Grass pea (Lathyrus sativus L.) stands out as an excellent choice for sustainable agriculture, thanks to its favorable agronomic characteristics, including a robust root system that penetrates deeply into the soil and its resilience against various biotic and abiotic stressors. In this study, dry-matter yield and seed yield of 16 grass pea genotypes were evaluated in rain-fed conditions at "Gachsaran", "Mehran", "Kuhdasht", and "Shirvan-Chardavol" locations in Iran for three consecutive years. The experimental field trials were carried out using a randomized complete block design, and each experimental setup was replicated three times. The descriptive statistics showed a mean value of 4.030 (ton/ha) and 1.530 (ton/ha), with phenotypic coefficients of 54.77 and 61.56 for dry-matter yield and seed yield, respectively. The projection of geographical, climatic, and edaphic variables into yield measurements depicted remarkable divergence among the four studied environments. Elevation exerts a greater influence on both dry matter and seed yields in the Mehran location as compared to other environments. The climatic factors of rainfall and relative humidity played an important role in "Gachsaran" and "Shirvan-Chardavol", respectively. While for seed yield, the temperature-related attributes were more significant in the "Mehran" location. Low broad-sense heritability was observed, and the R