Effect of organic and mineral fertilizers on soil P and C levels, crop yield and P leaching in a long term trial on a silt loam soil

• We conducted a long term field trial, to compare several types of organic fertilizers.
• We examined changes in P availability, soil P and C levels, crop yield and P leaching.
• Compost, farmyard manure and cattle slurry lead to minor differences in crop yield.
• Farmyard manure increased P availability and P leaching.
• Application of compost increased the soil C levels without increasing P leaching risks.

The main objective of the present study was to compare fertilizer types in their ability to increase the soil organic matter content without increasing potential P leaching losses. Differences in soil organic carbon content, crop yield, P-CaCl2, P-AL, P export by the crop and P leaching from soil supplied with three compost types, cattle slurry, farmyard manure or mineral fertilizers were compared in a 8 years field experiment with arable, vegetable and fodder crops. P leaching losses were assessed separately in a soil column leaching experiment. As expected, farmyard manure and compost are the better options to increase the soil organic carbon level. Cattle slurry and mineral fertilizers tended to produce lower crop yields. P-CaCl2 was increased when farmyard manure was used as organic fertilizer, leading to an increased P leaching but not to an increased crop P export. Therefore it seems that the higher dissolved P concentrations in the soil solution for farmyard manure, measured as P-CaCl2 in the soil, are a source of potential P losses. All three compost types could gradually increase soil organic carbon levels without increasing P leaching losses.