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Chitosan effects on soil properties were analysed both under laboratory conditions by incubation with constant humidity and temperature and under field conditions in two persimmon field plots with conventional and ecological management. Chitosan was applied in solution or as coacervates. Application of chitosan reduced soil pH, conductivity (CE), and cation exchange capacity (CEC) in pots when applied at field capacity. Chitosan did not affect field soil respiration, which is greatly dependent of soil moisture and temperature. Metabarcoding showed that chitosan significantly modifies the fungal genera composition of ecologically managed field soil. On the contrary, chitosan caused no significant differences in bacterial taxa composition of soil under field conditions. Chitosan coacervates increased naturally occurring nematophagous fungus Purpureocillium (ca. 50-fold) in soil with respect to chitosan solution-treated soil and untreated controls. In addition, chitosan reduced the inoculum of plant pathogenic fungi Alternaria and Fusarium (20% and 50%, respectively) in field soil. Soil microbial network analysis for ITS2+V1–V2 regions revealed that the nematophagous fungus Pochonia promoted network clustering into modules. Furthermore, network analysis for ITS2+V3–V4 regions showed that the nematode trapping-fungus Orbilia and bacteria belonging to Acidimicrobiales and Cytophagales significantly contributed to network clustering in field soil. Our results show that chitosan coacervates increased soil nematophagous microbiota and that both nematode egg parasites and trapping fungi help to structure soil microbiota.

Rainfed Mediterranean agriculture is characterized by low water input and by soil water content below its field capacity during most of the year. However, erratic rainfall distribution can lead to deep drainage. The understanding of soil-water dynamics is essential to prevent collateral impacts in subsuperficial waters by leached pollutants and to implement suitable soil management (e.g., agronomic measures to avoid nitrate leaching). Soil water dynamics during two fallow years and three barley crop seasons was evaluated using the Leaching estimation and chemistry model in a semiarid Mediterranean agricultural system. Model calibration was carried out using soil moisture data from disturbed soil samples and from capacitance probes installed at three depths. Drainage of water from the plots occurred in the fall and winter periods. The yearly low drainage values obtained (<15 mm) indicate that the estimated annual nitrate leaching is also small, regardless of the nature of the fertilizer applied (slurries or minerals). In fallow periods, there is a water recharge in the soil, which does not occur under barley cropping. However, annual fallow included in a winter cereal rotation, high nitrate residual soil concentrations (~80 mg NO3−-N L−1) and a period with substantial autumn-winter rains (70-90 mm) can enhance nitrate leaching, despite the semiarid climate.

Chitosan reduced soil pH, conductivity (CE) and cation exchange capacity (CEC) in pots when applied at field capacity. However, chitosan did not affect these soil physicochemical properties, when applied monthly to agricultural fields. Chitosan did not affect field respiration. Increases in field soil respiration found in chitosan plots, especially in spring-midsummer, were not significant. Although, no differences in soil mineral nitrogen were found, chitosan influenced field soil microbiota. Metabarcoding showed chitosan significantly modifies fungal genera composition of ecologically managed field soil. On the contrary, chitosan caused no significant differences in bacterial taxa composition of field soil. Chitosan coacervates increase naturally occurring nematophagous fungus Purpureocillium in soil respect to chitosan solution treated soil and untreated controls. Besides chitosan reduces inoculum of plant pathogenic fungi Alternaria and Fusarium in field soil. Soil microbial co-occurrence network analysis clustering coefficient (CC) for ITS+V1-V2 regions show that the nematophagous fungus Pochonia promoted network clustering into modules. In addition, CC in ITS+V3-V4 regions show that the nematode trapping-fungus Orbilia and bacteria belonging to Acidimicrobiales and Cytophagales also significantly contributed to microbial network clustering in field soil. Our results show that chitosan coacervates increase soil nematophagous microbiota and that both nematode egg-parasites and trapping-fungi help to structure soil microbiota.