**2. Concept of phosphorus use efficiency (PUE)**

The variations in defining nutrient efficient plants and methods used in calculating nutrient use efficiency make it difficult to compare results of different studies [10–13]. Understanding the terminology and the context in which it is used is critical to prevent misinterpretation and misunderstanding and determination of NUE in crop plants is an important approach to evaluate the fate of applied chemical fertilizers and their role in improving crop yields. In order to develop a common framework for NUE, scientists

*Toward the Recent Advances in Nutrient Use Efficiency (NUE): Strategies to Improve… DOI: http://dx.doi.org/10.5772/intechopen.102595*

started to formulate concepts and definitions that should serve as a basis for comparison and discussion of research. Nutrient use efficiency in its broadest sense indicates how effectively a plant is able to capture and utilize nutrients to produce biomass. It is simply a measure of how well plants use the available mineral nutrients [10]. The earlier definition of NUE by [14] is simply increment of yield per applied nutrient (Eq. (1)).

$$NUE = \frac{\text{Total productivity} \left(\text{g cm}^{-2} \text{ year}^{-1}\right)}{\text{Rate of resource uptake or acquisition by plant } \left(\text{g N m}^{-2} \text{ year}^{-1}\right)} \tag{1}$$

While the most recent and complicated one used in crop modeling formula is (Eq. (2)) [12].

$$NUE = \frac{(R\_{ac} - R\_{\min}) \* NPP\_{\max}}{(R\_{ac} - R\_{\min} + a) \* N\_{ac}} \tag{2}$$

where *R*min is the estimated minimum resource requirement for positive growth, *Nac* is the amount of nutrient uptake by plant, *NPP*max is the production asymptote, and ∝ is the half-saturation constant with respect to resource.

Generally, nutrient use efficiency comprises both yield as a function of inputs and percentage of nutrient recovered respectively, contributing to yield and quality [15]. The NUE is based on (a) uptake efficiency (acquire from soil, influx rate into roots, influx kinetics, radial transport in roots are based on root parameters per weight or length, and uptake is also related to the amounts of the particular nutrient applied or present in soil), (b) incorporation efficiency (transports to shoot and leaves are based on shoot parameters), and (c) utilization efficiency (based on remobilization, whole plant, i.e., root and shoot parameters) [4].

Phosphorus use efficiency can be divided into (i) P acquisition efficiency [the capacity of a cultivar to extract P from soil] and (ii) P internal utilization efficiency [the capacity of a cultivar to transform the acquired P into biomass/grain yield] [16–18].

#### i. Phosphorus uptake or acquisition efficiency (PACE)

Uptake efficiency or the ability of the plant to extract the nutrient from the soil is calculated as [19] (Eq. (3)).

$$\text{P-update efficiency} (\text{PACE}) = \frac{\text{Total above} - \text{ground nutrient} (\text{P}) \text{ in the plant at maturity} (\text{Nt})}{\text{Nt} \text{return} (\text{P}) \text{ supplied} (\text{Ns})} \tag{3}$$

ii. Phosphorus utilization efficiency (PUTE)

Phosphorus utilization efficiency is defined as a crop's ability to convert the absorbed P into grain yield [19] (Eq. (4)) can be calculated as:

$$\text{P-utilization efficiency} (\text{PUTE}) = \frac{\text{Total above} - \text{ground plant dry weight at maturity} (\text{Tw})}{\text{Total above} \text{ground plant mutant at maturity} (\text{Nt})} \tag{4}$$

Utilization efficiency can also be calculates as suggested by [20], (Eqs. (5) and (6)) and expressed as follows:

Utilization efficiency ¼ Harvest index � Nutrient biomass production efficiency (5)

Utilization efficiency ¼ Harvest index � Inverse of total nutrient concentration in the plant*:* (6)

Generally, if P supply is limited or in more acidic and calcareous soil, P acquisition could be more important than P utilization and high fertilizer application necessary in order to provide sufficient plant-available P. On the other hand, with adequate P supply, PUTE could be considered more important than PACE for crop P efficiency [17]. Therefore, the improvement of both PACE and PUTE in the given species under different P supply conditions in the different soil types seems to be the perfect breeding approach (**Figure 1**) [17].

Hence, Nutrient use efficiency = Uptake efficiency � Utilization efficiency. All unit dry weights are in g m�<sup>2</sup> [19].

For nitrogen use efficiency in their various definitions and components (**Figure 2**) [21].

Apparent recovery efficiency is one of the more complex forms of nutrient use efficiency (NUE) expressions and is most commonly defined as the difference in nutrient uptake in above-ground parts of the plant between the fertilized and unfertilized crop relative to the quantity of nutrient applied. It is often the preferred NUE expression by scientists studying the nutrient response of the crop [22]. Reference [23] proposed that the balance method be used to assess fertilizer P efficiency (Eq. (7)). The balance method is described mathematically as:

$$\text{P-use efficiency} (\%) = \frac{\text{P taken up by crop (fortilized soil)}}{\text{Amount of P applied}} \times 100\tag{7}$$

#### **Figure 1**.

*Schematic representation of the possible mechanisms of P acquisition and utilization for better growth of modern crops grown in intensive cropping systems (adopted from [17]).*

*Toward the Recent Advances in Nutrient Use Efficiency (NUE): Strategies to Improve… DOI: http://dx.doi.org/10.5772/intechopen.102595*

#### **Figure 2.**

*Illustration of nutrient use efficiency parameters exemplified by NUE in wheat. Key process contributing to the NUE trait: nitrogen uptake efficiency, NUpE; nitrogen utilization efficiency, NUtE; nitrogen harvest index, NHI (adopted form [15]).*
