Effect of amending cattle urine with dicyandiamide on soil nitrogen dynamics and leaching of urinary-nitrogen

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Abstract

Oral administration of dicyandiamide (DCD) to grazing ruminants for excretion in urine represents an alternative delivery technique to conventional broadcast application of DCD to reduce urinary nitrogen (N) losses from grazed pastures. A field lysimeter trial and an allied plot mowing trial were conducted to examine the effects of intermixing DCD in cattle urine on soil and pasture N dynamics and leaching losses in a free-draining pumice soil. DCD was either intermixed with urine to achieve equivalent application rates of 10, 30 or 60 kg DCD ha−1, or surface broadcasted as a spray solution (10 or 30 kg DCD ha−1) onto the soil surface following urine application and compared to controls (urine and nil-controls without DCD). A single application of 15N-labelled artificial cattle urine (equivalent to 600 kg N ha−1) and corresponding DCD treatments were applied in late autumn and monitored over the following 300 days. DCD altered the partitioning of the applied urine-15N by increasing plant uptake of urinary-N by 32–60% and decreasing urine-15N in leachate, which was primarily influenced by the amount of DCD applied. The method of DCD application had no significant effect on leaching of any N constituent, except for ammonium-N, which was higher in the intermixed relative to the spray DCD treatments (26 vs. 18 kg N ha−1, respectively; P < 0.05). The total amount of nitrate-N leached was reduced from 217 kg N ha−1 in the urine-control to 143, 80 and 61 kg N ha−1 (P < 0.05) with increasing rates of DCD application of 10, 30 and 60 kg ha−1, respectively. Application of DCD also significantly (P < 0.05) decreased the total amounts of ammonium-N and dissolved organic-N (DON) leached, but led to leaching losses of DCD-N. Rapid and large leaching losses of DCD down the soil profile led to spatial separation from the ammonium-N retained in the surface layer. Leaching of DCD (below 600 mm) at 55–69% of that applied represented an important leachable organic-N source (equivalent to 4–27 kg N ha−1), and reduced the overall efficacy of DCD in decreasing total N leaching losses. The total N leaching losses from all measured N fractions were 332 kg N ha−1 in the urine-control compared to 236, 157 and 154 kg N ha−1 at DCD application rates of 10, 30 and 60 kg ha−1, respectively. This study highlights the potential benefit from delivering DCD in cattle urine to reduce urinary-N leaching losses, with the most effective targeted single application rate being 30 kg ha−1 under the experimental conditions of this study.

Highlights

► Urine amended directly with DCD is an alternative method to conventional surface broadcast application of DCD. ► Urine amended with DCD at 10, 30 or 60 kg ha−1 was effective in reducing urinary-N leaching losses. ► Application of DCD decreased leaching of nitrate-N, ammonium-N and dissolved organic N. ► Rapid and large DCD leaching losses led to spatial separation from NH4+-N in the soil profile. ► DCD use led to increased plant uptake of urinary-N by 32–60% and 10–20% more pasture growth.

Introduction

Nitrogen (N) losses from agro-ecosystems are recognised worldwide as an environmental and economic concern (Robertson and Vitousek, 2009). In New Zealand (NZ), agricultural systems have been identified as a major contaminant source for N loading to nutrient sensitive water bodies (Ledgard et al., 2000). The principal source of N loss from grazed pastures is from animal urine deposition with an application rate equivalent to 500–1000 kg N ha−1, which is well in excess of immediate pasture growth requirements (Haynes and Williams, 1993). After deposition onto soil, urine-N is vulnerable to being lost to the environment predominantly through nitrate-N (NO3-N) leaching into underlying groundwater systems and via gaseous emissions as nitrous oxide and ammonia to the atmosphere (Jarvis et al., 1995, Ledgard, 2001).

To reduce urinary-N leaching losses from grazed pasture systems, researchers have focused on improving N use efficiency through practises including improving plant N uptake (Crush et al., 2007), increasing N immobilisation (Shepherd et al., 2010) and restricting N inputs (de Klein et al., 2006). One technology that has gained considerable attention in NZ is the use of soil nitrification inhibitors, particularly dicyandiamide (DCD), to retard the microbial oxidation of urinary-derived ammonium-N (NH4+-N) to NO3-N by deactivating the ammonia monooxygenase enzyme in ammonia oxidizing microbes in soils (Di et al., 2010). These inhibitors have started to gain use in NZ pasture-based agriculture systems although aspects of economics, adoption and implementation are still to be investigated (Monaghan et al., 2009, Luo et al., 2010).

