Root Residue Amendment on Varietal Allelopathy and Autotoxicity of Replanted Asparagus (Asparagus officinalis L.)

This study evaluated the allelopathic potential and autotoxic interference with growth and nutrient uptake of two asparagus varieties; UC157 (U) and Gijnlim (G) from USA and Europe, respectively. The two varieties were cultivated in a continuous replanting system in different rotational patterns with soil amended by asparagus root residues, and unamended soil (control) under greenhouse conditions. The combinations consisted of: G, U and GU, UG, GG, UU and GUG, GGU, UGU, UUG, UGG, GGG, UUU for the first planting, first replanting and second replanting, respectively. In this study, UC157 showed higher varietal allelopathic and autotoxic effects as compared to Gijnlim. Root and shoot growth were significantly (P ≤ 0.05) inhibited by up to 83 and 91 %, respectively in the second replanting of UC157 (UUU) when grown in the root residues amended soil; suggesting that root residues were responsible for the replanting problem. Further, growth inhibition was correlated with nutrient uptake inhibition; phosphorus (P) uptake was the most inhibited nutrient among nitrogen (N), potassium (K), calcium (Ca), and magnesium (Mg). Contrastingly, UC157 altered soil composition significantly (P ≤ 0.05) more than Gijnlim after subsequent replanting; for instance pH, C: N ratio and N, P, K, Ca and Mg were decreased whereas electrical conductivity (EC) was increased. This study concluded the growth inhibition of asparagus could be mitigated by proper selection of varieties to reduce the persistence of autotoxins and accumulation of allelochemicals from root residues during replanting.