42 Liliana Suñer and Juan Galantini
dynamics and final destination of applied P. In terms of fertility, the higher the
Pe and organic carbon content, the higher the application rate needed to
replenish Pe levels. In terms of crop development, initial Pe availability did not
affect relative dry matter yield, but it did modify relative P-uptake; the initial
availability therefore affected crop quality but not crop growth. Worthy of
notice is how important it is to consider both organic and inorganic P-forms
when assessing soil fertility and recommending a fertilization scheme. A case
in point is the assay carried out on a typic Hapludoll and Haplustoll in the
Pampas semi-arid region in 2008, 2010, 2011 and 2012. Wheat (Triticum
aestivum L.) crops were fertilized with a combination of phosphorus (P) and
nitrogen (N) on an experimental completely randomized design with three
blocks and three replications on each plot, (Suñer, 2015). Phosphorus was
applied at 0, 7, 12, 16 kg P ha-^1 and the N-rate was 0, 25, 50 and 100 kg N ha-^1.
Before the trial, multiple soil properties were measured; after the assay, crop
yield parameters were determined. Figure 5 shows an analysis of the system
through the application of principal components (PC), with all analyzed
variables.
The most significant selected variables in the whole soil-plant system
included P in grain and in dry matter (dm), grain and dm yield, water use
efficiency (wue) and rainfall during the crop cycle (rcc). The most significant
soil P-forms were the available, inorganic and organic forms, and the Po/Po+Pi
ratio (Table 1). On the basis of the information from the biplot and the
correlation table, it can be inferred that one component associated moisture
and crop variables, and the second component associated the related variables
with P-forms (Table 2).
Figure 3. Electron micrograph (SEM) of a fertilized sample after 180 incubation days.