The value of catch crops and organic manures for spring barley in organic arable farming

Summary

The effect of nitrogen (N) supply and weeds on grain yield of spring barley was investigated in an organic farming crop rotation experiment on three different soil types in Denmark from 1997 to 2001. Three experimental factors were included in the experiment in a factorial design: 1) crop rotation (lupin or pea/barley as previous crop to barley), 2) cover crop (with and without), and 3) manure (with and without). The crop rotations included grass-clover as a green manure crop. Animal manure was applied as slurry in rates corresponding to 40% of the N demand of the cereal crops.
Application of 50 kg NH4-N ha-1 in manure (slurry) increased barley grain DM yield by 1.0 to 1.3 Mg DM ha-1, whereas the use of cover crops (primarily perennial ryegrass) increased grain DM yield by 0.4 to 0.7 Mg DM ha-1 with the smallest effect on the sandy loam soil and the highest effect on the coarse sandy soil. Model estimations showed that the yield reduction from weeds varied from 0.3 to 1.6 Mg DM ha-1 depending on weed species and density. The yield effects of N supply were thus more predictable and less variable than the effects of weed infestation.
The N use efficiency of NH4-N in applied manure varied from 25 to 39% corresponding to N use efficiencies obtained with mineral N fertilisers. The N use efficiency of above-ground weeds and cover crops sampled in November prior to the spring barley varied from 13 to 57%. Pea/barley and lupin increased grain yield by 0.2 and 0.8 Mg DM ha-1 over winter wheat as a previous crop. This could not be explained by N in the above-ground residues of the previous crop. Grass-clover as a green manure crop three years prior to the spring barley increased grain yield by about 0.5 Mg DM ha-1 at Flakkebjerg. Cropping history was thus equally important for grain yield as manure application.