Revista Temes Rurals núm. 1

soil status is of key importance to assess if the agronomic
practices used to manage them are beneficial or not for soil
microbial communities (Sofo et al., 2013). A study conducted
in Ferrandina was aimed at comparing soils from a mature Mediterranean
olive (Olea europaea L.) orchard subjected to two
different soil managements (sustainable and conventional) for
18 years. Sustainable soil management practices aimed at increasing
soil organic carbon (SOC) stocks, affected many soil
parameters (physical characteristics, chemical parameters,
CO 2
flushes), including microbial composition (Sofo et al. under
review). Results coming from data on soil profiles and litter,
C and N dynamics, and the genetic and functional diversity
of soil bacteria, highlighted that the sustainable system caused
an improvement in soil organic matter in the topsoil layers,
compared to the conventional one, with consequent increases
in the abundance of soil N-cycling bacteria.
In this scenario, the selection of indicators closely correlated
with the total carbon (C) and/or total nitrogen (N) soil contents
is of key importance for the quantification of soil quality. Biological
and biochemical parameters are sensitive indicators
for measuring the degree of soil degradation and its resilience
to stress. An indicator is generally a measure that provides
in-time information on the state and development of an environmental
phenomenon. A good soil quality indicator should
be sensitive to changes that occur in the soil and capable of
reflecting the improvement of the quality of degraded soils during
the recovery phase. Also, it should not be too sensitive
to fluctuations related to seasons and the effect of position,
because this could prevent the identification of changes due to
damage or environmental stresses.
We applied microbial indicators of soil quality in olive and peach
orchards managed with sustainable agricultural practices.
Two parameters were followed: a biochemical soil indicator
(Nc/Nk ratio) based on soil N/C turnover and soil enzyme activities
(Trasar-Cepeda et al., 2000), and the abundance of three
important N-cycling genes (nifH, amoA and nosZ). The aim of
this study was to characterize the microbial component responsible
for the biochemical processes of transformation of
the different forms of soil N and their availability for plants
and the expression of genes of N-cycling bacterial communities,
involved in the N-cycle. Results confirmed the need for
Mediterranean orchards to encourage farmers to practice soil
management based on organic matter inputs associated with
zero tillage and the reduction of mineral fertilizers, in order to
improve soil fertility and increase the uptake of nutrients already
available in the soil (Pascazio et al. 2018).
Nitrogen is an important key nutrient element for supporting
plant growth and it is often a limiting factor in the field but, if
mismanaged, it can lead to severe environmental problems.
When nitrogen is converted to nitrate it becomes very mobile
and it leaches through the soil, representing one of the most
important sources of soil and water pollution. Controlling and
reducing nitrate leaching can be a challenge for farmers because
it requires simultaneous management of two essentials
of plant growth: nitrogen and water. Any factor influencing soil
moisture (such as rainfall, irrigation, evaporation and transpiration)
will impact nitrate movement. In general, more water
infiltration results in nitrates moving deeper into the profile.
Soil properties also have a major impact on the extent of nitrate
movement. Farmers cannot change some soil properties
(such as texture), but can profoundly influence others (such
as structure) through the application of agricultural practices.
One key practice for reducing leaching losses is to minimize
the amount of nitrate in the soil. In particular when fruit orchards
are located in a NVZ area (Nitrate Vulnerable Zone) like
the Metapontino area in Basilicata region (Southern Italy), it is
important to monitor soil nitrate content frequently (every 15
days during the irrigation season and once per month the rest
of the time) at several soil depths (0-20 cm; 20-40 cm…), in
order to avoid both soil and water pollution but also deficiency
of nitrogen for plants.
The increase of knowledge in biochemical processes of the
soil microorganism involved in soil N dynamics influencing N
availability for plants can lead to optimizing management strategies
for a modern and multifunctional concept of agriculture,
based on product quality, environmental protection, resource
saving and promotion of human health.
Endophytes
In the last two decades, particular attention has been paid
towards endophytic microorganisms. They have been appreciated
for their capacity to protect their hosts against insects,
pests and pathogens. They could confer other important characteristics
to plants, such as greater resistance to stress conditions,
alteration in physiological properties, and production
of phytohormones and compounds of biotechnological interest.
Endophytes establish a symbiotic relationship with the
plant and colonize an ecological niche like that of phytopathogens
and are possible candidates for biocontrol agents. The
soil microenvironment affects the colonization of bacterial
endophytes and their community composition. The microbial
colonization depends on some key factors, such as plant genotype,
tissue, growth stage and physiological status, and on
soil environmental conditions, as well as on some agricultural
practices. A metagenomic analysis of microbial communities’
composition was conducted, and it compared a sustainable
and a conventional olive grove located in Ferrandina. The metagenomic
approach was used to detect all microorganisms
including those that are extremely difficult to find by culture-dependent
methods in order to estimate microbial diversity
and abundance and to identify taxa among different analyzed
compartments. Results revealed that a long period of sustainable
management increased the richness and diversity of the
microbial community in phyllosphere and xylem sap (Fausto et
al., under review). These findings demonstrated that the application
of sustainable agricultural practices in an olive grove
positively affects the variability and composition of microbial
communities, promoting plant growth and plant protection
with benefits to the whole agroecosystem stability.
Paisatge i ecosistemes
Fruit orchard management: How can we adapt to/face climate change?
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