No abstract

Nitrogen (N) leaching losses from grazed pasture systems pose a risk to the environment with mitigation strategies urgently required to achieve regulatory limits. There has been increased interest in alternative forages to manipulate excretion of urinary-N of livestock. This review summarises research on key forage attributes which affect the pattern of urine-N excretion. The literature showed an opportunity to alter both N concentration and moisture concentration of forages to reduce urine patch N loading. Complementary mitigations of extending the grazing rotation and reducing fertiliser were tested in simulations in addition to a diuresis effect on nitrate leaching in pastoral dairy systems. Findings suggested that forage species alone could not substantially reduce (by more than 20%) nitrate leaching. Combining all forage, management and systems-based solutions led to the greatest reductions in nitrate leaching, 59 and 31% for Waikato and Canterbury. Nonetheless, reductions in N loss came at the expense of pasture productivity which will likely affect profitability and farmer adoption of this suite of solutions in the absence of other drivers. The role of plant secondary metabolites in microbial dynamics has implications on N recycling in soil and rumen environments and this was identified as an area for further research.

The nitrification inhibitor dicyandiamide (DCD) is mobile in drainage water, which has implications for its effectiveness in reducing nitrate leaching from urine patches. Lysimeters had been used to investigate the effect of soil type (clay, silt loam, or sandy loam) and precipitation (target ~1140 or 2280 mm/year) on the effectiveness of DCD to decrease nitrate leaching. This paper reports the associated effects on DCD in drainage water. DCD was applied in May and July at a rate of 10 kg/ha, and natural rainfall was supplemented with irrigation to ensure that the target precipitation was achieved for each treatment. The experiment was undertaken twice. The pattern of DCD concentrations in drainage water suggested that movement of DCD in the silt loam and sandy loam soils was typical of convective–dispersive flow. Although there was some preferential flow of DCD from the soil surface to depth in the clay soil, DCD concentration profiles suggested that the main transport mechanism was also by convective–dispersive flow. There were significant soil-type and precipitation effects on DCD leaching (P < 0.05). The soil-type effect could be attributed to differences in drainage volume between soils. Combining data from the two experimental years, DCD leaching losses ranged from 12 to 46% of applied, with annual drainage in the range 422–1292 mm. DCD was detected in drainage up to 15 months after application, demonstrating the longevity of the compound. The experiment demonstrates that leaching of DCD on all of the soil types tested can be substantial under high rainfall. This is likely to have implications for the effectiveness of DCD to decrease nitrogen losses from urine patches under such rainfall conditions, as well as being a source of nitrogen itself.

No abstract

Here, we report a study which was designed to examine the effect of a nitrification inhibitor dicyandiamide (DCD) on N 2 O emissions from pasture urine patches. The aspects of DCD use that were studied were delivery method, application rate, and timing of dairy cow urine deposition. Dairy cow urine (700 kg N ha −1 ) was applied to pasture on a free draining Otorohanga silt loam soil in New Zealand in the autumn and winter of 2013 with DCD applied at different rates (0, 10, 30, and 60 kg ha −1 ). In the autumn, DCD was delivered to the soil either by mixing DCD with the urine collected from dairy cows or by using urine from cows that had ingested DCD while being kept in a stall. In the winter, only treatments with DCD mixed in urine were used. Total N 2 O emissions from urine applied in the autumn or the winter were 1.66 or 1.79 kg N 2 O-N ha −1 year −1 , respectively. This resulted in an annual emission factor (EF 3 , as a percentage of applied urine N lost as N 2 O-N) of 0.21 and 0.20 %, respectively. The EF 3 was reduced equally with either DCD delivery method with the reductions increasing with increasing DCD rate. This indicates that DCD in urine, excreted by cows that are provided DCD-amended feed, can effectively reduce N 2 O emissions and that a higher DCD rate will be more effective. Further work is required to ensure that DCD applied using this innovative technique is also effective using different feed and animal types under a range of environmental conditions.