Search

Urine deposited by grazing animals is the main source of nitrous oxide (N 2 O) emissions in New Zealand. Recent studies have suggested that certain pasture plants, for example plantain (Plantago lanceolata), can curb N 2 O emissions from livestock systems. This study aimed to i) evaluate the potential of plantain for reducing N 2 O emissions from cattle urine patches; ii) determine the effect of including plantain in animal diets on urine-N loading and its influence on N 2 O emissions; and, iii) evaluate whether any effects on N 2 O emissions reduction could be attributed to a 'urine' or a 'plant' effect. A static chamber method was used to measure N 2 O fluxes from urine collected from cows fed a 0, 15, 30 or 45% plantain mixed with "standard" ryegrass/clover (Lolium perenne / Trifolium repens) diet and applied to plots with the corresponding percentage of plantain in the sward. In addition, we measured N 2 O emissions from different proportions of plantain in the sward (0, 30, 60 and 100%) that received urine collected from cows fed on ryegrass/clover. The urine N loading rates of animals fed plantain, significantly reduced with increasing proportions of plantain in the diet (r2 = 0.987, P < 0.01). There was a trend of lower N 2 O emissions with an increasing proportion of plantain in the diet (r2 = 0.830, P < 0.08). However, there was no significantly difference in the N 2 O emission factors (P > 0.10). Following applications of standard urine, total N 2 O emissions and emission factor reduced linearly as the proportion of plantain in the sward increased (r2 = 0.969, P < 0.05 and 0.974, P < 0.05, respectively). The results suggest that the efficacy of plantain as a N 2 O mitigation option is due to both a reduction in urinary N excretion and a plant effect. The latter could be due to biological nitrification inhibition (BNI) caused by the release of root exudates and/or changes in the soil microclimate. Unlabelled Image • The urine-N loading rates decreased with increasing proportions of Plantain in the animal diet. • EF and total emissions of N 2 O decreased with the increase of Plantain proportions in the sward. • There was a trend of lower N 2 O emissions with increasing proportion of plantain in the diet. • The effect of plantain in the sward on N 2 O emissions may be due to the BNI activity. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) emissions from pasture-based livestock systems represent 34% of Brazil's agricultural greenhouse gas emissions. The forage species Brachiaria humidicola is known for its biological nitrification inhibition (BNI) capacity and N 2 O emissions reduction ability from urine patches under tropical conditions. However, there is little information about the effect of BNI on N 2 O emission and ammonia (NH 3) volatilisation in the subtropics. This study aimed to: (i) evaluate the potential of Brachiaria humidicola , compared with Panicum maximum (Jacq. cv. Áries; guinea grass), a broadly used grass (with no BNI capacity), to reduce N 2 O emissions under subtropical conditions; (ii) determine the efficacy of nitrification inhibitor dicyandiamide (DCD) to decrease N 2 O emissions; and (iii) determine the effect of brachiaria and DCD application on NH 3 volatilisation. A field experiment was carried out using a Cambisol, where cattle urine ± DCD was applied to brachiaria and guinea grass. Over the 67-day measurement period, cumulative N 2 O emissions were 20% lower from urine patches in the brachiaria treatment (1138 mg N m−2, Emission factor = 1.06%) compared to guinea grass (1436 mg N m−2, Emission factor = 1.33%) (P <.10). A greenhouse experiment, using pots with the same treatments as in the field experiment, suggested that this could have been due to lower soil nitrate levels under brachiaria forage compared to guinea grass, indicating that BNI could be a possible mechanism for lower N 2 O emissions from brachiaria. The DCD application was effective in both forage species, decreasing N 2 O emissions by 40–50% (P <.10) compared with the urine only treatment. Approximately 25% of the urine applied N was lost via NH 3 volatilisation, however the NH 3 loss was not affected by forage species or DCD application (P >.10). Overall, the results demonstrated that brachiaria and DCD use are strategies that can reduce N 2 O emissions from urine patches. Unlabelled Image • N 2 O emissions from cattle urine applied to brachiaria were 20% lower than guinea grass. • DCD application reduced N 2 O emissions by 40–50% from both forage species. • NH 3 volatilisation from urine patches was not affected by either DCD or brachiaria grass. • EF% from cattle urine (averaged 1.2%) was lower than IPCC default value (2%). [ABSTRACT FROM AUTHOR]