Response of two soybean (Glycine max L.) cultivars to different levels of humic acid and mineral fertilization

The present work was carried out at experimental farm, faculty of agriculture, Al-Azhar University, Assuit, Egypt, during 2020 and 2021 summer seasons, to study response of two soybean (Giza 111 and Giza 22) cultivars to mineral fertilization (NPK); mineral fertilizer at rates 50%, 75% and 100% of the recommended dose of N, P and K (RDF) and humic acid (HA) at rates 0, 6 and 12 kg HA/fed, as soil application. The results indicated that Giza 22 surpassed Giza 111 in seeds yield/feddan (feddan = 4200 m2), biological yield/feddan and 100- seed weight in both seasons, respectively, as well as oil percentage in first season only and protein percentage in second season only. While Giza 111 surpassed Giza 22 in plant height, number of branches per plant and seeds yield per plant in both seasons, as well as the protein percentage in first season only and oil percentage in second season only. Application recommended dose of mineral fertilization (NPK) at rate 100% led to a significant increase in all traits under study.  Using highest level of humic acid, which is 12 kg per feddan (feddan = 4200 m2), led to a significant increase in all studied traits in this respect. Concerning the interaction between cultivars and mineral fertilization, data focus a significant effect on the characteristics of plant height (cm), seed yield per feddan in both seasons, oil and protein ratio, 100- seeds weight in the first season only, farther biological yield per feddan in the second season only. While the interaction between cultivars and humic acid showed a significant effect on the characteristics of plant height (cm), seed yield per feddan, biological yield per feddan in both seasons, protein percentage, of 100- seed weight in the first season only, and the number of branches per plant in the second season only. Here too, the interaction between mineral fertilization and humic acid also showed a significant effect on the characteristics of seed yield per feddan, biological yield per feddan, weight of 100 seeds, protein percentage in both seasons, plant height and seed yield per plant in the first season only, and the percentage of oil in the seed in the second season only. Finally, the interaction between the three study factors, cultivars, mineral fertilization and humic acid, had a significant effect on the characteristics of the biological yield per feddan in both seasons, seed yield per feddan, weight of 100 seeds in the second season only, while plant height and seed yield per plant in the first season only, respectively.