The stagnating maize
yields in Nigeria savannas have consistently been linked to the low nutrient
availability and poor soil fertility as a result of nutrient mining and the
existence of blanket fertilizer recommendation. Nutrient mining and depletion
as a result of continuous cropping pose a serious threat to food security. This
calls for the need to develop more profitable fertilizer recommendation that
target crop needs and primary nutrient deficiencies (Vanlauwe et al., 2015).
Similarly, the presence of soil fertility gradients on the smallholder farms
have been documented to significantly affect crop response to nutrients such
that two categories of soils were delineated as responsive and non-responsive
soils. Responsive soils are soils that respond well to the standard application
of nutrient while poorly responsive soils show negligible responses due to
other constraints besides those contained in the standard fertilizer
(Rusinamhodzi et al., 2013). The
occurrence of poorly responsive soils generally reduces crop yields and also
leads to low economic returns from fertilizer use (Vanlauwe et al., 2015). According to Osman,
(2014) nutrient imbalances are the result of chemical soil degradation
processes which can be reversed if timely diagnose. They can be expressed as deficient and/or

Plant nutrient deficiency
and imbalance are more directly diagnose using foliar analysis as opposed to
soil analysis (Wairegi and Asten, 2011; Hallmark and Beverly, 1991). Perhaps,
the concentration of a particular nutrient in indicative plant part e.g leaf,  Foliar analysis have shown to be a powerful tool
that can be used to measure crop response to nutrient and as a diagnostic
technique in assessing nutrient status of crops and possibly be used to develop
fertilizer recommendation based on target nutrient deficiency. Maize ear leaf
among several organs is one of greater metabolic activity and it best response
the crop’s response to the nutrient application (Parent 2011, Urano et al., 2006).

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The critical nutrient
concentrations in the leaf have frequently been used to diagnose nutritional
causes of the crop underperformance (Munson and Nelson 1990). These criteria
have been evaluated for a wide range of crops including maize (Gott et al., 2017; Singh et al., 2012; Khiari et al.,
2001; Sumner., 1997; Elwali et al.,
1985, Soltanpour et al., 1995), rice
(Singh and Agrawal; 2007), Sorghum (Dagbenonbakin et al., 2013); Cowpea (García-Hernández et al.,
Sweet potato (Ramakrishna et al.,
2009; O’Sullivan et al. 1997), Banana
(Wairegi and Asten., 2011; Memon et al.,
2005) cotton (Serra et al., 2010a,b).

Several approaches can be
used to diagnose foliar nutrient status, i.e., critical value approach (CVA,
Bates, 1971), diagnosis and recommendation integrated system (DRIS, Walworth
and Sumner, 1987), and compositional nutrient diagnosis (CND, Parent and Dafir,
1992; Parent et al., 1994).
Generally, diagnostic approaches are grouped in to three; univariate, bivariate
and multivariate approach.