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Cover crops (CC) have great potential to enhance the sustainability of agroecosystems. However, the wide range of possible rotations of CC and cash crops (CaC) means that important knowledge gaps persist on how CC affects CaC. We investigated the legacy effects of five common CC (three monocultures: vetch, melilotus, and barley, and two mixtures: barley-vetch and barley-melilotus) on two of the most important CaC, maize and wheat. A microcosm, semi-controlled experiment was established simulating warm, low-income Mediterranean conditions. After two cycles, soil physicochemical and microbial properties, as well as plant growth and nutrition variables, were measured at the CC early growth CaC stage. In maize, barley CC had the best soil microbial and nutritional legacy effects, which resulted in the highest biomass and nutrient status. In contrast, barley produced the worst results on wheat, showing the disadvantages of growing two crops from the same tribe consecutively. CC mixtures also did not offer a productive advantage over pure CC. Additionally, our findings suggest that archaea seem to play a role in increasing N and Zn content in maize shoots. Furthermore, shoot B contents showed highly significant regressions with the CaC biomass. These results can help select the appropriate CC in each case.

The use of natural-origin biomaterials in bioengineering has led to innovative approaches in agroforestry. Bacterial cellulose (BC), sharing the same chemical formula as plant-origin cellulose (PC), exhibits significantly different biochemical properties, including a high degree of crystallinity and superior water retention capacity. Previous research showed that natural-origin glucose-based chitin enhanced plant growth in both herbaceous and non-herbaceous plants. In this study, we produced BC in the laboratory and investigated its effects on the substrate and on Solanum lycopersicum seedlings. Soil amended with BC increased root growth compared with untreated seedlings. Additionally, under limited irrigation conditions, BC increased global developmental parameters including fresh and dry weight, as well as total carbon and nitrogen content. Under non-irrigation conditions, BC contributed substantially to plant survival. RNA sequencing (Illumina®) on BC-treated seedlings revealed that BC, despite its bacterial origin, did not stress the plants, confirming its innocuous nature, and it lightly induced genes related to root development and cell division as well as inhibition of stress responses and defense. The presence of BC in the organic substrate increased soil availability of phosphorus (P), iron (Fe), and potassium (K), correlating with enhanced nutrient uptake in plants. Our results demonstrate the potential of BC for improving soil nutrient availability and plant tolerance to low irrigation, making it valuable for agricultural and forestry purposes in the context of global warming.

Legumes provide important benefits in rotations. Interseeding cover crops (CCs) allows an additional legume CC in case of a short window after the main crop. However, legume input level and management could modify the expected benefits. In a Mediterranean irrigated agroecosystem, we evaluated the responses of topsoil (0–10 cm) and early maize development to increasing legume CC input in a biannual maize–wheat rotation under traditional tillage (TT; CC incorporated) and minimum tillage (MT; CC rolled-crimped). In the third year, at two early maize stages, we tested three legume input levels: (i) R0, non-CC; (ii) R1, barley–vetch CC; (iii) R2, vetch interseeded into maize in addition to the CC mixture. Overall, MT enhanced soil properties, but frequently conditioned to legume input level. The tillage system affected R1 the most, with MTR1 showing the better overall soil response while TTR0 showed the poorest. MTR2 was the best combination for early maize development, but not for soil health. Moreover, a better overall soil health did not lead to a better early maize performance in the short term. In this alkaline soil, CC favored early maize growth, whereas mycorrhization, enhanced under TT, favored crop nutrition. Increased legume input under MT should be monitored to avoid negative effects in soil in the mid–long term.

Cover crops (CC) promote soil health, but the termination method can condition the benefits for soil microorganisms. In a greenhouse experiment, we evaluated the legacy effects of four common CC termination methods on mycorrhization, soil microbial abundance, structure, and activity, as well as other soil properties, and its interaction with water levels (well-watered and water deficit). Mowing and residue incorporation (INC), glyphosate (GLY), roller crimper (ROL) and glyphosate + roller crimper (RGL) were evaluated, together with no CC, at two sampling dates of a subsequent maize. The water level modulated the soil microbial response to CC termination methods, especially in the glyphosate methods. Legacy effects on soil microbial attributes were notable and evolved differently from maize, from pre-emergence to ~3 months later. At final sampling, INC showed the best microbial response at both water levels, enhancing most microbial attributes. ROL was the second most beneficial method, especially in well-watered soil, promoting fungi but nullifying the CC positive effect on bacteria. Regardless of water level, GLY and RGL showed a similar microbial response. In well-watered soil, GLY and RGL had a negative effect on the total fungi, which separated the RGL response from the ROL. Overall, the time since CC termination and water level modulated the soil microbial response to the termination methods. Further research is needed to investigate CC termination impacts under different environmental conditions, in order to better understand the processes involved and provide farm-level recommendations.

BACKGROUND AND AIMS: The high metal bioavailability and the poor conditions of mine soils yield a low plant biomass, limiting the application of phytoremediation techniques. A greenhouse experiment was performed to evaluate the effects of organic amendments on metal stabilization and the potential of Brassica juncea L. for phytostabilization in mine soils. METHODS: Plants were grown in pots filled with soils collected from two mine sites located in Central Spain mixed with 0, 30 and 60 t ha⁻¹ of pine bark compost and horse- and sheep-manure compost. Plant biomass and metal concentrations in roots and shoots were measured. Metal bioavailability was assessed using a rhizosphere-based method (rhizo), which consists of a mixture of low-molecular-weight organic acids to simulate root exudates. RESULTS: Manure reduced metal concentrations in shoots (10–50 % reduction of Cu and 40–80 % of Zn in comparison with non-amended soils), bioconcentration factor (10–50 % of Cu and 40–80 % of Zn) and metal bioavailability in soil (40–50 % of Cu and 10–30 % of Zn) due to the high pH and the contribution of organic matter. Manure improved soil fertility and was also able to increase plant biomass (5–20 times in shoots and 3–30 times in roots), which resulted in a greater amount of metals removed from soil and accumulated in roots (increase of 2–7 times of Cu and Zn). Plants grown in pine bark treatments and in non-amended soils showed a limited biomass and high metal concentrations in shoots. CONCLUSIONS: The addition of manure could be effective for the stabilization of metals and for enhancing the phytostabilization ability of B. juncea in mine soils. In this study, this species resulted to be a potential candidate for phytostabilization in combination with manure, differing from previous results, in which B. juncea had been recognized as a phytoextraction plant.

