The research, led by Juan Nieto-Cantero of the University of Seville together with colleagues at the Institute of Agricultural and Fisheries Research and Training in Seville and the University of Palermo, set out to answer a question that has received surprisingly little attention. While cover crops are well established as nitrogen suppliers, particularly when legumes fix atmospheric nitrogen into the soil, their influence on phosphorus cycling and on the fate of phosphorus fertilizer applied to the following cash crop has remained poorly understood. The team designed a pot experiment under controlled growing-chamber conditions to isolate the effects of cover crop species, soil chemistry, and phosphorus fertilization on durum wheat, one of the Mediterranean region’s staple cereals.

The experimental design was deliberately rigorous. The researchers selected two soils that were otherwise similar in texture and pH but differed sharply in the properties that govern phosphorus dynamics: one rich in carbonates, where phosphorus tends to precipitate as calcium phosphates, and one rich in iron oxides, where adsorption onto oxide surfaces dominates. Both soils had Olsen phosphorus values below the established threshold for a fertilizer response, ensuring genuinely phosphorus-limiting conditions. Onto these soils they grew five cover crop treatments: oat (Avena sativa), the common vetch Vicia sativa, the rustic Mediterranean legume Vicia narbonensis, and two mixtures of oat with each vetch, alongside a bare-soil control. After two months of growth, the cover crop residues were chopped and incorporated into the soil, and durum wheat was then grown to maturity, both with and without a dose of 50 milligrams of phosphorus per kilogram of soil applied as potassium phosphate.

The first striking finding concerned what happened to soil phosphorus during the cover crop phase. As the cover crops grew, they drew down the labile phosphorus pool, and Olsen phosphorus measurements declined significantly by the time the crops were terminated. This might seem like bad news for the following wheat, and it echoes recent reports that cover crop cultivation can deplete readily available phosphorus. Yet the picture changed after the residues were incorporated and incubated in the soil for a month. Olsen phosphorus partially recovered, driven by rapid turnover of phosphorus from decaying plant material and by a surge in microbial activity fed by the fresh organic carbon. In other words, the phosphorus the cover crops had locked up was not lost; it was cycling back into the system through decomposition.

The researchers went further, calculating an operational index they call P cycling potential, defined as the difference between the phosphorus taken up by the cover crop and the estimated decline in plant-available soil phosphorus. When this value is positive, it means the cover crop has accessed phosphorus from pools that do not normally contribute to the plant-available reservoir, effectively replenishing it from less labile sources. Three treatments showed this behavior: Vicia narbonensis grown alone, and the two mixtures containing it. Vicia narbonensis achieved the highest value, averaging 3.4 milligrams of phosphorus per pot across both soils, while Vicia sativa alone showed no net cycling benefit. The mechanism, the authors argue, lies in the phosphorus-mobilizing toolkit of legumes: exudation of organic acids such as citric acid that dissolve calcium phosphates or desorb phosphorus from mineral surfaces, and phosphatase enzymes that cleave organic phosphorus into plant-usable forms. Legumes need abundant phosphorus to sustain their nitrogen-fixing symbiosis, which partly explains their aggressive mobilization strategies.

Enzyme assays and microbial measurements added a crucial layer of mechanistic detail. One month after residue incorporation, acid and alkaline phosphatase activities were significantly elevated in soils that had carried cover crops. Treatments containing Vicia sativa showed the highest acid phosphatase activity, a 55 percent increase over the bare-soil control, and also the highest alkaline phosphatase activity, with gains of 66 percent in the carbonate-rich soil and 40 percent in the iron-oxide soil. Vicia sativa also produced the largest microbial biomass carbon, while treatments dominated by oat produced the smallest, likely because oat’s high carbon-to-nitrogen ratio slows decomposition. Interestingly, microbial biomass phosphorus did not track microbial biomass carbon, and the authors suggest that microbial immobilization of phosphorus, rather than depletion, explains why the treatment with the greatest microbial biomass also left the lowest Olsen phosphorus after incorporation: the phosphorus was temporarily held in microbial cells, a reservoir that mineralizes over time and feeds the following crop.

