The effect of various fertilizing strategies on soil organic matyter, soil P fractions and P leaching potential in Flanders

Nutrient leaching caused by over-fertilization has led the Flemish and Dutch governments to regulate fertilizer and manure applications. Restrictions on the N and P supply have decreased nutrient leaching somewhat, but nutrient losses are still substantial. Further restrictions on fertilizer dosing are needed to protect the environment from eutrophication. In Flanders, the total organic carbon content of agricultural soils has declined over the last 20 years. Further restrictions on manure application may lead to an even faster decrease in organic carbon content of the soil. The objective of this research is to study the effects of different types of organic fertilizers on the P fractions of the soil, the P leaching, and the soil organic matter (SOM) content. Which soil management strategies allow for reducing P losses from agricultural fields while maintaining the SOM at an acceptable level? This research is based upon 3 long-term field trials and a percolation experiment. In these field trials, several types of organic fertilizers are compared to each other and to a mineral fertilizer. The evolution in the soil organic C and P fractions is followed by measuring the total organic carbon content, hot water extractable C and P, Porg, P(CaCl2) and the ammonium-lactate extractable P. In addition, soil samples are taken and placed into glass fiber filters under constant suction, above which water is continuously added via a peristaltic pump. The sampled percolation water is measured at regular intervals for concentrations of total P, total dissolved P, orthophosphate, and total dissolved organic carbon.