29Si MAS‐NMR, and Ca‐EXAFS experiments have been conducted on calcium silicate hydrates (C‐S‐Hs) with structure derived from wollastonite. Crystalline compounds (wollastonite, xonotlite, hillebrandite, foshagite, 1.1 nm and 1.4 nm tobermorites, and jennite) and C‐S‐H were synthesized and characterized. 29Si NMR provides information on silicate chains and EXAFS on calcium environment. The refined EXAFS values are in agreement with XRD data, except for tobermorite. The calcium order in C‐S‐H (C/S molar ratio from 0.7 to 1.4) is similar to that of tobermorite but different from that of jennite. Structural models of C‐S‐H are discussed.

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 µl or 0.1 µl) 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 µl 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 µl drop was similar, but lower in magnitude. The results of the second series were analogous. Comparison of statistical models provided significant evidence of a growthstabilising 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.

Background The use of biostimulants like humic substances is a promising innovative approach in agriculture to activate and sustain physiological plant processes. The development of specific bioassays is required to study their bioactivity in laboratory conditions. In previous investigations, a soil-less bioassay with cress seedlings (Lepidium sativum L.) was developed for a biostimulant used in the biodynamic agriculture, the horn-manure preparation (HMP), a fermented cow manure sprayed at low concentrations onto fields. Objectives of the present study were to refine the bioassay by investigating the interactions between the HMP bioactivity and the test factors (i) water volume, (ii) gravistimulation, and (iii) exposure to fluorescent light. Results The interactions between the test factors and the HMP treatment were significant in all series (p < 0.05, Wald F-test). Water overdose and gravitropic stress reduced root growth (down to − 24.2% and − 19.9%, respectively, p < 0.0001, Tukey–Kramer test). The HMP treatment partly compensated these effects by enhancing root growth by (i) water overdose (up to + 4.3%, p = 0.048, n = 4), and (ii) gravitropic stress (up to + 9.5%, p = 0.0004, n = 8). (iii) Furthermore, under the combined stress factors, fluorescent light exposure enhanced the HMP enhancing effect (up to + 12.3%, p = 0.007, n = 6). Conclusions The HMP bioactivity appeared to consist of a compensatory mode of action regarding the stress factors water overdose and gravistimulation, and a synergetic interaction with fluorescent light exposure. The HMP seems to interact with the plant sensory systems, likely stimulating the plant’s adaptability to its environment by increasing self-regulating processes. The bioassay sensitivity was successfully increased by integrating these interactions in the experimental set-up and adjusting the growth environment. This approach can be used to adjust the bioassay to other biostimulants.