Cover crop and cereal straw management influence the residual nitrogen effect

Summary

Cover crops (CC) may play an essential role in the recycling of nutrients in organic farming systems with cereals.
Harvest time of cereals and management of straw in the field can affect the growth of CC and subsequent
nitrogen (N) fertiliser replacement value (NFRV) in the following crop. This study investigates 1) the effect of
harvest time, 2) cutting height of straw and 3) straw removal from the main crop on CC growth, composition,
uptake and NFRV in the following crop and 4) the effect of CC harvest in autumn on the NFRV in the succeeding
crop.
A CC mixture of mainly red clover, with chicory and ryegrass was sown under a spring barley crop in 2017,
and replicated in 2018. Four strategies of barley harvest were conducted: 1) early harvest as whole crop or 2)
early harvest of the upper parts only, 3) at maturity with straw removed or 4) at maturity with straw left on the
field surface. Subsequently, CC and high stubbles of left straw were harvested and removed in autumn in half of
the field replicates. The residual effect was measured in spring barley in the succeeding year.
The CC aboveground biomass dominated by the clover had an N uptake for both years of 40−77 kg N ha−1.
Variability was significant between years but not caused by the harvest time or by straw management. In the
succeeding year, residues from barley and CC could replace 61−85 kg N ha−1 of mineral N fertiliser, which were
mostly derived from CC roots and stubble. High straw stubble left (40 cm length) significantly reduced the NFRV
of CC shoots by 20%.
Root residues (including barley and CC roots) contributed a substantial N supply to the following crop irrespective
of aboveground CC biomass. The availability of N derived from CC shoot mineralisation differed
significantly in the two years and was also influenced by straw left from the previous crop.