Impact of Bentonite and Humic Acid on the Growth and Flowering of Catharanthus roseus L. in Sandy Soil

Bentonite is a very useful material for improving soil properties, which enhances the ability of plants to grow and produce in different conditions. The experiment was carried out in an agricultural nursery in one of the areas of the City of Diwaniyah, in a house covered with green netting, with a shade rate of 25%, to study the effect of bentonite and humic acid on the growth and flowering of a Catharanthus roseus L. plant in sandy soil. The experiment included two factors: the first factor was bentonite clay, and the second factor was humic acid. Using a randomized complete block design (R.C.B.D) with three replications, data were analyzed using the analysis of variance (ANOVA) method, and comparison was made according to the least significant difference (L.S.D) test at a probability level of 0.05. The experiment consisted of adding bentonite clay at 0, 2, 6, and 8 g L–1, humic acid at 0, 0.5, 1, and 10 g L–1. The results showed that adding bentonite clay and humic acid to sandy soil can have a significant positive effect on the growth and flowering of the Catharanthus roseus plant grown in poor sandy soil conditions. Bentonite, clay and humic acid were added at concentrations of 8 and 10 g L–1, which led to an increase in plant height and number of leaves and leaf area. They reached 30.07, 23.84 cm2, 76.62, 63.42 cm2 for leaf–1 and 24.73, 20.22 cm2 for leaf–1, respectively. The results also showed an increase in the content of nitrogen (N), phosphorus (P), and potassium (K) in leaves by 2.27, 1.92, 1.99% and 1.51, 1.22, 1.77%. This also led to an increase in chlorophyll pigment and anthocyanin at the highest concentration and gave the highest value. Therefore, adding bentonite and humic acid together gave the highest values in vegetative and chemical characteristics, compared to treatments without addition.