Exploring nitrogen losses from urine patches between upland and lowland grazing systems

<p>Urine patches in grassland ecosystems present unique environments where extreme nitrogen (N) loading occurs. This results in N losses into the atmosphere or leaching from soil. N losses vary due to climate conditions, soil conditions, and management practices. However, we do not fully understand how these factors influence N cycling and nitrous oxide (N<sub>2</sub>O) emissions from urine patches. Much of the current literature on urine patch N cycling has focused on typical lowland agricultural systems. Very little work has explored other grazing systems, such as upland farming which is conducted across much of Wales. We have investigated this by using a catena sequence crossing both upland and lowland agricultural grazing systems. The range of soil types allowed us to explore how N<sub>2</sub>O emissions and N losses vary under different conditions. Here we report on both a laboratory incubation and a mesocosm experiment examining these issues. This work should help to fill the knowledge gap around how emissions from urine patches could vary between UK uplands and lowlands. We hope to improve understanding of N losses and provide more realistic, regional, and accurate emission factors for upland farming systems.</p>

Urine patch size and nitrogen load: effects on nitrogen uptake from the urine patch in plantain and ryegrass/white clover pastures

Field measurements from micro-plots (0.20 - 0.36 m2) of perennial ryegrass/white clover and of pure plantain were used to mimic a urine patch (UP) and to test the effects of UP nitrogen (N) load and size on pasture N offtake. Urine N offtake was greater with plantain than with standard pasture; however, the relative contribution to uptake from the wetted area and surrounding edge was the same for both species. Most (>90%) of the apparent offtake of urine N by plantain and standard pastures was within 20 cm of the edge of the UP. For the two urine patch sizes tested, edge contribution to urine N offtake was on average about 30% of the total from the UP, but was higher for at 600 kg N/ha urine N (45%) than at 300 kg N/ha (18%). Understanding this edge contribution is important for model improvement, and for the development of mitigations to decrease N leaching.

Specific genotypes of plantain (Plantago lanceolata) vary in their impact on sheep urine volume and nitrification in the urine patch

Plantain has the potential to reduce nitrate leaching through a number of mechanisms. In an indoor study, sheep were offered either perennial ryegrass or different plantain genotypes while aiming to achieve similar dry matter and water intakes. Supplementary water was sprayed on the feed to achieve the latter objective. Animals fed two cultivars (‘Tonic’ and ‘Agritonic’, marketed as “Ecotains” with claims around the potential to reduce nitrate leaching, and breeding lines (from a breeding program aimed at improving aspects of leaching mitigation) produced significantly more urine (4925 and 4887 ml/day, respectively) than those fed a range of commercial plantain cultivars (averaging 4333 ml/day) or perennial ryegrass (3993 ml/day). These results suggest the plantains marketed as “Ecotains” and those in the environmental breeding program may have diuretic effects on sheep, thereby reducing the concentration of nitrogen in the urine. In a soil incubation experiment, urine from sheep grazing either perennial ryegrass or ‘Agritonic’ plantain was applied to soil microcosms (70 ml vials containing 20 g of soil). Urine from sheep grazing the plantain, showed a slower overall nitrification rate (especially in the first 28 days post-application) when a significantly lower proportion of the urinary N was converted to nitrate. Both these observations support the use of specific genotypes of plantain to assist in reducing nitrate leaching.