Response of lentil (Lens culinaris) to graded phosphorus application under varying soil phosphorus availability

Introduction

Phosphorus is the most yield-limiting nutrient for lentil after nitrogen, yet P management recommendations for this crop are often borrowed from soybean or common bean, ignoring lentil's comparatively shallow and fibrous root system that explores less soil volume [1,2] . In European cropping systems, lentil is experiencing a revival as a rotational crop, but P response data under temperate European conditions are surprisingly thin [3] . Lentil's responsiveness to P depends heavily on background soil P availability. On low-P soils, large yield gains are expected, while on well-fertilized soils, additional P may offer no economic return and could contribute to environmental P loading [4,5] . This research established sitespecific P response curves for lentil across three soil P categories to develop more precise fertilizer recommendations for European production.

Research area description

The trials were established at the University of Bonn's Klein-Altendorf Research Station (50.62°N, 6.99°E, elevation 160 m) on three adjacent fields with contrasting P histories. Low-P field: Olsen P 6.8 mg/kg; medium-P field: 14.7 mg/kg; high-P field: 27.3 mg/kg. All fields shared a silt loam Luvisol with pH 6.4-6.8 and organic carbon 1.2-1.5 percent. Mean annual rainfall is 625 mm with a growing season from March to August.

Experimental design

A split-plot design was used with soil P category as the main plot and P₂O₅ rate (0, 20, 40, 60, 80 kg/ha as triple superphosphate) as the subplot, with four replications per field. Subplot size was 6 × 2 m. Lentil cv. Castelluccio was sown at 300 seeds/m² in late March each year. Basal fertilization included 20 kg K₂O/ha and Rhizobium inoculation at sowing. No nitrogen fertilizer was applied.

Material and Methods

Material

Soil samples (0-20 cm) were collected before sowing for Olsen P, pH, and organic carbon. Plant tissue was sampled at flowering (50% bloom) and maturity for P concentration by nitric-perchloric acid digestion and colorimetric determination. Grain, straw, pod wall, and root fractions were separated at maturity for P partitioning analysis.

Methods

Grain yield was determined from a 4 m² harvest area per subplot, adjusted to 14 percent moisture. P uptake was calculated as tissue P concentration × dry matter. P use efficiency (PUE) was defined as kg grain per kg P₂O₅ applied. P harvest index = grain P ÷ total plant P × 100. Economic optimum P rate was determined by marginal analysis using local fertilizer price (€1.20/kg P₂O₅) and lentil grain price (€0.85/kg). Data were analyzed by split-plot ANOVA in R 4.3.1 with Tukey's HSD at P≤0.05. Yield response was steep on low-P soils, with a 131 percent increase from 0 to 80 kg P₂O₅/ha (Table 1). However, the marginal return above 60 kg was small, making 60 kg the economic optimum for low-P sites. On high-P soils, yields plateaued at 20 kg P₂O₅/ha, with no further response saving 40-60 kg P₂O₅/ha compared to blanket recommendations. P harvest index was consistently high at 66-68 percent regardless of soil P level (Table 2), confirming strong preferential P loading into grain. PUE was three times higher on high-P soils than low-P soils at their respective optima, as background soil supply met most crop demand.

Results

Limitations

The research covered only two growing seasons at one location, limiting extrapolation to other European lentil-growing areas with different soils and climates. Only one cultivar was tested, and genotypic variation in P efficiency exists among lentil germplasm. The economic analysis used fixed prices, which fluctuate. Mycorrhizal colonization, an important contributor to lentil P uptake, was not assessed.

Discussion

The steep yield response on low-P soils confirms lentil's high P requirement relative to soil supply, consistent with its shallow rooting habit that limits exploration of subsoil P reserves [6,7] . The 67.3 percent P harvest index higher than most cereal crops means that lentil grain removes a disproportionate share of system P, accelerating depletion if not replaced [8] . The absence of yield response above 20 kg P₂O₅/ha on high-P soils is economically and environmentally important. Blanket recommendations of 60 kg P₂O₅/ha would waste 40 kg/ha on these soils, contributing to P runoff risk without yield benefit [9,10] . Site-specific management based on Olsen P soil tests could reduce P fertilizer use across European lentil production by an estimated 30 percent [11] .

Conclusion

Lentil yield response to phosphorus was strongly dependent on soil P status. Economic optimum rates ranged from 20 kg P₂O₅/ha on high-P soils to 60 kg on low-P soils. The high P harvest index (67%) underscores the importance of P replacement fertilization to sustain soil fertility. Site-specific P management using soil test categories would improve both economic returns and environmental outcomes for European lentil production. Routine Olsen P testing before sowing should become standard practice for this crop.

References

1. Gahoonia TS, Ali O, Sarker A, Nielsen NE, Rahman MM. Genetic variation in root traits and nutrient acquisition of lentil genotypes. J Plant Nutr. 2006;29(4):643-655.
2. Bolland MDA, Siddique KHM, Loss SP, Baker MJ. Comparing responses of grain legumes, wheat and canola to applications of superphosphate. Nutr Cycl Agroecosyst. 1999;53(2):157-175.
3. Materne M, Siddique KHM. Agroecology and crop adaptation. In: Erskine W, Muehlbauer FJ, Sarker A, Sharma B, editors. The lentil: Botany, production and uses. Wallingford: CABI; 2009. p. 47-63.
4. Syers JK, Johnston AE, Curtin D. Efficiency of soil and fertilizer phosphorus use. Rome: FAO; 2008. p. 1-108.
5. Johnston AE, Poulton PR, Fixen PE, Curtin D. Phosphorus: Its efficient use in agriculture. Adv Agron. 2014;123:177228.
6. Brand JD, Tang C, Graham RD. The effect of soil moisture on the tolerance of Lens culinaris to lime. Plant Soil. 2000;219(1-2):27-33.
7. Gahoonia TS, Nielsen NE. Root traits as tools for creating phosphorus efficient crop varieties. Plant Soil. 2004;260(12):47-57.
8. Veneklaas EJ, Lambers H, Bragg J, Finnegan PM, Lovelock CE, Plaxton WC, Price CA, Scheible WR, Shane MW, White PJ, Raven JA. Opportunities for improving phosphorus-use efficiency in crop plants. New Phytol. 2012;195(2):306-320.
9. Sharpley AN, Chapra SC, Wedepohl R, Sims JT, Daniel TC, Reddy KR. Managing agricultural phosphorus for protection of surface waters: Issues and options. J Environ Qual. 1994;23(3):437-451.
10. Cordell D, Drangert JO, White S. The story of phosphorus: Global food security and food for thought. Glob Environ Change. 2009;19(2):292-305.
11. Jordan-Meille L, Rubaek GH, Ehlert PAI, Genot V, Hofman G, Goulding K, Recknagel J, Provolo G, Barraclough P. An overview of fertilizer-P recommendations in Europe: Soil testing, calibration and fertilizer recommendations. Soil Use Manag. 2012;28(4):419-435.
12. Rao IM, Friesen DK, Osaki M. Plant adaptation to phosphorus-limited tropical soils. In: Pessarakli M, editor. Handbook of plant and crop stress. New York: Marcel Dekker; 1999. p. 61-95.