Effect of of Humic Acid Spraying at Different Flowering Stages on Seed Yield and Its Components of Berseem (Trifolium alexandrinum L.)

Abstract

This experiment was conducted in an agricultural field in the Musayib district, located 37 km from the city center of Babil Governorate, Iraq, during the period from mid-October 2024 to mid-June 2025, in order to study the effect of humic acid concentrations (0, 2, 4, 6 g L1-) and three spraying stages: (10% of flower buds open, 50% of flower buds open, and 75% of flower buds open) The local variety of alfalfa was used in this study. The experiment was conducted using a randomized complete block design (R.C.B.D.) with split-plot arrangement and three replications. The spraying stages constituted the main treatments, while the humic acid concentrations constituted the secondary treatments.  The following traits were studied (number of seeds per inflorescence, 1,000-seed weight, seed yield, biological yield, and harvest index). The results showed that spraying humic acid led to a significant increase in the number of seeds per inflorescence, seed yield, and biological yield. Spraying with humic acid at concentrations of 4 and 6 g L1- yielded the highest average number of seeds per inflorescence, reaching 48.1 and 50.53 seeds per inflorescence, respectively, as well as the highest average seed yield of 473.47 and 477.83 kg ha 1-, respectively, and also yielded the highest average biological yield of 3.36 and 3.354 tons ha1-, respectively, with no significant difference between them. The spraying stage at 10% flowering of the inflorescences outperformed the others in terms of the average number of seeds per inflorescence (49.7 seeds per inflorescence), seed yield (486.77 kg ha1-), and biological yield (3.6 tons ha1-). There was a significant interaction between humic acid concentrations and application stages for both the number of seeds per inflorescence, seed yield, biological yield, and harvest index. The results indicated that there was no statistical evidence that the weight of 1,000 seeds was affected by either factor, and the harvest index was not affected by the spraying concentrations of humic acid.