Mineral nitrogen in the course of a cash crop and two livestock rotations - first results from the long-term monitoring Trenthorst

Summary

The long-term monitoring Trenthorst, situated near Lübeck in a temperate maritime climate on loamy soils, was established in 2003 and compares two cash crop and three livestock farming systems. We studied the soil mineral nitrogen contents of one cash crop and two livestock farms, specialised in dairy cows and goats/oilseeds resp., with the hypothesis that the livestock farms show a more even course of Nmin in the rotation and a higher rotation mean. The rotation average of Nmin in the cash crop farm was not lower than the ones in the livestock farms. But in the course of the rotations differences became evident: compared to the livestock farms the cash crop farm showed higher Nmin-values after the first rotation year (mulched vs. cut grass clover) but lower values in the fourth and fifth year of the rotation. As a precise nitrogen supply via manure as in the livestock farms is impossible in a self-sustaining cash crop farm, the excess of nitrogen at the beginning and the lack of it towards the end of the rotation could not be balanced. A way to improve this might be the use of green manure crops for biogas production and the application of the residues as manure. But as no full rotation period has yet passed, a longer study period is necessary to confirm the results.