# Popular Biochar as an Alternative Substrate for Curly Endive Cultivated in a Soilless System
## 4 Discussion
Others have reported that K content increases with higher levels of biochar ([PERSON] et al.) [15]. Moreover, our data are in agreement with those by [PERSON] et al. [32] who found that the addition of spruce wood biochar to peat allowed the preservation of stable and high levels of K in the pore water, both in the root free substrate and in the rhizosphere in planted and non-planted soilless growing media. Nonetheless, our results on K concentration are in contrast to [PERSON] et al. finding [26] who report no influence of the pyrolysis temperatures on substrate K concentrations for sugarcane straw, rice husk, poultry litter and sawdust biochars. Outcomes displayed that Ca, Mg and Na contents decreased with the biochar percentage increase in the growing media. Furthermore, pyrolysis temperature did not influence Ca, Mg and Na concentrations. This is confirmed by [PERSON] et al. [15]. Additionally, our findings agree with [PERSON] et al. [26], who affirm that pyrolysis temperature has no effect on Mg concentration. Our work highlighted that increasing poplar biochar percentage in the growing substrates corresponds with an increase of particle density and bulk density. These results are supported by several authors [11; 15; 24; 33]. Outcomes on yield traits pointed out that an increase of poplar biochar percentage (until 70% of the total volume) and pyrolysis temperature (700 \({}^{\circ}\)C) can improve curly entive crop performance. This is probably because biochar can retain high amounts of exchange cations due to its high porosity and surface/volume ratio and, consequently, can enhance plant nutrients uptake and availability [9; 34; 35]. Furthermore, we found that increasing biochar percentage results in an increase of biomass. Similarly, [PERSON] et al. [24] refer that mixing green waste biochar with peat provides a better physical environment than biochar alone or peat alone in growing media for _Calathea rotundifolia_ cv. Fasciata. However, our data remarked that the lowest plant yield performance was recorded from plants grown on 100% biochar or 100% peat. This is probably due to the decline of growing medium physicochemical traits such as high pH and EC levels. Our results agree with those of [PERSON] et al. [15] and [PERSON] et al. [36] who, by studying the biological nitrogen fixation in common beans (_Phaseolus vulgaris_ L.) with bio-char additions, reported that adding a high rate of Eucalyptus wood biochar to a poor soil in a soilless study crop performance possibly due to a micronutrient shortage caused by an augmentation of soil pH. Outcomes on total phenolic revealed that the highest values were found in plants from biochar 70%_450 and biochar 100%_450 treatments. These findings are supported by those of [PERSON] et al. [37] who, by inquiring the effects of the amendment of a biochar (BC) or a biochar-compost mixture (BioComp) to a peat-based substrate at 20% by volume on the growth of _Syngonium podophyllum_, found that total phenolic contents were higher in plants grown in BC- or BioComp-amended media. In our study, the lowest curly entive crop performance was observed in plants cultivated in a growing substrate with 100% biochar. This remarks that the unfavorable plant growing conditions of the media and the stressful conditions induce an accumulation of phenolics [38; 39; 40; 41]. Therefore, we could hypothesize that the higher total phenolic content is due to a stress caused by a non-optimal curly entive-cultivation environment (pH and EC stresses). Our study revealed, also, that the higher SSC and ascorbic acid contents were recorded in curly entive plants grown on biochar at 70% and a pyrolysis temperature of 450 \({}^{\circ}\)C and that TA was not affected by the growing substrates tested. Our resultshighlighted a decrease of N content and an increase of K in leaves as the biochar content in the growing mediums increased.