Functional and mechanistic assessment of plant-available soil phosphorus greatly improved the multisite diagnosis of maize yield response

Context or problem

Plant-available soil phosphorus (P) is commonly assessed by chemical extractions with the purpose of diagnosing and advising fertilizer P application. However, for a given crop, this approach only poorly predicts yields obtained from several experimental sites. To solve this major drawback, a functional and mechanistic evaluation has been developed to mimic dominant processes involved in the absorption of phosphate ions.

Objective or research question

In this study, we investigated the predictive ability of a mechanistic approach to diagnose maize (Zea mays L.) yields, in comparison to the common Olsen's method (0.5 M bicarbonate solution).

Methods

The processes-based assessment consists of parameterizing relationships between amount of diffusible phosphate ions (P_r) at the solid-to-solution interface equilibrating the phosphate ions concentration in solution (C_P) with time (t). We parameterized [P_r vs. (C_P, t)] relationships for stored and archived soil samples (plough layer) of nine long-term field experiments (LTFEs) on increasing rates of P applications including the zero-P treatment (P0). LTFEs were located in different soils (Luvisol, Podzol, Arenosol, Calcosol) with large variations in physico-chemical properties. We also used LTFEs database of maize yields.

Results

The C_P values ranged from 0.02 to 3.86 mg P L⁻¹ for 40 (LTFE×year of maize cropping) combinations. The (P_r=v×C_P^w×t^p) equation closely described the [P_r vs. (C_P, t)] datasets, with (v, w, p) parameters being soil specific. Maximum yields ranged from 5.5 to 14.7 t DM ha⁻¹ depending on LTFEs and years. Yields decreased significantly only in P0, and did not differ for other P rates. The relationship between the relative maize yield and C_P was sites-specific with C_P thresholds to obtain a relative yield of 0.95 ranged from 0.07 to 0.88 mg P L⁻¹ solution. Taking into account amounts of phosphate ions which balance C_P by diffusion using (P_r=v×C_P^w×t^p) equations, a single response curve is observed for the 9 LTFEs when the replenishment time is 1500 minutes (i.e. about one day). The critical C_P thresholds closely correlated to the ability of the soil solid phase to buffer phosphate ions in solution.

Conclusions

For the 9 studied LTFEs on P fertilization, the [P_r vs. (C_P, t)] relationships were more able to account for maize response curves than P extracted by Olsen method, improving the precision and reliability of the multisite diagnosis of maize yield response.

Implications or significance

As a result, P fertilization recommendations are more reliable regardless of soil type. Further progress could be gained by taking into account for the role of the soil layer beneath the plough layer.