Response of shaftal (Trifolium resupinatum L. var. majus Boiss.) to phosphorus fertilization: implications for forage yield and quality

Abstract

This study evaluated the effects of different phosphorus (P) doses (0-30-45-60-75-90 kg P ha-1) on morpho-agronomic traits,yield, and forage quality of shaftal. The research was conducted in the Thrace region of southeastern Europe (Türkiye) from2019 to 2021 for two years. The plant height was varied between 101.17 to 114.54 cm, leaf length 21.44 to 25.45 cm, leaflet length3.97 to 4.48 cm, leaflet width 2.37 to 2.89 cm number of leaves per plant 9.23 to 10.19 pcs, stem diameter 6.89 to 7.93 mm, greenfodder yield 56.49 to 83.65 t ha-1, dry matter yield 7.30 to 10.72 t ha-1, crude protein 17.13 to 20.37%, crude fiber 24.23 to 27.74%,NDF 34.33 to 36.53%, ADF 21.92 to 24.54%, RFV 177.74 to 194.64%, Ca 24.12 to 29.10 g kg-1, Mg 2.45 to 2.71 g kg-1, P 2.62 to 2.88g kg-1, K 24.86 to 28.54 g kg-1, tetany ratio 0.89 to 0.97, β caroten 249.02 to 357.91 mg kg-1, α-tocopherol 116.00 to 125.49 µg kg-1,DDM 69.78 to 71.82%, DMI 3.28 to 3.50%, TDN 68.13 to 71.14%, NEl 0.70 to 0.74 Mcal lb-1, NEm 0.77 to 0.81 Mcal lb-1, NEg 0.44to 0.48 Mcal lb-1 at P levels, respectively. P application significantly affected plant growth characteristics, green fodder and drymatter yields, chemical composition, fiber fractions, mineral content, vitamin concentrations, digestibility indices, and net energyvalues. Increasing P doses generally enhanced biomass production, crude protein content, digestibility parameters, mineralcomposition, and antioxidant vitamin levels, while reducing structural fiber fractions. The most consistent improvements inboth yield and forage nutritive value were observed at an application rate of approximately 60 kg P ha-1, whereas higher ratesresulted in diminishing returns. These findings indicate that balanced P fertilization is critical for optimizing productivity andforage quality in the shaftal.