Digestate and Manure Use in Kohlrabi Production: Impact on Plant-Available Nutrients and Heavy Metals in Soil, Yield, and Mineral Composition

Digestate is a residue of the anaerobic decomposition of organic waste for biogas extraction, but it can be reused as a source of nutrients. To examine the effect of digestate in kohlrabi production, field experiments were conducted during three seasons in two calendar years. The fertilization treatments included the application of solid digestate (two rates-DS1 and DS2), liquid digestate (two rates-DL1 and DL2), solid manure (two rates-MS1 and MS2), and mineral fertilizer (NPK) and were compared with a plot without fertilization (empty set). The results showed a significant increase in the yield with the use of solid and liquid digestate, as well as with NPK, in all growing seasons, while the microelement contents (Zn, Mn, and Cu) in the leaves were at optimum level. The applied treatments did not increase the plant-available nutrients (AL-P2O5, AL-K2O, Fe, Cu, and Zn) in the soil (except Mn). The application of DL2, MS1, and MS2 led to a higher Pb content in kohlrabi stems compared to the control, but the Pb content remained below the maximum permitted limit. Our research showed that digestate can be used as a valuable source of nutrients for kohlrabi production, with a low risk of soil and plant contamination by heavy metals. However, the control of soil, digestates, and manure quality is recommended.

Automated summary

This study investigated the effects of digestate on the yield and nutrient content of kohlrabi through field experiments. The results showed that the use of digestate significantly increased the yield and optimized the microelement content in the leaves. However, the application of digestate did not increase the plant-available nutrients in the soil, and it had an impact on the lead content in kohlrabi stems.