The current method of application of DCD on farms in NZ is to uniformly broadcast DCD onto the soil surface over the entire area within seven days of grazing at a rate equivalent to 10 kg ha−1 during autumn and winter (Di and Cameron, 2004, Di and Cameron, 2005). However, surface broadcast application of DCD is non-specific at targeting cattle urine patches which can represent up to 6% of the area in a single grazing (or about 23% annually; Moir et al., 2011). As an alternative approach to surface broadcast application of DCD, Ledgard et al. (2008) showed that individual urine patches can be specifically targeted by orally administering grazing animals with DCD which was then excreted in the urine in an unaltered form and was effective in inhibiting nitrification of urinary-N in soil. Their study showed that individual sheep excreted 86% of the administered DCD in urine although with a high variability (up to 12-fold) in DCD concentration between individual animals. This suggests that at a paddock scale there would be a mosaic of urine patches deposited onto the soil varying in DCD concentration.

While the effectiveness of surface-applied DCD on NO3-N leaching from urine-affected pasture has been demonstrated (Di and Cameron, 2005, Sprosen et al., 2009), there is little information on the effectiveness of DCD dissolved in urine when deposited on pastoral soil. To our knowledge, only the studies of Akai et al. (2001) and Menneer et al. (2008a) have amended bovine urine with DCD and showed increased urinary N uptake by pasture and reduced NO3-N leaching. However, no studies have quantified N leaching losses from urine patches receiving different rates of DCD in the urine and compared this mode of delivery to conventional surface-applied DCD. Furthermore, limited information exists on the direct effect of rate of surface-applied DCD on N leaching losses from urine-affected pasture. Studies (Di and Cameron, 2005, Zaman and Blennerhassett, 2010) have compared relatively low DCD application rates of 5–10 kg ha−1 and showed an optimum rate of 10 kg ha−1 under a relatively low drainage regime (c. 300 mm annually). However, under moderate-high drainage regimes (>500 mm annually) there could be additional benefits in applying higher rates of DCD.

It has been shown that DCD is susceptible to biodegradation in soil and the rate of decay is influenced by a range of factors (e.g. soil temperature and moisture, Puttana et al., 1999). Some studies have also shown that DCD is vulnerable to leaching from the soil profile and these losses are variable, ranging from 2 to 58% of that applied (Corré and Zwart, 1995, Williamson et al., 1998, Menneer et al., 2008a, Monaghan et al., 2009, Shepherd et al., 2012). The highest DCD leaching loss was reported by Menneer et al. (2008a) who recovered 58% of the applied DCD (15 kg ha−1) at a depth of 500 mm in a pumice soil. Given the potential for high leaching losses of DCD, there is a requirement to investigate the movement, distribution and fate of DCD in relation to urinary-N in the soil profile to provide a detailed description and understanding of urine-N and DCD dynamics in grassland soils.

Our primary objective was to quantify N leaching losses from urine patches receiving varying levels of DCD dissolved in urine when deposited on grassland compared to surface-broadcast DCD application. A second objective was to examine the relative movement of DCD and urinary-N with depth through the soil profile. The study consisted of two concurrent field experiments: a lysimeter study for measuring N leaching losses and the recovery of the applied urine-N (using a 15N isotope recovery technique), and a plot mowing trial for soil sampling to measure levels of DCD and urinary-N throughout the soil profile over time.

Section snippets

Site description and preparation

The study was undertaken on a beef cattle farm located in the Lake Taupo catchment of the central North Island, NZ (NZMG 2749010E, 6278545N). The long-term (>25 years) permanent mixed pasture was predominantly perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) on free-draining pumice soil (Immature Orthic Pumice Soil, Hewitt, 1998). Measured soil chemical and physical characteristics prior to treatment application are presented in Table 1. The pasture had been grazed

Results

Results from Experiments 1 and 2 presented herein have been amalgamated.

General implications

This study has demonstrated that amending urine with DCD was effective in reducing total N leaching losses by 37–54% and that there was no significant difference between methods of DCD application on total N leaching losses (Table 4). This finding supports the use of animal delivery of DCD (Ledgard et al., 2008) as an alternative technique to conventional surface-applied DCD to reduce urinary-N leaching losses. Further field based experiments are required to determine the practicality of this

Acknowledgments

The research was supported by the New Zealand Ministry of Science and Innovation. The authors thank John Waller and Martin Upsdell for support with statistical analyses; Mike Sprosen, Alec McGowan, Sheree Balvert and Justin Wyatt for assistance in setting up and running the study; and Moira Dexter, Bridget Wise, Stuart Lindsey and Martin Kear for invaluable analytical expertise. We also gratefully acknowledge Mike and Sharon Barton for provision of the experimental field site.

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