Nitrogen and phosphorus surpluses on Danish dairy and pig farms in relation to farm characteristics

Abstract

N and P surpluses per hectare at farm level were determined on 63 private pilot farms with data from 2 to 7 years between 1997 and 2003 (a total of 245 observations). Farms were classified in the following four farm types: Conventional mixed dairy, organic mixed dairy, conventional pig farms (indoor) and conventional pig farms with outdoor sows. Import of nutrients with concentrate and fertilizer was the major input to all conventional farm types. On the organic dairy farms major input was N fixation, but also import of nutrients with concentrate and manure were important inputs. Output from the dairy farms was dominated by nutrients in milk. On pig farms nutrients in meat dominated the output, but also export of nutrients with cash crops and manure were important outputs. Farm type, year and farm within farm type significantly affected both N and P surpluses per hectare. Farm type was the major source of variation in both N and P surpluses. In the period investigated N surplus decreased by 6.5 kg N ha − 1 yr − 1 and P surplus decreased by 0.7 kg P ha − 1 yr − 1 . The N and P surpluses observed on the conventional dairy farms significantly exceeded surpluses observed on the organic dairy farms. At equal number of livestock units (LU) per hectare (1.28 LU ha − 1 ) the difference was 43 kg N ha − 1 and 6 kg P ha − 1 . At equal rates of N or P in manure to fields (147 kg N ha − 1 , 29 kg P ha − 1 , respectively) the difference was 45 kg N ha − 1 and 4 kg P ha − 1 . Conventional dairy farms and pig farms with sows indoors had equal N and P surpluses at equal rates of N or P in manure to fields. Corrected to the average year (1999.5) the estimated average N and P surpluses showed highest levels on pig farms with outdoor sows (251 kg N ha − 1 , 42 kg P ha − 1 ) and lowest levels on organic dairy farms (113 kg N ha − 1 , 7 kg P ha − 1 ). Surpluses on the conventional dairy farms were 175 kg N ha − 1 and 16 kg P ha − 1 and on the indoor pig farms they were 123 kg N ha − 1 and 13 kg P ha − 1 . The N and P surpluses observed on Danish conventional mixed dairy farms were comparable with intensive dairy farming systems in other European countries.