Effectiveness of solid and liquid biogas-derived organic fertilizers on growth, yield, and nutrient status of arugula in calcareous soils

This study aimed to evaluate the effectiveness of solid and liquid organic fertilizers derived from biogas waste in crop production, with the goal of promoting their use as sustainable fertilizers. The experimental design included a control, two doses of liquid organic fertilizer (200 L ha −1 and 400 L ha −1 ), and three doses of solid organic fertilizer (0, 3,000 kg ha −1 , and 6,000 kg ha −1 ). The combined application of solid and liquid organic fertilizers promoted faster plant height growth in arugula ( Eruca sativa ) within the same growth period, thereby enabling earlier harvest. Solid and liquid organic fertilizer applications had a significant effect on plant tissue concentrations of nitrogen, phosphorus, potassium, calcium, magnesium, iron, zinc, manganese, and copper. Significant period and treatment means were detected for phosphorus, magnesium, zinc, and copper, while potassium, calcium, and magnesium were significantly influenced by period alone. The highest manganese and iron concentrations were achieved exclusively with the liquid organic fertilizer treatments. Soil analyses revealed that the treatments significantly affected total nitrogen, available phosphorus, exchangeable magnesium, available iron, zinc, manganese, and copper levels, as well as soil pH, electrical conductivity (EC), and organic matter content. The results indicate that, in short-cycle crops such as arugula, liquid organic fertilizers applied through fertigation are generally more effective than solid forms. The use of low-compaction pelletized or powdered formulations is recommended to enhance the effectiveness of solid organic fertilizers.