Abstract
The use of reactive rock phosphate (RP) in acidic soils as a phosphate (P) source for pastures and crops presents attractive economic advantages with respect to soluble phosphate. However, some studies have demonstrated that the short-term (1-year) efficiency of RP, compared with that of water-soluble P, is relatively poor. This fact penalizes not only the yield and quality of the earlier harvests, but even the whole final yield when the crop is affected by some abiotic or biotic stress at the beginning of the cycle. In the present study, we investigated the ability of new edaphic biostimulants to increase the short-term efficiency of RP-based fertilizer as a P source for pastures cultivated in acid soils. To this end, we have granulated rock phosphate with two edaphic biostimulants: tryptophan and a heteromolecular organic complex formed by humic acid and tryptophan through iron bridges, and compared their short-term P fertilizer efficacy with that of single superphosphate and rock phosphate. Soil incubation studies showed that the heteromolecular complex humic acid–tryptophan and Tryptophan were able to increase soil CO2 production compared with native soil, rock phosphate, and superphosphate. Likewise, the presence of humic acid–tryptophan complex and Trp significantly increases plant-available phosphate compared with rock phosphate, up to levels similar to those of superphosphate. Plant (ray grass)–soil–pot studies showed that rock phosphate/(humic acid–tryptophan) formulation yielded values for both ray grass dry matter production and shoot P concentration, clearly higher than those of rock phosphate and rock phosphate/tryptophan. In addition, the results associated with rock phosphate/(humic acid–tryptophan) were similar to those for superphosphate, after 3 months of cultivation. Taken together, these results showed the suitability of the use of specific humic acid-based edaphic biostimulants to improve the short-term effect of rock phosphate fertilizers as a phosphate source for pastures cultivated in acid soils.
Highlights
The use of reactive rock phosphate (RP) in acidic soils as a phosphate (P) source for pastures and crops presents attractive economic advantages with respect to soluble phosphate
The aim of our study is to investigate whether the granulation of micronized RP along with (HA–Trp) complex is able to increase the short-term fertilizer action of RP by improving P solubilization rates in the rhizosphere
We have investigated the effect of a granulated fertilizer made from RP and coated with (HA–Trp) (RP/ (HA–Trp)) and corresponding control treatments including RP coated with Trp alone (RP/Trp), RP, and SSP, on the early yield and P leaf concentration (1–3 months) of ray grass (Lolium perenne) cultivated in pots containing an acidic soil
Summary
The use of reactive rock phosphate (RP) in acidic soils as a phosphate (P) source for pastures and crops presents attractive economic advantages with respect to soluble phosphate. Some studies have demon‐ strated that the short-term (1-year) efficiency of RP, compared with that of water-soluble P, is relatively poor. We investigated the ability of new edaphic biostimulants to increase the short-term efficiency of RP-based fertilizer as a P source for pastures cultivated in acid soils. To this end, we have granulated rock phosphate with two edaphic biostimulants: tryptophan and a heteromolecular organic complex formed by humic acid and tryptophan through iron bridges, and compared their short-term P fertilizer efficacy with that of single superphosphate and rock phosphate.
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