Production of watermelon seedlings in different substrates under salt stress

Salt stress affects the production of watermelon (Citrullus lanatus) seedlings. However, substrates with alternative materials in their composition can mitigate the harmful effects on the formation of watermelon seedlings. Thus, the objective of the present study was to evaluate the emergence and production of watermelon seedlings grown in different substrates under salt stress. The research was conducted in an agricultural greenhouse belonging to the Universidade da Integração Internacional da Lusofonia Afro-Brasileira, Redenção, Ceará, Brazil. The experimental design used was completely randomized in a split-plot scheme. The plots were five levels of electrical conductivity of irrigation water (ECw: 0.5, 1.5, 2.5, 3.5, and 4.5 dS m-1) and the subplots consisted of two formulations of substrates (SB1: sandy soil + sand + bovine manure; and SB2: sandy soil + sand + biochar; both in a 1:1:1 proportion on volume basis), with five repetitions of 25 seeds. The increase in the electrical conductivity of irrigation water from 1.5 dS m-1 reduces the percentage, speed index, and mean speed of emergence and increases the mean time of emergence of the watermelon crop. Substrate formulated with biochar reduces the time and increases the emergence indexes, besides enabling higher growth and biomass accumulation of watermelon seedlings. Salt stress reduces the growth, biomass, and quality of watermelon seedlings, but with less intensity with the addition of biochar.