Manure Fertilization Gives High-Quality Earthworm Coprolites with Positive Effects on Plant Growth and N Metabolism

Abstract

Humic substances (HS) are important soil components playing pivotal roles in guaranteeing long-term soil fertility. In this study, the chemical and biological properties of HS extracted from earthworm coprolites collected in soils subjected to different fertilization inputs (no fertilization, NF; fertilization with farmyard manure, FM; mineral input, M; mixed inputs, FMM, half farmyard manure plus half mineral input) were investigated. Results indicated a relationship between fertilization input and composition, molecular complexity and apparent molecular weight distribution of HS produced by earthworms. Coprolites from FM and FMM soils were the most enriched in organic carbon (OC), and HS from coprolites of FM soil were the highest in humic carbon (HC). Also, soil amendment with manure increased carboxylate and aromatic groups in HS, and the fraction with a high degree of polycondensation, thus indicating a positive impact of manure on plant residues’ degradation processes. These HS were the only to display hormone-like activity, which likely accounted for their most pronounced positive effects on plant growth and metabolism, including accumulation of chlorophylls, mineral nutrition, and activity of nitrogen assimilation enzymes, in oat (Avena sativa L.) plants growing in a soil-less system. We conclude that manure input favored the turnover of OC towards the humification process that led to the production of high-quality coprolites and HS with superior biological activity, and suggests that OC in coprolites and HC in HS from earthworms might be used as reliable indicators of soil fertility.

Bioactivity of Size-Fractionated and Unfractionated Humic Substances From Two Forest Soils and Comparative Effects on N and S Metabolism, Nutrition, and Root Anatomy of Allium sativum L

“…A possible explanation is that nitrate and sulfate ions were more consumed in plantlets receiving LMS because of higher assimilation rates, as suggested by higher activity of N (nitrate reductase and glutamine synthetase) and S (OAS-sulphydrilase) assimilation enzymes, and increased content of certain amino acids (e.g., Ile, Asn, Ser, Cys). So far, many studies have reported the stimulation of N metabolism in plants by either HS or other biostimulants (Schiavon et al, 2008;Santi et al, 2017;Palumbo et al, 2018;Zanin et al, 2018;Schiavon et al, 2019), while scarce literature exists on the effects of HS on the S pathway. Jannin et al (2012) in particular, showed that treating Brassica napus plants with HS positively impacted on C, N and S metabolism, as the expression of several genes implied in primary metabolic pathways and in N and S uptake was substantially upregulated.…”

“…A clear relationship between HS dose and early effects on biochemical attributes of garlic plantlets was also determined in this study within a short-period (48 h) of plantlet treatment with HS. This short period has long been used to evaluate the biostimulant activity of HS and other products on hasty changes in plant metabolism ( Schiavon et al., 2008 ; Schiavon et al., 2010 ; Ertani et al., 2018 ; Schiavon et al., 2019 ). To estimate the dose-response function, several concentrations of unfractionated and size-fractionated HS were tested, and fitting curves were build-up.…”

Chemical Structure and Biological Activity of Humic Substances Define Their Role as Plant Growth Promoters

“…Overall, they are more abundant in the rhizosphere than in the bulk soil, likely because of greater microbial biomass and activity and root exudation activity [ 88 ]. HS also contain aromatic groups of high biological activity, especially phenol-C groups, which account for part of their IAA-like activity [ 89 , 90 ]. Zandonadi et al [ 82 ] postulated that HS and auxins trigger root development by exploiting mechanisms that make use of NO as a messenger, whose accumulation at specific sites of root emergence—i.e., pericycle cells—is critical in the early stages of lateral root development ( Figure 7 ).…”

The preventive impact of vermicompost on bell pepper (Capsicum annuum L.) salinity resistance: An evaluation

“…Therefore, this suggests the interaction between salt stress and VCL towards improving the K+ nutrition. Moreover, its inherent humic substances may interact with membrane transporters, which has been reported previously, as well as with H+-ATPases (Schiavon et al, 2019) and nitrate Additionally, these humic substances may be capable of stimulating the gene expression, specifically those encoding two putative maize nitrate transporters (du Jardin et al, 2020). Therefore, VCL interaction with K+ transporters should not be dismissed, despite NaClinduced salt stress and its effect on such interaction possibly necessitating future investigation.…”