A comparison of N and P inputs to the soil from fertilizers and manures summarized at farm and catchment scale

Abstract

Use of fertilizers and manures during 1994 were studied at the farm and catchment scale in the largely agricultural Ythan catchment, north-east Scotland, using farm level census data supplemented by questionnaire data. Grassland accounted for 40% of the agricultural land, and seven farm types represented 87% of the total land, having an average size of 90 ha. The average livestock density of 1·2 livestock units/ha was high compared to Scotland as a whole (0·5). Rates of inorganic fertilizer applied to individual crops in the area corresponded with the national average and current advisory recommendations. At the catchment scale, most fertilizer N was applied to grassland (47%), whereas spring crops received the greatest proportion of the fertilizer P (35%). The annual manure production equated to an average over the catchment of 63 and 16 kg/ha of N and P, respectively. When calculated for farm types these figures ranged from 27 and 6 kg/ha on ‘cereal’ farms to 384 and 163 kg/ha on ‘pig’ farms. The ratio of applied fertilizer N and P varied from 4[ratio ]1 for ‘general cropping’ to 10[ratio ]1 for ‘cattle and sheep (lowground)’ farms. There was no significant compensatory reduction in inorganic fertilizer applications on crops, which also had received manures.