Nutrients from agriculture can be lost to the atmosphere as gaseous emissions such as ammonia, nitrous oxide, nitric oxide and dinitrogen. Other forms of nutrients, such as nitrates, may also be lost by leaching down into soils and possibly entering aquifers, or as organic molecules and solutes that can runoff into surface waters. These nutrient losses can pose risks to the environment and public health, and to society in general and because of this, the livestock sector is often under public scrutiny for its role in nutrient management. Producers who improve their on-farm nutrient management methods stand to benefit by reducing fertilizer use through incorporating nitrogen-fixing legumes, or extending their grazing to minimize manure spreading costs and gaseous losses.
Nutrient inputs – such as fertilizer, manure and biologically fixed nitrogen – enter a production system while outputs – like hay or livestock – are the result. If a system’s inputs exceed the outputs, there will be nutrient “leaks” through losses to the atmosphere, or leaching into soils. Biological and chemical processes in the soil and plants change the chemical composition of nutrients such as nitrogen, phosphorus, or sulphur. Each time a nutrient changes forms, there is a positive effect (better uptake) or negative effect (greater losses) on the whole farm system. In some cases there can be both positive and negative effects, such as when ammonium converts to nitrate which is more plant available yet more prone to leaching or nitrous oxide formation.
Beef cattle produce approximately 634,000 tonnes of manure nitrogen in Canada annually, more than half of which is deposited directly on pasture. Forages are critical to beef cattle systems and play a valuable role in cycling nutrients and reducing losses to the environment. Producers can make efforts to manage nutrients from cattle manure and forage fertilization to reduce their environmental impact and also improve their bottom line.
During a BCRC webinar, Shabtai Bittman, PhD, a researcher with Agriculture and Agri-Food Canada, explained nutrient cycling in forage ecosystems, including:
- How much nitrogen from manure is actually taken up by forage crops?When compared with fertilizer, manure nitrogen uptake by forage plants is lower. Over time, however, more manure nitrogen remains in the soil compared to fertilizer nitrogen sources. (Jump to 37:28 in the webinar recording to learn more)
- What effect does grassland conversion have on nutrient loss?Forage stand rejuvenation or termination can cause nitrogen loss following tillage or herbicide application, so it is important to minimize the time that the soil is bare. (Jump to 41:46)
- Do forages lose nutrients during the winter?Ongoing research is showing nutrient loss due to soil bacterial activity can occur even on frozen soils, particularly in clay-soils-based forage systems. (Jump to 43:26)
- Can pasture plant communities shift with the application of different nutrients?Nitrogen-only fertilizer applications can skew communities toward less useful forage species, such as Kentucky blue grass, or reduce legume and forb species. A more balanced application of nitrogen, phosphorus and sulphur support a more productive and suitable stand of forage species. (Jump to 47:53)
The way in which nutrients are cycled through forage and cattle-based production systems is far from simple. Many different practices can be applied to mitigate nutrient losses and simultaneously increase nutrient absorption by plants, however this can vary by region and local knowledge is very useful.
As with all previous BCRC webinars, you can watch the full recording on managing nutrients in forages here.