Carbohydrate Content Variation in Local Rice from Tidal Swamp and Rainfed Lowland Agroecosystems in South Sumatra

South Sumatra possesses diverse local rice varieties cultivated in tidal-swamp and rainfed-lowland agroecosystems. This study described variation in calculated starch-equivalent carbohydrate content among 30 local rice varieties (17 tidal-swamp and 13 rainfed-lowland) and examined its association with agroecosystem of origin and soil pH. Prepared rice samples were analyzed by the Luff–Schoorl procedure following acid hydrolysis, and the resulting glucose-equivalent percentages were multiplied by 0.90 to estimate starch-equivalent content. On the basis of the currently reconciled worksheet, values ranged from 58.27% in Jasmine Sticky Rice (P14) to 85.34% in Rantai Rice (P22). Mean values were 71.30 ± 6.98% in the tidal-swamp group and 74.74 ± 6.21% in the rainfed-lowland group, with no significant difference (Welch’s t-test, p = 0.165). Soil pH was not significantly correlated with calculated carbohydrate content in the tidal-swamp group (r = −0.202, p = 0.438) or the rainfed-lowland group (r = −0.439, p = 0.134). The findings describe variation among individual varieties but do not establish causal environmental effects. They provide preliminary baseline information for further rice germplasm characterization. Verification of the laboratory conversion-table calculations is required before the numerical estimates are regarded as final.