Improvement of nitrogen uptake and dry matter content of Swiss chard by pre‑incubation of duckweeds in soil


School of Agricultural Earth and Environmental Sciences, University of KwaZulu-Natal, Scottsville, South Africa


Purpose Recovery of nutrients from water using duckweed and their reuse has significance in closing the loop on nutrient transfer from anthropogenic sources. This study investigated the effect of rate of application and pre-incubation period of duckweed on biomass and nutrient uptake of Swiss chard (Fordhook giant).
Method Two glasshouse experiments were laid out in randomized complete block designs with three replicates. In the first experiment, Swiss chard was grown on two soils (ferralsol and regosol) amended with Wolfa arrhiza biomass at 0, 50,100 and 200% of the recommended nitrogen rate. In the second experiment, the same vegetable was grown on the ferralsol amended with W. arrhiza and Lemna minor at recommended nitrogen rate, with pre-incubation periods of 0, 14 and 28 days.
Results Application of W. arrhiza biomass increased Swiss chard dry matter by 23–45% compared to the negative control. The positive control (urea at100 kg N ha−1 rate) had highest Swiss chard biomass. Higher rates than100 kg N ha−1 had no added benefit on dry matter accumulation and nitrogen uptake of Swiss chard. Pre-incubation of duckweed for 28 days improved nutrient uptake, resulting in higher dry matter than shorter periods. The Swiss chard dry matter after pre-incubation for 28 days was similar to that from urea application.
Conclusion Findings from this study suggest that duckweed is a resource with beneficial use for nutrient supply to vegetables, especially when appropriate rates are used with pre-incubation.