WATERMELON INITIAL GROWTH UNDER DIFFERENT HYDROGEL CONCENTRATIONS AND SHADING CONDITIONS

ABSTRACT Watermelon (Citrullus lanatus) belongs to the plant family Cucurbitaceae. It is cultivated in many regions of Brazil, particularly in rainfed areas; thus, it is subject to the problems arising from irregular rainfall. Hydrogel is a soil conditioner used to retain and provide water to plants for long periods of time. Therefore, incorporating hydrogel into the soil should increase water availability for watermelon cultivation, and may be an alternative method to reduce the risk of water deficit. This study evaluated the effect of different concentrations of hydrogel on the initial growth of watermelon cv. 'Crimson Sweet' under different shading conditions. The experiment was carried out in a greenhouse with completely randomized design with a 4×3 factorial scheme. The treatments consisted of four hydrogel doses (0.0; 1.5; 3.0; and 6.0 g L-1 substrate), three shading conditions (under full sun; black shade net, and red shade net, both with 50% shading), and five replicates per treatment. The variables evaluated were plant height; stem diameter; shoot, root, and total dry matter; and leaf area. The best hydrogel dose for watermelon cultivation was 1.5 g L-1, but the higher doses impaired plant growth, regardless of shading conditions. The black net improved biomass accumulation in 'Crimson Sweet' watermelon, whereas the red net induced plant etiolation.

摘要：西瓜（Citrullus lanatus）隶属于葫芦科（Cucurbitaceae）。该作物在巴西诸多区域均有种植，尤其集中于雨养农区，因此易受降雨不规则性引发的各类问题影响。水凝胶（hydrogel）是一类可长期留存并为植物提供水分的土壤调理剂，将其施入土壤能够提升西瓜种植过程中的水分供给量，或可作为降低水分亏缺风险的有效替代方案。本研究针对不同遮光条件下，不同浓度水凝胶对‘Crimson Sweet’西瓜品种初始生长的影响展开了评价。试验于温室中开展，采用完全随机设计，设置4×3因子试验方案。试验处理包含4个水凝胶施用剂量（0.0、1.5、3.0及6.0 g·L⁻¹基质）、3种遮光条件（全光照环境、黑色遮阳网及红色遮阳网遮光，两种遮阳网遮光率均为50%），每个处理设置5次重复。测定指标包括株高、茎粗、地上部干物质量、地下部干物质量、总干物质量及叶面积。研究结果显示，适配西瓜种植的最优水凝胶施用剂量为1.5 g·L⁻¹，而更高剂量则会抑制植株生长，且该效应不受遮光条件影响。黑色遮阳网可提升‘Crimson Sweet’西瓜的生物量积累，而红色遮阳网则会诱导植株出现黄化徒长现象。