After being absorbed by crops, humic acid can promote the growth of crops and improve the quality and stress resistance of crops. So what factors affect the absorption of humic acid by crops?
The absorption of humic acid by crops varies depending on the molecular weight of humic acid. Small molecular weight humic acid components (maximum molecular weight less than 3500 D) can easily reach the plasma membrane of higher plant cells and are partially absorbed; while the number of large molecular weight humic acid components (minimum molecular weight greater than 3500 D) entering the root system of crops is lower than that of small molecular weight humic acid.
By comparing the absorption of small molecular weight humic acid and large molecular weight humic acid by pea roots under the condition of equal addition amount (10~250 mg/L), the researchers found that pea roots have absorption effects on both small molecular weight humic acid and large molecular weight humic acid, but the absorption of small molecular weight humic acid is more than twice that of large molecular weight humic acid. Therefore, it can be concluded that the small molecular weight component is the most active part of humic acid, which is more easily absorbed by crops and has a better stimulating effect on the growth of crop roots and the absorption of nutrient ions. Nevertheless, high molecular weight humic acid also has strong biological activity because it can regulate the root growth of crops. At the same time, high molecular weight humic acid treatment induced higher root differentiation and stimulated the activity of enzymes in metabolic processes related to crop growth and differentiation.
In summary, molecular weight is the main influencing factor of crop absorption of humic acid.