Manure as an opportunity

After 20 years, the Louis Bolk Institute's longest-running trial into the balance between crop yields and the sustainable maintenance of soil fertility (relating to soil quality, soil life, and contribution to CO2 sequestration) shows remarkable differences.

Three main strategies were compared: (i) fertilisation mainly aimed at feeding the plants, such as through artificial fertilisers and slurry; (ii) fertilisation mainly aimed at feeding the soil, such as with various composts and (iii) fertilisation aimed at feeding both the plant and the soil: poultry manure, a combination of compost & slurry, and deep stable manure.

The yields of vegetable crops differ widely for the 3 strategies. With artificial fertiliser and slurry, yields remain stable. With the soil feeding strategies, the yields decreased over the years, while in the soil and plant feeding strategies, increasing yields were achieved - especially with deep stable manure and a compost & slurry combination.

The largest increase in soil organic matter and thus CO2 storage and climate gains was found for natural compost, deep stable manure and the compost & slurry combination. The organic matter content remained stable in both the artificial fertiliser and slurry. Extra soil fertility is mainly built up with deep stable manure, but also with a compost & slurry combination. This provides extra 'old power' from which a farmer can derive added value. The chance of nitrogen leaching under the composts remains remarkably small.

The soil life appears to influence mainly in the short term, but in the longer term - 17 years – soil life is hardly dependent on the type of manure or compost applied.

All in all, it can be concluded that in the long term the best yields and soil quality can be achieved with fertilisers that both feed the crop and build up soil fertility: deep stable manure and compost in combination with slurry. Within the legal frameworks, these combinations also yield the most climate gains through CO2 storage in the soil.

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