Project news Nitrogen effects of cut green manures in relation to application method and soil condition

ILVO, Inagro, PCG and UGent investigated the effect of cut green manures (grass-clover) on crop yields in recent years. They concluded that grass clippings produced on the own farm can be an alternative for farmyard manure, with the added advantage of fixing nitrogen without phosphorus.

Grass-clover mixes (fresh or ensiled) can be applied as a cut green manure in field and greenhouse crops. ILVO, Inagro, PCG and UGent evaluated whether the depth at which the cut green manure is introduced into the soil when preparing the soil has an influence on the decomposition rate of the fertilizer in the soil preparation, and thus on its nitrogen effect.

At ILVO, the cut green manure was applied before plowing and after plowing, after which the cut green manure was incorporated with the vibratory tine cultivator. The trial was conducted in the retaining part of a multi-year soil management trial that also included the compost application factor, with one variant with and one without compost. Also at Inagro, PCG and UGent, trials were carried out with cut green manures and farmyard manure, including in crops of potatoes, tomatoes and peppers, spinach and pak choi.

The different trials showed 4 important elements. First, the nitrogen action of the mowing fertilizer varied widely across the trials, from less than 10% to more than 30%. Second, the quality of the mowing fertilizer (mainly C/N ratio) appears to be important for its nitrogen action, but other factors (field conditions) also play a major role. Third, the application method (depth of application in the furrow) has a limited effect on the nitrogen action of the cut green manure. And fourth, the nitrogen action coefficient as measured under controlled lab conditions does not always correspond to that measured under field conditions.

The generally relatively limited nitrogen action of the cut green manure indicates that a cut green manure will effectively contribute to organic matter accumulation and thus to the nitrogen supply capacity of the soil. Thus, this type of fertilizer can be a full-fledged alternative to farmyard manure. However, cut green manures have the advantage of generally supplying more nitrogen per unit of phosphorus, which can be important in the context of the stricter phosphorus standards.

Project title: Maaimeststoffen (Cut green manures)
Term: 2015-2017
Partners: Inagro, PCG, Universiteit Gent
Funding: ADLO-project with funding from the Flemish Department of Agriculture and Fisheries

Link: (In Dutch) full project report