Op dinsdag 30 oktober j.l. heeft ir. Joan Reijs met succes bij Wageningen Universiteit zijn proefschrift verdedigd met als titel: Improving slurry by diet adjustments: a novelty to reduce N losses from grassland-based dairy farms. Promotor was prof. dr.ir. J.D. van der Ploeg.
Dr.ir. Joan Reijs is sinds september 2006 werkzaam op het LEI. Daarvoor werkte hij bij de Animal Sciences Group van Wageningen UR, waar hij ook het grootste deel van zijn proefschrift heeft geschreven.
Dr.ir. Joan Reijs:
Improving slurry by diet adjustments: a novelty to reduce N losses from grassland-based dairy farms.
Abstract
In order to reduce environmental losses of N, several dairy farmers in the Netherlands aim at a modification of the composition of cow slurry. Basic idea of this strategy is that feeding grass silages with lower protein and higher fibre contents will result in slurry that is less susceptible to N losses. In this thesis, this modification of dairy cow slurry is regarded as a novelty, i.e. a configuration observed in practice that contains the promise to effectively change established routines.
The effect of diet adjustments on the composition of slurry was explored in a controlled experiment and through on-farm monitoring. Furthermore, a simulation model was developed to predict slurry composition from dietary information. It was shown that the proposed strategy results in slurry with relatively high C:Ntotal ratio’s and low Ninorganic : Ntotal ratio’s and thus reduced risks for N losses with ammonia. A grassland experiment revealed that these changes will also reduce first-year plant N availability. From model simulations it was concluded that this reduced N availability will be compensated for by increased soil N mineralization on the long term.
The success of the strategy in terms of economic and environmental performance appeared to be variable. It is concluded that the strategy can be an effective instrument to reduce N losses from dairy farms with predominantly grassland aiming at a moderate milk production level.