ICOM1 Abstract

DEKKERS, DORINE, PETER VAN DER WERFF & PETRA FRISSEN. Ecological Agriculture, Wageningen Agricultural University, Wageningen, 6709 RZ, The Netherlands.-AMF colonization, phosphate uptake and nitrogen management in spring barley as affected by different precrops The influence of sugarbeet, flax and fieldbean as a precrop was examined on the indigenous AMF colonization, phosphate management and nitrogen management in spring barley. For this purpose a field experiment was conducted on an organic farm in Flevoland, The Netherlands, which had a silty clay loam soil with pH=8.0 and organic matter=2.8%. At the beginning of the growing season soil samples were taken, plant and root samples were taken during the growing season. The precrops did not influence the direct phosphate availability of the soil. In all experimental plots the Pwater=6.4 mg P2O5/l soil and the Ptotal=540 mg/kg dry soil. However, the precrops did affect the amount of mineral nitrogen in the soil. The initial amount of mineral nitrogen in the soil was higher after flax and fieldbean, compared with sugarbeet. The organic material originated from the sugarbeets residues mineralized later in the growing season. The crop density of spring barley was 275 plant/m2 for all mentioned precrops. The tillering of spring barley was positively correlated to the initial amount of mineral nitrogen, and was higher in flax and fieldbean. The AMF colonization reached its highest point just before flowering. At this time the colonization after flax (65%) and fieldbean (71%) were significantly higher than after sugarbeet (51%). The good tillering and AMF colonization after flax and fieldbean were positively correlated with a higher phosphate uptake before flowering. Between flowering and ripening nitrogen originated from the organic material of the sugarbeets mineralised. In this period this resultaed in a significantly higher phosphate uptake rate after sugarbeet than after flax or fieldbean. Finally the crop yield was equal for sugarbeet, flax and fieldbean. From this we conclude that precrops do not only influence the AMF colonization but have also an important impact on the timing of nitrogen mineralization.