Forests and agroforestry systems in the tropics play a decisive role in global carbon fixation strategies. The amount and type of coverage, along with the specific land use and land use change in a given area, determines whether carbon is stored or released into the atmosphere. The aim of this study was to evaluate the traditional silvopastoral systems (TSPS) through quantitative analysis of biomass and soil carbon storage whilst simultaneously qualitatively determining the ecological structure in terms of tree richness and diversity. The study was carried out in Matiguás, a sub-humid tropical region of Nicaragua, on five land use types: shrubland; intervened secondary forest; pasture with high tree density; pasture with low tree density and degraded pasture. Biomass carbon was estimated by allometric equations and soil organic carbon was evaluated at four depths (0–10, 10–20, 20–40 and 40–100 cm). Of the land uses studied, shrubland had the highest diversity. The biomass carbon ranged from 1.9 to 13.2 t C ha−1 for degraded pasture and intervened secondary forest, respectively. The highest soil organic carbon (SOC) storage at 1 m depth was for intervened secondary forest (163 t C ha−1), whereas degraded pastures had the lowest value (76 t C ha−1). Since SOC was the largest pool of total carbon in all cases, it should be evaluated down to a depth of at least 1 m. Increasing tree coverage in degraded and low-tree density pastures can contribute not only to enhance carbon sequestration but also to restore degraded lands in livestock landscapes.

Phytoremediation of contaminated mine soils requires the use of fast-growing, deep-rooted, high-biomass, and metal-tolerant plants with the application of soil amendments that promote metal uptake by plants. A pot experiment was performed to evaluate the combined use of vetiver grass ( Chrysopogon zizanioides ) and humic acid for phytoremediation of Cu and Zn in mine soils. Vetiver plants were grown in soil samples collected from two mine sites of Spain mixed with a commercial humic acid derived from leonardite at doses of 0, 2, 10, and 20 g kg −1 . Plant metal concentrations and biomass were measured and metal bioavailability in soils was determined by a low molecular weight organic acid extraction. Results showed that humic acid addition decreased organic acid-extractable metals in soil. Although this extraction method is used to estimate bioavailability of metals, it was not a good estimator under these conditions due to competition with the strong chelators in the added humic acid. High doses of humic acid also promoted root growth and increased Cu concentrations in plants due to formation of soluble metal-organic complexes, which enhanced removal of this metal from soil and its accumulation in roots. Although humic acid was not able to improve Zn uptake, it managed to reduce translocation of Zn and Cu to aerial parts of plants. Vetiver resulted unsuitable for phytoextraction, but our study showed that the combined use of this species with humic acid at 10–20 g kg −1 could be an effective strategy for phytostabilization of mine soils.

We studied the effects of commercial humic substances derived from leonardite at different rates (0, 0.25, 2, 10 g kg−1) and pH (4.5, 6.0, 8.0) on Cu and Zn mobility, to evaluate their use for remediation of metal contaminated mine soils and to optimize their application conditions. We conducted a single-step extraction experiment and analyzed extracts for metal concentrations, soluble organic carbon and their E4/E6 ratio (ratio of absorption at 465 to 665 nm). Metal speciation in a soil solution was simulated by the non-ideal competitive adsorption-Donnan (NICA-Donnan) model. Increasing the amount of humic substances and the pH caused higher release rates of soluble organic carbon with a lower humic/fulvic acids ratio. This led to a higher mobility of metals (up to 110 times Cu concentration in control and 12 times for Zn) due to the formation of soluble metal-humic complexes. Speciation modeling predicted that increasing rates of humic substances would result in a higher proportion of Cu and Zn associated with fulvic acids, more mobile than the humic acids fraction. Application of commercial leonardite humic substances at 2–10 g kg−1 and with pH levels similar to or below natural soil could be useful for assisted-phytoextraction of contaminated anthropogenic soils. High rates of humic substances in more alkaline conditions could entail a considerable risk of metal leaching to groundwater, toxicity and transfer to the trophic chain.

Composting of pruning waste, leaves and grass clippings was monitored by different parameters. A windrow composting pile, having the dimensions 2.5 m (height) x 30 m (length) was establish. The maturation of pruning waste compost was accompanied by a decline in NH₄ ⁺-N concentration, water soluble C (WSC) and an increase in NO₃ –-N content. Both organic matter (OM) content and total N (TN) losses during composting followed a first-order kinetic equation. These results were in agreement with the microbiological activity measured either by the CO₂ respiration or dehydrogenase (DH-ase) activity during the process. Statistically significant correlations were found between DH-ase activity, easily biodegradable organic C forms, NH₄ ⁺-N and NO₃ –-N concentrations and organic matter content and N losses. For this reason, DH-ase activity and the CO₂ evolution could be used as good indicators of pruning waste compost maturity. In contrast, humification parameters data from the organic matter fractionation did not agree with the initially expected values and did not contribute to the assessment of compost maturity. Neither the cation exchange capacity nor the germination index showed a clear tendency during the composting time, suggesting that these parameters are not suitable for evaluating the dynamics of the process.