Abstract

A field experiment was conducted during the autumn growing season of 2024 at one of the experimental fields of the College of Agricultural Engineering Sciences, University of Baghdad, Iraq (44.38° E, 33.2° N), to investigate the effect of zeolite application, humic acid levels, and potassium fertilization on potassium use efficiency, NPK concentration in plants, growth, and productivity of cabbage (Brassica oleracea L.). The experiment was arranged in a randomized complete block design with three replications and included three factors: zeolite at two levels (0 and 12 t ha?¹), humic acid at two levels (0 and 10 L ha?¹), and potassium at three levels (0, 50%, and 100% of the recommended fertilizer rate of 125 kg K ha?¹), applied as potassium sulfate containing 41.5% K. The results showed significant differences due to zeolite application, where the Z1 treatment (12 t ha?¹) produced the highest concentrations of nitrogen, phosphorus, and potassium in the inner leaves (3.94%, 0.41%, and 3.65%, respectively), in addition to the highest total yield (60.4 t ha?¹) and the largest head diameter (18.38 cm) compared with the Z0 treatment. The H1 level (10 L ha -1) of humic acid application gave the most favorable levels of nitrogen (3.88), phosphorus (0.39), and potassium (3.52), total yield (62.9 t ha -1) and head diameter (18.18 cm) in terms of the highest concentrations and largest total yield and head diameter respectively compared to the non-application (H0) treatment. Potassium fertilization greatly enhanced phosphorus and potassium levels in the inner leaves to 0.38 and 3.93 respectively and yielded the highest total (66.8 t ha -1) and head diameter (17.79 cm) than potassium non-application (K1). The combination of the triple interaction of zeolite, humic acid, and potassium led to the highest nitrogen, phosphorus and potassium concentration in the inner leaves (4.42%, 0.38 and 4.61, respectively), greatest total yield (75.3 t ha -1), and an overall head diameter of 17.79 cm compared with the Z0H0K1 treatment.