Growth responses of garden cress (Lepidium sativum L.) to biodynamic cow manure preparation in a bioassay

Natural substances are extensively used as biostimulants in agriculture. Notably, horn-manure preparation (HMP) is fermented cow manure sprayed at low concentrations onto biodynamically cultivated fields. The present study investigated the effect of HMP on the growth of garden cress (Lepidium sativum L.) cultivated in a bioassay (randomized block design, n = 20). Seedlings were cultivated in a water medium. Treatments of a drop of HMP suspension (1 mu l or 0.1 mu l) or of water (Control) were added to the medium. Long-term series of trials, with two different HMPs, were conducted over 18 and 9 months with 76 and 38 trials, respectively. In the first series, the effect of a 1 mu l drop of HMP suspension on root growth was significant overall (-2.4%, p = 0.004, Tukey-Kramer-test) and in 35.5% of the individual trials (p < 0.05). However, the effects fluctuated strongly between the trials (from -25.7% to +19.1%). The effect of a 0.1 mu l drop was similar, but lower in magnitude. The results of the second series were analogous. Comparison of statistical models provided significant evidence of a growth-stabilising effect. An additional series of 22 negative control trials indicated an acceptable false positive rate. It was concluded that HMP, at low doses, significantly influenced root growth at early stages, with a stabilising pattern of action. Further development of the bioassay should improve its power and stability over time. A stabilising effect may induce an increased resilience of the agricultural system.