The network of interactions among soil quality variables and nematodes: short-term responses to disturbances induced by chemical and organic disinfection

Anthropogenic pressures that involve different kinds of inflows (chemical vs organic) to soils are likely to induce different responses of individual soil components as well as to affect the web of interactions between them. The aim of this paper was to explore whether chemical or organic disinfection constitute two different types of disturbance, regarding both their severity on individual soil components and the structural changes they induce on the network of interactions among soil biochemical variables and nematode functional guilds. Network analysis, a novel approach in the context of soil ecology, was used to explore these interactions.Different plots within a field cultivated conventionally with Phaseolus vulgaris for many years were disinfected either with metham sodium or with a mixture of plant-based alternatives (neem and essential oils). Control plots receiving no disinfectants were also included in our study. One month after the treatments were applied, we estimated microbial C and N, activities of asparaginase, glutaminase, urease and phosphatase, organic C and N, inorganic N and P as well as the functional diversity of nematodes.Chemical disinfection had a direct lethal effect on all nematodes, while the effect on the microbial community was less obvious, implying that at the time of sampling, microbial populations, especially bacterial ones had started to recover from disturbance. Urease and phosphatase activities were inhibited, which may partly be responsible for the reduced amounts of inorganic N and P. Organic disinfectants reduced microbial populations, mainly the fungal ones, but they did not inhibit enzyme activities. The availability of N and P increased and nematode abundance was not affected significantly.The results demonstrate the usefulness of network analysis in providing insight into the structure and robustness of the soil network and its response to disturbance. Despite the pronounced reduction in nematode numbers due to chemical disinfection, the importance of nematode guilds within the interaction network was amplified and a more compact network was formed. On the other hand, interactions within organic plots were found to be primarily dictated by soil biochemistry. Finally, the analysis showed that both types of disinfection increased the vulnerability of the interaction network and this was more pronounced in chemically treated plots.     

The response of properties of soil cropped with shell beans and treated with disinfectant and fertiliser during the plant growing season

Disinfectants and fertilisers exert strong impact on soil processes by affecting the structure and the activity of the soil microbial community. Most relevant studies examined these impacts independently, under laboratory conditions and without crop cover. In this study, we have monitored the response of soil chemical, microbial, and biochemical properties to disinfectant and fertiliser treatments in field plots cultivated with beans. The measured properties comprised microbial C and N, asparaginase, gultaminase, urease, and acid phosphomonoesterase activities and contents of organic N, organic C, inorganic N, and inorganic P. We ran four different treatments using different combinations of chemical (metham sodium) and biological disinfectant (a mixture of neem cake and essential oils) and fertilisers (NPK 8-16-24 and cow manure) in plots cultivated with shell beans, while the control soil was neither treated nor cropped with beans. The data were expressed as percentage (%RC) in relation to the control values. The disinfectant and fertiliser treatments had less impact on soil properties compared to bean crop growth (except for microbial C and N, and content of organic C). In comparison to the control, higher activities of urease and asparaginase and content of inorganic N were recorded in bean cropped plots at the stage of seedlings (June), while higher activities of acid phosphomonoesterase and glutaminase and content of organic N were recorded at the stage of plant flowering (August). In October, the values of all properties were higher in the control plots compared to the treated plots. The joint effect of disinfectants x fertilisers affected the response of content of organic C and N and extractable P and glutaminase activity. The %RC of the properties exhibited more negative values in plots treated with chemical disinfectant and chemical fertiliser than in the other treatments. We suggested that the response of soil properties to disinfectants and fertilisers were influenced by the growth of P. vulgaris.     

Predictability of soil succession patterns under different agricultural land use practices: Continual conventional cultivation versus transformation to organic cultivation or fallow periods

Changes in agricultural management practices create conditions that directly or indirectly promote the onset of secondary succession processes in the soil. Previous research has demonstrated that the succession of temperate forests follows the Markov principle, which states that the next state of a process depends only on the preceding state; hence, we set out to test this principle for soils subjected to different land uses over a 2 year period. Specifically, (1) continued conventional cultivation (i.e. the monoculture of shell beans, Phaseolus vulgaris L., with chemical fertilisers); (2) transformation of land-use from conventional cultivation to organic cultivation (shell beans fertilised with manure); and (3) transformation of land-use to a fallow state. The soil was sampled three times at specific shell bean growth stages (June, the seedling stage; August, mid-growth; October, one month after harvest) in both years, with various chemical and biochemical soil profiles being conducted (including carbon, nitrogen and phosphorus levels, and enzymatic activity). Correlations among successive soil chemical and biochemical profiles were stronger (two successive events: June and August, August and October) in the first year compared to the second year (one successive event: August and October) for the organic plots. For soils in which conventional land management was continued, significant correlation was only detected for one successive profile (August–October) in both years, whereas no significant correlation was obtained for any successive profiles in the fallow plots. Therefore, the Markov principle only holds for the entire cultivation period under certain conditions for bean crops; specifically, initial conventional cultivation followed by transformation to organic cultivation. In the case of continued conventional monoculture, the Markov principle is partially supported. In contrast, fallow plots did not follow any predictable pattern of changes in soil chemical and biochemical profiles. In conclusion, agricultural management causes soil succession processes to be predictable, due to the environmental homogeneity induced by manure and/or the limited plant effect, rather than natural processes.