The most consequential result emerged when phosphorus fertilizer entered the picture. The apparent phosphorus recovery, an estimate of the fraction of applied fertilizer actually taken up by the wheat, was consistently and substantially higher after cover crops. In the carbonate-rich soil, recovery averaged 2.2 times the bare-soil control, with Vicia sativa delivering the highest value at 10.5 percent. In the iron-oxide soil the effect was even more dramatic: oat alone lifted apparent recovery to 11 percent, compared with a mere 1 percent in the control, an average sixfold improvement across cover crop treatments. The species-specific pattern is telling. In the carbonate soil, the best performers were the cover crops with the highest microbial biomass, pointing to microbially driven processes such as organic acid exudation that slow calcium phosphate precipitation. In the iron-oxide soil, oat excelled, plausibly because cereals exude phytosiderophores to acquire iron, compounds that indirectly liberate phosphorus held on oxide surfaces. The practical message is clear: the optimal cover crop for phosphorus efficiency depends on the soil’s dominant phosphorus-retention chemistry.

Equally important was what did not happen. Despite the temporary dip in Olsen phosphorus after cover crop termination, unfertilized wheat following cover crops showed no significant reduction in phosphorus uptake compared with wheat on bare soil. The feared short-term penalty of cover cropping in phosphorus-poor systems did not materialize, a finding the authors attribute to the steady release of phosphorus from decaying residues and microbial biomass, supported by elevated phosphatase activity throughout the wheat growth phase. Bicarbonate-extractable organic phosphorus, considered a readily mineralizable pool, did not decline during wheat cultivation, confirming that the organic phosphorus supplied by residues acts as a buffer that sustains availability. With fertilizer applied, phosphorus uptake by wheat increased by an average of 30 percent after cover crops, with oat alone driving a 45 percent increase over the control.

The study also surfaced nuances that complicate a simple success story. Physiological phosphorus use efficiency, the grain produced per unit of phosphorus taken up, worsened by about 17 percent on average when fertilizer followed cover crops, and the harvest index and phosphorus harvest index both declined under some treatments, particularly in the carbonate soil and with the cover crops that had built the largest microbial biomass. The authors suggest this reflects a stimulation of vegetative growth over grain production, possibly mediated by rhizosphere microorganisms energized by the influx of organic carbon. In agronomic terms, cover crops may shift how the wheat partitions its phosphorus even as they improve how much fertilizer phosphorus it captures, a trade-off that field trials will need to weigh against yield outcomes.

The implications extend well beyond the pot experiment. As rock phosphate reserves dwindle and agriculture confronts the twin demands of food security and reduced nutrient losses, strategies that squeeze more crop uptake from every kilogram of applied phosphorus become essential. This study demonstrates that cover crops can enhance soil phosphorus cycling without penalizing the subsequent cash crop, and can multiply fertilizer recovery two- to sixfold depending on soil type and species choice. The authors emphasize that their results must be validated under real field conditions, and they highlight a further frontier: interactions between cover crops and bio-based fertilizers derived from recycled phosphorus, which are expected to play a growing role as conventional supplies tighten. If those trials confirm the controlled-environment findings, the humble practice of sowing vetches and oats between cash crops could become a cornerstone of sustainable phosphorus management, tailored deliberately to the chemistry of the soil beneath the farmer’s boots.

Subject of Research: Effect of cover crop species and soil properties on phosphorus cycling and fertilizer-use efficiency in a subsequent durum wheat crop

Article Title: Cover crop cultivation and incorporation improve phosphorus fertilizer-use efficiency by subsequent wheat crop

Article References: Nieto-Cantero, J., Perea, F., Laudicina, V. A., & Delgado, A. (2026). Cover crop cultivation and incorporation improve phosphorus fertilizer-use efficiency by subsequent wheat crop. Plant and Soil. https://doi.org/10.1007/s11104-026-08955-0

Image Credits: AI Generated

DOI: 10.1007/s11104-026-08955-0

Keywords: cover crops, phosphorus use efficiency, durum wheat, soil phosphorus cycling, legumes, oat, phosphatase activity, microbial biomass, calcareous soil, iron oxides, apparent phosphorus recovery, sustainable agriculture