Production of plant and soil substrates: formulation and drying

Not all fertilizers are the same. Depending on the type of agricultural use, farmers have different requirements for fertilizers. For this reason, the Fraunhofer IGB develops tailor-made solutions for the respective needs.

Formulation and stability studies of fertilizers

Plants can be fertilized in two ways: through their leaves and the soil. Unlike fertilization of soil, the so-called foliar fertilization permits the targeted and precise dosage of various nutritional elements at a fixed time without the influence of soil nutrient fixation and washing-out. Nutrients are sprayed in a diluted form directly onto the leaves of the plant and absorbed by it. Not only macro-nutrients (N, P, K, Ca, Mg and S) are used for foliar fertilization, but also micro-nutrients, e.g. manganese, iron and trace elements. All of these nutrients contribute beneficially to plant growth.

Besides fertilizers, “plant strengtheners” are increasingly widespread in agriculture. These compounds do not have a fertilizing effect, but they contribute to the nutrient uptake of plants. Moreover, plants are verifiably more resistant to pest infestation and pathogenic organisms. For these reasons, plant strengtheners – especially when they are made from inartificial substances – are a reasonable and ecological alternative to classical pesticides and herbicides.

Leaf fertilization

Nutrients can be supplied to the plants through their leaves and through the soil. Unlike soil fertilization, leaf fertilization allows the targeted and precise dosage of various nutritional elements at a fixed time without the influence of the soil (specification of the nutrients, washing-out, etc.). The nutrients are sprayed in a diluted form directly onto the leaves of the plant and absorbed by them. Leaf fertilization is gaining importance to prevent and eliminate nutrient deficiencies in the plant.

Drying processes play an important role in the production of fertilizers or pesticides. They facilitate the transport and storage of extracted nutrients and active ingredients, for example in the form of powders. Drying thus also forms the basis for the production of fertilizer pellets.

Plant protection products are indispensable in agriculture to protect the cultivated plants from pests. The dilemma: chemicals offer effective protection, but are themselves harmful to the environment and, in the worst case, can also impair product quality. For this reason, the Fraunhofer IGB is developing biologically based crop protection products that are produced sustainably and do not harm the environment.

Drying of organic residues and cyanobacteria with superheated steam dryer

In the EcoBug project, the drying of the digested manure and cyanobacteria was carried out with a novel superheated steam dryer (SHSD). This dryer offers significant advantages in comparison with common hot air dryers.

Due to the superior heat transfer of steam, higher drying rates are achievable with SHSD at the same temperature. This leads to a lower specific energy consumption of
0.75–0.90 kW·h/kg water removed for SHSD compared to 1.10–1.70 kW·h/kg water removed in a comparable hot air dryer [1].

Moreover, higher thermal conductivity and heat capacity of superheated steam compared with hot air results in enhanced heat transfer to microorganisms, enabling pasteurization and/or sterilization. As superheated steam is recirculated and reheated in a closed loop, an excess of evaporated water develops which is carried off along with NH₃ and volatile organic carbon (VOC) from SHSD. In our approach VOCs and NH₃ are condensed out with the excess steam enabling condensable valuable organic substances including volatile fatty acids (VFA) and NH₃ to be recovered. This eliminates the environmental problem of VOC and NH₃ emissions in conventional hot air dryers.

Literature

[1] Desai, D. K. et al. (2009) Superheated Steam Drying of Brewer’s Spent Grain in a Rotary Drum, Advanced Powder Technology, Vol. 20, Issue 3, pp. 240-244