Effect of outdoor production, slurry management and buffer zones on phosphorus and nitrogen runoff losses from Finnish cattle farms

Summary

This thesis sums up studies on phosphorus (P) and nitrogen (N) losses to water from forested feedlots and slurry-amended grass fields. Moreover, different ways of mitigating the losses in a boreal climate are discussed. Studies were conducted in 1996-2008 at Jokioinen, Tohmajärvi, Ruukki and Taivalkoski.
Water samples representing surface runoff were collected from open ditches and analysed e.g. for total solids (sediment) as well as total P (TP), dissolved reactive P (DRP) and total N (TN) to estimate nutrient losses from forested feedlots with different stocking rates (animal units per hectare, AU/ha) and from slurry-amended grass. Surface runoff samples were similarly analysed to evaluate the efficacy of 10 m wide buffer zones to decrease and retain nutrient losses from pasture and tilled soil. The soil was sampled for plant-available P and mineral nitrogen (SMN) analyses.
Fairly high TP (0,9-1,4 kg/ha/yr) and TN (4-16 kg/ha/yr) losses occurred in ditch water from forested feedlots where cattle has been reared for 1-3 years. These amounts correspond to the annual losses from cropped felds. The plant-available P (up to 20 mg/L) in surface soil and the amount of SMN (up to 100-400 kg/ha) in the 60 cm deep soil layer were highest in places where the cattle gathered, such as bedded and feeding areas (called high-input areas).
High losses of TP and DRP (4,4 and 3,6 kg/ha/yr, respectively) also occured in surface runoff from the grass fields where surface application of slurry (40 t/ha) in autumn was followed by rainfall. Injection of the slurry into the soil decreased TP and DRP losses by 79 and 86 %, respectively.
The buffer zones along watercourses were less important in the grazed field than in autumn-tilled soil due to the smaller erosion and nutrient losses from grass than from tilled soil. The surface runoff losses of sediment, TP and TN decreased by more than 50, 30 and 50 %, respectively, by buffer zones on tilled soil.