The N and S status in cropping systems with white cabbage as influenced by organic fertilizers
2012
Elfstrand, Sara | Båth, Birgitta | Lundegårdh, Bengt
Fresh and anaerobically digested red clover were compared as N and S sources in a incubation experiment without plants and a pot experiment with white cabbage, both conducted in climate chambers. The hypothesis was that anaerobic digestion would increase S availability in relation to N and that arylsulphatase activity would be higher in treatments with S deficiency. Besides the two red clover-based treatments, two treatments, one unamended and the other Biofer, an organic fertilizer with 7% S containing by-products from the slaughter industry, were included in the experiments. The availability of S in relation to N was higher in biogas slurry than in fresh red clover. In the incubation, an equal percentage (approx. 50%) of N was mineralized from all three fertilizers, while in the pot experiment, N mineralization was highest in the red clover treatment (approximately 70%). The highest S mineralization in both experiments occurred in the Biofer treatment. Growth of white cabbage was higher in the biogas slurry than in the red clover treatment despite high N availability in the latter treatment. Immobilization of S due to more readily available C in the clover treatment could have reinforced the difference and given a less well adjusted relationship between N and S for white cabbage demand than in the biogas slurry treatment. Arylsulphatase activity in the bulk soil was higher in the red clover-based treatments than with Biofer, while the activity in the rhizosphere soil did not differ between treatments. Arylsulphatase activity in the bulk soil was negatively correlated with white cabbage S concentration and positively correlated with N:S ratio in white cabbage shoots, while that in the rhizosphere soil was positively correlated with white cabbage S concentration.
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