Urine patches within pasture soils are hotspots for nitrogen (N) cycling and losses, where nitrification inhibitors (NI) offer a means of reducing such losses. Within urine influenced soil, more research has been conducted for dicyandiamide (DCD) than 3,4-dimethylpyrazole phosphate (DMPP). Differences in the efficacy of these NI are often ascribed to a greater mobility of DCD, which may lead to spatial separation from NH 4 + and nitrifying microorganisms. We tested the mobility of 14 C-labelled DCD and DMPP relative to sheep urine-derived NH 4 + in soil columns of contrasting texture and organic matter content, following simulated rainfall. We also assessed factors influencing the vertical mobility of these NI in soils, including solubility, sorption/ desorption processes and microbial degradation and uptake. Following 40-mm rainfall, without the presence of sheep urine, the distribution of both NI were similar in the soil columns; however, there was a greater retention of DCD compared to DMPP in the top 1 cm. Both NI appeared to co-locate well with urine-derived NH 4 + , and the presence of sheep urine altered the leaching profile of the NI (compared to rainfall application alone), but this effect was inhibitor and soil-type dependent. A greater sorption to the soil matrix was observed for DCD in comparison to DMPP in all three studied soils, and the presence of urine generally increased desorption processes. Of the NI applied to the soil columns, 18-66 % was taken up within 30 min by the microbial community. However, only small amounts (<1 %) were mineralized during this period. In conclusion, due to the greater adsorption of DCD as opposed to DMPP and similarity in the degree of co-location of both NI with urine NH 4 + , the results of this study suggest that differences in microbial uptake and degradation may be more important parameters for explaining differences in the efficacy of reducing nitrification. Further work is required to determine the comparative efficacy of both NI in reducing nitrification rates under field conditions in a range of soil types and environmental conditions.

In semi-arid vineyard agroecosystems, highly vulnerable in the context of climate change, the soil organic matter (OM) content is crucial to the improvement of soil fertility and grape productivity. The impact of OM, from compost and animal manure, on soil properties (e.g., pH, oxidisable organic C, organic N, NH4+-N and NO3−-N), grape yield and direct greenhouse gas (GHG) emission in vineyards was assessed. For this purpose, two wine grape varieties were chosen and managed differently: with a rain-fed non-trellising vineyard of Monastrell, a drip-irrigated trellising vineyard of Monastrell and a drip-irrigated trellising vineyard of Cabernet Sauvignon. The studied fertiliser treatments were without organic amendments (C), sheep/goat manure (SGM) and distillery organic waste compost (DC). The SGM and DC treatments were applied at a rate of 4600 kg ha−1 (fresh weight, FW) and 5000 kg ha−1 FW, respectively. The use of organic amendments improved soil fertility and grape yield, especially in the drip-irrigated trellising vineyards. Increased CO2 emissions were coincident with higher grape yields and manure application (maximum CO2 emissions = 1518 mg C-CO2 m−2 d−1). In contrast, N2O emissions, mainly produced through nitrification, were decreased in the plots showing higher grape production (minimum N2O emissions = −0.090 mg N2O-N m−2 d−1). In all plots, the CH4 fluxes were negative during most of the experiment (−1.073−0.403 mg CH4-C m−2 d−1), indicating that these ecosystems can represent a significant sink for atmospheric CH4. According to our results, the optimal vineyard management, considering soil properties, yield and GHG mitigation together, was the use of compost in a drip-irrigated trellising vineyard with the grape variety Monastrell.