Subproject 9
The effect of catch crops on sulphate leaching and availability of S in the succeeding crop
Participant
Jørgen Eriksen, Department of Agroecology, Danish Institute of Agricultural Sciences.
Email: Jorgen.Eriksen@agrsci.dk
Background
Leaching is an important item on the sulphur balance. The plant-available form of S, sulphate, is easily leached and there is a high risk of losing S through autumn and winter.
Purpose
This part of the project investigates to what extend different catch crops are able to reduce the soil sulphate content in autumn and winter and through that reduce leaching. Following incorporation of catch crops is investigated the plant-availability of catch crop S focussing on factors that may synchronise the release with plant demand.
Activities and results
Catch crops turn out to be efficient in the reduction of not only nitrate, but also sulphate leaching. Especially crucifers like fodder radish, but also ryegrass were efficient. In the figure is shown the sulphate content in bare soil or soil cropped by ryegrass and fodder radish in the autumn and in the following spring after incorporation. Both catch crops were able to collect some of the sulphate on its way down the profile. After incorporation the following spring the S in fodder radish was released in the topsoil. At the time of sampling in May ryegrass-S was not released yet.
Thus, crucifers can be important for keeping S in the system making it available for the main crop at the right time. Of course this property is most important in systems without use of mineral fertiliser. In the organic crop rotation experiment on sandy soil, yield increases in spring barley have been found when applying gypsum. In this system there is a huge need for catch crops to not only retain S in the soil but also to synchronise the availability with the demand of the cereals.
Figure 1
Soil sulphate under catch crops in November and in May after incorporation.
Figure 2
Experiments in pots.
Publications in preparation
Eriksen, Thorup-Kristensen & Askegaard: Plant-availability of catch crop S following spring incorporation.
Eriksen: Gross transformation rates of sulphur in soil amended with plant materials.
Eriksen: Svovl til økologisk sædskifter.
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