Agriculture Reference
In-Depth Information
nutritional status at high temporal and spatial resolution represents the first step
towards the setup of site-specific FBMPs. In the last years, several sensor-based
techniques to assess parameters indicative of the nutritional status of soil-plant
systems have been proposed to replace, or support traditionally used physical
measures and chemical analysis. Results on soil properties obtained from electro-
magnetic induction sensors along with those derived from the use of ground
conductivity meters and radiometers analysing canopy reflectance, appear to pro-
vide data which can be used to target N-fertilisation to specific field conditions
(Adamchuck et al. 2011 ). However, soil and plant chemical analyses are still widely
used in developing methods for the evaluation of the nutritional status of the crops.
In particular, the evaluation of elemental concentrations in plant tissues can be
helpful in diagnosing nutrient deficiency. This strategy is currently used to assess
nutrient availability and guide fertility programmes for many fruit tree crops.
Nevertheless, the usefulness of this approach in order to develop FBMPs for
herbaceous crops is rather debatable, since the concentration of a specific element
may change among the leaves of a single plant, and may also change over time
within a single leaf (Barker and Pilbeam 2007 ). Thus, plant sampling, in term of
timing and tissues to choose, is the most critical step (Kalra 1998 ). Moreover,
elemental analysis detects only severe and long-term deficiency since a plant
s
initial response to nutrient limitation is to activate mechanisms aimed at
maintaining the ionic homeostasis of their cells (Schatchtman and Shin 2007 ;
Gojon et al. 2009 ). Finally, conferring a diagnostic value to the concentration of a
single element could be misleading since complex cross-talk connections between
the regulatory mechanisms controlling the ionic homeostasis in plants exist
(Rouached et al. 2010 ).
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Nutrient-Critical Concentration and Dilution Curve
The critical concentration of a nutrient ( n c ) stands for the concentration of the
nutrient in the shoots above which, in the absence of other growth limiting factors,
the plant is sufficiently supplied with the nutrient to achieve its maximum potential
yield. In other words, when the n c is achieved and maintained, further supplies of
the nutrient will not influence the growth of the plants and, in the absence of any
sort of demand-driven negative-regulation of its uptake, it could be uselessly
accumulated in the plant tissues. For some nutrients it is possible to define the
so-called toxicological value , which indicates the concentration above which fur-
ther nutrient accumulation induces damage on cell metabolism and structure. All
the concentrations of the nutrient between its critical and toxicological values
define the so-called luxury range (Fig. 10.1 ), which depends on the chemical
properties of the element and on its biochemical roles . The fine-tuning of the
application of fertiliser to maintain the concentration of the mineral nutrients in
the plant tissues as close as possible to their critical values represents a FBMP
approach.
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