Effect of manure on crop yield and quality in an organic agricultural system

Field experiments were carried out on the organically-run experimental farm at the University of Bonn (Wiesengut) to investigate the effects of different distributions of farmyard and liquid manure on yield and crop quality of potatoes and winter wheat after ploughing grass-clover in spring. The amounts of organic manure applied were limited by the nutrient equivalent of the manure produced by 0.6-1.4 livestock units (LU) ha(-1). Tests were done to discover the effect of fertilizing only one crop (potatoes or winter wheat) as well as of applying equal amounts to both crops. Increasing amounts of FYMC to potatoes caused no significant difference in total yield after grading, but the number of rotted tubers as well as big tubers (> 65 mm) increased. No effects could be measured on the nitrate content of the tubers. In all fertilizing variants it remained below 100 mg NO3 kg(-1). The application of the total available amount of manure directly to winter wheat improved the yield as well as the protein content of grains. Liquid manure, depending on the date of application, added to the increase. The comparison of differently treated FYMC (3-4 and 12 months respectively on a heap) did not reveal any differences in the yield and crop quality because of the equal levels of N, which was evenly spread. However, when the FYMC was composted for 12 months, 50% higher rates were required in order to reach the equivalent fertilization level. The results show that when rotation is carried out under similar conditions, it is recommended that limited amounts of organic manure should be applied to winter wheat.