Nykänen, Arja (2008) Nitrogen dynamics of organic farming in a crop rotation based on red clover (Trifolium pratense) leys. Thesis, MTT Agrifood Research Finland. Agrifood Research Reports, no. 121. .
In agricultural systems which rely on organic sources of nitrogen (N), of which the primary source is biological N fixation (BNF), it is extremely important to use N as efficiently as possible with minimal losses to the environment. The amount of N through BNF should be maximised and the availability of the residual N after legumes should be synchronised to the subsequent plant needs in the crop rotation. Six field experiments in three locations in Finland were conducted in 1994-2006 to determine the productivity and amount of BNF in red clover-grass leys of different ages. The residual effects of the leys for subsequent cereals as well as the N leaching risk were studied by field measurements and by simulation using the CoupModel. N use efficiency (NUE) and N balances were also calculated. The yields of red clover-grass leys were highest in the two-year-old leys (6700 kg/ha) under study, but the differences between 2- and 3-year old leys were not high in most cases. BNF (90 kg/ha in harvested biomass) correlated strongly with red clover dry matter yield, as the proportion of red clover N derived from the atmosphere (>85%) was high in our conditions of organically farmed field with low soil mineral N. A red clover content of over 40 % in dry matter is targeted to avoid negative N-balances and to gain N for the subsequent crop. Surprisingly, the leys had no significant effect on the yields and N uptake of the two subsequent cereals (winter rye or spring wheat, followed by spring oats). On the other hand, yield and C:N of leys, as well as BNF-N and total-N incorporated into the soil influenced on subsequent cereal yields. NUE of cereals from incorporated ley crop residues was rather high, varying from 30 % to 80 % (mean 48 %). The mineral N content of soil in the profile of 0-90 cm was low, mainly 15-30 kg/ha. Simulations of N dynamics by CoupModel functioned satisfactorily and is considered a useful tool to estimate N flows in cropping systems relying on organic N sources. Understanding the long-term influence of cultivation history and soil properties on N dynamics remains to be a challenge to further research.
|Thesis Type:||Ph.D. thesis|
|Keywords:||biological nitrogen fixation, mineral nitrogen, modelling, nitrogen use efficiency|
|Subjects:||Soil > Nutrient turnover|
|Research affiliation:||Finland > Luke Natural Resources Institute|
|Deposited By:||Koistinen, Riitta|
|Deposited On:||26 May 2008|
|Last Modified:||12 Apr 2010 07:37|
|Refereed:||Peer-reviewed and accepted|
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