Phosphate fertilization influences macronutrient accumulation in watermelon cv Magnum

ABSTRACT Studies on nutrient uptake are important to understand nutritional needs of crops, which demand may also be influenced by fertilization management, particularly P fertilization. Thus, the aim of this study was to evaluate macronutrient accumulation and distribution in watermelon cv. Magnum, under two forms of phosphate fertilization. The experiment was carried out in a sandy-textured Argisol in Mossoró-RN. The experimental design was a randomized block design, arranged in split plot in time, with four replicates. We evaluated dose of 137 kg ha-1 of P2O5 under two forms of fertilization [pre-planting (F0) and pre-planting + topdressing (F1)]. Triple superphosphate (SFT) was used for pre-planting applications and topdressing applications were done through fertigation using monoammonium phosphate (MAP, 34 kg ha-1 of P2O5). Shoot samples (stem + leaf + fruit) of the experimental plots were collected at 27, 34, 40 and 55 days after emergence (DAE), and quantitative values of the accumulated nutrients were determined. In general, the highest accumulation of macronutrients occurred in the last third of the crop cycle. General accumulation of macronutrient was altered by fertilization form. An increase in P accumulation was observed using F1 fertilization, both in total and in fruits. Macronutrient accumulation rates increased during the evaluation period, except for Ca and Mg in F1 fertilization. F1 fertilization provided higher total accumulations of Ca and Mg, but the same did not occur for the accumulation in fruits.

摘要
关于作物养分吸收的研究，对明确作物养分需求至关重要；而作物养分需求亦会受到施肥管理，尤其是磷肥施用的影响。据此，本研究旨在评估两种磷肥施用方式下，‘Magnum’品种西瓜的大量元素积累与分配特征。
本试验于巴西北里奥格兰德州莫索罗市的砂质质地老成土（Argisol）中开展，采用裂区随机区组设计，以时间作为裂区，设置4次重复。试验设置137 kg·ha⁻¹的五氧化二磷（P₂O₅）施用量，采用两种施肥方式：播前施肥（F0）以及播前施肥+追肥（F1）。播前施肥采用重过磷酸钙（Triple superphosphate, SFT）；追肥则通过水肥一体化施用磷酸一铵（monoammonium phosphate, MAP），施用量为34 kg·ha⁻¹的P₂O₅。
分别于出苗后27、34、40和55天（DAE）采集试验小区的地上部样品（茎+叶+果实），并定量测定了养分积累量。总体而言，大量元素的最高积累量出现在作物生育期的最后三分之一阶段。施肥方式显著改变了大量元素的总积累量：采用F1施肥方式时，无论是植株整体还是果实中的磷素积累量均有所提升。在试验评估期内，除F1施肥方式下的钙（Ca）和镁（Mg）外，其余大量元素的积累速率均呈上升趋势。F1施肥方式下植株整体的钙、镁总积累量更高，但果实中的钙、镁积累量并未呈现相同变化趋势。