Effect of Humic Acid Addition on Buffering Capacity and Nutrient Storage Capacity of Soilless Substrates

Abstract

Excessive application of fertilizers has become a major issue in croplands of intensive agricultural systems in China, resulting in severe non-point source pollution; thus, reduction in the use of chemical fertilizers has received significant attention. Improving the nutrient storage capacity of soils or substrates is an effective approach for solving this problem. Humic acids (HA) are excellent soil conditioners. Thus, in the present study, their ability to improve the physico-chemical properties of three substrates with different textures was evaluated. HA treatments included 1% HA root application in three different types of substrates, including pure sand, pure cocopeat, and a mixture of sand:cocopeat (1:1, v/v) and their relative controls. We examined the morphological parameters of cucumber seedlings as well as pH buffering capacity (pHBC), total organic carbon (TOC), organic matter (OM), cation exchange capacity (CEC), and nutrient storage capacity of the three substrates. The results show that HA application improved the morphological parameters of cucumber seedlings (plant height, stem diameter, and biomass) in pure cocopeat and cocopeat-sand mixture treatments. On the contrary, HA addition had harmful effects on the cucumber seedlings cultivated in sand due to the low pHBC of sand. The seedlings cultivated in pure cocopeat showed the best morphological parameter performances among the seedlings grown in the three substrates. Furthermore, pHBC, TOC, OM, and CEC were enhanced by HA application. Incorporation of HA improved ammonium (NH4+) and potassium (K+) storage capacity while decreasing phosphorus (P) storage. Pure cocopeat had the highest pHBC, TOC, OM, CEC, and nutrient storage capacity among the three substrates. In conclusion, mixing 1% HA into substrates promoted cucumber growth, improved substrate properties, and enhanced fertilizer use efficiency. Pure cocopeat is a suitable substrate for cucumber cultivation, and mixing cocopeat with sand amends the substrate properties and consequently improves plant growth.

Deciphering the Effectiveness of Humic Substances and Biochar Modified Digestates on Soil Quality and Plant Biomass Accumulation

“…We hypothesized that the long-term effect of digestate + biochar on nutrient mineralization would be negative, because of the tendency for biochar-mediated immobilization and sequestration. Both humic acids and biochar represent amendments that are rich sources of carbon and also act as nutrient storehouses [51][52][53][54]. However, biochar contains both labile (easily available) and recalcitrant carbon, leading to higher heterogeneity of organic matter in the digestate.…”

Coated Diammonium Phosphate Combined With Humic Acid Improves Soil Phosphorus Availability and Photosynthesis and the Yield of Maize

“…However, the yield in CP 100% + HA was significantly higher than that in CP 100% in 2018. This is because the combination of CDAP and HA exerts beneficial effects on plant growth by improving the soil structure, fertility, and quality ( Calvo et al, 2014 ; Raiesi, 2021 ; Xu et al, 2021 ), and two consecutive years of application eventually resulted in significant changes. The combination of CDAP and HA provides an HA-incorporated enhanced-efficiency P fertilizer for environmentally friendly fertilization ( Figure 9 ), and future research should include P-inefficient crops (e.g., wheat).…”

“…HA consists of aromatic and aliphatic structures harboring various functional groups (mainly oxygen-containing), such as carboxyl (–COOH) and phenolic hydroxyl (–OH). Studies have shown that HA application reduced P fixation, improved the efficiency of low and high solubility P sources, increased P availability, and improved PUE ( Çimrin et al, 2010 ; Rosa et al, 2018 ; Shafi et al, 2020 ; Xu et al, 2021 ). HA improved soil structure by encouraging the formation of stable aggregates, which increased the productivity of soil crops ( Zhou et al, 2019 ).…”

“…In addition, HA has been shown to improve certain aspects of growth in essential agronomic crops like soybean, wheat, rice, and maize ( Calvo et al, 2014 ; Rosa et al, 2018 ). As a plant biostimulant, HA increases photosynthesis, reduces transpiration, stimulates root and shoot growth, and enhances stress resistance of plants ( Canellas et al, 2013 ; Dantas et al, 2018 ; Xu et al, 2021 ), and is linked with changes in the hormone contents and enzyme activities and enhancement of H + -ATPase activity ( Zandonadi et al, 2010 ; Calvo et al, 2014 ). However, since HA is a weak nutritional material, it cannot supply the nutrient requirements in crop production on its own.…”

“…Many research has been conducted on the effects of HA application, the combination of water-soluble P fertilizer and HA, and HA mixed with urea or controlled-release urea on soil quality, plant development, and fertilizer use efficiency ( Shafi et al, 2020 ; Li Z. L. et al, 2021 ; Xu et al, 2021 ). Rosa et al (2018) found that combining HA with phosphate fertilizers (e.g., single superphosphate) boosted root dry matter, and nutrient uptake increased the shoot dry matter output, as compared to biomass produced in soil that had not been treated with HA.…”