Application of Humic Substances Results in Consistent Increases in Crop Yield and Nutrient Uptake

ABSTRACT

The effect of humic substances on yield and nutrient uptake of grass, maize, potato and spinach was investigated in six field experiments and two pot experiments in a high input cropping system. The humic substances originating from leonardite formations in Canada were applied as liquid solution to the soil (Humifirst liquid) or as a solid incorporated in mineral fertilizers (Humifirst incorporated). Formal meta-analysis of the results of all executed experiments showed that the application of humic substances had an overall positive effect on dry matter yield of the crops and this effect was statistically significant for Humifirst incorporated. In the case of permanent grassland, humic substances promoted mainly the production of the first grass cut, which has the highest grass quality among all cuts during the growing season. Tuber production on the potato field trial showed a high response on the application of humic substances. Total potato yield increased with 13 and 17% for Humifirst liquid and Humifirst incorporated, respectively. The effect of humic substances on maize yield was limited, probably due to the rather high nutrient status of both soils. Finally, the formal meta-analysis showed a consequent increase in nitrogen and phosphorus uptake of all studied crops as well. The effect on potassium and magnesium uptake was also mainly positive, while sodium and calcium uptake were not affected in most of the experiments.

Keywords:

• humic substances
• leonardite
• macronutrients
• grass
• maize
• potato
• spinach

ACKNOWLEDGMENTS

We would like to thank the Institute for the Promotion of Innovation by Science and Technology in Flanders (IWT) and the ‘users committee’ for their financial support.

Notes

¹Organic carbon measured with a modified Walkley and Black method.

²pH determined in a soil-solution ratio of 1:1 (1 M potassium chloride).

³Measured in ammonia-lactate extract.

¹The uptake of P, K, Mg, Na and Ca expressed as the uptake of P₂O₅, K₂O, MgO, Na₂O and CaO in kg ha⁻¹.

∗,

∗∗,

∗∗∗: significant difference between Humifirst and control treatment with respectively p < 0.05, p < 0.01, p < 0.001 (Tukey test).

¹The uptake of P, K, Mg, Na and Ca expressed as the uptake of P₂O₅, K₂O, MgO, Na₂O, and CaO in mg pot⁻¹.