Effects of Foliar Application of Humic Acid and NPK Fertilisers on the Soil Ion Important Growth Indices of Black Mustard (Brassica nigra L.)

Mustard—specifically the Brassica nigra L. variety—is a crop of industrial significance, as its seeds are renowned for containing between 41% and 48% high-quality oil. Amidst global climate change, there is an urgent need to utilize humic acid to enhance mustard growth. In this context, a field experiment was conducted in Babylon Governorate, Iraq, during the 2024–2025 growing season to investigate the effects of compound fertilizer (NPK) and organic fertilizer (humic acid) on the growth and productivity of black mustard, employing a Randomized Complete Block Design (RCBD) with three replicates. Using variance analysis and means comparison with the LSD test at a probability level of 0.05, the results showed that the foliar application of humic acid had a significant impact on the growth parameters of black mustard. A 3x3 two-factor experiment was conducted. Adding a balanced NPK complex fertilizer (20:20:20) was the first factor. In two batches, the first two weeks following germination and the second when blooming starts, at concentrations of (0, 30, or 60) kg/dunum. . After placing the fertilizer in the furrows approximately 10 cm beneath the plant and covering it with dirt, the plant was watered. Spraying three different quantities of organic fertilizer (humic acid) (0, 2, or 4) ml.l-1 was the second factor. It was observed from the results that adding NPK complex fertilizer and organic fertilizer (Humic acid) has a significant effect on the characteristics of vegetative growth, as is evident from the fact that the levels of NPK complex fertilizer and spraying with organic fertilizer (Humic acid) have a significant effect on the productive characteristics of the plant The experiment's conclusion is that the 60 kg overlap treatment is the most efficient way to feed the black mustard plant under the given circumstances, and it produced the best outcomes in terms of enhancing the plant's vegetative and productive qualities. 1 dunam-1 NPK with three 2 ml sprays.l-1 of organic fertilizer (Humic acid), which increased the features of vegetative development and delivered the greatest rate of mustard number. Plant-1 and seed count.  Mustard-1 and seed weight. Plant-1 and the amount of seed yield per dunum. application of 45 ppm humic acid with 60/kg – per dunum (per 2500 square meters) would be the best option to maintain better growth, yield and quality in black mustard.