Abstract:
Among the various soil erosion processes threatening sustainable agriculture, soil losses due to
root, tuber and bulb harvesting are poorly documented, particularly in tropical environments. A
study was thus conducted in two villages with contrasting agro-ecological conditions on Acrisols
and Fluvisols in Western Usambara Mountains, Tanzania. The aim was to investigate the mass of
soil and nutrients lost and the factors influencing variation of soil loss due to crop harvesting
(SLCH) for Carrot (Daucus carrota), Onion (Allium cepa L.) and Potato (Solanum tuberosum L.) under low input agriculture. A total of 108 farm plots were sampled from the two villages. The mean
SLCH values were significantly higher for carrot (7.1 Mg/ha/harvest) than for onion (3.8
Mg/ha/harvest) than for potatoes (0.7 Mg/ha/harvest). Soil nutrient losses in kg/ha/harvest were
higher for carrot than for onion and potatoes (e.g. 30 N, 0.1 P, 1.5 K for carrot vs 6.3 N, 0.04 P, 0.2
K for onion) in Majulai village. SLCH was greater in Migambo (humid cold) than in Majulai (dry
warm) for all the studied crops. Soil water content at harvest time played a significant (P = .05) role
in inducing SLCH for onion while bulk density for carrot, whereas for potato they were not
significantly influenced by soil water content and bulk density. Soil texture played only a minor role
to SLCH of the studied crops. The observed soil and nutrient losses in the current study are
substantial and pose a challenge that calls for immediate attention to the harvesting practices in the
study area. However, combating water erosion is far more urgent.
