**6. Importance of assessing phosphorus use efficiency**

Using phosphorus efficiently means that the phosphorus taken up by plant per unit produces yield or biomass [78] and is distinguished when relevant by using subscripts, PUEt and PUEy, respectively. Phosphorus use efficiency may improve through strong agronomic practices, like the calculated amount of fertilizers, suitable timing, right place, and right crops. Mostly, the biomass for any plant is taken from the above-ground parts. There are so many limitations to reserves rock phosphate globally, and awareness is increasing. These reserves are used to increase or maintain the present agricultural productivity and produce crops [5]. Around 57% of the annual grain crops like pulses, cereals, and oil seeds cover the dietary energy for the present world's rapid growing population [79].

The primary goal of testing soils for P is to identify the supplementary P needed to prevent crop losses due to P-deficiency. Plant-available phosphorus in soil can be estimated using a soil test that offers an index of plant-available P. Second, soil testing for P is used to track the amount of accessible P in the soil. For evaluating fertilization procedures and the selection of waste disposal options, the data can be valuable.

A wide variety of chemical forms of P can be found in soil. All of these factors influence the plant-available pool to variable degrees. The amount of plant-available P in a given soil is not a fixed figure. According to a variety of soil and plant root properties and the environment, this can vary. A soil's plant-available P-content can be challenging to forecast. However, some effective P extraction methods have been established, which correlate well with P-uptake in controlled conditions. Routine soil fertility tests typically refer to a relatively rapid nutrient extraction, which results in an accessible soil nutrient value connected with crop response to fertilization. It is usual to practice to employ Mehlich-1 (M1) and Mehlich-3 (M3) for fertilizer P and K rate recommendations. There may be some variations in fertilizer rate recommendations even if the numerical soil test findings are the same, even if soil testing laboratories utilize equivalent extraction and quality control techniques and comparable instruments [80–82].

Soil testing relies heavily on developing standardized techniques (extract and analytical methodologies), test interpretation, and nutrient recommendations, all of which are based on field calibration and validation.

The following documents contain extensive information on soil testing, soil test extractant, and the correlation and calibration processes, as well as fertilizer recommendation regulations:


Test results for specific soil features and P-availability are affected by some different soil parameters.

#### *Sustainable Management of Phosphorus in Agriculture for Environmental Conservation DOI: http://dx.doi.org/10.5772/intechopen.113086*

There is a perception that carbonates in soils pose a barrier to robust acid extraction procedures like Bray and Kurtz or Mehlich I. The Bray PI test for calcareous soils is lower than the NaHCO3 test [83]. CaCO3 neutralizes the acid, releasing Ca, which precipitates the fluoride. This reduction has largely been attributed to this process. Thus, the ability of the extractant to remove P is diminished. However, the Bray PI and NaHCO3 tests have been performed equally on calcareous soils in Colorado and Nebraska in other correlation investigations [84]. As a result, factors other than the total CaCO3 level may be involved in deciding whether the acid tests are unsuccessful. The use of acid tests on calcareous soils is generally avoided because of these additional unknown issues. Soil-to-solution ratios of 1:100 or 1:100 have enhanced correlations on neutral and calcareous soils and appear to alleviate the problem of soil toxicity [85–87].

The pH of noncalcareous soils has been identified as another factor influencing soil test performance, although not consistently. A field study in British Columbia showed that correlations were higher for alkaline soils than acid soils for both Bray PI and NaHCO3 tests [88]. A South Dakota study showed that correlations were lowest in the pH range of 6.6–7.0 for both tests [86]. An Ohio study demonstrated only slight reductions in correlations when the pH exceeded 5.5 for Bray PI and NaHCO3 tests [89].
