. fescue WC which remained at a concentration of 68 mg NO 3 -N/L after 540 mm of drainage water .

Pasture species had a highly significant effect on total NO 3 -N leaching losses from the urine-treated soil during the 2010/2011 season.

For the 2010/2011 season, pasture species had a highly significant effect on total DM yield and ranged from 10,694 kg DM/ha (T. fescue WC) to 16,856 kg DM/ha.

In the 2010/2011 season, there was a highly significant correlation between average daily N uptake (May–September) and total NO 3 -N leached.

Root length densities (cm root/cm3 soil) at 10 cm depth increments from 0 to 80 cm soil depth for the 2010/2011 season are illustrated in Figure 6a. At 0–10 cm depth, P. ryegrass WC, It. ryegrass WC and Diverse root length ranged from 8.9 to 10.3 cm/cm3.

The results of this study show that when urine is applied at 1000 kg N/ha, NO 3 -N leaching losses are affected by the pasture species.

Final Comment

These results suggest that in grazed pasture systems, high plant winter activity (plant growth/root metabolic activity) is more important than specific root architecture to reduce NO 3 -N leaching losses.

2014 - New Zealand - Malcolm, Brendon & C. Cameron, K & J. Di, H & Edwards, G.R. & Moir, Jim. - Article in Soil Use and Management
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