Closing the loop: Utilization of composted tomato plant residues as fertilizer and soil amendment

Objective

Resource waste and an environmental burden are consequences of improper disposal of horticultural waste, making it a significant concern in horticulture. Tomato plant residues that accumulate from tomato production in greenhouses, contain a lot of nutrients and organic matter. In the composting process, microorganisms decompose residues into nutrient rich substrates. If these were amended to arable land, this could save fertilizer and help to close nutrient cycles.

Methods

In the present study, it was investigated in a pot experiment whether compost from tomato residues is suitable as fertilizer and soil amendment to produce lettuce (Lactuca sativa 'Speedway'). Therefore, conventional organic fertilizer was substituted either by 100 % or 50 %. In addition, control treatments, with or without conventional organic fertilizer were cultivated.

Results

The results show that the addition of tomato plant compost increases water holding capacity, carbon content, pH, total amount of macro nutrients as well as available P, K and Mg, but reduces ammonium and nitrate content compared to the fertilized control. The 100 % substitute leads to reduced yield and water use efficiency. Therefore, using composted tomato plant residues as a sole N fertilizer is not efficient due to limited plant available N release. Yet, substituting 50 % of conventional organic fertilizer with composted tomato plant residues maintains yields while preserving the aforementioned positive effects.

Conclusion

We demonstrated that composted tomato plant residues are suitable as fertilizer and soil amendment. The residues from one hectare of tomato production have the potential to substitute 50 % of conventional fertilizer for lettuce production on one and the same hectare. This could effectively reduce waste, close nutrition cycles, and promote environmentally friendly horticulture.